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Minimum Motoring Torque

Introduction

Applications sometimes require a minimum amount of torque to maintain motor rpm or remove system backlash. For example, a geared hub may require a certain amount of torque applied to reduce backlash related control issues and drivetrain damage.

Note

This function does not meet EN regulations as there must be no motor current when not commanding motor current.

Minimum motoring torque is used to set the amount of current as a per-unit value of Rated motor current when off throttle since the torque is approximately proportional to the motor phase current for a brushless DC motor. 

Upon initial start-up of the system or after triggering motor cutout, the motor current will remain 0 until motor power is commanded, after which the motor current when not commanding power is equal to the value set by Minimum motoring torque.

Enabling Features2 bit 2 Free wheel with no throttle bypasses the need to trigger the throttle first to enable Minimum motoring torque.

Caution

Setting these values incorrectly can cause the motor to be uncontrollable, or behave in an unexpected manner to unfamiliar users.

This should not be used as a form of "cruise control".

Configuration

  1. Enable Features bit 6 Motor stall shutoff enable.

  2. Set Minimum motoring torque as a per-unit value of Rated motor current.

    • For example: setting Minimum motoring torque to 0.01 will provide 1% of rated motor torque after initially commanding motor power until motor cutouts are triggered.

Note

If the required minimum motoring torque (current) is not known, this value will need to be derived experimentally through trial and error. Keep in mind that what works on the ground may cause the motor to maintain a non-zero rpm while the wheel is in the air and unloaded.

  1. Optional, see above: Enable Features2 bit 2 to Free wheel with no throttle.