Stepper Motor Torque and Tic T249

Support Motor controllers/drivers and motors
1

Basic problem is that I am not getting anywhere near the expected torque out of a NEMA 23 motor driven by a Tic T249 board.

Larger context:

  • Main system is controlled by an Arduino which is communicating speed and direction of rotation via serial to the Tic T249 board.
  • Power is an DC power supply with 24V and max 3.8A output
  • Motor is a Bipolar NEMA 23 with a planetary gearbox driving some larger gears.
  • Tic board is set to Full Step mode, with current limit of 1840mA. AGC is off.
  • When I drive at 220.0000 pulses/s, the motor draws about 330mA without any other torque load

However, when running at 220.0000 pulses/s I can stall the motor and cause missed steps with finger pressure at the end of the gear train. Watching a power supply, the current draw is about 440mA just before the stall.
If I try and run at lower RPM, e.g. 80.0000 pulses/s, I get a lot of skipped steps - we don’t move in a single direction.

I can run up to 1200.0000 pulses/s and see a draw at the power supply of about 450mA. With light finger pressure, I can watch the draw go up to 550mA and at about that point the motor stalls and the draw drops to 170mA.

If I drop, on the Tic board, the current limit to about 1440mA, there is less shuddering and things seem to run smoother(e.g. no halting at 80.0000 pulses/s), but same torque issues persist.

My sense is that it shouldn’t be this easy to stall the motor and torque closer to the max permissible torque of 40Nm.

Thanks for any insight and help

2

Hello.

Can you explain how you are measuring the current and post more information about your motor and gearbox, like its datasheet or a product page link for it? Posting some pictures of your setup as well as a copy of your Tic’s settings file would also be helpful. You can save your settings file from the “File” drop-down menu of the Tic Control Center software while your Tic is connected.

By the way, it seems like you might be expecting the current draw to increase proportionally with torque like a brushed DC motor, but that is stepper motors do not operate that way (though the Tic T249 can enable something like that kind of behavior with the AGC feature). Instead, stepper motors will generally draw a consistent average current regardless of the torque (though the instantaneous current is dynamic and depends on several factors, like the microstepping mode).

- Patrick