 # Stall Torque and Bus Voltage

I was playing around with the Odrive Motor spreadsheet and noticed that changing bus voltage did not change the torque for each of the motors. When I have used brushed DC motors in the past, I believe that their stall torque was proportional to bus voltage. Is this not the case for brushless motors? I am trying to size motors for use in a drivetrain, but I am not running the motors at their rated voltage. Instead, I am trying to run them at 12v and I don’t understand how this will affect torque.

Looking at the equation v = IR + wK, where K is the back emf constant and w is angular velocity, consider when w = 0. This should be at stall. Then, v = IR. Since I is proportional to torque, stall torque is proportional to bus voltage. If this is the case, I am failing to understand why the stall torque doesn’t change.

Any help would be great. Thank you!

Because R is very low (on the order of 0.1 ohms), and I is limited below what would normally be calculated here.

V = IR \\ 12V = I * 0.1\Omega \\ I = 120A \\

But I is limited to ~ 60A, so the ODrive will be sitting there at 50% duty cycle (6V) to maintain 60A current.

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This makes sense. Thanks for the help!