I'm running a µSpirit with a motor tail. The problem I'm having is that the tail motor spins up even when throttle hold is on. This makes it almost impossible to safely disconnect the battery.

It has been suggested that this is probably caused by a configuration problem. My question is: what part of the configuration should I check? I've been through the setup several times and haven't found anything wrong.

Motor is selected and Throttle hold is well under zero. I'm using a Castle ESC for the main motor and do not use the µSpirit governor.

What is your Tail ESC? It is likely the problem is there. You can easily check behavior with a servo at the RUD port. After engaging Throttle Hold it should move immediately to position which is set in the Stop parameter - Limits tab.

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Spirit System developer

Sorry I didn't mention the tail ESC because I didn't think it was relevant. It's a BLHELI flashed XP7A with a fast switching mod (3 resistors replaced to achieve 150-180ohms). Also using a 12-magnet tail motor bell in case that's important too.

Just to be clear - when throttle hold is on, the tail motor only spins up when the model is moved as the µSpirit gyro tries to correct the yaw.