Spoilerons on Conscendo Advance -- left aileron servo not going full travel?

[claussen]

Hey y'all,
I recently crashed my Conscendo and decided to get rid of the Y harness while rebuilding so I can use spoilerons. I've managed to get them working RealFlight 9 (yay!), and I've managed to get them kind-of working on the bench, but I ran into a weird problem:
Left aileron servo doesn't go full travel with full stick or full flaps alone -- only with both.
Right aileron servo works as expected.

TX is a DX7s, RX is the stock AR636.
TX Profile is Acro, Flaperon-type wing.
Right Aileron is on Channel 2.
Left Aileron is on Channel 6.

All trims at zero, and ailerons have been centered using the clevises.
At full spoilers (flap position 2), left stick still moves the left aileron up further. Right stick doesn't move the right aileron -- it's at the end of the servo travel where it should be.

In order to correct this, I've had to use a *huge* amount of LAL sub-trim on the TX, which just seems... wrong -- like -80 or something.

I also created a mix of THR -> RAL and THR -> ELE, which replicates the flap switch, just for kicks/tuning fun. The problem is the same there.
The TX reports outputs of 100 on both RAL and LAL with full stick, so it seems to at least *think* it's doing the right thing :/

Why would one servo, on a glider which was previously trimmed just fine, suddenly be not running full travel just because it's now on Channel 6 instead of Channel 2?
I'm sure I'm just being thick...

thanks!

[xviper]

You say you crashed this plane. You also say you “centered” the servo arm. Are you using the same servos? It’s possible that the crashed caused one servo to be forced and skipped a few teeth so that even though you centered the arm, the servo itself may no longer be in the original neutral position. Also, when utilizing spoilerons and/or flaperons, you need to reduce the AIL rate for each deflection or you can easily drive the servo to one of its end points and then overdrive it when you use ailerons heavily. That could also cause teeth stripping.

[claussen]

Thanks!

Yeah, it was a lawn-dart situation -- the wings were intact, but the front of the fuselage was smashed. I did notice that the arm positions were off by maybe one click between the two, so I reattached the L arm one position over to get it a bit closer to even with the R arm. But I suspect that was always the case.

I tried swapping the R/L servo channels and the same behavior happened on the R side in that case -- so seems like it's something in the signal path, not the servos themselves.

Thanks for the tip on not overdriving -- setting it up in simulation, that didn't occur to me.

How do people maintain as much AIL range as possible without overdriving? An offset in a mix or something?
Or do folks just not plan to use much AIL when in spoiler mode anyway because, well, they're probably on approach?

[xviper]

How do people maintain as much AIL range as possible without overdriving? An offset in a mix or something?
Or do folks just not plan to use much AIL when in spoiler mode anyway because, well, they're probably on approach?

An offset is one way. I chose to use a lower rate on the AIL. When I hit flaps, I also throw the AIL rate switch to the middle or lowest position, depending on how much flap I choose. With the flaps at neutral, you work the AIL at your highest rate (throw). You can see how far the ailerons go in each direction. You can play with the travel and increase to max. Now you kinda know that your are getting close to the end of the travel. You might have a little remaining but that can be your safety buffer. Now, when you flip the switch for spoilerons or flaperons, work the AIL stick till you mimic what you saw for max travel. You can also see (or give a good guess as to) how much more stick travel is left. Now reduce your travel (rate) for that spoiler/flap deflection so that you get only that much travel at full stick in each rate position.
I sold a jet to a guy and I warned him to set his flaps from scratch. Select the wing type, "zero" flaps and flap sub-trim BEFORE you power the plane up for the first time and don't use the default flap setting (no wing type selection). Disconnect the rods just in case. Well, he forgot. First he plugged the thing in, he overdrove the flap servos and killed one. When he brought it to the field, he complained that one of the flap servos was dead. When he showed me what he was talking about, he plugged the thing in again and after working the flap switch once, he blew the other servo. In this case, it was stupidly easy to kill a servo.

[claussen]

Interesting, thanks -- I'll take it easy on the servos then!
Do you have any suggestions for how I might debug the different travel on Ch 2 vs Ch 6? That seems to be the core issue here -- from what I can see in the MONITOR page, the TX is outputting the signals identically on those two channels, but I don't have a way to confirm that other than at the RX, and the results are clearly different. Is it time to break out the oscilloscope?

I connected the AR636 to the Spektrum programmer on my PC, but it didn't show any obvious asymmetry in the setup either. Weird.

[xviper]

The asymmetry you are witnessing may be due to several factors that may be very difficult to diagnose and test. I wouldn't even begin to know how an oscilloscope could help in this situation. Being a model with AS3X and SAFE, control surfaces are affected by all kinds of intervention from the receiver. Originally, the aileron servos were "Y'd" together. Now separated, AS3X and SAFE may need to be re-assessed and maybe even re-tweaked. Are there extensions? These may have some involvement in what's going on. A crash like that could even cause some irregularities in the receiver. Maybe one aileron is now moving with more difficulty than the other. Is one aileron hinge damaged? Was a repair done that might cause some difference in resistance in the way one aileron moves? Is the difference significant? If it's not too bad, you may be able to do a work around with the transmitter features - travel, sub-trim, offset, differential? Or, you just live with it if it doesn't adversely affect flight too badly.

[claussen]

Yeah, the ailerons were mostly cracked free in the crash -- I've retaped them on both sides, but I can imagine a bit of difference in resistance. Not a huge amount, though. And the fact that the asymmetry manifests on whichever side is driven by Channel 6 suggests that's not the issue.
I'll try turning off all the SAFE/AS3X stuff and see what happens :)

[xviper]

Most of the time, when a control surface comes completely off and then tape used for repair, there can be some inconsistencies. Make yourself a small weight (an oz. or 2) on something like a fishhook. Disconnect the rod and get the aileron to as level as possible, hang the weight from the trailing edge and in the middle of the aileron and measure where the thing comes to rest. Do it to the other side. If they are different, it doesn't take much of a difference to affect what is likely a 9g servo, especially near the control surface's highest defection.

[claussen]

You were 100% right -- I reprogrammed the AR636 with 1.x non-SAFE FW (wasn't using SAFE anyway), configured the RX with flaperons, the TX for 1-ail + 1-flap and now everything is working as expected. Have dialed back the travel on the flap settings and gonna go give it a try now :)
Thanks for your help! I owe you a beer!

[xviper]

I'll be danged!