Trying to hold stepper motor and measuring

[aleksa]

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

 

[John Fields]

On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <aleksazr@gmail.com>
wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

---
Google "torque sensor".

 

[John Larkin]

On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <aleksazr@gmail.com>
wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

Orient the motor horizontally, wrap a string around the shaft, and see
how much weight it can lift. If it's a husky motor, you may need to
increase the shaft diameter somehow. The radius of the shaft
multiplied by the force from the weight is torque, measured in
foot-pounds or newton-meters or some such units. The stepper should be
rated in such units, too.

You could also use the string to pull on a spring scale and see how
much force you can get before the motor starts missing steps.

You can also un-mount the motor, apply a load, and measure the
reaction torque on the motor body.

http://en.wikipedia.org/wiki/Torque

John

 

[Tim Wescott]

On Tue, 13 Oct 2009 08:13:42 -0700, John Larkin wrote:

On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <aleksazr@gmail.com
wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

Orient the motor horizontally, wrap a string around the shaft, and see
how much weight it can lift. If it's a husky motor, you may need to
increase the shaft diameter somehow. The radius of the shaft multiplied
by the force from the weight is torque, measured in foot-pounds or
newton-meters or some such units. The stepper should be rated in such
units, too.

You could also use the string to pull on a spring scale and see how much
force you can get before the motor starts missing steps.

You can also un-mount the motor, apply a load, and measure the reaction
torque on the motor body.

http://en.wikipedia.org/wiki/Torque

John

Or clamp a stick to the shaft, and turn the motor to lift the stick.
Then use the known mass and center of gravity of the stick, plus some
trigonometry, to figure out the motor torque at the point of stall.

--
www.wescottdesign.com

 

[John Larkin]

On Tue, 13 Oct 2009 14:33:31 -0700 (PDT), aleksa <aleksazr@gmail.com>
wrote:

Sorry, I wasn't clear..

The method you are proposing is mechanical,
but I'm searching for a pure electrical method.

I don't want to measure how much the motor
CAN lift, but how much the motor IS lifting.

A stepper has its driver, transistors etc,
and when I apply a resistance to the shaft,
something in the circuit probably happens
that can be electrically measured, right?

Yes, something. Steppers are complex and waste essentially 100% power
at standstill or when stepping slowly, so there's no simple
relationship between power consumed and power delivered like you'd see
from a brush-type DC motor. It depends on the driver, too... L/R
drivers behave different from choppers.

I'd vote to measure reaction torque on the can. Or do the
string-torque thing and calibrate something observable in the drive
electronics against torque at some given speed, and then use that.

Try measuring power supply current as you load the shaft, and see if
that's a useful indicator of torque. It might be at some speeds.

John

 

[Jamie]

aleksa wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.
A stepper isn't the proper type of motor to use if you're trying to

sense torque/weight of objects/stall resistance.
For simplicity, you can use a DC motor with a incremental quadrature
encoder attached to the shaft to detect forward or reverse movements.
This detected signal would then drive the motor to maintain position.
From there, you can measure the amount of current the DC motor is
using which can then translate to torque or foot pounds of the object
pulling on it.

You can make your own encoder from a disc with holes in it and use
2 U-type Optical Rx and Tx units, offset from each another to generate
a quadrature signal. Or, I suppose a plastic gear could be used with 2
U-type sensors.

In any case, you need to be able to detect shaft movement to lock it
into position so that you can then take a current reading on the supply
that is driving the motor.

One could use another DC motor attached to the same shaft which would
generate DC voltage that is polarized, give you the direction and speed
of the motor how ever, you wouldn't be able to bring it to a complete
stand still this way.

 

[aleksa]

Sorry, I wasn't clear..

The method you are proposing is mechanical,
but I'm searching for a pure electrical method.

I don't want to measure how much the motor
CAN lift, but how much the motor IS lifting.

A stepper has its driver, transistors etc,
and when I apply a resistance to the shaft,
something in the circuit probably happens
that can be electrically measured, right?

Maybe "torque sensor", as John Fields said,
I haven't searched yet.

John Larkin wrote:

On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <aleksazr@gmail.com
wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

Orient the motor horizontally, wrap a string around the shaft, and see
how much weight it can lift. If it's a husky motor, you may need to
increase the shaft diameter somehow. The radius of the shaft
multiplied by the force from the weight is torque, measured in
foot-pounds or newton-meters or some such units. The stepper should be
rated in such units, too.

You could also use the string to pull on a spring scale and see how
much force you can get before the motor starts missing steps.

You can also un-mount the motor, apply a load, and measure the
reaction torque on the motor body.

http://en.wikipedia.org/wiki/Torque

John

 

[aleksa]

On Oct 13, 11:33 pm, aleksa <aleks...@gmail.com> wrote:

Sorry, I wasn't clear..

The method you are proposing is mechanical,
but I'm searching for a pure electrical method.

I don't want to measure how much the motor
CAN lift, but how much the motor IS lifting.

In one word, a dynamometer.

A stepper has its driver, transistors etc,
and when I apply a resistance to the shaft,
something in the circuit probably happens
that can be electrically measured, right?

Maybe "torque sensor", as John Fields said,
I haven't searched yet.



John Larkin wrote:
On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <aleks...@gmail.com
wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

Orient the motor horizontally, wrap a string around the shaft, and see
how much weight it can lift. If it's a husky motor, you may need to
increase the shaft diameter somehow. The radius of the shaft
multiplied by the force from the weight is torque, measured in
foot-pounds or newton-meters or some such units. The stepper should be
rated in such units, too.

You could also use the string to pull on a spring scale and see how
much force you can get before the motor starts missing steps.

You can also un-mount the motor, apply a load, and measure the
reaction torque on the motor body.

http://en.wikipedia.org/wiki/Torque

John

 

[John Fields]

On Tue, 13 Oct 2009 14:33:31 -0700 (PDT), aleksa <aleksazr@gmail.com>
wrote:

Sorry, I wasn't clear..

The method you are proposing is mechanical,
but I'm searching for a pure electrical method.

I don't want to measure how much the motor
CAN lift, but how much the motor IS lifting.

A stepper has its driver, transistors etc,
and when I apply a resistance to the shaft,
something in the circuit probably happens
that can be electrically measured, right?

Maybe "torque sensor", as John Fields said,
I haven't searched yet.

---
This is USENET, not email, so please don't top post.

Instead, bottom post or in-line post when it's appropriate.

Thanks,

JF

 

[John Fields]

On Tue, 13 Oct 2009 19:08:15 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

aleksa wrote:
The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.
A stepper isn't the proper type of motor to use if you're trying to
sense torque/weight of objects/stall resistance.

---
Dumbass, whether you think it's "proper" or not, what he wants to do is
sense and measure the torque being generated by a _stepping_ motor when
its rotation is being resisted.

 

[George Herold]

On Oct 13, 6:08 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 13 Oct 2009 14:33:31 -0700 (PDT), aleksa <aleks...@gmail.com
wrote:

Sorry, I wasn't clear..

The method you are proposing is mechanical,
but I'm searching for a pure electrical method.

I don't want to measure how much the motor
CAN lift, but how much the motor IS lifting.

A stepper has its driver, transistors etc,
and when I apply a resistance to the shaft,
something in the circuit probably happens
that can be electrically measured, right?

Yes, something. Steppers are complex and waste essentially 100% power
at standstill or when stepping slowly, so there's no simple
relationship between power consumed and power delivered like you'd see
from a brush-type DC motor. It depends on the driver, too... L/R
drivers behave different from choppers.

I'd vote to measure reaction torque on the can. Or do the
string-torque thing and calibrate something observable in the drive
electronics against torque at some given speed, and then use that.

Try measuring power supply current as you load the shaft, and see if
that's a useful indicator of torque. It might be at some speeds.

John

Measuring change in the electronics sounds complicated... (holding
current vs torquing current.)

I can imagine some spring loaded 'gizmo' that couples the shafts
together and flexes under different torques. But now you have to get
the signal out of a spinning thing... doable but...

How about measuring the force where the motor mounts to whatever is
holding it in place? A little strain gauge or something? (Not sure
exactly how this would be done.)

George H.

 

[Jamie]

John Fields wrote:

On Tue, 13 Oct 2009 19:08:15 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


aleksa wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

A stepper isn't the proper type of motor to use if you're trying to
sense torque/weight of objects/stall resistance.


---
Dumbass, whether you think it's "proper" or not, what he wants to do is
sense and measure the torque being generated by a _stepping_ motor when
its rotation is being resisted.

Oh excuse me..

Since I've done this sort of thing many times in various applications,
why don't you step up to the plate and show us how's it done with a
stepper motor? God of all Electronics and what ever else you hold
yourself so high on the pedestal.

Since I offered no viable solution with a stepper motor and suggested
a DC PM/SHUNT type, I must of had a reason?

Varying the current to the coils of the stepper until the slip takes
place, to me, isn't a very accurate method. But don't let me stand in
the way of progress. I'm sure you have a solution.

A stepper motor can perform that task how ever, you still need a feed
back/angle sensor and special control over the current in the coils to
allow movement so the weight of the object can be accounted for.

No matter how you look at it, it's still not a good option, so I'll
wait for your solution with that superior intellect of yours!.

 

[John Fields]

On Wed, 14 Oct 2009 20:12:20 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Fields wrote:
On Tue, 13 Oct 2009 19:08:15 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


aleksa wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

A stepper isn't the proper type of motor to use if you're trying to
sense torque/weight of objects/stall resistance.


---
Dumbass, whether you think it's "proper" or not, what he wants to do is
sense and measure the torque being generated by a _stepping_ motor when
its rotation is being resisted.

Oh excuse me..

Since I've done this sort of thing many times in various applications,
why don't you step up to the plate and show us how's it done with a
stepper motor? God of all Electronics and what ever else you hold
yourself so high on the pedestal.

---
Oh, my, you certainly get testy when you're corrected, don't you?
---

Since I offered no viable solution with a stepper motor and suggested
a DC PM/SHUNT type, I must of had a reason?

---
Not must _of_ had a reason, must _have_ had a reason, the reason most
probably being just to hear yourself talk, since you certainly didn't
address OP's problem.
---

Varying the current to the coils of the stepper until the slip takes
place, to me, isn't a very accurate method. But don't let me stand in
the way of progress. I'm sure you have a solution.

---
Yes, I do.
---

A stepper motor can perform that task how ever, you still need a feed
back/angle sensor and special control over the current in the coils to
allow movement so the weight of the object can be accounted for.

---
Really?

Why don't you explain how that works, then?
---

No matter how you look at it, it's still not a good option, so I'll
wait for your solution with that superior intellect of yours!.

---
Ready?

Here we go:

One way to do it is to take a rod, machine away its middle so that
there's a thin strip between the two cylindrical ends and glue a strain
gage to the strip it so its (the strain gage's) resistance changes with
torsion, then you connect the stain gage electrically to a pair of slip
rings and use a pair of brushes to bring the signal from the strain gage
to the outside world as the shaft (rod) rotates, supported by bearings.

One end of the shaft is connected to the shaft of the stepping motor and
the other end is connected to a frictional load which can be varied.

In use, the motor is caused to rotate by its normal driver and the load
varied until the motor just stalls.

Because the resistance of the strain gage changes because the shaft is
being twisted, its resistance will be proportional to the torque causing
the twist to occur.

In the OP's case, what he'd do would be to increase the load until the
motor stalled, and then, since he wanted to know what the maximum torque
would be while it was running, back off just enough to let it run and
then read the torque off the dial.

So now I guess you want me to explain all about the stuff between the
sensor and the readout???

Another, more elegant way to do it would be to machine down the middle,
polish a couple of spots on each end to a mirror finish and use laser
diodes and photodiodes to generate pulses which would be separated in
time more and more as the torque on the shaft increased.

Happy now?


JF

 

[Jamie]

John Fields wrote:

On Wed, 14 Oct 2009 20:12:20 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


John Fields wrote:

On Tue, 13 Oct 2009 19:08:15 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:



aleksa wrote:


The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

A stepper isn't the proper type of motor to use if you're trying to
sense torque/weight of objects/stall resistance.


---
Dumbass, whether you think it's "proper" or not, what he wants to do is
sense and measure the torque being generated by a _stepping_ motor when
its rotation is being resisted.


Oh excuse me..

Since I've done this sort of thing many times in various applications,
why don't you step up to the plate and show us how's it done with a
stepper motor? God of all Electronics and what ever else you hold
yourself so high on the pedestal.


---
Oh, my, you certainly get testy when you're corrected, don't you?
---


Since I offered no viable solution with a stepper motor and suggested
a DC PM/SHUNT type, I must of had a reason?


---
Not must _of_ had a reason, must _have_ had a reason, the reason most
probably being just to hear yourself talk, since you certainly didn't
address OP's problem.
---


Varying the current to the coils of the stepper until the slip takes
place, to me, isn't a very accurate method. But don't let me stand in
the way of progress. I'm sure you have a solution.


---
Yes, I do.
---


A stepper motor can perform that task how ever, you still need a feed
back/angle sensor and special control over the current in the coils to
allow movement so the weight of the object can be accounted for.


---
Really?

Why don't you explain how that works, then?
---


No matter how you look at it, it's still not a good option, so I'll
wait for your solution with that superior intellect of yours!.


---
Ready?

Here we go:

One way to do it is to take a rod, machine away its middle so that
there's a thin strip between the two cylindrical ends and glue a strain
gage to the strip it so its (the strain gage's) resistance changes with
torsion, then you connect the stain gage electrically to a pair of slip
rings and use a pair of brushes to bring the signal from the strain gage
to the outside world as the shaft (rod) rotates, supported by bearings.

One end of the shaft is connected to the shaft of the stepping motor and
the other end is connected to a frictional load which can be varied.

In use, the motor is caused to rotate by its normal driver and the load
varied until the motor just stalls.

Because the resistance of the strain gage changes because the shaft is
being twisted, its resistance will be proportional to the torque causing
the twist to occur.

In the OP's case, what he'd do would be to increase the load until the
motor stalled, and then, since he wanted to know what the maximum torque
would be while it was running, back off just enough to let it run and
then read the torque off the dial.

So now I guess you want me to explain all about the stuff between the
sensor and the readout???

Another, more elegant way to do it would be to machine down the middle,
polish a couple of spots on each end to a mirror finish and use laser
diodes and photodiodes to generate pulses which would be separated in
time more and more as the torque on the shaft increased.

Happy now?


JF
Yes

 

[George Herold]

John Fields wrote:

On Wed, 14 Oct 2009 20:12:20 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Fields wrote:
On Tue, 13 Oct 2009 19:08:15 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


aleksa wrote:

The stepper is turning and I try to hold it (with my fingers, or
something stronger).

How can I sense and measure the resistance I'm applying to the
stepper?
The resistance in not strong enough for stepper to miss any steps.

I'm new to electronics.. need some links and phrases on this topic.

A stepper isn't the proper type of motor to use if you're trying to
sense torque/weight of objects/stall resistance.


---
Dumbass, whether you think it's "proper" or not, what he wants to do is
sense and measure the torque being generated by a _stepping_ motor when
its rotation is being resisted.

Oh excuse me..

Since I've done this sort of thing many times in various applications,
why don't you step up to the plate and show us how's it done with a
stepper motor? God of all Electronics and what ever else you hold
yourself so high on the pedestal.

---
Oh, my, you certainly get testy when you're corrected, don't you?
---

Since I offered no viable solution with a stepper motor and suggested
a DC PM/SHUNT type, I must of had a reason?

---
Not must _of_ had a reason, must _have_ had a reason, the reason most
probably being just to hear yourself talk, since you certainly didn't
address OP's problem.
---

Varying the current to the coils of the stepper until the slip takes
place, to me, isn't a very accurate method. But don't let me stand in
the way of progress. I'm sure you have a solution.

---
Yes, I do.
---

A stepper motor can perform that task how ever, you still need a feed
back/angle sensor and special control over the current in the coils to
allow movement so the weight of the object can be accounted for.

---
Really?

Why don't you explain how that works, then?
---

No matter how you look at it, it's still not a good option, so I'll
wait for your solution with that superior intellect of yours!.

---
Ready?

Here we go:

One way to do it is to take a rod, machine away its middle so that
there's a thin strip between the two cylindrical ends and glue a strain
gage to the strip it so its (the strain gage's) resistance changes with
torsion, then you connect the stain gage electrically to a pair of slip
rings and use a pair of brushes to bring the signal from the strain gage
to the outside world as the shaft (rod) rotates, supported by bearings.

One end of the shaft is connected to the shaft of the stepping motor and
the other end is connected to a frictional load which can be varied.

In use, the motor is caused to rotate by its normal driver and the load
varied until the motor just stalls.

Because the resistance of the strain gage changes because the shaft is
being twisted, its resistance will be proportional to the torque causing
the twist to occur.

In the OP's case, what he'd do would be to increase the load until the
motor stalled, and then, since he wanted to know what the maximum torque
would be while it was running, back off just enough to let it run and
then read the torque off the dial.

So now I guess you want me to explain all about the stuff between the
sensor and the readout???

Another, more elegant way to do it would be to machine down the middle,
polish a couple of spots on each end to a mirror finish and use laser
diodes and photodiodes to generate pulses which would be separated in
time more and more as the torque on the shaft increased.

Happy now?


JF

Hi John, I hate the slip rings part. (but I've never used slip rings
maybe they are better than I guess.) I did think about mirrors and
lasers... It still sounds to complicated. I've got to measure time
delays between the arrival of pulses. (OK maybe not that hard, but
someone has to do the optical alignment.... what happens if things
move under load? OK you can make it beefier.)

What's wrong with putting a strain gauge under the motor mount. I can
make the other half of the motor mount a swivel joint and almost get a
calibrated torque readout.

George H.