Heng Long Challenger 2 steering problem

[wibblywobbly]

Having eradicated the gearboxes, motors and RX18, the last gasp is indeed the transmitter. If you can get it to run straight by moving the trim across, then it would confirm it. Trims are there to solve issues like this. The only way ro have centre trims and a centre stick would be to take the tx apart and rotate the pot, this isn't always possible, and it is fiddly to do.