Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds. I
have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the ones
I have seen that can provide enough drag have too much drag when not
energized and have too large a diameter. About 3 inches diameter by
about 3.5 inches long is the space the clutch or brake must fit in. I
am considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By varying
the field strength the resistance to rotation would increase. Whatever
the solution is the resistance to rotation must be linear to the
current that actuates the device. That's one of the reasons I like the
magnetic particle barkes.
Thanks,
Eric

On 11/02/16 19:31, wrote:
Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds. I
have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the ones
I have seen that can provide enough drag have too much drag when not
energized and have too large a diameter. About 3 inches diameter by
about 3.5 inches long is the space the clutch or brake must fit in. I
am considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By varying
the field strength the resistance to rotation would increase. Whatever
the solution is the resistance to rotation must be linear to the
current that actuates the device. That's one of the reasons I like the
magnetic particle barkes.
Thanks,
Eric
Have you looked at automotive aircon clutches. I don't know if they're
suitable and normally used for on/off operation but likely cheap to get
one from a breaker to test or play with.

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or something.
I'm turning handwheels that need some sort of instantly variable
resistance to turning . Anywhere from 0 to 40 inch pounds. I have been
looking at magnetic particle clutches and brakes, eddy current brakes,
and disc type clutches and brakes. The magnetic particle brakes would
seem to be a good solution except that the ones I have seen that can
provide enough drag have too much drag when not energized and have too
large a diameter. About 3 inches diameter by about 3.5 inches long is
the space the clutch or brake must fit in. I am considering rolling my
own devices but am not sure how I would do it. Maybe some sort of
generator feeding a resistive load. By varying the field strength the
resistance to rotation would increase. Whatever the solution is the
resistance to rotation must be linear to the current that actuates the
device. That's one of the reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise, what?

I'm pretty sure that when you say "turning ... that need ... turning" you
mean you're making things on a lathe that need resistance to someone
twisting them.

Does the resistance need to be viscous, tapering off to zero as the speed
tapers off? Does it need to be constant down to zero speed? Something
else?

The excruciatingly high-tech way to do this is with a direct-drive motor,
position sensor, and a fancy control system. That's overkill for a whole
lot of applications, but I've done it for something that really needed it.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Thu, 11 Feb 2016 19:33:18 +0000, David Billington
wrote:

On 11/02/16 19:31, wrote:
Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds. I
have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the ones
I have seen that can provide enough drag have too much drag when not
energized and have too large a diameter. About 3 inches diameter by
about 3.5 inches long is the space the clutch or brake must fit in. I
am considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By varying
the field strength the resistance to rotation would increase. Whatever
the solution is the resistance to rotation must be linear to the
current that actuates the device. That's one of the reasons I like the
magnetic particle barkes.
Thanks,
Eric
Have you looked at automotive aircon clutches. I don't know if they're
suitable and normally used for on/off operation but likely cheap to get
one from a breaker to test or play with.
Greetings David,
Those clutches are way too large. But thanks anyway.
Eric

On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or something.
I'm turning handwheels that need some sort of instantly variable
resistance to turning . Anywhere from 0 to 40 inch pounds. I have been
looking at magnetic particle clutches and brakes, eddy current brakes,
and disc type clutches and brakes. The magnetic particle brakes would
seem to be a good solution except that the ones I have seen that can
provide enough drag have too much drag when not energized and have too
large a diameter. About 3 inches diameter by about 3.5 inches long is
the space the clutch or brake must fit in. I am considering rolling my
own devices but am not sure how I would do it. Maybe some sort of
generator feeding a resistive load. By varying the field strength the
resistance to rotation would increase. Whatever the solution is the
resistance to rotation must be linear to the current that actuates the
device. That's one of the reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise, what?

I'm pretty sure that when you say "turning ... that need ... turning" you
mean you're making things on a lathe that need resistance to someone
twisting them.

Does the resistance need to be viscous, tapering off to zero as the speed
tapers off? Does it need to be constant down to zero speed? Something
else?

The excruciatingly high-tech way to do this is with a direct-drive motor,
position sensor, and a fancy control system. That's overkill for a whole
lot of applications, but I've done it for something that really needed it.
The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn. I want to be able to feel the machine
working. All the way down to zero speed. I thought a hysteresis brake
would work until I found out about the cogging effect. I though about
using a BLDC motor kit I have to make a skewed rotor to avoid cogging
but I'm not sure if it would work, and if it did would it be fairly
linear.
Eric

wrote:
On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds.
I have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the
ones I have seen that can provide enough drag have too much drag
when not energized and have too large a diameter. About 3 inches
diameter by about 3.5 inches long is the space the clutch or brake
must fit in. I am considering rolling my own devices but am not
sure how I would do it. Maybe some sort of generator feeding a
resistive load. By varying the field strength the resistance to
rotation would increase. Whatever the solution is the resistance to
rotation must be linear to the current that actuates the device.
That's one of the reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise,
what?

I'm pretty sure that when you say "turning ... that need ...
turning" you mean you're making things on a lathe that need
resistance to someone twisting them.

Does the resistance need to be viscous, tapering off to zero as the
speed tapers off? Does it need to be constant down to zero speed?
Something else?

The excruciatingly high-tech way to do this is with a direct-drive
motor, position sensor, and a fancy control system. That's overkill
for a whole lot of applications, but I've done it for something that
really needed it.
The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn. I want to be able to feel the machine
working. All the way down to zero speed. I thought a hysteresis brake
would work until I found out about the cogging effect. I though about
using a BLDC motor kit I have to make a skewed rotor to avoid cogging
but I'm not sure if it would work, and if it did would it be fairly
linear.
Eric

Hysteresis ... How about a small PM DC motor hooked to a load and geared to
turn faster than the hand wheel , might reduce or eliminate the cogging . ?

--
Snag

wrote:


The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn.
What you want is a small servo motor controlled by a servo amplifier. The
torque is proportional to motor current. Just take the current monitor
signal from the servo amp, amplify and apply to the handwheel motor.

Trying to do this with clutches or brakes will lead to great frustration.
Only the most exotic clutches and brakes are very smooth, and otherwise
would put a lot of stick-slip friction into a systemw here you really DON'T
want that.

If the main motor is a DC brush servo, it is possible that a resistor can be
put in series with it, and the handwheel motor connected across that
resistor. Then you would not require a separate small servo amplifier.

Jon

On Thursday, February 11, 2016 at 2:33:50 PM UTC-8, Terry Coombs wrote:
wrote:
On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning


Hysteresis ... How about a small PM DC motor hooked to a load and geared to
turn faster than the hand wheel , might reduce or eliminate the cogging . ?

I'd call it a 'generator' because that's what it is when it dumps power
into a load resistor, but yeah, this is a sensible way to go.
One could also consider using an AC motor with variable DC exciting current
to act as a kind of adjustable brake.

On Thu, 11 Feb 2016 13:59:30 -0800, etpm wrote:

On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or
something.
I'm turning handwheels that need some sort of instantly variable
resistance to turning . Anywhere from 0 to 40 inch pounds. I have been
looking at magnetic particle clutches and brakes, eddy current brakes,
and disc type clutches and brakes. The magnetic particle brakes would
seem to be a good solution except that the ones I have seen that can
provide enough drag have too much drag when not energized and have too
large a diameter. About 3 inches diameter by about 3.5 inches long is
the space the clutch or brake must fit in. I am considering rolling my
own devices but am not sure how I would do it. Maybe some sort of
generator feeding a resistive load. By varying the field strength the
resistance to rotation would increase. Whatever the solution is the
resistance to rotation must be linear to the current that actuates the
device. That's one of the reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise,
what?

I'm pretty sure that when you say "turning ... that need ... turning"
you mean you're making things on a lathe that need resistance to someone
twisting them.

Does the resistance need to be viscous, tapering off to zero as the
speed tapers off? Does it need to be constant down to zero speed?
Something else?

The excruciatingly high-tech way to do this is with a direct-drive
motor, position sensor, and a fancy control system. That's overkill for
a whole lot of applications, but I've done it for something that really
needed it.
The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put a
drag on the handwheel. So more work for the servo makes the handwheels
harder to turn. I want to be able to feel the machine working. All the
way down to zero speed. I thought a hysteresis brake would work until I
found out about the cogging effect. I though about using a BLDC motor
kit I have to make a skewed rotor to avoid cogging but I'm not sure if
it would work, and if it did would it be fairly linear.
Eric

Oooh. If you want to sound trendy, you're building a system with haptic
feedback. That'll get you a _lot_ more funding than "a servo motor that
you can feel when it sticks".

You can get motors with low or no cogging torque. I'm not sure if you
can get them _cheaply_, but they're out there. Coreless motors are most
definitely of this variety.

Gear a DC motor down, not too far that the drag of the gear train or the
inertia of the motor is noticeable. Then run a current through the DC
motor that's proportional to the current draw of your servo motor.

The 1940 way to do this would be to use DC motors for servo drive and
haptic feedback, select them carefully, and just connect them in series.
The torque on the feedback motor will, automagically, be proportional to
the torque on the drive motor, without you wasting too many vacuum tubes
or relays (since this in 1940) on making it so.

You'll probably have all sorts of bandwidth issues that'll be easier to
settle if you use fancy electronics and whatnot.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Thu, 11 Feb 2016 16:33:48 -0600, "Terry Coombs"
wrote:

wrote:
On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds.
I have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the
ones I have seen that can provide enough drag have too much drag
when not energized and have too large a diameter. About 3 inches
diameter by about 3.5 inches long is the space the clutch or brake
must fit in. I am considering rolling my own devices but am not
sure how I would do it. Maybe some sort of generator feeding a
resistive load. By varying the field strength the resistance to
rotation would increase. Whatever the solution is the resistance to
rotation must be linear to the current that actuates the device.
That's one of the reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise,
what?

I'm pretty sure that when you say "turning ... that need ...
turning" you mean you're making things on a lathe that need
resistance to someone twisting them.

Does the resistance need to be viscous, tapering off to zero as the
speed tapers off? Does it need to be constant down to zero speed?
Something else?

The excruciatingly high-tech way to do this is with a direct-drive
motor, position sensor, and a fancy control system. That's overkill
for a whole lot of applications, but I've done it for something that
really needed it.
The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn. I want to be able to feel the machine
working. All the way down to zero speed. I thought a hysteresis brake
would work until I found out about the cogging effect. I though about
using a BLDC motor kit I have to make a skewed rotor to avoid cogging
but I'm not sure if it would work, and if it did would it be fairly
linear.
Eric

Hysteresis ... How about a small PM DC motor hooked to a load and geared to
turn faster than the hand wheel , might reduce or eliminate the cogging . ?
I dunno Terry, You idea sounded good until I tried it a little bit
ago. with a couple BLDC motors I had laying around. I just couldn't
get enough drag, even with fairly high speeds and high performance
motors. Your idea has merit but not with my constraints.
Cheers,
Eric

On Thu, 11 Feb 2016 17:40:20 -0600, Jon Elson
wrote:

wrote:


The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn.
What you want is a small servo motor controlled by a servo amplifier. The
torque is proportional to motor current. Just take the current monitor
signal from the servo amp, amplify and apply to the handwheel motor.

Trying to do this with clutches or brakes will lead to great frustration.
Only the most exotic clutches and brakes are very smooth, and otherwise
would put a lot of stick-slip friction into a systemw here you really DON'T
want that.

If the main motor is a DC brush servo, it is possible that a resistor can be
put in series with it, and the handwheel motor connected across that
resistor. Then you would not require a separate small servo amplifier.

Jon
Greetings Jon,
The brakes and clutches I have seriously considered are non-contact
devices so the stick-slip problem is one I wouldn't need to deal with.
I thought about using a small motor as the brake but n oit the way
you describe. The main servos are DC brush servos and will be using 20
amps max for about 4 minutes max, with maybe a 7 second period of a 4
amp draw and then 20 amps again and so on. There will be peaks of much
higher current draws, maybe 80 amps, but these peaks will be quite
short and the servo amps can handle the loads. Can you explain a
little about how the resistor in series with the main servo and the
handwheel servo, which supplies the drag, connected in parallel with
the resistor, would work?
Thanks,
Eric

On Thu, 11 Feb 2016 19:33:18 +0000, David Billington
wrote:

On 11/02/16 19:31, wrote:
Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds. I
have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the ones
I have seen that can provide enough drag have too much drag when not
energized and have too large a diameter. About 3 inches diameter by
about 3.5 inches long is the space the clutch or brake must fit in. I
am considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By varying
the field strength the resistance to rotation would increase. Whatever
the solution is the resistance to rotation must be linear to the
current that actuates the device. That's one of the reasons I like the
magnetic particle barkes.
Thanks,
Eric
Have you looked at automotive aircon clutches. I don't know if they're
suitable and normally used for on/off operation but likely cheap to get
one from a breaker to test or play with.

A/C clutches aren't made to slip at all, David. This won't work.
Band clutch/brakes have been used in auto tranny setups and on old
emergency brakes for early vehicles.

Eric, band brake setups might work for you, with solenoid actuation.
Variable voltage to the solenoid could facilitate varied braking.
https://www.youtube.com/watch?v=fSRWf8PY_4Y Something like this.
But done a teeny bit more professionally? g
https://www.youtube.com/watch?v=RwVeIbRx7wE

--
I would be the most content if my children grew up to be the kind of people
who think decorating consists mostly of building enough bookshelves.
-- Anna Quindlen

On Thu, 11 Feb 2016 18:17:51 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 13:59:30 -0800, etpm wrote:

On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or
something.
I'm turning handwheels that need some sort of instantly variable
resistance to turning . Anywhere from 0 to 40 inch pounds. I have been
looking at magnetic particle clutches and brakes, eddy current brakes,
and disc type clutches and brakes. The magnetic particle brakes would
seem to be a good solution except that the ones I have seen that can
provide enough drag have too much drag when not energized and have too
large a diameter. About 3 inches diameter by about 3.5 inches long is
the space the clutch or brake must fit in. I am considering rolling my
own devices but am not sure how I would do it. Maybe some sort of
generator feeding a resistive load. By varying the field strength the
resistance to rotation would increase. Whatever the solution is the
resistance to rotation must be linear to the current that actuates the
device. That's one of the reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise,
what?

I'm pretty sure that when you say "turning ... that need ... turning"
you mean you're making things on a lathe that need resistance to someone
twisting them.

Does the resistance need to be viscous, tapering off to zero as the
speed tapers off? Does it need to be constant down to zero speed?
Something else?

The excruciatingly high-tech way to do this is with a direct-drive
motor, position sensor, and a fancy control system. That's overkill for
a whole lot of applications, but I've done it for something that really
needed it.
The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put a
drag on the handwheel. So more work for the servo makes the handwheels
harder to turn. I want to be able to feel the machine working. All the
way down to zero speed. I thought a hysteresis brake would work until I
found out about the cogging effect. I though about using a BLDC motor
kit I have to make a skewed rotor to avoid cogging but I'm not sure if
it would work, and if it did would it be fairly linear.
Eric

Oooh. If you want to sound trendy, you're building a system with haptic
feedback. That'll get you a _lot_ more funding than "a servo motor that
you can feel when it sticks".

You can get motors with low or no cogging torque. I'm not sure if you
can get them _cheaply_, but they're out there. Coreless motors are most
definitely of this variety.

Gear a DC motor down, not too far that the drag of the gear train or the
inertia of the motor is noticeable. Then run a current through the DC
motor that's proportional to the current draw of your servo motor.

The 1940 way to do this would be to use DC motors for servo drive and
haptic feedback, select them carefully, and just connect them in series.
The torque on the feedback motor will, automagically, be proportional to
the torque on the drive motor, without you wasting too many vacuum tubes
or relays (since this in 1940) on making it so.

You'll probably have all sorts of bandwidth issues that'll be easier to
settle if you use fancy electronics and whatnot.
Greetings Tim,
I am indeed designing a haptic system. The mechanical parts I
understand pretty well but the electrotonical and automagical stuff I
need a little help with. Terry suggested the gear train DC motor idea
but I don't think it will work for what I am trying to do. Please
correct me if I am wrong but it seems to me that with the system you
describe above the servo connected to the handwheel will have the same
current passing through it as the servo that is doing all the work. Is
this the case? The handwheel torque resisting device will need to
provide, at most, 40 inch pounds of resistive torque, and this will
require little current, or more accurately, few watts. Less than15
watts on a continuous basis.The servo motor that the handwheel is
controlling, the one that is actually doing the work will oftentimes
be consuming 1800 watts. Would this work with your scheme? As
mentioned in my original post each handwheel will be connected to an
encoder. These encoders will be providing the information needed to
control the position and speed of the main servo motors. I am not
considering something like a SloSyn system. If I turn the handwheel
such that an axis should move .0001" inch I expect that it will. I
can, and have, done this in the past. Used a hand wheel to turn an
encoder to provide a signal to a servo amp connected to a servo motor
connected to a ballscrew connected to a slide in order to move it in
..00005" increments. What I haven't done is to add drag to the
handwheel that is proportional to the load on the servo. Even if the
drag on the handwheel isn't exactly proportional the positioning will
and must always be correct, the encoder to circuitry to servo motor
cannot be affected by whatever is used to add drag to the handwheel.
Cheers,
Eric

wrote:

Can you explain a
little about how the resistor in series with the main servo and the
handwheel servo, which supplies the drag, connected in parallel with
the resistor, would work?
Well, a very small resistance would be put in series with the main motor.
This resistor would be of much lower value than the DC resistance of the
handwheel motor. The handwheel motor would then be put across the resistor.
Some portion of the main motor current would flow through the handwheel
motor, producing a torque. Possibly, you'd also place an adjustable
resistor in series with the handwheel motor to set the level of torque feel.

I really don't know if this will work, as when turning the handwheel fast
that motor will generate a voltage that will be dumped in the resistor.
But, since the servo system with the encoders will make the main motor synch
to the handwheel, these back EMF's should be able to be equalized.

This would be a cheat that would allow you to do this without a bunch of
electronics, like an extra, small servo amp. As I say, I'm not sure it
would work.

Jon

wrote in message
...

Perhaps the mechanism from a force feedback gamer steering wheel would
work?
http://www.amazon.com/Wireless-Force.../dp/B0057OW94E

--jsw

On Thu, 11 Feb 2016 22:49:33 -0600, Jon Elson
wrote:

wrote:

Can you explain a
little about how the resistor in series with the main servo and the
handwheel servo, which supplies the drag, connected in parallel with
the resistor, would work?
Well, a very small resistance would be put in series with the main motor.
This resistor would be of much lower value than the DC resistance of the
handwheel motor. The handwheel motor would then be put across the resistor.
Some portion of the main motor current would flow through the handwheel
motor, producing a torque. Possibly, you'd also place an adjustable
resistor in series with the handwheel motor to set the level of torque feel.

I really don't know if this will work, as when turning the handwheel fast
that motor will generate a voltage that will be dumped in the resistor.
But, since the servo system with the encoders will make the main motor synch
to the handwheel, these back EMF's should be able to be equalized.

This would be a cheat that would allow you to do this without a bunch of
electronics, like an extra, small servo amp. As I say, I'm not sure it
would work.

Jon
Greetings Jon,
If it works it is not a cheat. The handwheel motor would need to be
wired backward with respect to the rotation of the main servo so that
it will oppose rotaton of the handwheel. I will investigate your idea.
Simple and easy to implement. If it works.
Cheers,
Eric

On Thu, 11 Feb 2016 19:47:55 -0800, etpm wrote:

On Thu, 11 Feb 2016 18:17:51 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 13:59:30 -0800, etpm wrote:

On Thu, 11 Feb 2016 13:41:56 -0600, Tim Wescott
wrote:

On Thu, 11 Feb 2016 11:31:49 -0800, etpm wrote:

Everybody,
I'm working on a project that needs a slip clutch or brake or
something.
I'm turning handwheels that need some sort of instantly variable
resistance to turning . Anywhere from 0 to 40 inch pounds. I have
been looking at magnetic particle clutches and brakes, eddy current
brakes,
and disc type clutches and brakes. The magnetic particle brakes
would seem to be a good solution except that the ones I have seen
that can provide enough drag have too much drag when not energized
and have too large a diameter. About 3 inches diameter by about 3.5
inches long is the space the clutch or brake must fit in. I am
considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By
varying the field strength the resistance to rotation would
increase. Whatever the solution is the resistance to rotation must
be linear to the current that actuates the device. That's one of the
reasons I like the magnetic particle barkes.

Not enough information.

These handwheels are to be used to control something, for exercise,
what?

I'm pretty sure that when you say "turning ... that need ... turning"
you mean you're making things on a lathe that need resistance to
someone twisting them.

Does the resistance need to be viscous, tapering off to zero as the
speed tapers off? Does it need to be constant down to zero speed?
Something else?

The excruciatingly high-tech way to do this is with a direct-drive
motor, position sensor, and a fancy control system. That's overkill
for a whole lot of applications, but I've done it for something that
really needed it.
The handwheels turn an encoder that makes a servo motor turn a
leadscrew. I want to monitor the servo current draw and use it to put
a drag on the handwheel. So more work for the servo makes the
handwheels harder to turn. I want to be able to feel the machine
working. All the way down to zero speed. I thought a hysteresis brake
would work until I found out about the cogging effect. I though about
using a BLDC motor kit I have to make a skewed rotor to avoid cogging
but I'm not sure if it would work, and if it did would it be fairly
linear.
Eric

Oooh. If you want to sound trendy, you're building a system with haptic
feedback. That'll get you a _lot_ more funding than "a servo motor that
you can feel when it sticks".

You can get motors with low or no cogging torque. I'm not sure if you
can get them _cheaply_, but they're out there. Coreless motors are most
definitely of this variety.

Gear a DC motor down, not too far that the drag of the gear train or the
inertia of the motor is noticeable. Then run a current through the DC
motor that's proportional to the current draw of your servo motor.

The 1940 way to do this would be to use DC motors for servo drive and
haptic feedback, select them carefully, and just connect them in series.
The torque on the feedback motor will, automagically, be proportional to
the torque on the drive motor, without you wasting too many vacuum tubes
or relays (since this in 1940) on making it so.

You'll probably have all sorts of bandwidth issues that'll be easier to
settle if you use fancy electronics and whatnot.
Greetings Tim,
I am indeed designing a haptic system. The mechanical parts I understand
pretty well but the electrotonical and automagical stuff I need a little
help with. Terry suggested the gear train DC motor idea but I don't
think it will work for what I am trying to do.

I think that some gearing could be part of it, but not a lot. Probably
no more than 10:1 gearing. If you don't use gearing then you'll need to
find a big pancake motor with low or no cogging -- such things exist for
aerospace applications, but they're expensive new, and it'd take a
monstrous stroke of luck to find one surplus.

Please correct me if I am
wrong but it seems to me that with the system you describe above the
servo connected to the handwheel will have the same current passing
through it as the servo that is doing all the work. Is this the case?

Yup.

The handwheel torque resisting device will need to provide, at most, 40
inch pounds of resistive torque, and this will require little current,
or more accurately, few watts. Less than15 watts on a continuous
basis.The servo motor that the handwheel is controlling, the one that is
actually doing the work will oftentimes be consuming 1800 watts. Would
this work with your scheme?

Yup. The trick is to get a motor with a significantly lower torque
constant than your servo motors. It takes some careful motor choosing.

It may not be possible without custom-wound motors (which would be the
1940 way to do it) -- if that's the case, then sensing the current to the
servo motors and echoing it, suitably scaled, to the feedback motors
would be the way to go.

As mentioned in my original post each
handwheel will be connected to an encoder. These encoders will be
providing the information needed to control the position and speed of
the main servo motors. I am not considering something like a SloSyn
system. If I turn the handwheel such that an axis should move .0001"
inch I expect that it will. I can, and have, done this in the past. Used
a hand wheel to turn an encoder to provide a signal to a servo amp
connected to a servo motor connected to a ballscrew connected to a slide
in order to move it in .00005" increments. What I haven't done is to add
drag to the handwheel that is proportional to the load on the servo.
Even if the drag on the handwheel isn't exactly proportional the
positioning will and must always be correct, the encoder to circuitry to
servo motor cannot be affected by whatever is used to add drag to the
handwheel. Cheers,
Eric

I think you need to stop thinking in terms of "drag" on the handwheel and
start thinking in terms of "torque". It's mostly the same thing, but not
entirely quite.

--
www.wescottdesign.com

wrote:
Everybody,
I'm working on a project that needs a slip clutch or brake or
something. I'm turning handwheels that need some sort of instantly
variable resistance to turning . Anywhere from 0 to 40 inch pounds. I
have been looking at magnetic particle clutches and brakes, eddy
current brakes, and disc type clutches and brakes. The magnetic
particle brakes would seem to be a good solution except that the ones
I have seen that can provide enough drag have too much drag when not
energized and have too large a diameter. About 3 inches diameter by
about 3.5 inches long is the space the clutch or brake must fit in. I
am considering rolling my own devices but am not sure how I would do
it. Maybe some sort of generator feeding a resistive load. By varying
the field strength the resistance to rotation would increase. Whatever
the solution is the resistance to rotation must be linear to the
current that actuates the device. That's one of the reasons I like the
magnetic particle barkes.
Thanks,
Eric

handhwheel speeds are usually slow. gear or belt drive up to a DC motor
and short it out with some type of bridge recitfier (for use in
both directions) constant current setup. Even a cheapo
hacked LM317 might work if you can adjust it with whatever your controls
are. Hell, maybe just PWM it if you're using a computer. A single triac
might pull this off.

If you want it to feel nice, use coreless motors as they don't cog as
much. Yaskawa "Minertia" type servo motors are good too as they don't cog
and feel REAL smooth when run backwards.

wrote:
On Thu, 11 Feb 2016 22:49:33 -0600, Jon Elson
wrote:

wrote:

Can you explain a
little about how the resistor in series with the main servo and the
handwheel servo, which supplies the drag, connected in parallel with
the resistor, would work?
Well, a very small resistance would be put in series with the main motor.
This resistor would be of much lower value than the DC resistance of the
handwheel motor. The handwheel motor would then be put across the resistor.
Some portion of the main motor current would flow through the handwheel
motor, producing a torque. Possibly, you'd also place an adjustable
resistor in series with the handwheel motor to set the level of torque feel.

I really don't know if this will work, as when turning the handwheel fast
that motor will generate a voltage that will be dumped in the resistor.
But, since the servo system with the encoders will make the main motor synch
to the handwheel, these back EMF's should be able to be equalized.

This would be a cheat that would allow you to do this without a bunch of
electronics, like an extra, small servo amp. As I say, I'm not sure it
would work.

Jon
Greetings Jon,
If it works it is not a cheat. The handwheel motor would need to be
wired backward with respect to the rotation of the main servo so that
it will oppose rotaton of the handwheel. I will investigate your idea.
Simple and easy to implement. If it works.
Cheers,
Eric

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

--
Steve W.

On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

wrote:
On Thu, 11 Feb 2016 22:49:33 -0600, Jon Elson
wrote:

wrote:

Can you explain a
little about how the resistor in series with the main servo and the
handwheel servo, which supplies the drag, connected in parallel with
the resistor, would work?
Well, a very small resistance would be put in series with the main motor.
This resistor would be of much lower value than the DC resistance of the
handwheel motor. The handwheel motor would then be put across the resistor.
Some portion of the main motor current would flow through the handwheel
motor, producing a torque. Possibly, you'd also place an adjustable
resistor in series with the handwheel motor to set the level of torque feel.

I really don't know if this will work, as when turning the handwheel fast
that motor will generate a voltage that will be dumped in the resistor.
But, since the servo system with the encoders will make the main motor synch
to the handwheel, these back EMF's should be able to be equalized.

This would be a cheat that would allow you to do this without a bunch of
electronics, like an extra, small servo amp. As I say, I'm not sure it
would work.

Jon
Greetings Jon,
If it works it is not a cheat. The handwheel motor would need to be
wired backward with respect to the rotation of the main servo so that
it will oppose rotaton of the handwheel. I will investigate your idea.
Simple and easy to implement. If it works.
Cheers,
Eric

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.
How would that work? How are AC servos made? I'll look online.
Eric

On Friday, February 12, 2016 at 3:45:34 PM UTC-8, wrote:
On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

How would that work? How are AC servos made? I'll look online.

Most AC motors (the ones without brushes) will brake if you feed 'em
some DC. Steppers (but they cog), shaded-pole, or hysteresis types,
all have a rotor without driven windings, and DC on the stator makes
them into brakes.

On Fri, 12 Feb 2016 16:39:36 -0800, whit3rd wrote:

On Friday, February 12, 2016 at 3:45:34 PM UTC-8,
wrote:
On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

How would that work? How are AC servos made? I'll look online.

Most AC motors (the ones without brushes) will brake if you feed 'em
some DC. Steppers (but they cog), shaded-pole, or hysteresis types,
all have a rotor without driven windings, and DC on the stator makes
them into brakes.

This gets you back to something that brakes proportionally to speed,
though.

--
www.wescottdesign.com

On Fri, 12 Feb 2016 16:39:36 -0800 (PST), whit3rd
wrote:

On Friday, February 12, 2016 at 3:45:34 PM UTC-8, wrote:
On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

How would that work? How are AC servos made? I'll look online.

Most AC motors (the ones without brushes) will brake if you feed 'em
some DC. Steppers (but they cog), shaded-pole, or hysteresis types,
all have a rotor without driven windings, and DC on the stator makes
them into brakes.
I thoughty they only braked while spinning and once stopped there is
no braking force. I ordered some MR fluid and will try making my own
magnetorheological brake.
Eric

On 2016-02-18, wrote:
On Fri, 12 Feb 2016 16:39:36 -0800 (PST), whit3rd
wrote:

On Friday, February 12, 2016 at 3:45:34 PM UTC-8, wrote:
On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

How would that work? How are AC servos made? I'll look online.

Most AC motors (the ones without brushes) will brake if you feed 'em
some DC. Steppers (but they cog), shaded-pole, or hysteresis types,
all have a rotor without driven windings, and DC on the stator makes
them into brakes.
I thoughty they only braked while spinning and once stopped there is
no braking force.

That is true for AC motors. For steppers, since they have a
permanent magnet rotor, the braking continues, but things are a bit
rough until it gets to a stop. Perhaps sense the speed, and when it
comes close enough to a stop, switch from AC motor to stepper. (Make
things biggern than you want. :-)

I ordered some MR fluid and will try making my own
magnetorheological brake.

Have fun with that -- and let us know how it goes.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | (KV4PH) 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 ---

On 18 Feb 2016 20:57:16 GMT, "DoN. Nichols"
wrote:

On 2016-02-18, wrote:
On Fri, 12 Feb 2016 16:39:36 -0800 (PST), whit3rd
wrote:

On Friday, February 12, 2016 at 3:45:34 PM UTC-8, wrote:
On Fri, 12 Feb 2016 16:26:54 -0500, "Steve W."
wrote:

How about using DC to brake an AC servo? Higher the voltage the more
resistance to motion.

How would that work? How are AC servos made? I'll look online.

Most AC motors (the ones without brushes) will brake if you feed 'em
some DC. Steppers (but they cog), shaded-pole, or hysteresis types,
all have a rotor without driven windings, and DC on the stator makes
them into brakes.
I thoughty they only braked while spinning and once stopped there is
no braking force.

That is true for AC motors. For steppers, since they have a
permanent magnet rotor, the braking continues, but things are a bit
rough until it gets to a stop. Perhaps sense the speed, and when it
comes close enough to a stop, switch from AC motor to stepper. (Make
things biggern than you want. :-)

I ordered some MR fluid and will try making my own
magnetorheological brake.

Have fun with that -- and let us know how it goes.

Good Luck,
DoN.
I'm looking forward to finding out myself. I looked online for small
quantities but couldn't find any. Looked on ebay with no luck and then
a couple days later some showed up. It sounds like the perfect stuff
for my needs.
Eric