Ok, I have now wired a Hobbywing RPM sensor, and enabled the governor in the settings. I get an RPM indication in the setup screen, but the tail motor still does not start even when the main motor is running. If I touch the right rudder stick, the tail motor starts, but stops when I let go.
Have I missed something in the setup?

This behavior is correct, but you can change it with Rudder ESC - Low RPM parameter in the Servos tab.
This parameter is for adjusting motor speed for lift off actually.

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Spirit System developer

Still no success. I adjusted the Rudder ESC - Low RPM parameter in the Servos tab so that the motor keeps running. After saving the settings, I re-powered the heli and tried to take off with a Normal throttle curve. The main rotor spools up, but the tail motor does not start. If I apply right rudder, the tail motor starts and runs for a second or two before stopping again. Surely the tail motor should start once the throttle input increases from -100?
I contacted the originator of this thread p.i.engineer by pm to see whether he had any success. He replied that he gave up and changed to an Oxy 2 instead.

Bump - I really need a solution for this.

More information: If I spool up to near lift off speed, the tail motor does not start by itself, even if the rotor torque causes the tail to move. If I then apply some right rudder, the tail motor starts. If I then apply more collective, the tail starts moving in very jerky movements. The problem is that the tail motor slows too much, causing the tail to move clockwise. (The main rotor turns clockwise.) The tail motor then speeds up to correct, but then drops out again. The end result is very jerky tail movements.

I was trying to keep the brushed tail motor, but I suspect that it is actually a 1S motor (my battery is 2S), because trying to adjust the maximum revs did not show much variation, and the motor was running very fast. So I suspect that the jerking of the tail may be due to the uSpirit not being able to control the motor smoothly.
I have ordered a brushless motor and ESC, and will try again when those parts arrive.

Hello,

please make sure that the Throttle channel is assigned. This will tell the unit when you want to lift off. Otherwise it is detecting from model vibrations.

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Spirit System developer

Yes, the throttle channel is assigned. I also have an RPM sensor connected and showing in the governor setup screen.

Thank you for the details.

When you are configuring Rudder ESC - Low RPM the motor must be running at the low RPM. This RPM will be always used once Throttle Hold is disengaged. So please make sure that it is really spinning. If not, please try to increase it little bit.

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Spirit System developer

Thank you. I am waiting for a brushless tail motor, then I will set it up per your advice.