Tested redesign of the throttle arm for the Spektrum DX6i transmitter.
Combine this arm with the spring hook to make both sticks self -centering.
You also need to make 3 metal pins.
I used a 1.6mm drill bit.
Cut to 11mm and 2x 8mm.
The 11mm is for the arm and the 8mm go into the swivel. It is a bit hard to take the swivel out but it can be done without taking the potentiometer out.
The spring can be replaced by a small elastic band.
You may need to shave a bit off the part to make the stick perfectly centered. That is: the 2 flat surfaces left and right of the axle notch.