On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
OK, here it is again with more pictures and explanations. Sorry for

starting a new thread, but it seemed reasonable given that I did such a

poor job of getting the design problem stated in the last one.



I'm building a gizmo, which, for lack of a better name I'm calling a "fan

trainer". It consists of an arm about 30" long with a small DC motor and

propeller on one end, and a pivot and counterweight on the other. The

thing is pivoted on a frame which has a controller circuit board. The

controller monitors the motor current and the arm position, and drives

the motor voltage.



This isn't an executive toy that you sit back and watch move (that would

get old very fast). Rather, it is a platform to provide a series of

exercises for a student to tune the control system, and to do it in a way

that you can see and feel it working. I'd use it in conjunction with

seminars, and perhaps make it part of a "seminar at home" package.



So my larger problem is to manufacture this in small quantities (20 to

100 a year), and sell them at a reasonable price without losing my ass.

"Not losing my ass" translates to a total bill-of-materials cost of $50

or so, and if I could get it way lower then I'd just sell it for less and

increase my potential market.



My immediate problem is that the potentiometer that senses the arm

position is getting punched off of the board in shipping. The

potentiometer has a hole, through which you pass a 4mm shaft with a flat

milled into it. If you mill the flat so that you can easily pass the

shaft through the pot then the control is not smooth -- the arm hunts

across the rotational slop caused by the shaft rotating within the pot.

If you shim the flat for a snug fit (very very light press fit?) then

when you chuck the thing into a box and fly with it in checked baggage,

the pot gets punched off of the board, apparently by getting hit from

behind.



The shaft on which the arm pivots is restrained in the housing by a

couple of model airplane wheel collars. On the trip out, both of these

collars, and the arm, loosened on the shaft, and the pot was punched

out. On the return trip I loosened the arm and tied it to the back plate

of the frame -- the wheel collars were fine then, but the pot was still

punched out.



I really like that pot: it costs less than $2.00 for onsies (less,

obviously, in higher quantities), it has undetectably small friction, it

isn't noisy, and because it's board mounted it saves me from needing a

bunch of brackets which would just drive up my BOM cost. So any

alternative that involves not using the pot has to compete with that

price, and being practical to do in small quantities in an environment

where labor is not free.



So I'm thinking at this point that perhaps I just need to be happy with

what I have, and to warn people not to drop the thing off of a table or

to ship it without disassembling it first. But it would be nice if there

was a way to make it more robust (by isolating the pot from the shaft

somehow).



The best suggestion I got from the other thread, assuming that I can do

it cheaply, is to put a slit in the end of the shaft, so I basically have

a D-shaped shaft with some spring. I would like that idea a lot if I

knew what it would cost to have a batch of 20 shafts made with the slit,

vs. without, and if that cost wasn't much greater than just making the

shafts.



The second-best suggestion is to use a flat coupling. This would require

(essentially) two shafts and the coupling, which is clearly going to

drive up the BOM cost, but I'm still toying with how to make it cheap.



Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from the

construction of the thing that this would just result in _part_ of the

now-destroyed pot remaining on the board.



Here's a general arrangement shot:

https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k



And the thing in action:

https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k



And, finally, a close-up of the potentiometer in question:

https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E



--

My liberal friends think I'm a conservative kook.

My conservative friends think I'm a liberal kook.

Why am I not happy that they have found common ground?



Tim Wescott, Communications, Control, Circuits & Software

http://www.wescottdesign.com

I think you ought to focus on *why* the wheel collars loosened. I am assuming that had they stayed secure on the shaft that the pot would have survived. If that is a correct assumption, how about a dimple in the shaft for the setscrew, or perhaps some loctite?

This is a pretty neat training gizmo for control loops. Sort of like the ball balancer, but better.

On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
OK, here it is again with more pictures and explanations. Sorry for

starting a new thread, but it seemed reasonable given that I did such a

poor job of getting the design problem stated in the last one.



I'm building a gizmo, which, for lack of a better name I'm calling a
"fan

trainer". It consists of an arm about 30" long with a small DC motor
and

propeller on one end, and a pivot and counterweight on the other. The

thing is pivoted on a frame which has a controller circuit board. The

controller monitors the motor current and the arm position, and drives

the motor voltage.



This isn't an executive toy that you sit back and watch move (that
would

get old very fast). Rather, it is a platform to provide a series of

exercises for a student to tune the control system, and to do it in a
way

that you can see and feel it working. I'd use it in conjunction with

seminars, and perhaps make it part of a "seminar at home" package.



So my larger problem is to manufacture this in small quantities (20 to

100 a year), and sell them at a reasonable price without losing my ass.

"Not losing my ass" translates to a total bill-of-materials cost of $50

or so, and if I could get it way lower then I'd just sell it for less
and

increase my potential market.



My immediate problem is that the potentiometer that senses the arm

position is getting punched off of the board in shipping. The

potentiometer has a hole, through which you pass a 4mm shaft with a
flat

milled into it. If you mill the flat so that you can easily pass the

shaft through the pot then the control is not smooth -- the arm hunts

across the rotational slop caused by the shaft rotating within the pot.

If you shim the flat for a snug fit (very very light press fit?) then

when you chuck the thing into a box and fly with it in checked baggage,

the pot gets punched off of the board, apparently by getting hit from

behind.



The shaft on which the arm pivots is restrained in the housing by a

couple of model airplane wheel collars. On the trip out, both of these

collars, and the arm, loosened on the shaft, and the pot was punched

out. On the return trip I loosened the arm and tied it to the back
plate

of the frame -- the wheel collars were fine then, but the pot was still

punched out.



I really like that pot: it costs less than $2.00 for onsies (less,

obviously, in higher quantities), it has undetectably small friction,
it

isn't noisy, and because it's board mounted it saves me from needing a

bunch of brackets which would just drive up my BOM cost. So any

alternative that involves not using the pot has to compete with that

price, and being practical to do in small quantities in an environment

where labor is not free.



So I'm thinking at this point that perhaps I just need to be happy with

what I have, and to warn people not to drop the thing off of a table or

to ship it without disassembling it first. But it would be nice if
there

was a way to make it more robust (by isolating the pot from the shaft

somehow).



The best suggestion I got from the other thread, assuming that I can do

it cheaply, is to put a slit in the end of the shaft, so I basically
have

a D-shaped shaft with some spring. I would like that idea a lot if I

knew what it would cost to have a batch of 20 shafts made with the
slit,

vs. without, and if that cost wasn't much greater than just making the

shafts.



The second-best suggestion is to use a flat coupling. This would
require

(essentially) two shafts and the coupling, which is clearly going to

drive up the BOM cost, but I'm still toying with how to make it cheap.



Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of the

now-destroyed pot remaining on the board.



Here's a general arrangement shot:

https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k



And the thing in action:

https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k



And, finally, a close-up of the potentiometer in question:

https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E



--

My liberal friends think I'm a conservative kook.

My conservative friends think I'm a liberal kook.

Why am I not happy that they have found common ground?



Tim Wescott, Communications, Control, Circuits & Software

http://www.wescottdesign.com

I think you ought to focus on *why* the wheel collars loosened. I am
assuming that had they stayed secure on the shaft that the pot would
have survived. If that is a correct assumption, how about a dimple in
the shaft for the setscrew, or perhaps some loctite?

This is a pretty neat training gizmo for control loops. Sort of like the
ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was still
punched off the board. Not by as far -- but all leads broken is still
all leads broken. I suspect that any sort of collar that rides close to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop between
shaft and pot (which messes up the educational value of the thing), the
current setup (which leaves it fragile, but possibly manageably so), some
sort of a flex coupling or spring (assuming I can figure out how to do
that well and cheaply), or some sort of a spring-loaded means of holding
the shaft-pot joint to be snug in rotation, but still low friction to
axial motion.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

On 11/13/2012 1:47 PM, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
OK, here it is again with more pictures and explanations. Sorry for

starting a new thread, but it seemed reasonable given that I did such a

poor job of getting the design problem stated in the last one.



I'm building a gizmo, which, for lack of a better name I'm calling a
"fan

trainer". It consists of an arm about 30" long with a small DC motor
and

propeller on one end, and a pivot and counterweight on the other. The

thing is pivoted on a frame which has a controller circuit board. The

controller monitors the motor current and the arm position, and drives

the motor voltage.



This isn't an executive toy that you sit back and watch move (that
would

get old very fast). Rather, it is a platform to provide a series of

exercises for a student to tune the control system, and to do it in a
way

that you can see and feel it working. I'd use it in conjunction with

seminars, and perhaps make it part of a "seminar at home" package.



So my larger problem is to manufacture this in small quantities (20 to

100 a year), and sell them at a reasonable price without losing my ass.

"Not losing my ass" translates to a total bill-of-materials cost of $50

or so, and if I could get it way lower then I'd just sell it for less
and

increase my potential market.



My immediate problem is that the potentiometer that senses the arm

position is getting punched off of the board in shipping. The

potentiometer has a hole, through which you pass a 4mm shaft with a
flat

milled into it. If you mill the flat so that you can easily pass the

shaft through the pot then the control is not smooth -- the arm hunts

across the rotational slop caused by the shaft rotating within the pot.

If you shim the flat for a snug fit (very very light press fit?) then

when you chuck the thing into a box and fly with it in checked baggage,

the pot gets punched off of the board, apparently by getting hit from

behind.



The shaft on which the arm pivots is restrained in the housing by a

couple of model airplane wheel collars. On the trip out, both of these

collars, and the arm, loosened on the shaft, and the pot was punched

out. On the return trip I loosened the arm and tied it to the back
plate

of the frame -- the wheel collars were fine then, but the pot was still

punched out.



I really like that pot: it costs less than $2.00 for onsies (less,

obviously, in higher quantities), it has undetectably small friction,
it

isn't noisy, and because it's board mounted it saves me from needing a

bunch of brackets which would just drive up my BOM cost. So any

alternative that involves not using the pot has to compete with that

price, and being practical to do in small quantities in an environment

where labor is not free.



So I'm thinking at this point that perhaps I just need to be happy with

what I have, and to warn people not to drop the thing off of a table or

to ship it without disassembling it first. But it would be nice if
there

was a way to make it more robust (by isolating the pot from the shaft

somehow).



The best suggestion I got from the other thread, assuming that I can do

it cheaply, is to put a slit in the end of the shaft, so I basically
have

a D-shaped shaft with some spring. I would like that idea a lot if I

knew what it would cost to have a batch of 20 shafts made with the
slit,

vs. without, and if that cost wasn't much greater than just making the

shafts.



The second-best suggestion is to use a flat coupling. This would
require

(essentially) two shafts and the coupling, which is clearly going to

drive up the BOM cost, but I'm still toying with how to make it cheap.



Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of the

now-destroyed pot remaining on the board.



Here's a general arrangement shot:

https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k



And the thing in action:

https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k



And, finally, a close-up of the potentiometer in question:

https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E



--

My liberal friends think I'm a conservative kook.

My conservative friends think I'm a liberal kook.

Why am I not happy that they have found common ground?



Tim Wescott, Communications, Control, Circuits& Software

http://www.wescottdesign.com

I think you ought to focus on *why* the wheel collars loosened. I am
assuming that had they stayed secure on the shaft that the pot would
have survived. If that is a correct assumption, how about a dimple in
the shaft for the setscrew, or perhaps some loctite?

This is a pretty neat training gizmo for control loops. Sort of like the
ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was still
punched off the board. Not by as far -- but all leads broken is still
all leads broken. I suspect that any sort of collar that rides close to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop between
shaft and pot (which messes up the educational value of the thing), the
current setup (which leaves it fragile, but possibly manageably so), some
sort of a flex coupling or spring (assuming I can figure out how to do
that well and cheaply), or some sort of a spring-loaded means of holding
the shaft-pot joint to be snug in rotation, but still low friction to
axial motion.

If this was "checked" luggage instead of carry-on, then suspect the bag
was x-rayed, and the inspector removed the items to play with it and
broke it. then replaced it in your luggage.

Paul

On Tue, 13 Nov 2012 14:11:17 -0800, Paul Drahn wrote:

On 11/13/2012 1:47 PM, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
OK, here it is again with more pictures and explanations. Sorry for

starting a new thread, but it seemed reasonable given that I did such
a

poor job of getting the design problem stated in the last one.



I'm building a gizmo, which, for lack of a better name I'm calling a
"fan

trainer". It consists of an arm about 30" long with a small DC motor
and

propeller on one end, and a pivot and counterweight on the other.
The

thing is pivoted on a frame which has a controller circuit board.
The

controller monitors the motor current and the arm position, and
drives

the motor voltage.



This isn't an executive toy that you sit back and watch move (that
would

get old very fast). Rather, it is a platform to provide a series of

exercises for a student to tune the control system, and to do it in a
way

that you can see and feel it working. I'd use it in conjunction with

seminars, and perhaps make it part of a "seminar at home" package.



So my larger problem is to manufacture this in small quantities (20
to

100 a year), and sell them at a reasonable price without losing my
ass.

"Not losing my ass" translates to a total bill-of-materials cost of
$50

or so, and if I could get it way lower then I'd just sell it for less
and

increase my potential market.



My immediate problem is that the potentiometer that senses the arm

position is getting punched off of the board in shipping. The

potentiometer has a hole, through which you pass a 4mm shaft with a
flat

milled into it. If you mill the flat so that you can easily pass the

shaft through the pot then the control is not smooth -- the arm hunts

across the rotational slop caused by the shaft rotating within the
pot.

If you shim the flat for a snug fit (very very light press fit?) then

when you chuck the thing into a box and fly with it in checked
baggage,

the pot gets punched off of the board, apparently by getting hit from

behind.



The shaft on which the arm pivots is restrained in the housing by a

couple of model airplane wheel collars. On the trip out, both of
these

collars, and the arm, loosened on the shaft, and the pot was punched

out. On the return trip I loosened the arm and tied it to the back
plate

of the frame -- the wheel collars were fine then, but the pot was
still

punched out.



I really like that pot: it costs less than $2.00 for onsies (less,

obviously, in higher quantities), it has undetectably small friction,
it

isn't noisy, and because it's board mounted it saves me from needing
a

bunch of brackets which would just drive up my BOM cost. So any

alternative that involves not using the pot has to compete with that

price, and being practical to do in small quantities in an
environment

where labor is not free.



So I'm thinking at this point that perhaps I just need to be happy
with

what I have, and to warn people not to drop the thing off of a table
or

to ship it without disassembling it first. But it would be nice if
there

was a way to make it more robust (by isolating the pot from the shaft

somehow).



The best suggestion I got from the other thread, assuming that I can
do

it cheaply, is to put a slit in the end of the shaft, so I basically
have

a D-shaped shaft with some spring. I would like that idea a lot if I

knew what it would cost to have a batch of 20 shafts made with the
slit,

vs. without, and if that cost wasn't much greater than just making
the

shafts.



The second-best suggestion is to use a flat coupling. This would
require

(essentially) two shafts and the coupling, which is clearly going to

drive up the BOM cost, but I'm still toying with how to make it
cheap.



Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of
the

now-destroyed pot remaining on the board.



Here's a general arrangement shot:

https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k



And the thing in action:

https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k



And, finally, a close-up of the potentiometer in question:

https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E



--

My liberal friends think I'm a conservative kook.

My conservative friends think I'm a liberal kook.

Why am I not happy that they have found common ground?



Tim Wescott, Communications, Control, Circuits& Software

http://www.wescottdesign.com

I think you ought to focus on *why* the wheel collars loosened. I am
assuming that had they stayed secure on the shaft that the pot would
have survived. If that is a correct assumption, how about a dimple in
the shaft for the setscrew, or perhaps some loctite?

This is a pretty neat training gizmo for control loops. Sort of like
the ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was
still punched off the board. Not by as far -- but all leads broken is
still all leads broken. I suspect that any sort of collar that rides
close to the board to limit travel in that direction will either rub or
have too much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop
between shaft and pot (which messes up the educational value of the
thing), the current setup (which leaves it fragile, but possibly
manageably so), some sort of a flex coupling or spring (assuming I can
figure out how to do that well and cheaply), or some sort of a
spring-loaded means of holding the shaft-pot joint to be snug in
rotation, but still low friction to axial motion.

If this was "checked" luggage instead of carry-on, then suspect the bag
was x-rayed, and the inspector removed the items to play with it and
broke it. then replaced it in your luggage.

Paul

It was a box, and I would have seen that it was re-taped.

I don't think I have any excuses the it was a combination of my
design, my packing, and a normal level of knocking around from the
airline.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

"Tim Wescott" wrote in message
...

This is a pretty neat training gizmo for control loops. Sort of
like the
ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost
less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was
still
punched off the board. Not by as far -- but all leads broken is
still
all leads broken. I suspect that any sort of collar that rides
close to
the board to limit travel in that direction will either rub or have
too
much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop
between
shaft and pot (which messes up the educational value of the thing),
the
current setup (which leaves it fragile, but possibly manageably so),
some
sort of a flex coupling or spring (assuming I can figure out how to
do
that well and cheaply), or some sort of a spring-loaded means of
holding
the shaft-pot joint to be snug in rotation, but still low friction
to
axial motion.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

http://www.dynapar.com/uploadedFiles...nting%20WP.pdf
#3, Direct mount with tether. The tether might be the connecting
wires.
jsw

On Tuesday, November 13, 2012 4:47:14 PM UTC-5, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:



On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:

OK, here it is again with more pictures and explanations. Sorry for



starting a new thread, but it seemed reasonable given that I did such a



poor job of getting the design problem stated in the last one.







I'm building a gizmo, which, for lack of a better name I'm calling a

"fan



trainer". It consists of an arm about 30" long with a small DC motor

and



propeller on one end, and a pivot and counterweight on the other. The



thing is pivoted on a frame which has a controller circuit board. The



controller monitors the motor current and the arm position, and drives



the motor voltage.







This isn't an executive toy that you sit back and watch move (that

would



get old very fast). Rather, it is a platform to provide a series of



exercises for a student to tune the control system, and to do it in a

way



that you can see and feel it working. I'd use it in conjunction with



seminars, and perhaps make it part of a "seminar at home" package.







So my larger problem is to manufacture this in small quantities (20 to



100 a year), and sell them at a reasonable price without losing my ass..



"Not losing my ass" translates to a total bill-of-materials cost of $50



or so, and if I could get it way lower then I'd just sell it for less

and



increase my potential market.







My immediate problem is that the potentiometer that senses the arm



position is getting punched off of the board in shipping. The



potentiometer has a hole, through which you pass a 4mm shaft with a

flat



milled into it. If you mill the flat so that you can easily pass the



shaft through the pot then the control is not smooth -- the arm hunts



across the rotational slop caused by the shaft rotating within the pot..



If you shim the flat for a snug fit (very very light press fit?) then



when you chuck the thing into a box and fly with it in checked baggage,



the pot gets punched off of the board, apparently by getting hit from



behind.







The shaft on which the arm pivots is restrained in the housing by a



couple of model airplane wheel collars. On the trip out, both of these



collars, and the arm, loosened on the shaft, and the pot was punched



out. On the return trip I loosened the arm and tied it to the back

plate



of the frame -- the wheel collars were fine then, but the pot was still



punched out.







I really like that pot: it costs less than $2.00 for onsies (less,



obviously, in higher quantities), it has undetectably small friction,

it



isn't noisy, and because it's board mounted it saves me from needing a



bunch of brackets which would just drive up my BOM cost. So any



alternative that involves not using the pot has to compete with that



price, and being practical to do in small quantities in an environment



where labor is not free.







So I'm thinking at this point that perhaps I just need to be happy with



what I have, and to warn people not to drop the thing off of a table or



to ship it without disassembling it first. But it would be nice if

there



was a way to make it more robust (by isolating the pot from the shaft



somehow).







The best suggestion I got from the other thread, assuming that I can do



it cheaply, is to put a slit in the end of the shaft, so I basically

have



a D-shaped shaft with some spring. I would like that idea a lot if I



knew what it would cost to have a batch of 20 shafts made with the

slit,



vs. without, and if that cost wasn't much greater than just making the



shafts.







The second-best suggestion is to use a flat coupling. This would

require



(essentially) two shafts and the coupling, which is clearly going to



drive up the BOM cost, but I'm still toying with how to make it cheap.







Several people suggested reinforcing the mounting of the pot to the



board: it probably doesn't show in the pictures, but it is clear from

the



construction of the thing that this would just result in _part_ of the



now-destroyed pot remaining on the board.







Here's a general arrangement shot:



https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k







And the thing in action:



https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k







And, finally, a close-up of the potentiometer in question:



https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E







--



My liberal friends think I'm a conservative kook.



My conservative friends think I'm a liberal kook.



Why am I not happy that they have found common ground?







Tim Wescott, Communications, Control, Circuits & Software



http://www.wescottdesign.com



I think you ought to focus on *why* the wheel collars loosened. I am

assuming that had they stayed secure on the shaft that the pot would

have survived. If that is a correct assumption, how about a dimple in

the shaft for the setscrew, or perhaps some loctite?



This is a pretty neat training gizmo for control loops. Sort of like the

ball balancer, but better.



I considered doing a ball balancer, but I figured this would cost less.



For that matter, I really wanted to do an inverted pendulum -- but I

couldn't see how to do the mechanism cheaply.



The wheel collars stayed tight on the flight home, yet the pot was still

punched off the board. Not by as far -- but all leads broken is still

all leads broken. I suspect that any sort of collar that rides close to

the board to limit travel in that direction will either rub or have too

much play to be safe -- but I could be wrong.



At this point what I see is a choice between some rotational slop between

shaft and pot (which messes up the educational value of the thing), the

current setup (which leaves it fragile, but possibly manageably so), some

sort of a flex coupling or spring (assuming I can figure out how to do

that well and cheaply), or some sort of a spring-loaded means of holding

the shaft-pot joint to be snug in rotation, but still low friction to

axial motion.



--

Tim Wescott

Control system and signal processing consulting

www.wescottdesign.com

How about mounting the pot semi-ridgedly on kinked or s-bent pieces of bus wire? Pretty much free (except for 30 seconds or so of extra assembly) and easily repairable. If the pot really has very low rotational friction, the wires shouldn't bed in normal usage, but will give enough to prevent damage.. You could even try some springy piano wire.

On Tue, 13 Nov 2012 17:55:15 -0500, Jim Wilkins wrote:

"Tim Wescott" wrote in message
...

This is a pretty neat training gizmo for control loops. Sort of like
the
ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was
still
punched off the board. Not by as far -- but all leads broken is still
all leads broken. I suspect that any sort of collar that rides close
to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop
between
shaft and pot (which messes up the educational value of the thing), the
current setup (which leaves it fragile, but possibly manageably so),
some
sort of a flex coupling or spring (assuming I can figure out how to do
that well and cheaply), or some sort of a spring-loaded means of
holding
the shaft-pot joint to be snug in rotation, but still low friction to
axial motion.

--
Tim Wescott
Control system and signal processing consulting www.wescottdesign.com

http://www.dynapar.com/uploadedFiles.../White_Papers/
Encoder%20Mounting%20WP.pdf
#3, Direct mount with tether. The tether might be the connecting wires.
jsw

If I use this pot then my situation is just about backwards from their
assumptions: the pot _doesn't_ have bearings, and by construction its
designed to be soldered onto the board.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On Tue, 13 Nov 2012 15:02:26 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 4:47:14 PM UTC-5, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:



On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:

OK, here it is again with more pictures and explanations. Sorry for



starting a new thread, but it seemed reasonable given that I did
such a



poor job of getting the design problem stated in the last one.







I'm building a gizmo, which, for lack of a better name I'm calling a

"fan



trainer". It consists of an arm about 30" long with a small DC
motor

and



propeller on one end, and a pivot and counterweight on the other.
The



thing is pivoted on a frame which has a controller circuit board.
The



controller monitors the motor current and the arm position, and
drives



the motor voltage.







This isn't an executive toy that you sit back and watch move (that

would



get old very fast). Rather, it is a platform to provide a series of



exercises for a student to tune the control system, and to do it in
a

way



that you can see and feel it working. I'd use it in conjunction
with



seminars, and perhaps make it part of a "seminar at home" package.







So my larger problem is to manufacture this in small quantities (20
to



100 a year), and sell them at a reasonable price without losing my
ass.



"Not losing my ass" translates to a total bill-of-materials cost of
$50



or so, and if I could get it way lower then I'd just sell it for
less

and



increase my potential market.







My immediate problem is that the potentiometer that senses the arm



position is getting punched off of the board in shipping. The



potentiometer has a hole, through which you pass a 4mm shaft with a

flat



milled into it. If you mill the flat so that you can easily pass
the



shaft through the pot then the control is not smooth -- the arm
hunts



across the rotational slop caused by the shaft rotating within the
pot.



If you shim the flat for a snug fit (very very light press fit?)
then



when you chuck the thing into a box and fly with it in checked
baggage,



the pot gets punched off of the board, apparently by getting hit
from



behind.







The shaft on which the arm pivots is restrained in the housing by a



couple of model airplane wheel collars. On the trip out, both of
these



collars, and the arm, loosened on the shaft, and the pot was punched



out. On the return trip I loosened the arm and tied it to the back

plate



of the frame -- the wheel collars were fine then, but the pot was
still



punched out.







I really like that pot: it costs less than $2.00 for onsies (less,



obviously, in higher quantities), it has undetectably small
friction,

it



isn't noisy, and because it's board mounted it saves me from needing
a



bunch of brackets which would just drive up my BOM cost. So any



alternative that involves not using the pot has to compete with that



price, and being practical to do in small quantities in an
environment



where labor is not free.







So I'm thinking at this point that perhaps I just need to be happy
with



what I have, and to warn people not to drop the thing off of a table
or



to ship it without disassembling it first. But it would be nice if

there



was a way to make it more robust (by isolating the pot from the
shaft



somehow).







The best suggestion I got from the other thread, assuming that I can
do



it cheaply, is to put a slit in the end of the shaft, so I basically

have



a D-shaped shaft with some spring. I would like that idea a lot if
I



knew what it would cost to have a batch of 20 shafts made with the

slit,



vs. without, and if that cost wasn't much greater than just making
the



shafts.







The second-best suggestion is to use a flat coupling. This would

require



(essentially) two shafts and the coupling, which is clearly going to



drive up the BOM cost, but I'm still toying with how to make it
cheap.







Several people suggested reinforcing the mounting of the pot to the



board: it probably doesn't show in the pictures, but it is clear
from

the



construction of the thing that this would just result in _part_ of
the



now-destroyed pot remaining on the board.







Here's a general arrangement shot:



https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k







And the thing in action:



https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k







And, finally, a close-up of the potentiometer in question:



https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E







--



My liberal friends think I'm a conservative kook.



My conservative friends think I'm a liberal kook.



Why am I not happy that they have found common ground?







Tim Wescott, Communications, Control, Circuits & Software



http://www.wescottdesign.com



I think you ought to focus on *why* the wheel collars loosened. I am

assuming that had they stayed secure on the shaft that the pot would

have survived. If that is a correct assumption, how about a dimple in

the shaft for the setscrew, or perhaps some loctite?



This is a pretty neat training gizmo for control loops. Sort of like
the

ball balancer, but better.



I considered doing a ball balancer, but I figured this would cost less.



For that matter, I really wanted to do an inverted pendulum -- but I

couldn't see how to do the mechanism cheaply.



The wheel collars stayed tight on the flight home, yet the pot was
still

punched off the board. Not by as far -- but all leads broken is still

all leads broken. I suspect that any sort of collar that rides close
to

the board to limit travel in that direction will either rub or have too

much play to be safe -- but I could be wrong.



At this point what I see is a choice between some rotational slop
between

shaft and pot (which messes up the educational value of the thing), the

current setup (which leaves it fragile, but possibly manageably so),
some

sort of a flex coupling or spring (assuming I can figure out how to do

that well and cheaply), or some sort of a spring-loaded means of
holding

the shaft-pot joint to be snug in rotation, but still low friction to

axial motion.



--

Tim Wescott

Control system and signal processing consulting

www.wescottdesign.com

How about mounting the pot semi-ridgedly on kinked or s-bent pieces of
bus wire? Pretty much free (except for 30 seconds or so of extra
assembly) and easily repairable. If the pot really has very low
rotational friction, the wires shouldn't bed in normal usage, but will
give enough to prevent damage. You could even try some springy piano
wire.

Hmm. Good thought, but it'd take a lot more than 30 seconds. It's a
surface-mount part, so mounting it as designed is very quick while
mounting it just about any other way isn't so.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On Nov 13, 4:47*pm, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:
On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
OK, here it is again with more pictures and explanations. *Sorry for

starting a new thread, but it seemed reasonable given that I did such a

poor job of getting the design problem stated in the last one.

I'm building a gizmo, which, for lack of a better name I'm calling a
"fan

trainer". *It consists of an arm about 30" long with a small DC motor
and

propeller on one end, and a pivot and counterweight on the other. *The

thing is pivoted on a frame which has a controller circuit board. *The

controller monitors the motor current and the arm position, and drives

the motor voltage.

This isn't an executive toy that you sit back and watch move (that
would

get old very fast). *Rather, it is a platform to provide a series of

exercises for a student to tune the control system, and to do it in a
way

that you can see and feel it working. *I'd use it in conjunction with

seminars, and perhaps make it part of a "seminar at home" package.

So my larger problem is to manufacture this in small quantities (20 to

100 a year), and sell them at a reasonable price without losing my ass..

"Not losing my ass" translates to a total bill-of-materials cost of $50

or so, and if I could get it way lower then I'd just sell it for less
and

increase my potential market.

My immediate problem is that the potentiometer that senses the arm

position is getting punched off of the board in shipping. *The

potentiometer has a hole, through which you pass a 4mm shaft with a
flat

milled into it. *If you mill the flat so that you can easily pass the

shaft through the pot then the control is not smooth -- the arm hunts

across the rotational slop caused by the shaft rotating within the pot..

If you shim the flat for a snug fit (very very light press fit?) then

when you chuck the thing into a box and fly with it in checked baggage,

the pot gets punched off of the board, apparently by getting hit from

behind.

The shaft on which the arm pivots is restrained in the housing by a

couple of model airplane wheel collars. *On the trip out, both of these

collars, and the arm, loosened on the shaft, and the pot was punched

out. *On the return trip I loosened the arm and tied it to the back
plate

of the frame -- the wheel collars were fine then, but the pot was still

punched out.

I really like that pot: it costs less than $2.00 for onsies (less,

obviously, in higher quantities), it has undetectably small friction,
it

isn't noisy, and because it's board mounted it saves me from needing a

bunch of brackets which would just drive up my BOM cost. *So any

alternative that involves not using the pot has to compete with that

price, and being practical to do in small quantities in an environment

where labor is not free.

So I'm thinking at this point that perhaps I just need to be happy with

what I have, and to warn people not to drop the thing off of a table or

to ship it without disassembling it first. *But it would be nice if
there

was a way to make it more robust (by isolating the pot from the shaft

somehow).

The best suggestion I got from the other thread, assuming that I can do

it cheaply, is to put a slit in the end of the shaft, so I basically
have

a D-shaped shaft with some spring. *I would like that idea a lot if I

knew what it would cost to have a batch of 20 shafts made with the
slit,

vs. without, and if that cost wasn't much greater than just making the

shafts.

The second-best suggestion is to use a flat coupling. *This would
require

(essentially) two shafts and the coupling, which is clearly going to

drive up the BOM cost, but I'm still toying with how to make it cheap.

Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of the

now-destroyed pot remaining on the board.

Here's a general arrangement shot:

https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k

And the thing in action:

https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k

And, finally, a close-up of the potentiometer in question:

https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E

--

My liberal friends think I'm a conservative kook.

My conservative friends think I'm a liberal kook.

Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software

http://www.wescottdesign.com

I think you ought to focus on *why* the wheel collars loosened. I am
assuming that had they stayed secure on the shaft that the pot would
have survived. If that is a correct assumption, how about a dimple in
the shaft for the setscrew, or perhaps some loctite?

This is a pretty neat training gizmo for control loops. Sort of like the
ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was still
punched off the board. *Not by as far -- but all leads broken is still
all leads broken. *I suspect that any sort of collar that rides close to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop between
shaft and pot (which messes up the educational value of the thing), the
current setup (which leaves it fragile, but possibly manageably so), some
sort of a flex coupling or spring (assuming I can figure out how to do
that well and cheaply), or some sort of a spring-loaded means of holding
the shaft-pot joint to be snug in rotation, but still low friction to
axial motion.

--
Tim Wescott
Control system and signal processing consultingwww.wescottdesign.com- Hide quoted text -

- Show quoted text -

How about a thermal thing for control loop education?

TEC, air fin heatsink, heater as variable load, maybe a couple of
sensors. It'd be nice to have variable thermal 'lengths' in the
system.
(More than $50 though I'd guess.)

George H.

On 11/13/2012 1:47 PM, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:
OK, here it is again with more pictures and explanations. Sorry for

starting a new thread, but it seemed reasonable given that I did such a

poor job of getting the design problem stated in the last one.



I'm building a gizmo, which, for lack of a better name I'm calling a
"fan

trainer". It consists of an arm about 30" long with a small DC motor
and

propeller on one end, and a pivot and counterweight on the other. The

thing is pivoted on a frame which has a controller circuit board. The

controller monitors the motor current and the arm position, and drives

the motor voltage.



This isn't an executive toy that you sit back and watch move (that
would

get old very fast). Rather, it is a platform to provide a series of

exercises for a student to tune the control system, and to do it in a
way

that you can see and feel it working. I'd use it in conjunction with

seminars, and perhaps make it part of a "seminar at home" package.



So my larger problem is to manufacture this in small quantities (20 to

100 a year), and sell them at a reasonable price without losing my ass.

"Not losing my ass" translates to a total bill-of-materials cost of $50

or so, and if I could get it way lower then I'd just sell it for less
and

increase my potential market.



My immediate problem is that the potentiometer that senses the arm

position is getting punched off of the board in shipping. The

potentiometer has a hole, through which you pass a 4mm shaft with a
flat

milled into it. If you mill the flat so that you can easily pass the

shaft through the pot then the control is not smooth -- the arm hunts

across the rotational slop caused by the shaft rotating within the pot.

If you shim the flat for a snug fit (very very light press fit?) then

when you chuck the thing into a box and fly with it in checked baggage,

the pot gets punched off of the board, apparently by getting hit from

behind.



The shaft on which the arm pivots is restrained in the housing by a

couple of model airplane wheel collars. On the trip out, both of these

collars, and the arm, loosened on the shaft, and the pot was punched

out. On the return trip I loosened the arm and tied it to the back
plate

of the frame -- the wheel collars were fine then, but the pot was still

punched out.



I really like that pot: it costs less than $2.00 for onsies (less,

obviously, in higher quantities), it has undetectably small friction,
it

isn't noisy, and because it's board mounted it saves me from needing a

bunch of brackets which would just drive up my BOM cost. So any

alternative that involves not using the pot has to compete with that

price, and being practical to do in small quantities in an environment

where labor is not free.



So I'm thinking at this point that perhaps I just need to be happy with

what I have, and to warn people not to drop the thing off of a table or

to ship it without disassembling it first. But it would be nice if
there

was a way to make it more robust (by isolating the pot from the shaft

somehow).



The best suggestion I got from the other thread, assuming that I can do

it cheaply, is to put a slit in the end of the shaft, so I basically
have

a D-shaped shaft with some spring. I would like that idea a lot if I

knew what it would cost to have a batch of 20 shafts made with the
slit,

vs. without, and if that cost wasn't much greater than just making the

shafts.



The second-best suggestion is to use a flat coupling. This would
require

(essentially) two shafts and the coupling, which is clearly going to

drive up the BOM cost, but I'm still toying with how to make it cheap.



Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of the

now-destroyed pot remaining on the board.



Here's a general arrangement shot:

https://docs.google.com/open?id=0B5l...0MxMEM3b1l2c0k



And the thing in action:

https://docs.google.com/file/d/0B5lS...0MxMEM3b1l2c0k



And, finally, a close-up of the potentiometer in question:

https://docs.google.com/open?id=0B5l...TBCc3VzWDYxZ0E



--

My liberal friends think I'm a conservative kook.

My conservative friends think I'm a liberal kook.

Why am I not happy that they have found common ground?



Tim Wescott, Communications, Control, Circuits& Software

http://www.wescottdesign.com

I think you ought to focus on *why* the wheel collars loosened. I am
assuming that had they stayed secure on the shaft that the pot would
have survived. If that is a correct assumption, how about a dimple in
the shaft for the setscrew, or perhaps some loctite?

This is a pretty neat training gizmo for control loops. Sort of like the
ball balancer, but better.

I considered doing a ball balancer, but I figured this would cost less.

For that matter, I really wanted to do an inverted pendulum -- but I
couldn't see how to do the mechanism cheaply.

The wheel collars stayed tight on the flight home, yet the pot was still
punched off the board. Not by as far -- but all leads broken is still
all leads broken. I suspect that any sort of collar that rides close to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.

At this point what I see is a choice between some rotational slop between
shaft and pot (which messes up the educational value of the thing), the
current setup (which leaves it fragile, but possibly manageably so), some
sort of a flex coupling or spring (assuming I can figure out how to do
that well and cheaply), or some sort of a spring-loaded means of holding
the shaft-pot joint to be snug in rotation, but still low friction to
axial motion.

How about this?
http://www.chinajiaho.com/6-in-1-diy...kit_p1763.html

Start with the configuration that rotates around the vertical pole.
put two solar cells back to back. It should track a focused light
source around the circle. If the dead zone is too big, put the cells in
series in a bridge and the motor in a full-bridge and chop the power into
a fan voltage that nulls the input bridge.
Costs you $8 for the toy and the one you stole the other solar cell
from. Free shipping.
If you can stand the dead zone, you have a very tight visual coupling
between the sensor and the positioning mechanism. And you don't need
batteries or electronics or nothin'. It just works.
There will be balance issues.
Lots of other possibilities with all the kit parts.
Use the car configuration for your inverted pendulum.

The pot thing is a loser until you use one with a bearing that can
support the weight and the abuse of shipping and students.
I'd try to put the fan on the bottom, out of harm's way and use
something light, like a soda straw out the top for an indicator.

Are we having fun yet?

On Tue, 13 Nov 2012 15:29:41 -0800, George Herold wrote:

How about a thermal thing for control loop education?

TEC, air fin heatsink, heater as variable load, maybe a couple of
sensors. It'd be nice to have variable thermal 'lengths' in the system.
(More than $50 though I'd guess.)

George H.

I'm thinking of doing something like that next. There's not much visual
interest there (unless I can do something cool with liquid crystal
thermometers), but I think I could get it below $50 and it'd be of
interest to someone who happens to be living and breathing thermal
control when they set out to learn the stuff.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On Tuesday, November 13, 2012 6:06:29 PM UTC-5, Tim Wescott wrote:
On Tue, 13 Nov 2012 15:02:26 -0800, rangerssuck wrote:

[trimmed]

How about mounting the pot semi-ridgedly on kinked or s-bent pieces of
bus wire? Pretty much free (except for 30 seconds or so of extra
assembly) and easily repairable. If the pot really has very low
rotational friction, the wires shouldn't bed in normal usage, but will
give enough to prevent damage. You could even try some springy piano
wire.

Hmm. Good thought, but it'd take a lot more than 30 seconds. It's a
surface-mount part, so mounting it as designed is very quick while
mounting it just about any other way isn't so.

If you mount the pot on a separate little board, it would be easy. If you're making printed circuit boards, just add the little pot board to the layout with either a score line or a tab route separating them. If you're going to breadboard this (as in your photos), just make up a bunch of little boards that hold nothing but the pot and four mounting wires.

IIRC, you were talking about small (20-100/year) quantities. Even if it took an extra three minutes per assembly (which it won't), you're only talking 1 - 5 hours PER YEAR. I personally have probably a half hour into this project already, between reading and writing.

Just sayin'

On Nov 13, 7:26*pm, Tim Wescott wrote:
On Tue, 13 Nov 2012 15:29:41 -0800, George Herold wrote:
How about a thermal thing for control loop education?

TEC, air fin heatsink, heater as variable load, maybe a couple of
sensors. *It'd be nice to have variable thermal 'lengths' in the system.
(More than $50 though I'd guess.)

George H.

I'm thinking of doing something like that next. *There's not much visual
interest there (unless I can do something cool with liquid crystal
thermometers), but I think I could get it below $50 and it'd be of
interest to someone who happens to be living and breathing thermal
control when they set out to learn the stuff.

Yeah, I have no 'showy' thermal thing to control. But that's not so
important from my perspective. I’d be more interested in the control
details, different control loops, different source detector distances
(materials) So that thermal diffusion effects could be seen.
It would be really nice to have different cooling sources.
(TEC and air fins and then a heater and some sort of cryogen. But the
cryogen part looks more expensive.. (CFC’s are out), or dangerous,
(boiling water)

Do you mind if I ask whom you think you might sell this to?
Add on labs for your book? Engineering schools?
Does the $50 include all the electronics?
(you can always reply in private... gherold@teachspin (dot) com)

George H.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com

On 2012-11-13, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:

[ ... ]

Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of the

now-destroyed pot remaining on the board.

[ ... ]

The wheel collars stayed tight on the flight home, yet the pot was still
punched off the board. Not by as far -- but all leads broken is still
all leads broken. I suspect that any sort of collar that rides close to
the board to limit travel in that direction will either rub or have too
much play to be safe -- but I could be wrong.

Hmm ... one possibility which I have not yet seen mentioned is
that it is not actually the lever's mass which is the problem, but
instead the length and spring constant of the leads, and the mass of the
pot, happening to resonate at a frequency which matches that of
vibration present in the aircraft. Just for the fun of it, try a second
pot on the board with no lever attached during transist.

Good Luck,
DoN.

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On Thu, 15 Nov 2012 00:48:41 +0000, DoN. Nichols wrote:

On 2012-11-13, Tim Wescott wrote:
On Tue, 13 Nov 2012 13:14:02 -0800, rangerssuck wrote:

On Tuesday, November 13, 2012 2:28:05 PM UTC-5, Tim Wescott wrote:

[ ... ]

Several people suggested reinforcing the mounting of the pot to the

board: it probably doesn't show in the pictures, but it is clear from
the

construction of the thing that this would just result in _part_ of
the

now-destroyed pot remaining on the board.

[ ... ]

The wheel collars stayed tight on the flight home, yet the pot was
still punched off the board. Not by as far -- but all leads broken is
still all leads broken. I suspect that any sort of collar that rides
close to the board to limit travel in that direction will either rub or
have too much play to be safe -- but I could be wrong.

Hmm ... one possibility which I have not yet seen mentioned is
that it is not actually the lever's mass which is the problem, but
instead the length and spring constant of the leads, and the mass of the
pot, happening to resonate at a frequency which matches that of
vibration present in the aircraft. Just for the fun of it, try a second
pot on the board with no lever attached during transist.

The pot is plastic, probably weighs less than a gram, and it's surface
mount, so the leads are short and stiff.

I think there'd be other things falling off the board in vibration severe
enough to cause problems with the pot.

--
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Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Hi Tim,

Interesting concept :-)

Just an idea.
Mount the boom in the center of a thin, broad flexible strip of spring
steel. Make a quadrant with a line of perforations on the edge and use
a pair of slot photo detectors, a bit like the slotted wheel in a ball
mouse to detect the movement. This would do away with the pot and a
cheap mouse IC could do the rest. You could even use flexible pcb on
the strip of spring steel to provide power to the fan motor.

--
Best Regards:
Baron.