I have now fitted a brushless tail motor and ESC to the XK120 heli. Testing this without the uSpirit and just a receiver I get beautiful control between -100 (motor off) and +100 full speed.
When plugged in to CH4 on the uSpirit the operation seems reversed. I have Motor selected in the Advanced settings. This forces CH4 to be ticked in the Servo Reverse tab, and I cannot change this. When I power up the tail motor does not give the normal tones. If I apply Rudder nothing happens. If I then go to the Limits tab in the 'Rudder ESC - Stop' section and move the slider to the right, the tail ESC arms when the value goes above 170. If I then move the slider to the left, the tail motor starts. Lower revs with slider to the right, higher revs with the slider to the left, max at the end with value 32.
In diagnostics left rudder gives -100, right rudder gives +100.
Am I doing something wrong?

More information - With the Rudder Stop setting such that the tail motor spins (after first pushing the slider above 170 so that the ESC arms), the tail motor does not work when powering up, because the ESC does not arm. If I leave the setting above 170, the ESC arms after power up. But the tail motor does not start when the main rotor starts.
Part of the issue is that the tail motor output must go to -100 first to arm the ESC, before going to the tail motor running setting.

Hello,

I am not sure if I understand the problem correctly.
But could you confirm that with Rudder - Stop you can configure point when tail motor is not running at all, but ESC can initialize?

Also with Rudder - Full can you configure point when the motor is running in a full speed?

Make sure to assign Throttle in the Channels tab (usually Channel 1). In this way the motor will start immediately once main rotor will start.

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Spirit System developer

Hi Tomáš

Yes, with Rudder - Stop I can configure a point when tail motor is not running at all, but ESC can initialize. However, in this case the tail motor does not start when the main rotor starts, even though I have assigned Throttle in the Channels tab (I used Channel 1). It only starts when I apply Rudder. I was able to take off after applying Rudder. The hover was unstable, but that may just be need tuning.

If I configure a Rudder - Stop point where the tail motor is running, the ESC does not initialize.

With Rudder - Full I can configure a point where the motor is running in a full speed.

Please set also Rudder - Low RPM parameter which is in the Servos tab.
This will set the lowest RPM for the motor to spin. And this is also used whenever Throttle Hold is disengaged - motor will spin immediately.
With default 0 value it is equal to Rudder - Stop value. For this reason it is not spinning after disengaging Hold.

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Spirit System developer

Ok I have set the Rudder - Low RPM parameter in the Servos tab so that the motor spins. However, the tail motor does not reliably start when the main rotor starts, even with the main rotor at high speed. As soon as I touch the Rudder stick, it starts. It started by itself once or twice while I was varying the main rotor speed.

I have also tried with the Rudder - Low RPM parameter at a higher setting, but it makes no difference.