Author Topic: Can I directly buy a motor driver to control the torque for a DC or AC motor?  (Read 425 times)

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Offline kevinthesunTopic starter

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I need to control the output torque of my motor. It is difficult for me to build a torque control circuit by myself. So can I directly buy one? If I can, which one is good?

Offline jwatte

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Yes. Any motor controller should be able to do this.
Which one you should buy depends on your requirements -- type of motor, amp draw, voltage rating, duty cycle, etc.

Offline kevinthesunTopic starter

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But most motor drivers are designed for speed or position control. I need to output some values of torque regardless of the speed, which means maybe the output power needs to be changed during the control process, I don't know whether these motor drivers could do that.

Offline jwatte

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How precise is the torque value needed?

In general, the torque from a motor is proportional to the amperage through the windings. Thus, you can use a motor controller and a current sensor to build a closed-loop controller. There are also some controllers that have torque control built in, in the upper end of the price spectrum.

So, again, what are your power, voltage, current, and other requirements? A 1W motor in a lab environment is very different from a 100kW motor in a human-safety role.


Offline kevinthesunTopic starter

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Thank you for ur patience! The motor is for lab use. Operating Voltage: 4.8-6.0 Volts;Stall Torque (4.8V): 274.96 oz/in.
Stall Torque (6.0V): 343.01 oz/in. Current Drain (4.8V): 8mA/idle and 700mA no load operating. Current Drain (6.0V): 8.7mA/idle and 830mA no load operating

Offline jwatte

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The stall current is actually the most important metric, so if you could find that, too, that'd help you find the right driver!

Do you have a torque sensor of any kind? If not, you probably will not be able to reach 100% closed-loop torque control.

If you want to emulate torque control with current draw, there are a number of controllers that read current consumption that you can build a rough control loop on top of, such as the RoboClaw 2x5A from Orion Robotics. You'd also need a microcontroller to continually read the current and adjust the duty cycle.

Other options include using a plain PWM DC motor controller, and a current sensor such as the ACS series. Pololu has some:
http://www.pololu.com/product/1212 (3A may be less than your stall current, so you may need something beefier)
http://www.pololu.com/product/1185 (sensor only, needs driver)

The "torque control" drivers that I know of typically come in factory motion control systems, are expensive, and require specific motors/sensors to work.

 


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