Torque control for DC-motor 24 Volts, 50 Watts with encoder

[robert63]

I have a Samba SM43-J-T20.

I need to control a brushed DC-motor with 24 V/50 Watt with an optical encoder. I need a suitable motor driver with current sense for this.

The task is to control the torque of the motor. I need a constant torque characteristic (Like if the motor would be supplied by a constant current source). This means that the motor delivers a defined torque regardless of the RPM. The RPM shall only be limited to an adjustable value. 

Can you make a recommendation for the motor driver and maybe a sample program for this job?

[Joe Tauser]

I did some Googling and could come up with a small DC motor torque control.  The application you describe is usually done with a servo in constant torque mode.

Anyone else?

Joe T.

[kratmel]

I use in torque mode this driver configured without taho (encoder do not needed)

https://www.motiontech.com.au/wp-content/uploads/2018/04/MT-Copley-Brush-Servo-Motor-Drive-241115.pdf

The main problem is that your SM43-J-T20 do not provide analog output for control something like this.

Only PWM output present on SM43-J-T20.   But DC motor driver use analog setpoint.

CANopen DC drive also present but you must install CANopen card and run CAN network.

 

Maybe the best solution is to use 50Watt Unitronics SERVO motor with Unitronics servo drive, but you must ask support - is  it possible to configure Samba with CAN card to control Unitronics servo in torque mode.

 

[robert63]

Thanks for your comments. I thought that I could probably do it by measuring the current in the motor by one of the analogue inputs and then control the duty cycle. Reduce the duty cycle when the current is too high and vice versa. Like a closed loop.

[kratmel]

For driving motor maybe is useful info in this topic:

for current sensor maybe must be used 24vdc powered 0...10V or 0..20mA output isolated Hall effect DC current sensor.

http://www.current-sensors.de/CurrentSensor-DC.htm

ADC input in samba is not isolated.  I do not recommend to use direct ADC to motor shunt connection due to noise generated by DC motor.

You can try to run control loop but it is not possible to predict motor behavior in your system setup.