Stepper Question

Questions, Suggestions, Tips, Etc

Stepper Question

Postby happyhour » Sun Nov 11, 2012 8:30 pm

I am buying parts off the EXCEL BOM I found in this Form. As I find extra money I am buying parts and in this batch of parts I need the steppers. The BOM calls for a 200 spr stepper and the ones in the store are 400spr. I would think the BOM is wrong, or the steps per rev can be programmed into mach or any other controller software.
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Re: Stepper Question

Postby kbob » Sun Nov 11, 2012 11:41 pm

400 steps per revolution will require your controller to run faster for a given motor speed. If you're planning to use an FPGA or DSP, that is probably not an issue. If you are using a PC parallel port or other software-driven step pulses, it may well be.

Also note that you need steppers whose shaft sticks out both ends, and the BOM assumes your motors have a 5mm shaft. I bought steppers with a 1/4" shaft and had to get different pulleys and couplers to compensate.

400 SPR also has an advantage, at least theoretically: At 200 SPR, full steps (not microsteps) are about 1/125th of an inch apart. I expect that to lead to irregular engraving when using higher than 125 DPI as the Y motor drifts back toward its full step position. (My motor control is not finished, so that's speculative. Hopefully someone with first hand experience can confirm/deny.)
Bob
"If you didn't code it, it will never own you." (-:
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Re: Stepper Question

Postby jv4779 » Mon Nov 12, 2012 3:31 am

In practice I don't think 200 vs 400 makes a difference. Most people run with some level of microstepping so if you were going to run 8x with a 200 spr, just run 4x with 400 spr. Either way the controller sees the same steps per rev.
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Re: Stepper Question

Postby r691175002 » Mon Nov 12, 2012 4:44 am

Step frequency will not be an issue with timing belts regardless of whether you choose 400 or 200 spr.

400 Step motors should always be preferred for positioning with timing belts because they have less error than 1.8 degree motors. Due to friction/imperfect windings, a stepper motor will never perfectly achieve its commanded position.
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