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Universal motors

MartinBonner

As Universal Motors can be powered by AC and DC power I understand that if there’s a different ratio of power (positive) going to one side of the armature , there’s a difference between torque and speed . More positive power to the armiture than the field , it results in more torque at the expense of speed , more speed , less torque if reversed . 

how can I automate the torque/speed ratio if/when the motor is under load (or not) 

I tried asking on another forum and they were less than helpful

  • I don´t have a particular experience with universal motors, BUT modern stepper/BLDC drivers allow to monitor the current drawn and the motor position a suitable driver for a universal motor might be able to do the same.
    if you constantly read the current with an mcu you can detect stalling and usie it for sensorless homing. Now imagine doing the same but Increasing Voltage/current wheenver the drawn current rises and monitoring the results you could derive an equation that allows you to deliver the right amount of power for the load and keep the  force/ speed  constant.
    the TMC5160 for example is able to do this with a big stepper, in the demo application(comes with the devkit) you can set speed and force targets and the driver automatically adjusts for any loads.
    So maybe there is such a capable driver available for a universal motor.


    if not ,you might be able to do it from scratch with an mcu and you own control loop  code.
    Or swithc out your porjects motor for a type that has such a driver available.

    hope that helps

  • in reply to mayermakes

    Thanks for your reply .

    im looking towards changing the ration of positive power delivered to the armature/brushes and the field . 

    By splitting the power , positive and negative into two direction each , on leg of the positive will go to one brush and the other can go to the field , the same goes for the field/coil . By changing the positive power to the other brush , the motors direction can be reversed . Whatever DC power is used , the speed and torque will be governed by that . With no speed adjustment . More power , more speed and torque . If the positive power to the brushes were able be modified , speed and torque can be changed . 

    hopefully this can be done electronically without the use of a manual potentiometer . The universal motors from washing machines have a tachometer , which should be able to be used as a reference for another circuit , however an Arduino may not be able to handle higher power levels