Hi, I'm trying to rotate a bipolar stepper motor (50 oz-in torque) approximately 20 revs per second. Each revolution = 360 degrees. How should this be done? Is it possible to just use 4 steps (90, 180, 270, 360)? Thanks.

 

That is up to the internal design of the stepper. Many need 200 steps/revolution. What does it take for yours?

 

http://www.anaheimautomation.com/products/stepper/stepper-motor-item.php?sID=11&pt=i&tID=75&cID=19

1.8 Degree so its 200 steps per revolution ok. So how accurately do you think I can control a 360 degree rotation at around 20 rev/sec?

 

The accuracy would depend upon the load inertia, step rate ramp on acceleration and step rate ramp on deceleration. Is the torque of the motor sufficient to accelerate its own rotor at an instantaneous 1200 RPM jump? The only way I know to insure total accuracy with a stepper motor is to use secondary feedback. Otherwise, one missed step and the position is off until reset to a reference.

 

Allright, we are using an IR photo sensor to tell it when its reached 360 degrees. Is this a better idea?

 

Possibly. The problem you may have next is in controlling the motor. 20 RPS & 200 steps gives 4000 steps/sec. Most motors top out at 5000 steps/sec, and need to be ramped up to speed from a fairly low rate at the beginning. It gets worse if you have a mass to accelerate and stop (ramp up and down). If you try to apply the 4000 step pulse rate, chances are good the motor will just sit there and vibrate.

 

You'll need to use a chopper driver/PWM driver to approach those speeds.

The chopper driver/PWM driver can use several times the stepper motors' rated voltage, and limits the current through the motor via PWM or chopping. Using higher than the motors' rated voltage helps to overcome the large inductance of the winding much more quickly.

 

Great information! Would it be better to consider using a PM stepper motor (one with low steps)? Or would that be even worse? Thanks.

 

Would it be better to consider using a PM stepper motor (one with low steps)? Or would that be even worse?

We don't have a clue as to what your application is.

All you've told us so far is that you want to get about 20 revolutions per second out of this particular motor.

That may be do-able, depending upon your load, how you intend to drive it, your voltage supply, and a variety of other things.

 

Allright. The load is about .02 lbs. It is a small cylinderical object attached. I want it to stop at 0 degrees and cycle to 360 degrees with large accuracy.

 

Allright. The load is about .02 lbs. It is a small cylinderical object attached. I want it to stop at 0 degrees and cycle to 360 degrees with large accuracy.

In 50 milliseconds?????????

 

Yeah. Maybe I'm using the wrong motor for this operation??

 

Well, I'd be happy to even get 2-3 rev/sec. The speed isn't a big deal right now. Just the 0-360 degree rotation is the most important. Do I need a switch or can I just use a microcontroller for positioning?

 

I think you will need a microcontroller to accelerate and decelerate it, and move it an exact number of steps.

These mystery projects are very difficult to help people with!

If you state what the load is and what the purpose of rotating it is, people have a MUCH easier job helping you with suggestions and might be able to offer better, alternative ways of doing it.

 

The load is 0.02 lbs and the radius of the cylinder is about .625 inches. Basically it's as simple as rotating this around 360 degrees and stopping.

 

Put two pins on the cyl and two stationary stop pins offset by the diameter of the two pins on the cyl. Rotate one way till it hits the CW pin, rotate CCW until it hits the CCW pin. Apply many more pulses than needed to get the 360 degrees and run it to stall position.

 

How often does cylender rotate? If cycle rate is slow, use Bill3857's pin a short throw-spring return solenoid as a start-stop; rotate cyl. with "cord" and linear spring. Reset with step motor. Fast cycle rate, change linear spring to coiled spring, center driving cyl. shaft, outside attached to large gear, about size of spring OD. Small motor driven pinion maintains proper spring torque. A slightly faster cycle time might be possible with two solenoids @ 0 & 180 deg, & two offset pins,0-180 operating alternatley.

 

Gladiator wanted to rotate cylendar in 50ms for 360 deg; using a heavier load[ 1 5/16 dia X 1/2 in thick plastic disc + 2 in dia X 1/32 Al disc ] , spring drive rotates in 34 msec, 360 +_ 0deg. Disc has one pin held by solenoid which pulls in & resets in about 20 ms. A 22 uF charged to XX V enegises solenoid. Sorry that Gladiator is nolonger arround.