Driving a Gimbal Motor w/ Tinymovr

The upcoming Tinymovr firmware release adds the ability to drive gimbal motors.

https://tinymovr.com

What is a gimbal motor anyway?

A gimbal motor is a 3-phase brushless motor whose stator is wound with many turns, and as such exhibits much larger resistance and inductance compared to the high-current brushless motors used to provide lift to drones, rc planes etc. Gimbal motors are used in… well… camera gimbals mainly, because they offer smooth motion and require small currents to produce torque compared to the ‘regular’ brushless motors. This in turn can help minimize the size of the motor driver and associated wires etc. Note that we refer to reduction of current through the stator windings and not the power converted to heat as a result of Joule heating of stator windings, which is still the same for the same amount of torque.

To achieve closed-loop current control, motor controllers such as Tinymovr use current measurement resistors in each phase (usually in series with the low-side mosfet) to estimate the current in the motor windings. These resistors have low resistance (in the range of a few milliOhms at most), to limit power dissipation in the resistor and allow operation in wide current ranges (up to several tens of Amps, even hundreds). The drawback is that current measurements exhibit noise of 100s of mA, and as such do not offer accurate measurements of small currents.

The gimbal mode of Tinymovr disables closed-loop current control. The commanded currents are converted to voltages using resistance and inductance formulas.