04/01/2023 - Overvoltage Issue

Issue outline

The ESC overvoltage threshold can be influenced by the setup such that the unit enters a state where the commanded throttle will not drop until a 'zero' throttle command is received. This will almost always result in losing control and can be dangerous to the aircraft and surrounding users.

200 ms after ESC startup, the supply voltage is sampled, where the maximum regenerative braking voltage threshold is taken as 120% of this point. If the supply voltage is above this level at any time after that, an over-voltage error is raised. While an over-voltage error is raised, the throttle will not be reduced unless the flight controller commands a zero throttle. The issue affects a small group of setups where the rise time of the supply voltage is slow enough that the voltage reaches less than 80% of the actual supply voltage within 200 ms.

This can happen when using anti-spark connectors to connect the batteries, particularly with long wiring and significant levels of added capacitance.

This feature aimed to prevent motor braking from pushing too much power back into the batteries, which could lead to overcharging of the batteries or excessive spikes on the ESC inputs.

Units affected

The issue affects off-the-shelf hardware variants of the following APD ESCs:

Units running firmware dated before November 2022 are susceptible. Setups with an input voltage rise time (power-on time) of over 200 ms are affected. Setup characteristics such as long input leads, anti-spark connectors, large pre-charge resistors and large input bulk capacitance are especially susceptible.


A firmware update, which resolves the above issue, is available. Instructions to update units can be found below, depending on the hardware series. Units shipped from Jan 2023 onwards will be pre-flashed with updated firmware.

F Series Production Firmware - Minimum firmware is 2.3.0

UHV and HV Pro Firmware - Minimum firmware is 2.1.0

For any further details or support, please don't hesitate to contact APD.

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