Stepper motor ability to change direction very fast?

[randy217]

I'm in need of a small motor capable of moving about 1oz around 5 degrees and back at least 30 times per second. I've seen speed ratings that look sufficient but I've also seen videos of the motor in action and noticed it took a moment to get up to speed. Any help is much appreciated. Thanks.

 

[MikeHalloran]

A typical small stepper moves 1.8 degrees in about 1ms after its driver changes state.
( ... or, just wiggles a little if the load is too large. )
... then it moves another 1.8 degrees in about 1ms after its driver changes state.
... and repeat.

They don't really 'get up to speed' in the same sense as other motors, but they can reach higher speeds if the driver pulse periods are 'ramped'.
Their rotation is not continuous, but incremental.
... and considerable 'ringing' can be expected.
You should read up on steppers.
So far your specification has not ruled them out.



Mike Halloran
Pembroke Pines, FL, USA

 

[mikekilroy]

T=jw/t.....

u defined t with 30 sec cycle

u did not define j - 1 oz @ what radius? 1 oz is a weight or mass; u need to define an inertia. 1oz @ end of 10 foot pole is a lot more inertia than 1 oz @ 1" from center of rotation

u did not define w - you can need to go from 0 to 1,000rpm 30x/sec or u might need to only go 0-0.1rpm 30x/sec - big difference.

need these tidbits to do first step of calculating what u need to then see if it is possible by stepper or any other device.

 

[mikekilroy]

no edit button. sorry, not 30 sec cycle, meant 30x per sec cycle.

 

[waross]

I would consider a bell crank. If the cycles are not continuous I would investigate a clutch mechanism on the drive to the bell crank to allow the motor to run continuously.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[OperaHouse]

Is this a mirror optical scanner application, does it have to be linear, is it repetitive? If so it could be a cost effective solution with some tuning.

 

[MikeHalloran]

For optical scanning, a mirror oscillating on a galvanometer or a spinning mirrored polygon will work a lot better than a stepping motor.



Mike Halloran
Pembroke Pines, FL, USA

 

[randy217]

Hey Mike and others. Thank you for the help!

This is for an invention. I will show you as soon as it's ready.

Ok, the weight is actually going to be a little more than the motor itself, and the radius will be about 4 to 5 times the longest side of the motor. So this can scale. If the motor is 1 once and 1 inch wide then the radius will be about 5 inches. The motor only needs to move 5 to 10 degrees and then back 5 to 10 degrees and do this 30 times per second. I also need as much precision as possible so I can make tiny diversions during that one 5 to 10 degree movement.

Thanks again.
Randy, Houston TX

 

[MikeHalloran]

Ah. Precision doesn't really go with steppers. They can be microstepped, sort of, but by the time you get through adding hardware to do that, you're better off with a servomotor. In your case, because of the limited rotation, you could also use a torque motor. The expense involved will depend strongly on how small 'tiny' turns out to be.



Mike Halloran
Pembroke Pines, FL, USA

 

[mikekilroy]

Randy,

You sound like you could handle a motor sizing program that will help you pick rotary motion or linear motion with various mechanisms for either servo or stepper:

http://www.kollmorgen.com/en-us/service-and-support/technical/motioneering/

free.