Motorised Tail & TTA¶
Small helicopters often drive the tail rotor with its own motor instead of a variable-pitch tail. A motorised tail has plenty of authority in one direction -- spin the tail motor faster -- but little in the other: the slowest it can go is idle, and a fixed-pitch rotor can't push the other way.
Setup¶
On the Mixer tab, set Tail rotor type to Motorised. The tail ESC goes on motor output 2.
- Yaw calibration: leave at 100%.
- Motor idle throttle: just high enough that the tail motor keeps turning reliably.
- Yaw center offset: the tail throttle for a zero-yaw hover, so the controller starts from the right place.
Set the tail ESC's protocol on the Motors tab, and give it an RPM signal (a second frequency input or bidirectional DShot) so it shows up in logs and can be used for TTA. Turn off the tail ESC's braking -- see BLHeli_S to Bluejay.
Tail Torque Assist (TTA)¶
When the tail motor is already at idle and the helicopter needs more yaw in that direction, TTA briefly raises the main rotor headspeed. More headspeed means more main rotor torque, which turns the helicopter the way the tail can't. It needs the governor.
Settings, on the Profiles tab:
| Setting | Default | |
|---|---|---|
| TTA gain | 0 (off) | How strongly TTA raises the headspeed. Typically 50-150. |
| TTA limit [%] | 20 | The most headspeed increase allowed. Typically 20-50%. |
Tuning TTA¶
Push the helicopter into a situation where it runs out of tail authority:
- fly backwards fast, tail into the wind;
- tail slides and backward loops.
If the helicopter suddenly swings round -- sometimes up to 180° -- raise the TTA gain. Repeat until the swing is mostly gone.
You may never remove it completely. On some helicopters the main motor simply doesn't have the spare power to provide the torque needed.
Tune the governor with TTA off first, then bring TTA in.