# Thread: Need a little experiment carried out....

1. Originally Posted by irving2008
Hmmmm hadn't though about that. Should be powering both windings in parallel then?
If we're just using it as a load, since it doesn't look like we can get useful information from the other phase, then yes I tend to agree. Also you wouldn't get rated power with just one phase energized.

Originally Posted by irving2008
Maybe, but a dropping weight and pulley is easy to calibrate
Yep, could even use dropping a weight to calibrate the other system.

2. It's great seeing you two "talking dirty" with one another again

3. Originally Posted by Jonathan
Just spotted something interesting...

I measured the back-emf voltage from the 3.1Nm stepper motor at 1200rpm and it's 66 volts, so using those numbers k=0.525 Vs/rad. The unit Vs/rad is dimensionally equivalent to Nm/A ... i.e the 'torque constant' of the motor, so we can use this to find the torque for a given phase current. Rated phase current is 4.2A, so for both phases T=2^0.5*4.2*0.525=3.12Nm. That matches the holding torque specification rather nicely, so maybe this could be a simple way to find the rated torque of stepper motors. Or more usefully, use the formula for phase current (something like i(t)=V/R-(V/R-I)*e^(-t/(L/R))) multiply by k to get torque as a function of time then integrate to get the mean torque and then the torque vs speed curve for the motor. I think this should be more accurate than the usual approximation.
Yea i would have to agree with what he said....because i don't have a clue....what he just said....

Originally Posted by WandrinAndy
It's great seeing you two "talking dirty" with one another again
Agreed, all we need now is the shaft size equations to come into it...

.Me

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