Which Stepper Motor Configuration to Choose?

Hello Lyn,

I've been through guides like these, but havent found much information on which step motor to choose, except it indicates holding torque. I do not know how to interpret the required torque per motor in terms of specified holding torque.

Thanks

that isn't how I'd go about it

Fredski,

How would you go about it, then? :-

If you wish to do it right, I'd start here. This will give an in depth background on stepping motors without a bias to sell you a product.

The problem with the idea of doing anything precisely without feedback is that you and your controller will never really know if you are precise.

I can tell you right now that accelerating and stopping 1000 pound mass at .5 feet per second with any accuracy is going to take a considerable amount of starting and stopping power.

Depends on the speed and the mechanical inertia. I have learned (the hard way) to microstep and have a good controller that has adjustable amperage per phase.

Hello Parth:

The holding torque specification is slightly above the maximum driving torque that your motor will develop when start moving, after that point, you will loose torque as you approach the maximum speed (steps/sec.) of your motor.

Depending on the motor's design, the performance curve will show, that when you reach 40% of the speed, you will have already lost over 50% of your torque, and when you get to max. speed, you get only from 12% to 20% of your Max. torque.

There are newer designs that never loose as much as 40% thrughout the whole speed range.

I'd recommend you a Hi-Torq. motor from Kollmorgen, go bi-polar (higher torque at high speeds).

Select a holding torque of at least twice your figure of 50 in-lbs required.

Keep in mind that you will need a controller per each motor (mechanical design VS. control design).

Use acceleration and deceleration curves to avoid rotational "slipping" of the rotor.

Talk to a sales engineer, that is the best guidance you'll find.

Regards

good response, well done

Thanks Fredski !

What was not directly addressed in this discourse is not the matter of the motor selection.

Three issues:

1,. The breakout moment necessary to start movement. Measure it.

2,. The acceleration / deceleration of the mass. As it is a constant force applied for a set time, it is a question of a controller. As you desire an open loop design, the mass / acceleration is strictly limited. Otherwise cogging (slipping a pole or more) will occur. An angle decoder is cheap insurance to the microprocessor keeping track, and limiting acceleration / deceleration. The remainder is plain, carefully applied mechanical design.

3,. I would oversize the motor+controller 200-300%.

I do advise against any soft coupling to the wheel. It is a resonant system at some frequency. You do not need that complication.

This sounds simular to a problem I had doing automated welding. I found that with large loads, open loop control with precision was impossible. The solution was to use an off the shelf servo controller and size the servo amp and motor to the load. This solution worked for the small motors in the weld head, and the 10hp motor on the positioner. Development time was minimal and working precision to .001". The controller DMC 100 by Galil(STD bus), servo amps by Motion Science, and the 10hp AC motor and control by Daton, 10 axis of precision control monitored by 4Mhz. personal computer. Hope this gives you some alternative ideas.