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.

On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <a...@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".

On Tue, 13 Oct 2009 02:45:08 -0700 (PDT), aleksa <a...@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

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

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

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 <a...@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

On Oct 13, 11:33=A0pm, 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

On Tue, 13 Oct 2009 14:33:31 -0700 (PDT), aleksa <a...@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

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.

On Tue, 13 Oct 2009 14:33:31 -0700 (PDT), aleksa <a...@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 

On Tue, 13 Oct 2009 19:08:15 -0400, Jamie
<j...@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.