Is it necessary to (update)flash the Atmega32U2 (PPM encoder) on an APM 2.5 if using a Futaba system?

I'm constantly expanding my understanding of all the options and systems within the APM 2.5 by re-reading the wiki and looking for things that have changed or things that I hadn't considered before.

One thing that has recently caught my eye was the section here in the ArduPlane wiki titled

'How to flash the Atmega32U2 (PPM encoder) through USB'

The downloads section title description states

APM 2.x ArduPPM Firmware v2.3.13 (recommended update for Futaba radio users)

The wiki page was most recently updated almost a year ago (Dec 29, 2011) and doesn't specify what versions it applies to.....I don't know why this text is coming out italicized....I don't have Italics on...anyway the wiki instructions specifically refer to APM 2.0 not 2.x and the images are all of an APM 2.0 board. I realize that this is just a representation of the board at the time but it doesn't
make any reference to APM 2.5.
The downloads section here states
ArduPPM v2.3.13 ATMega32U2 firmware for APM 2.x

So is the upgrade necessary for APM 2.5 or not, and is there a list of Futaba receivers known to
n issue with the stock PPM encoder firmware? So perhaps if someone could clarify this itwould be great, also are the instructions in the wiki still applicable to an APM 2.5?
Nathaniel ~KD2DEY

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Latest generation Futaba receivers like the R6208SB is the only confirmed one with problem.

If you bench test for an hour or so and see no spikes in the GCS, it should be fine.

If you want to be absolutely sure, I recommend using a receiver with PPM output. Using PPM-passthrough there should not be a spike problem regardless of receiver brand or ArduPPM firmware revision. For this I would recommend this Futaba FASST compatible receiver.

I've also experienced problems with th R6008 receiver (in normal speed mode, not high speed) and the 3DR PPM encoder.


Yeah that's the standard receiver that ships with the Futaba T8FG Super 14 channel system. Personally I haven't noticed a problem yet, but I don't expect it would be as obvious in a fixed wing system. I'll be updating the encoder just to be sure.



Nathaniel ~KD2DEY

In my opinion unfortunately there is not a rule, may depend on the rx firmware, Orange Futaba and FR-Sky TFR8 (is the same rx) cause these problems here, tested with APM2/2.5 in different setup.
For this reason owners of Futaba update you encoder whatever, with the new one the problem is completely gone here.


I agree that the list shown in this post isn't complete, and may not be considered accurate until people add confirmed receivers to the list. I disagree however that there isn't a 'rule'. In my opinion this problem seems to affect any Futaba compatible receiver working in either MULT or MLT2 mode which makes the capable of reading a signal containing more than 7 channels. I thinks that all S-Bus compatible receivers and any native 8 channel Futaba compatible receiver. However until we start to see a list of confirmed receivers and the Transmission mode they are being used with it's only an opinion.


Nathaniel ~KD2DEY


I agree. I first experienced this issue with the standalone 3DR PPM encoder more than 18 months ago, so the myth that it's only recent/newer receivers is also flawed. If it's FASST and 8 channels or more (thus being MULT or MULT2) then multiple servo outputs will be updated at identical times. The degree to which the issue manifests will of course vary depending on numerous factors.

A glitch does not automatically make it a problem with the PPM encoder. It might just as well be a bad connector or electronic interference related problems. It might even be a bug in the radio system. Certain OrangeRX/FrSKy FASST receivers for example has a problem with throttle glitches because of compatibility problems with the Futaba radio fail-safe system.

So I what I am trying to say is that "I had a glitch using receiver xxx, fix it" does not really help. If we are not able to reproduce the problem, it can be close to impossible to fix at times. Simply because we might not even know what we are trying to fix.

At current the MULT channel grouping is the only thing that makes sense technically. And confirmed reports of fixing the glitch problem by improving the interrupt system response time, further validates that view.

I used to get twitches on my Tricopter firmware 2.6 using a Futaba 10c fitted with Frsky module

With the Usb connector on my APM2  trashed  I will have to pull the board and solder the isp header to update the PPM encoder. 

Are all Futaba radios  seeing the glitches?  The discussion had reference to some receivers  not displaying the problem. My FS617 receiver   in 7Ch mode  did not  have  motor  log spikes last  time I looked at the logs.  Does it just happen when CH 6 or 7 are used ?

In my experience it occurs on Futaba receivers with 8 or more channels. Maybe not all, but I've only tested a couple. I've never seen it on a 7 channel or less receiver.

Drone Savant,

Follow the link on Steve's reply Pg1 of this discussion and you will find many good descriptions of what occurs if and when you are having a problem. I don't think this is a problem that could have been foreseen or prepared for as it has to do worth a non standard output on some very specific receivers.

It wouldn't be a bad idea though to have a sketch that could read the incoming signals and determine if your receivers output is compatible.


Nathaniel ~KD2DEY

Based on what I've been able to find on Futaba's website I would suspect that the following receivers when used with the compatible transmitters (most but perhaps not all of which are listed following the list of receivers) outputting in either MULT or MLT2 modes will experience the same issue with the PPM encoder on the APM 2.5.

Receivers: R608FS, R6008HS, R6014FS, R6014HS, R6108SB, R6208SB, R6203SB, R6203SBE, R6202SBW, R6303SB, R6303SBE

Transmitters: T8FG, T8FG SUPER, T10C, T10CG, TM14, T18MZ, T14SG

If you have one of these Receivers/Transmitters and can cofirm or add to this list that would be great!

I can confirm that the R6208SB that ships with the T8FG Super does in fact have an issue with ArduPPM firmware before 2.3.13.


Nathaniel ~KD2DEY


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