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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Sorry if this is hard to read, I was having all sorts of format issues while typing! The text was italicized when I didn't want it to be, the font changed when I didn't change it, and the word wrap stopped working! Ah well I guess you'll get the point anyway.


Nathaniel ~KD2DEY

There's an interesting discussion here about Futaba it would appear yes you do need too, but check the details.


Thanks for the reply. After reading the entire post you referenced above, I am confident that you are correct; this appears to be a necessary update for Futaba users.

I would like to hear from 3DR on this issue and ask why they don't start an email notification system to alert buyers of affected hardware,

when there exists an issue on a hardware/firmware issue. It would seem to me that the PPM encoder is not something that the end user would typically need or think to update. The Forums are a vast resource to the end user but they can't be the only source for something this critical.

I have the exact same setup used in the post you referred to except I am using it with ArduPlane code not ArduCopter code. I would be very upset had I invested all the time, energy, and money in this system only to have a glitch in the PPM encoder cause a crash and then discover that buried in the forum or the appendix to the ArduPlane wiki (the appendix? Really the appendix!) there was a solution that I hadn't seen!

Having said that I realize that the issue lies with a system that is outside the control of the dev team and could not have been directly anticipated. However it can be supposed that there will be innovative ways of encoding/decoding PPM systems that don't conform to a standard practice. Perhaps it would be a good idea to develop a sketch routine to test the input from a given radio receiver that a user can implement to confirm compatibility of their RC system with the APM encoder.

I would further suggest that the wiki should be updated to reflect the importance of this update and to make it clearer what hardware it applies to, and lets move it out of the appendix! I commend the dev team on the resolution to this issue! Now that the holidays are over let's not forget the details and make sure all Futaba owners are aware of the issue and can clearly find and follow the instructions in the wiki to update their PPM encoder before they have an issue that results in a crash or worse.

Thanks again Bill and thanks to Steve, Oliver, Marco, Uwe, Mike, Arid, John and the entire dev team who contributed to this solution.


Nathaniel ~KD2DEY

Nathaniel, being the starter of the previous thread mentioned by Bill, I can confirm tha updating the PPM encoder for Futaba radios is a must. However the slight glitches that most were seeing which was subsequently attributed to the PPM encoder was generally seen on multirotor platforms.

Because of the way the encoder now handles Futaba signals, the error has been corrected. So personally I can't see any negativity in you upgrading.

The update notification was posted here:

However, I think it's a valid point for perhaps a sticky to be created by the mods with something as simple as what's the latest software version for each device / component, when it was released and where it can be downloaded.

That way people can subscribe to that post and be automatically notified of changes. It could contain listed updates for....

APM, PPM Encoder, GPS modules etc.

Mods - Your thoughts ?



First let me say thanks for your persistence in perusing this issue. Second thanks for your comments here. I do however disagree with you about Brian S. discussion 'New Firmware for Futaba Radios', the post basically is asking the same question I was. Do I need it and how do I install it. Also Brian S, is just a user like myself, not a developer or contributor. The discussion only received one post by John (Developer) and because of that would have quickly dropped off the DiyDrones Home page 'Latest Activity' section. I like the idea of being able to subscribe to a particular post/discussion announcing updates for particular hardware. personally I think something as important and specific as this should be posted in a banner format on the main DiyDrones home page and left there for a period of time say maybe a month or so to give ample time for users to become aware of the issue and make their own choices. I don't feel anyone ios trying to hide the issue, I just feel it isn't being treated as seriously as it should.

Unfortunately my board is buried fairly deep in the belly of the beast and will require a bit of work to remove so I can apply the update but I plan on doing it later today. I realize this doesn't seem to be as much of an issue with a fixed wing platform as with a MultiCopter but I still don't like the idea of flying with a glitch in the PPM encoder.

Thanks Steven,


Nathaniel ~KD2DEY

Happy to bring this up with the dev team, but I'm a little unclear about which Futaba's are affected. I use the regular Futaba 7C series, and there are no issues there. Is it some new Futaba model? 

Hi Chris, not sure if the "twitch glitch" (as I affectionately named it) affects older models, but it certainly affected the Futaba T8FG as I discovered and then Marco said he was experiencing the same along with other users.

Olivier gave an explanation to why this problem manifested itself and it was down to the way the PPM encoded the signals from the Rx which could be down to the newer Futaba radio protocol.

Thanks for considering the idea of a Sticky to announce new software releases only with no discussion on that thread.

Happy new year !!

Thanks. If we can get a list of affected models, we can post a notice in the manual. The PPM encoder software, like the rest of the code, is community created, so I hope the community can compile that list. There are no issues with any of the Futaba's we have, so I can't test this myself. 


Just speculation on my part, but I suspect it probably effects most modern Futaba radios that have more than 7 channels. What Steve and I as well as other who responded to his post have in common was the relatively new Futaba T8FG which with the newest firmware  is capable of up to 14 channels. I'd be curious to hear from anyone using a Futaba 12FG, 12Z or 14Mz. The difference with thise units is that they output 12 PPM channels to the trainer port and I suspect the PPM timing may be different with those models. All other Futaba radios, over 7 channels, output only 8 PPM channels to the trainer port. Though I don't directly have anything to support this I suspect you might find a correlation here.


Nathaniel ~KD2DEY

The whole issue is related to having limited hardware resources (shared pin interrupt for all RC inputs) making it hard to catch and get the timing of certain RC input sequences. The latest tweak seem to have fixed it, but there is no guarantee the problem won't come back, if some other receiver decides to get creative with the signals in the future. Latest generation futaba receivers are the ones confirmed to cause problems with groups of RC channels synchronously updated in rapid succession. But does it apply to all or them or just certain models? Older models without the channel group synchronization, does not have the problem. So without testing every receiver out there, there is no way to say for sure which ones will require the update.


Have you seen any receivers other than Futaba receivers with 8 or more channels being susceptible to this problem? Also do you see any reason not to update to this PPM encoder firmware revision if your not sure if your receiver is affected?


Nathaniel ~KD2DEY

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.

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