Projects Playing with a Spektrum AR636

[Tony]

So we had a member way back in the day that kept chasing a resonance in the helicopter causing all kinds of weird issues. Turns out, it was the carbon fiber tail boom. He put an aluminum tail boom on the helicopter and all issues went away.

CF is stronger and just as light, and will not dent, but sometimes, that denting can save other parts, and aluminum is cheaper.

 

[LooseNut]

I've heard of static buildup in the CF from the belts running. Maybe that's what caused it.
Everyone told me I'd be bending Tubes when I was starting off, so I stocked up a small supply in both CF and Alum. This is only the second time I had a strike, the other was my second attempt at flight on a beat up B400 and I cut down the A450 tube to use I got at a swap, and made a back up when I got the stock.

 

[D.O.G.]

Not sure what folks prefer, Carbon Fiber or Alum, but in my escapades I've found Alum dents and causes less damage, if any to blades.
Any opinions?

With DFC heads, like my birds have, CF or Aluminum tail has no chance when it come to blade strike

 

[Tony]

I've heard of static buildup in the CF from the belts running.

Yep, like cellophane and PCV rubbing together (Mythbusters lol)

 

[LooseNut]

With DFC heads, like my birds have, CF or Aluminum tail has no chance when it come to blade strike

Ouch! Guess then it wouldn't matter. I haven't done it yet with an FBL (knock on wood) and none of mine are DFC yet.
My ARC 500 is a FB and has an odd sized boom, I did get a spare with it but I hope I don't whack it. I think I'd end up making a new frame holder to take another size or sleeving it.
Best thing about my 3D printer, I can design up and print what I want, once I like it go fab an alum one.

 

[LooseNut]

Ok, all back together with some upgrades from the swap box. Couldn't help it, they were just calling out to me saying "I wanna fly!" I mean, how can you say no?

So yeah, the Cut down Align 450L boom, Alum tail housing and arm, CF Tail Feathers and blades. A set of Generic 450 Skids that are a smidge taller and a little wider stance, just in case I get a little tippy playing with gains. Dang it, I'll end up making it so I don't stick a tag on it and take it to the swap.

While I was doing all this wheel spinning with swap part upgrades I was thinking through the flight and the bent boom. Aside from some belt rub and the tail chasing with the stick, should the heading have been trying to hold? Or was it so far off that it couldn't decide where to correct to? Like, it starts moving, I correct, it corrects, it's over corrected and switches opposite as I'm chasing it and now it's grabbing a correction? I can see where the pilot induced oscillations might just be the problem.

Anyone have thoughts on that?

 

[Tony]

It definitely could have caused drag on the tail, possibly making the belt kind of bounce that could have caused vibration which the gyro was getting confused with. One thing, make sure the tail from servo to blade is super smooth.

 

[D.O.G.]

One thing I have learned from Geena on gyro is to make sure you use a good double-sided tape like 3-M tape and also to replace the tape like once a year. They do wear out too.

 

[LooseNut]

I'm thinking the bend in the tube and the way the program handles servo centering. With the angle induced by the bent tube the blades will naturally start rotating the Heli. With the programing there is a stick Priority that can be adjusted and tells the Rx how much leeway it has for override. Since the program is also expecting to do it's work with the servo at the center that would seem to be the point that it's trying to return to. Thus it sets you up for holding a tiger by the tail.
As far as controls, yes, they are set up to run smooth and freely, and the Rx is mounted well on the frame with a double thickness of foam tape. No problem there.
Now that it's repaired and straight we'll see what happens.
Part of the learning curve with experiments is always finding the faults before divining the success.

 

[D.O.G.]

Good luck and video if can.

 

[LooseNut]

I've been watching and re-watching this video so that I get a better idea of what I can or can't do. Of course it's aimed at fixed wing, but the information on the gain settings is what I'm really looking at.
Surprisingly, there is quite a bit of info out there on Salvaging and repurposing the AR636, you just need to weed through them.
Interesting is that if you want the Heading mode you need to stick with the 1.xx programing since the Heading was substituted for SAFE. Can't have both, just one or the other.
Something else I find interesting is the D/R and Expo. From what I am reading, you can set it from the Tx side as long as you don't try and set it in the Rx side. If you mix them it causes the trouble.
Here's the vid I was watching;

 

[LooseNut]

Well, been playing with it and running back and forth to mod the setup. Still no joy. I know the early models of the AR636 had issues with the Heading hold, usually it locked in at the wrong time. In this case it seems to be locking out. It will be sitting fine and all of a sudden spin. And not just slowly either, it was just like I'd slammed the "rudder" over.
No damage, no tip overs, but it got exciting all of a sudden.
Something I did find was where I had used Sub Trim in the Rx for the Rudder Servo, it didn't like it at all, once I zeroed it out and made adjustment to the pushrod to reset it cured some of the movement. What goes afoul is the slight offset of the arm giving differential movement, a possible culprit of the Tail chasing. The heading hold I suspect doesn't like it. Maybe I'm wrong and it doesn't care, but I think there's more to it.
I did read about there addition of the lower Aluminum case and a fellow that had made his own. It's supposed to be vibration cancelling as well and the foam tape mounting. So It could be an issue in that regard.
The whole point of the exercise was to be able to utilize the AR636 units and take advantage of the stabilization features and heading hold making it a cheap intro to Heli when stuck in someone's old dust collector that was purchased cheap. So far, I'm sure they'd toss it in the corner by now and have given up or at least just zero all the features making it a standard Rx and add a gyro. Easy for me to do since I have those parts around, as well as the Flybar parts to put it back as it was.
The Rx programming would require the USB cable or the Bluetooth to Zero it out though and it's added cost for a one time use.
I'll probably play with it some more, but unless I can come up with a groundbreaking solution, the AR's I have can go back to collecting dust. I didn't like them in my planes is why they ended up in the box in the first place.
I had really hoped the $160 spent on those two new would have found a good home.

 

[LooseNut]

Spent some time tonight going over everything with a fine tooth comb. Found the tail link arm had it's bushing come loose and was causing a lot of play. This is the bushing that captures the ball. Thinking that could cause quite a stir with the tail holding. Kinda like patching a kite in a tornado.
I cleaned the surfaces and bound it back in with a dab of CA.
Second I went through all the Tx and Rx programming, reviewed the settings in my F-Modes, zeroed all the expos in the Rx, made sure the D/R were still zero. pulled the head, checked the swash, back together and checked pitch angles, and then as a final step I rebound it all.
It's ready for another shot.

 

[James M. Lewis]

I really like the way you problem solve these issues and think outside the box

 

[LooseNut]

Thanks James, I'm persistent if nothing else.
Battery charging as the wind is coming down out there, almost time for another shot.

 

[James M. Lewis]

Go for it

 

[LooseNut]

Well, the wind went from strong and steady to gusting. Since I'm out on the driveway/parking pad, I'm limited to the area I can fly and the end of the side fence to one side, the House corner on the other. The gusts change quickly in that area coming around corners.
I did collect some data though. The Heading seems to be working, albeit, some drift with the wind that is easy to correct with a slight stick. Since I don't have any expo in the Yaw, the slight means SLIGHT. The carbon fiber blades have just a little width on the stock ones and the tail is pretty aggressive.
I think the Bushing was definitely the culprit of yesterdays cardio exercise.
To make sure of what I was seeing with the yaw, I also stopped and set it on different compass headings to the wind. That verified the small amount of drift directions was indeed wind and not a trim condition. Nice to confirm that.
Testing hopping. Wow! I had the gain too high and it was shuttering worse than a drug addict in lockup as soon as I'd break ground. So tinker.... test.... tinker... test.. charge battery, tinker... test. Yeah, the typical stuff.
I've got the gains for Roll and Pitch (Elevator) down at 45%, still in "Normal" F-Mode, spool and pitch probably around 60ish percent breaking ground on the short hops. I'm only allowing about a 2" hover in case something goes berserk. Instant set down with any gust that hits and rocks it. Expo for Roll and Pitch are set to 25%. I'm pretty sure the gain will need to be around 40%, maybe a little slightly less on Idle Up 1.
I'm leaning toward putting the parts back on the head for FB. Seems a bit twitchy for a beginner unit and the Rx is not a good substitute for an FBL unit. I think the Flybars will be a little more forgiving and docile.
Thoughts???

 

[LooseNut]

My test area, actually pretty good size. I can park 5 across and 3 deep with easy door access. I just have to watch for the occasional car passing by in case something goes awry.

And yes! That tree has reached out a couple times trying to snag the errant flyer unaware.

 

[James M. Lewis]

Now that's what I call a test area! NICE

 

[D.O.G.]

I think the Flybars will be a little more forgiving and docile.
Thoughts???

You have two ways to look at that. The flybar has more components to actually get them working correctly as one on taking off plus it's costly when it comes to crashing...which we all have done. FBL has fewer components but is not easy to get used to but when you do... it's the next best thing to peanut butter Can you tell us, unless I miss it, what pitch is your blades at? 10 degrees is a good place to start. Don't forget this is just my which doesn't buy much nowadays