Modifying a Turnigy 9XR for 4-Axis Flying
Posted by Tom Benedict on 06/08/2013
When I first ordered my Le Fish kit from Leading Edge Gliders back in March, I knew I wanted to set it up for 4-axis flying. In case the idea is as new to you as it was to me, this article should explain it:
I highly recommend you follow the link, but here it is in a nutshell:
Most planes are set up with two or three axes of control: elevator (aways), rudder and/or ailerons. Powered models use the fourth joystick axis for throttle. Thermal gliders often use it for variable spoilers or some other form of airbrakes (flaps, crow, etc.) A four-axis aerobat is set up so the fourth joystick axis dynamically controls the camber of the wing by controlling the flaps or flaperons. Push up on the stick, the flaps go up, and the wing reflexes. Pull down, the flaps go down, and you increase the wing’s camber.
The only catch with this is that you need the stick to move both up and down, and you need it to center automatically. The stick needs to spring to center on both axes!
And that’s the real trick with 4-axis flying: you need a radio on which both sticks spring to center on both axes. Radios typically come with one of the sticks unsprung, so there’s no way to do this right out of the box. It’s possible to modify most radios to add a spring to the throttle axis, but I took a different route.
When I got my Le Fish (and Zagi 5C and Raptor 2000 Advance) I picked up a Turnigy 9XR radio. Spare parts (like the spring lever) for the 9XR aren’t as common as for other radios, but spare assemblies (like entire joystick gimbals) are cheap and readily available. Rather than convert my left gimbal to a sprung gimbal, I simply replaced it with a new one that came that way.
My radio is a Turnigy 9XR radio set up for Mode 2. Mode 2 has the throttle on the left and the aileron/elevator stick on the right – typical for North America. This means the right stick is sprung, but the left is not. Mode 1 radios – popular in Europe – are set up the opposite way, with the sprung stick on the left and the non-sprung stick on the right. Left and right gimbals may not be interchangeable, but gimbals from mode 1 and mode 2 radios are.
Once you get the back cover off the 9XR, the gimbals are attached using four screws and are connectorized, so there’s no soldering involved in swapping them out. I picked up a left-hand gimbal for a Mode 1 radio and installed it in place of my un-sprung left-hand stick. Voila! Now I have two sticks that spring to center. (And I have a spare gimbal in case I want to swap back or build a customized KAP controller!)
The setup for four-axis flying is fairly straightforward. Rudder and elevator go straight in, and the flaperons are a 1:1 mix of aileron and flaps. I also added a 20% snap flap I can toggle using one of the radio’s switches. With snap flaps enabled, pulling back on the elevator stick moves both flaperons down to camber the wing slightly. This is typical for aerobatic gliders.
Unfortunately I haven’t been able to take out my Le Fish with the new setup. The only times I’ve flown it, I disabled the input for the flaps until I had the center-sprung gimbal. But the next time we hit the slopes, the Le Fish is coming with me.