Servo twitch using Futaba 8FG

I have been trying to isolate an intermittent servo twitch the last couple days. I have the APM 2.5 in an X8 running ArduPlane 2.68.

I have power going to the output rail with a 5V Castle BEC.

The twitch is very random and fairly small deflection. In manual mode if I slowly move the elevator or aileron stick I can get it to do it, just not 100% repeatable.

I have flown the plane a few times. I tested stabilize mode and it worked great, but while flying in either manual or stab mode the plane will twitch randomly as if a side gust hits it.

I started removing components one at a time to see if it would stop. I pulled out the BEC and have been using a JR 4.8v receiver pack for the rest of the testing.

I was down to just the APM (no GPS, telemetry or airspeed connected) and the Futaba receiver. It still did it. Straight out of the receiver it was OK.

I tried a new APM loaded with same firmware and I got the same results.

I have tried both analog and digital servos from Hitec, JR and Futaba.

I had the same APM in my Skywalker and it did not have a twitch. Only change was to add a airspeed sensor and elevon mixing when I installed it into the X8.

Just disabled the elevon mixing in the radio and the APM. Same results

Just tried another Futaba 8FG, calibrated it and same results.

 I just remembered that I had a DragonLink through a JR9303 radio on the other Skywalker.

Swapped out to a Spektrum DX7/AR7000, calibrated and twitch went away.

OK, so now I need to find out why the Futaba is causing a twitch. I am using the Futaba R6208SB receiver..

I will try a couple different rx's to see if that changes anything.

Before I swapped receivers I changed the output to MULT vs MLT2.

MLT2 mode enables channels 9-12.

That did not fix it either.

Tried a R617FS receiver and no more twitching!

This requires changing the "frequency" screen from MULT to 7CH

Any ideas what is changing in the Futaba radio to cause a twitch when an 8 channel or higher receiver is used?

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Replies

  • Developer

    Actually I had that same problem over the weekend when I tried to update the driver software.  I've added some instructions on updating the 32u2's driver on the wiki.

    I talked with Craig and the APMs are still not shipping with this new ppm encoder but should start in the near future.

  • Got it flashed. Found more info in another thread. Had to load the USB driver from the Flip software. Now I'll see if the twitch goes away.

  • 3692622735?profile=original

    Followed steps but I am getting a DLL error when I select USB.

  • Developer

    Ah, this problem is well known in arducopter-land.  I think you need to update to the latest ppm encoder.

    Here's the trouble shooting guide entry including a video with before and after upgrading the ppm encoder on an APM2.5 mounted on a big-ish hexacopter.

    Here's the guide for upgrading your ppm encoder for arduplane.

  • I noticed a twitch when I moved from direct attach to the Futaba RX to using S.BUS. Long story short I wanted my RX out on the wing.. When I reduced my travel from 100 to 75 in the menu and re-calibrated the twitch went away. I noticed my twitch was induced by slowly moving the elevator servo. The ailerons would twitch out. 

    I chalked it up as something funky S.BUS was doing. After I went back to direct attached to the Rx the problem went away. Interesting that another person is having the same trouble. 

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