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Brushed DC Motor

Chinmay Shah
Expert 1085 points

Dear Friend,

I want to purchase DRV8412-C2-Kit for BDC Motor Control. 

Can anybody suggest me the lowest speed of Motor Rotation with full torque with Current PI (Build Level 3/4 from control-suit code). You can take the reference motor of 1200 RPM. 

Can I achieve 0 speed control with a full torque? 

One more thing is can I Un-comment the entire eQEP MACROs from Control-suit project to utilize speed control in my project? 

  • 0
    TI__Expert 8885 points

    Shah,

    In level 3 and 4, motor runs in current control mode. Since motor current is proportional to electromagnetic torque, this effectively means torque developed by motor is fixed as decided by applied current.  In this mode, the speed will be decided by how much load torque is applied to motor shaft, so for same applied torque motor speed can shoot-up to very high value if it’s on no load or can be very low, if shaft torque is near to electromagnetic torque developed by motor. In summary, Speed is governed by following electro-mechanical equation with Tem decided by applied current and motor torque constant:

       J dwr/dt = Tem-TL-d*wr

    Here,

             Tem =Kt*Ia is electro-magentic torque developed in Nm

             Kt, motor torque constant in Nm/Amp

             Ia motor armature current in Amp

             J is moment of inertia for motor and load in Kgm2 

              ωr is rotor speed in mechanical rad/sec

             TL is shaft load torque in Nm

              d is friction co-efficient in Nm-sec/rad.

     For DC motor, yes theoretically it’s possible to achieve full torque at zero speed but in actual implementation achieving this is really challenging task. Its depends upon how good is behavior of   your closed loop speed PI controllers, dynamics and accuracy of speed feedback signals. Typically as speed reaches towards zero, getting fast speed feedback signal with sufficient accuracy becomes cumbersome.

    Yes you are free not to include QEP module and use your own code for speed control. In fact for 2-axis brushed DC project , QEP module is not used because the project ends level 4 in torque control mode itself.

     Best Regards

    Milan- Motor Application Team