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Mar 13, 2017, 01:55 PM
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Death of a stepper motor


Finally conceeded that the hardware in a cheap ESC isn't fast enough to make a continuous sine wave stepper controller. That's why we do minimal tests. But it can step in 120deg increments through the sine wave by only modulating N's. The reduced precision was probably good enough, but the FETs still got too hot when the motor was stalled.


The scope showed all the voltage drop in the FETs, so they were putting out 12W. The motor has to provide a minimal resistance greater than the FET resistance. Then ohm's law transfers all the voltage drop to the windings & the ESC can reach its ratings.

A custom, super motor driver is required, with active cooling & FETs placed farther apart with heat dissipating pads. The supply of Hobbyking 35A's will probably never be used, so the parts could be recycled. It would still be expensive. The ATMega pinout could be rearranged for hardware UART & encoder feedback. 2 Hobbykings would be combined on a single board, with all the FETs on the center of the board under a fan.
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