So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

--
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:

So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

--
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

Vertical clear acrylic tube with a fan at the bottom a ping-pong ball
and an ultrasonic ranger at the top. I seem to recall this being covered
in a Circuit Cellar issue actually.

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

Expecting that pot to survive shipment with a big lever attached is
optimistic.
Switch to a real pot that mounts by the shaft bearing, not
the element contacts and a setscrew to remove the lever for shipment.

Or you could leave it the way it is and demonstrate that the electrical
solution is worthless if the mechanical implementation fails. That's
probably a more valuable lesson.

On 11/12/2012 3:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

Comments appreciated.


Take a piece of aluminum channel and mount it to a 1"x6" with the sides
sticking up. Drill across the sides and put a 1/4" shaft through to use
as the pivot for the fan arm. Add a small right angle bracket to support
the pot. Connect the pot shaft to the support shaft with a piece of
vinyl tubing. The fan arm could be clamped to the board for shipping.

If you want lower friction, 1/4" ID flanged bearings are cheap at Enco,
and could be retained by a simple plate clamping them to the outside of
the channel.

BobH

On Mon, 12 Nov 2012 16:03:47 -0800, mike wrote:

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at
a commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this
week, and it didn't survive well. The position feedback from the pivot
is provided by a nice inexpensive potentiometer with a D-shaped hole,
into which one inserts a shaft of the correct dimensions. Here's a
close-up of the pot mounted on the board, with a shaft (and, if you've
sharp eyes, a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my
customer was able to repair the thing and I was able to use it for
demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different
way of putting the whole thing together so that it's easy to
disassemble for shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set
up a problem with the shaft transmitting too much force to the pot, and
-- ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So
not only am I very concerned about shipping, I'm a bit concerned about
this being a point of fragility in an otherwise reasonably stout
mechanism.

Comments appreciated.

Expecting that pot to survive shipment with a big lever attached is
optimistic.
Switch to a real pot that mounts by the shaft bearing, not the element
contacts and a setscrew to remove the lever for shipment.

Or you could leave it the way it is and demonstrate that the electrical
solution is worthless if the mechanical implementation fails. That's
probably a more valuable lesson.

That pot is less than $2.00, and very low friction.

Your "real" pots are big, clunky, expensive, high friction, and require
brackets which must be purchased which further ads to the cost.

So finding a way to isolate that pot from damage while still having it
work would be a big plus.

--
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
...
On Mon, 12 Nov 2012 16:03:47 -0800, mike wrote:

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at
a commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this
week, and it didn't survive well. The position feedback from the pivot
is provided by a nice inexpensive potentiometer with a D-shaped hole,
into which one inserts a shaft of the correct dimensions. Here's a
close-up of the pot mounted on the board, with a shaft (and, if you've
sharp eyes, a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my
customer was able to repair the thing and I was able to use it for
demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different
way of putting the whole thing together so that it's easy to
disassemble for shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set
up a problem with the shaft transmitting too much force to the pot, and
-- ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So
not only am I very concerned about shipping, I'm a bit concerned about
this being a point of fragility in an otherwise reasonably stout
mechanism.

Comments appreciated.

Expecting that pot to survive shipment with a big lever attached is
optimistic.
Switch to a real pot that mounts by the shaft bearing, not the element
contacts and a setscrew to remove the lever for shipment.

Or you could leave it the way it is and demonstrate that the electrical
solution is worthless if the mechanical implementation fails. That's
probably a more valuable lesson.

That pot is less than $2.00, and very low friction.

Your "real" pots are big, clunky, expensive, high friction, and require
brackets which must be purchased which further ads to the cost.

So finding a way to isolate that pot from damage while still having it
work would be a big plus.


Perhaps the other useful lesson is that it is best to nail down and publish
all the desired specs before having a design review or calling the
consultants. I am still not clear about what sort of weight and torque is
on that small pot. Just how little friction do you need? How cheap does the
solution have to be?

It sounds like you want a stronger bearing to take up the mechanical loads,
and then have a connecting arm from the pivoting portion to the pot. The
stationary part of the bearing would be mounted with a bracket to board
above the pot with its axis in-line with the pot. The connecting arm could
extend through the center of a ball bearing, or it could be U-shaped and
connected to the outside if you need less than 360 deg. movement and the
bearing is not hollow. A cheap, easy-to-make, super-low-friction pivot can
be made by tapering both ends of a hard shaft to a point, and then clamp
onto the ends with two cup-point setscrews. You adjust the set screws to
have minimal friction with no slop. You also need threadlocker or a locking
nut to keep the setcrews in place.

Another low friction pivot design for small angles is a cross-flexure. For
some reason these are expensive to buy but relatively easy to make if you
have some spring steel shim stock. You can find one in the read/write arm
pivot in some hardrives. Hell, any bearing they use there would probably be
good for your purposes.

On 11/12/2012 7:12 PM, anorton wrote:
I am still not clear about what sort of weight and
torque is on that small pot.


Seriously more that it could deal with!

Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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


Is that chrome tube on the back the arm you expect the pot to support?

The easier method with the shaft would be a split tapered shaft that
uses friction to compress and retain the
shaft.


On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

If that rear tube is what you plan on supporting the easiest way would
probably be a bracket on the opposite side
with a nylon busing supporting the shaft on the other side. If you plan
to keep that pot.


But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.


OK one possible solution would be to eliminate that pot. Instead use a
printed resister on the board with a wiper
mounted to the pivoted shaft. Then use a through shaft with nylon
bushings to support the pivot.
Take a look at just about every fuel level sensor out there.

Or switch to an optical encoder with a supported shaft.


--
Steve W.

On Mon, 12 Nov 2012 18:43:36 -0500, "Pete C."
wrote:


Tim Wescott wrote:

So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

Affix it to a gear resting on a bearing on the board, gear the pot
next to it, and you're fixed. And split the shaft at the gear so it's
can be broken down safely shipped.

Oh, and wire the pot backwards to accomodate the difference in shaft
spin.


Vertical clear acrylic tube with a fan at the bottom a ping-pong ball
and an ultrasonic ranger at the top. I seem to recall this being covered
in a Circuit Cellar issue actually.

Speaking of Circuit Cellar, has CC or anyone ever digitized those old
copies?

--
While we have the gift of life, it seems to me that only tragedy
is to allow part of us to die - whether it is our spirit, our
creativity, or our glorious uniqueness.
-- Gilda Radner

"Tim Wescott" wrote in message
...
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

--
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



Can you slit the shaft with a junior hacksaw & spring it apart just a
little. That would allow it to slide on & off easily whilst maintaining good
coupling.

Larry Jaques wrote:

On Mon, 12 Nov 2012 18:43:36 -0500, "Pete C."
wrote:


Tim Wescott wrote:

So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

Affix it to a gear resting on a bearing on the board, gear the pot
next to it, and you're fixed. And split the shaft at the gear so it's
can be broken down safely shipped.

Oh, and wire the pot backwards to accomodate the difference in shaft
spin.

Vertical clear acrylic tube with a fan at the bottom a ping-pong ball
and an ultrasonic ranger at the top. I seem to recall this being covered
in a Circuit Cellar issue actually.

Speaking of Circuit Cellar, has CC or anyone ever digitized those old
copies?

Last I knew you could get CC compilation CDs. I have the first 6 or 8
CDs worth of them. I presume you can get a DVD with a larger range now,
or perhaps a flash drive with everything.

Tim Wescott wrote:


Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.
First question is who'd you ship it with? If UPS, the
answer is clear. A little knocking around your shop is not
a valid test, you have to put it in the shipping box and throw it
20 feet. That's how UPS unloads their semis - they throw everything
off the truck into a big pile. Try sending it FedEx, they are much
more gentle with stuff.

Jon

On Mon, 12 Nov 2012 21:29:17 -0500, "Steve W."
wrote:


But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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


Is that chrome tube on the back the arm you expect the pot to support?

The easier method with the shaft would be a split tapered shaft that
uses friction to compress and retain the
shaft.


Hell..simply give the pot a bit of hotglue and glue the damed thing
down to the board. Wont take much and its easily removable


"The national budget must be balanced. The public debt must be
reduced; the arrogance of the authorities must be moderated and
controlled. Payments to foreign governments must be reduced,
if the nation doesn't want to go bankrupt. People must again
learn to work, instead of living on public assistance."

(Marcus Tullius Cicero, 55 B.C.)

"Gunner" wrote in message
news
On Mon, 12 Nov 2012 21:29:17 -0500, "Steve W."
wrote:


But I went and took it on an airline flight for the first time this
week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp
eyes,
a little paper shim that keeps things snug).

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


Is that chrome tube on the back the arm you expect the pot to support?

The easier method with the shaft would be a split tapered shaft that
uses friction to compress and retain the
shaft.


Hell..simply give the pot a bit of hotglue and glue the damed thing
down to the board. Wont take much and its easily removable


"The national budget must be balanced. The public debt must be
reduced; the arrogance of the authorities must be moderated and
controlled. Payments to foreign governments must be reduced,
if the nation doesn't want to go bankrupt. People must again
learn to work, instead of living on public assistance."

(Marcus Tullius Cicero, 55 B.C.)


Yet again, (yawn) your signature quote is a nearly complete fabrication:
http://www.truthorfiction.com/rumors/c/cicero-plan.htm

Besides, there was no concept of either bankruptcy or long-term public debt
in ancient Rome.

On Tue, 13 Nov 2012 01:14:54 -0800, "anorton"
wrote:


"Gunner" wrote in message
news
On Mon, 12 Nov 2012 21:29:17 -0500, "Steve W."
wrote:


But I went and took it on an airline flight for the first time this
week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp
eyes,
a little paper shim that keeps things snug).

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


Is that chrome tube on the back the arm you expect the pot to support?

The easier method with the shaft would be a split tapered shaft that
uses friction to compress and retain the
shaft.


Hell..simply give the pot a bit of hotglue and glue the damed thing
down to the board. Wont take much and its easily removable


"The national budget must be balanced. The public debt must be
reduced; the arrogance of the authorities must be moderated and
controlled. Payments to foreign governments must be reduced,
if the nation doesn't want to go bankrupt. People must again
learn to work, instead of living on public assistance."

(Marcus Tullius Cicero, 55 B.C.)


Yet again, (yawn) your signature quote is a nearly complete fabrication:
http://www.truthorfiction.com/rumors/c/cicero-plan.htm

Besides, there was no concept of either bankruptcy or long-term public debt
in ancient Rome.

And yet again, Im a Democrat. I can post any damned lie, error or
political expedient that I want. And there isnt a damned thing you or
any other Establishment fat cat can do or say about it.

Afterall...5 generations of predecesors in the Democratic Party have
set the bar.

Now was there anything else you wished to babble and blither about,
you mother****ing dong headed cocksuckin PIG?????

"The first duty of a revolutionary is to get away with it."
-Abbie Hoffman

"We can change the world, rearrange the world. It's dying - if you
believe in justice. It's Dying - if you believe in freedom. It's Dying
- let a man live his own life. It's Dying - rules and regulations, who
needs them! Open up the door."
-Crosby, Stills & Nash

Gunner


"The national budget must be balanced. The public debt must be
reduced; the arrogance of the authorities must be moderated and
controlled. Payments to foreign governments must be reduced,
if the nation doesn't want to go bankrupt. People must again
learn to work, instead of living on public assistance."

(Marcus Tullius Cicero, 55 B.C.)

On Mon, 12 Nov 2012 17:12:28 -0800, anorton wrote:

"Tim Wescott" wrote in message
...
On Mon, 12 Nov 2012 16:03:47 -0800, mike wrote:

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control
system that works to maintain the angle of the stick relative to its
mount at a commanded value. It does a good job of giving people a
visceral understanding of how a feedback control system works, and I
don't think it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this
week, and it didn't survive well. The position feedback from the
pivot is provided by a nice inexpensive potentiometer with a D-shaped
hole, into which one inserts a shaft of the correct dimensions.
Here's a close-up of the pot mounted on the board, with a shaft (and,
if you've sharp eyes, a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back),
the pot broke off the board. It was obviously punched out of the
board by the force of the shaft acting on the back of the pot.
Fortunately the training is for engineers, and it was at a corporate
site, so my customer was able to repair the thing and I was able to
use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem
and fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different
way of putting the whole thing together so that it's easy to
disassemble for shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the
slight play between pot and shaft messes up the control (the arm will
hunt within the slop of the connection). But shimming things seems
to set up a problem with the shaft transmitting too much force to the
pot, and -- ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So
not only am I very concerned about shipping, I'm a bit concerned
about this being a point of fragility in an otherwise reasonably
stout mechanism.

Comments appreciated.

Expecting that pot to survive shipment with a big lever attached is
optimistic.
Switch to a real pot that mounts by the shaft bearing, not the element
contacts and a setscrew to remove the lever for shipment.

Or you could leave it the way it is and demonstrate that the
electrical solution is worthless if the mechanical implementation
fails. That's probably a more valuable lesson.

That pot is less than $2.00, and very low friction.

Your "real" pots are big, clunky, expensive, high friction, and require
brackets which must be purchased which further ads to the cost.

So finding a way to isolate that pot from damage while still having it
work would be a big plus.


Perhaps the other useful lesson is that it is best to nail down and
publish all the desired specs before having a design review or calling
the consultants. I am still not clear about what sort of weight and
torque is on that small pot. Just how little friction do you need? How
cheap does the solution have to be?

I should have posted a 3/4 view of the assembly; much would have been
clear.

The shaft is supported by bearings in the framework, and the pot has some
lateral play. So in theory, the pot sees no lateral force at all. Where
I fell down on this is that when the pot sees no axial force it has too
much play in rotation; taking up that play means that the pot, rather
than the bearings, is locating the shaft.

Your idea of using a flex coupling has merit. I'm not sure if I can do
it cheaply, but I'll think on it.

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

On Tue, 13 Nov 2012 11:17:56 +0800, Dennis wrote:

"Tim Wescott" wrote in message
...
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at
a commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this
week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp
eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my
customer was able to repair the thing and I was able to use it for
demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different
way of putting the whole thing together so that it's easy to
disassemble for shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set
up a problem with the shaft transmitting too much force to the pot, and
-- ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So
not only am I very concerned about shipping, I'm a bit concerned about
this being a point of fragility in an otherwise reasonably stout
mechanism.

Comments appreciated.

--
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



Can you slit the shaft with a junior hacksaw & spring it apart just a
little. That would allow it to slide on & off easily whilst maintaining
good coupling.

I've been wondering that myself. It would certainly work, if the
machining cost didn't overwhelm the advantage of using a $2.00 part.

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

On Mon, 12 Nov 2012 23:59:20 -0600, Jon Elson wrote:

Tim Wescott wrote:


Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.
First question is who'd you ship it with? If UPS, the answer is clear.
A little knocking around your shop is not a valid test, you have to put
it in the shipping box and throw it 20 feet. That's how UPS unloads
their semis - they throw everything off the truck into a big pile. Try
sending it FedEx, they are much more gentle with stuff.

Alaska Air Lines and United -- it went as luggage.

I could certainly go a long way toward solving the problem with a bit of
disassembly before shipment, I do know that.

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

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at a
commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my customer
was able to repair the thing and I was able to use it for demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different way
of putting the whole thing together so that it's easy to disassemble for
shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set up
a problem with the shaft transmitting too much force to the pot, and --
ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So not
only am I very concerned about shipping, I'm a bit concerned about this
being a point of fragility in an otherwise reasonably stout mechanism.

Comments appreciated.

I think a little more forensic study is needed. Did the solder break?
Did the traces on the board pull off the board? Remember when we first
learned to solder we were told never to rely on solder to hold anything.

I would suggest you fabricate a tinned clamping piece with a hole for
the shaft and bent over the edges of the pot and then soldered to the
circuit board. Solder the clamp before you solder the legs of the pot so
there is no upward pressure on the clamp.

Paul, KD7HB

On Tue, 13 Nov 2012 10:22:57 -0800, Paul Drahn wrote:

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at
a commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

But I went and took it on an airline flight for the first time this
week,
and it didn't survive well. The position feedback from the pivot is
provided by a nice inexpensive potentiometer with a D-shaped hole, into
which one inserts a shaft of the correct dimensions. Here's a close-up
of the pot mounted on the board, with a shaft (and, if you've sharp
eyes,
a little paper shim that keeps things snug).

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

On the flight (two flights each way, Portland to Ottawa and back), the
pot broke off the board. It was obviously punched out of the board by
the force of the shaft acting on the back of the pot. Fortunately the
training is for engineers, and it was at a corporate site, so my
customer was able to repair the thing and I was able to use it for
demonstrations.

Unfortunately -- even though I thought I had identified the problem and
fixed it -- it broke on the way back, too.

Now, one solution to this may just be that I need to find a different
way of putting the whole thing together so that it's easy to
disassemble for shipping, and then don't ship it assembled.

But I also want to put it out to the group for suggestions: the shaft
needs to be shimmed to a snug fit in the hole of the pot, or the slight
play between pot and shaft messes up the control (the arm will hunt
within the slop of the connection). But shimming things seems to set
up a problem with the shaft transmitting too much force to the pot, and
-- ping!!!

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So
not only am I very concerned about shipping, I'm a bit concerned about
this being a point of fragility in an otherwise reasonably stout
mechanism.

Comments appreciated.

I think a little more forensic study is needed. Did the solder break?
Did the traces on the board pull off the board? Remember when we first
learned to solder we were told never to rely on solder to hold anything.

I would suggest you fabricate a tinned clamping piece with a hole for
the shaft and bent over the edges of the pot and then soldered to the
circuit board. Solder the clamp before you solder the legs of the pot so
there is no upward pressure on the clamp.

The solder broke on some pins, and the pins broke elsewhere. But the pot
is clearly not designed to be a bearing, either regular or thrust.
Reinforcing the solder joints enough will just make the housing break.

Isolating the pot from everything except for shaft rotation -- that
should work.

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

On 2012-11-13, Tim Wescott wrote:
On Tue, 13 Nov 2012 10:22:57 -0800, Paul Drahn wrote:

On 11/12/2012 2:27 PM, Tim Wescott wrote:
So, I'm working on a gizmo to go with a series of control systems
training seminars that I'm putting on.

The gizmo is basically a fan on a pivoted stick, with a control system
that works to maintain the angle of the stick relative to its mount at
a commanded value. It does a good job of giving people a visceral
understanding of how a feedback control system works, and I don't think
it's going to cost me much to produce.

[ ... ]

This thing has experienced a moderate amount of knocking around in my
shop, and use both on the property and around the local area without
breaking. But as soon as I go and ship the damn thing it breaks. So
not only am I very concerned about shipping, I'm a bit concerned about
this being a point of fragility in an otherwise reasonably stout
mechanism.

Comments appreciated.

I think a little more forensic study is needed. Did the solder break?
Did the traces on the board pull off the board? Remember when we first
learned to solder we were told never to rely on solder to hold anything.

I would suggest you fabricate a tinned clamping piece with a hole for
the shaft and bent over the edges of the pot and then soldered to the
circuit board. Solder the clamp before you solder the legs of the pot so
there is no upward pressure on the clamp.

The solder broke on some pins, and the pins broke elsewhere. But the pot
is clearly not designed to be a bearing, either regular or thrust.
Reinforcing the solder joints enough will just make the housing break.

Isolating the pot from everything except for shaft rotation -- that
should work.

Well ... there used to be pots designed for use in servo
assemblies (as position feedback) and similar things. 360 degrees
rotation, the ability to set taps wherever you want them on the
resistance element, and the shaft mounted in ball bearings (1/4"
shaft typically). One of these would certainly be strong enough, if
mounted structurally. It is not designed for printed circuit mounting,
but rather for mounting in a precise hole, held in by clamps, and
allowed to rotate to set the zero point before the clamps were
tightened. Given the bearings, and the very low contact force wiper, it
has almost no drag.

One of these would certainly handle the loads, but while I never
bought one of these new (just from eBay or at hamfests) I'm willing to
bet that they would be *very* expensive compared to what you need.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote:

Well ... there used to be pots designed for use in servo
assemblies (as position feedback) and similar things. 360 degrees
rotation, the ability to set taps wherever you want them on the
resistance element, and the shaft mounted in ball bearings (1/4"
shaft typically). One of these would certainly be strong enough, if
mounted structurally. It is not designed for printed circuit mounting,
but rather for mounting in a precise hole, held in by clamps, and
allowed to rotate to set the zero point before the clamps were
tightened. Given the bearings, and the very low contact force wiper, it
has almost no drag.

One of these would certainly handle the loads, but while I never
bought one of these new (just from eBay or at hamfests) I'm willing to
bet that they would be *very* expensive compared to what you need.


Those are similar to the Chromakey pot used in high end video
consoles. They had four 90° taps and cost ^ $1000 in the '70s.