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Science Fair and New Radio

Posted by Tom Benedict on 11/04/2013

Ok, so I have to eat crow. I thought I had a relatively simple science fair idea. I thought it would take two days, at most, to gather my data. This is how it actually went down:

Me: “Hey, can you give me a qualitative estimate of which of these foam/tape sandwiches is stiffest?”

Wife: “Yeah.” <takes samples>

Me: “Just be careful not to bend them so far that they snap!”

Wife: “Oh… Um… What if I snapped all of them?”

Me: “WHAT?!”

Yeah, this is what researchers call “scheduling setbacks”. And this is what co-authors call “crappy communication from the principal investigator”. After I recovered the tattered remains of my experimental samples, I told my wife that what I meant was that she should flex the samples, but not destructively test them. Not yet, anyway. So I’m going to start again this weekend.

Meanwhile my Turnigy 9XR radio arrived along with its FrSky DJT module and four receivers. The battery I bought for the radio hasn’t arrived yet, so I stuck one of my existing 2200mAh batteries into it and fired it up. In a word, coooooool!

But that coolness comes at a cost: it’s a lot more complicated than my good ol’ six channel 2.4GHz radio I borrowed from my KAP gear. Cripes, there are so many ways to tune this thing, I knew I’d make a mistake. Turns out I was right.

Last night I pulled the old radio out of my Bixler 2 and stuck the new one in. The whole point of getting this radio was to give me the flexibility to set up the Raptor Advance as a full-house glider, to set up the Le Fish as a 4-axis plane, and to still be able to do the minimal mixing necessary for the Zagi wing. So first things first, I cabled up the Bixler 2 as a full-house glider.

The whole idea behind a full-house setup is that you have six control surfaces, each of which is individually wired into the radio. The flaps can move in unison, but they don’t have to. The ailerons can move in opposition, but they don’t have to. Depending on how the transmitter is set up, the entire trailing edge – ailerons and flaps – can move as a single control surface (FTE), or the flaps and ailerons can move in opposite directions to act as air brakes (crow or butterfly), or the entire trailing edge can be tuned up or down to introduce camber or reflex along the entire wing, and all of this can be mixed in with the normal control inputs for ailerons and flaps. It opens up all sorts of options for tuning the entire airframe, depending on what you want it to do.

The Raptor Advance and the Bixler share the same control surfaces: rudder, elevator, ailerons, and flaps. Both have a motor and throttle. Seven inputs in all. So I set up the Bixler to use seven of its eight channels so each control surface has its own input from the transmitter. Then came the fun part: setting up the 9XR to take advantage of that.

Which… I didn’t. Not for now, anyway. Ailerons are ganged, flaps are ganged, and basically I made it work exactly like my old radio. Because let’s face it, with that much flexibility I was bound to get something wrong. Better to get the plane back into flying shape first, and then start to add the bells and whistles.

I’m glad I did. I took it out this morning and found out just how utterly I’d botched it. Any time I make changes to my Bixler 2, I’ve made a habit of throwing it out without the throttle on so I can dead-stick it back to the ground. That way when the inevitable happens, it will tap the ground at a glide rather than slam the ground under power. Let’s see if I can remember everything I did wrong. The list includes: ailerons reversed, rudder reversed, endpoints on elevator, ailerons, and flaps all wonky (I had about 10% down-travel in the elevator, and maybe 120% up-travel), and all kinds of tweaking required to center up the control surfaces. It took a while to sort out everything I’d done wrong, but by the time I was done the plane was flying great under throttle and while gliding.

There’s still some clean-up to do. On the old radio the flaps were wired in through a Y-harness, so one side had a servo reverser wired in with it to make it move correctly. That reverser is still there. I’d like to clean up the wiring inside the plane, get rid of that reverser, and make it look exactly like the Raptor. Then one more session of cleaning up all of my mistakes, and then I can start to add the full-house mixes.

It’s a learning experience. But it sure is a lot of fun!

– Tom


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