Maximum Stepper Speed



  • So this question is slightly different to most on here.

    I'm using a Duet3D board to drive a stepper in a test rig we're building for a home made centrifuge.

    Why, you may ask?

    I already know the board from building a Core XY machine earlier in the year, and the touch panel and ability to be programmed via G-Code makes for an easy way of controlling steppers for non electrical engineers. The acceleration/de-acceleration helps too.

    We're using a Nema 23 motor to drive an alumin(i)um platter at up to 1500 rpm. Everything is in a safety cage, so I'm not worried about that. We're probably going with a 2:1 or 3:1 drive ratio, so moving the stepper at 800rpm would be nice.

    We set the movement so 1mm equals 1 revolution to make calculations easier. Everything is running on 24v. Motors are 200 steps per rev.

    I've found the online spreadsheet for stepper motor speed calculations, but we're very low torque anyway

    So some questions:

    1. Does the microstepping affect the maximum speed? We have found 4 microsteps to sound the smoothest, but speed is more important.

    2. What is the theoretical maximum speed we can drive a stepper using a Duet3D?

    3. Would I be better off with NEMA 17 motors? We only need enough torque to get the disk spinning.

    4. Some stepper suppliers do not show the inductance, so I can't be sure what we're getting (https://www.mcmaster.com/#6627t67/=1as5sbe)

    5. Can anyone suggest a simple way of verifying the speed?

    Thanks

    Mike


  • administrators

    The microstepping only affects the maximum speed if you hit the step rate limit, which is about 300kHz if you are driving just one motor. The spreadsheet tells you the step pulse rate at the speed at which torque starts to drop, assuming x16 microstepping. You can reduce microstepping if you are too close to the limit.

    I suggest you avoid buying any stepper motors for which full specifications are not provided. I usually buy from omc-stepperonline.com because they have a wide range and provide adequate specifications.



  • Great - thank you for the response.

    I'm really impressed by the board, and the support on here is wonderful.3



  • In what unit is the step pulse frequency calculated in the spreadsheet? kHz?


  • administrators

    The "Microsteps/sec" values at the bottom are given in Hz. They assume x16 microstepping.



  • Ah, I see, thank you. I worded my question poorly, but your answer confirms that the unit for the previous cells labelled "Step pulse frequency at this speed and x16 microstepping" is kHz. Thank you.



  • Lin Engineering also has torque/RPM curves at given voltages and the graph lets you estimate torque at a given RPM. The biggest lesson seemed to be to use parallel wound motors, which I think is where the maxim to use "low inductance" motors comes from, in a roundabout way. The graphs also show that higher voltage (within reason) is better than lower for getting a broader torque curve and faster RPM. This is why 24V is preferred for better, higher performance 3d printers.

    At one time I wanted to make a dynamometer to help chart these things for different stepper motors, but I had other goals, and even 3dp machine designers don't seem to care much.


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