Program tips > Undercarriage door sequencer

by Mark Powell

13 March 2012

It is possible to program an undercarriage door sequencer, so that you do not have to buy one, or fiddle about with micro switches, rubber bands, and similar.

In Servo assignment assign two channels to ‘L. gear’:

Then set ‘L. gear’ time to (say) 4 seconds. The numbers above do not of course have to be ‘100’ but can be adjusted to suit your mechanisms.

On moving the retract switch to ‘down’ the door will open and after a short delay the leg will come down. On moving the switch to ‘up’ the leg will go up and after a short delay the door will close.

If you use air valves you will only need one servo for the legs and another for the doors. If using separate servos for each leg/door assembly then Y-lead the door servos and the leg servos and you are done. If you should need different timing for the nose leg and doors you can of course use two separate channels for the nose.

As a refinement I also create a mixer with a rudder channel only and connect the nosewheel steering servo to this. It has a switch, in my case ‘Mx1’ assigned to the same switch as ‘L. gear’ in Transmitter assignment. Thus the nosewheel centres and the servo stops moving when the undercarriage retracts. This of course is not essential.