[ Update at the end ]
You bought a brand new FRSky with 8 channel and a promise of a helpful PPM Sum output.
Be warned that you cannot use this with 8 channels. Only 6 channels could be used with some risks (only 5 for real safety). [Note #1 at the end] It's really disappointing.
Yes. FRSky's CPPM signal has a BIG problem: It has a period of only 18 milliseconds. What does that means? Here we go:
A PPM Sum signal usually has a period of 20ms. As each channel uses up to 2ms so you need 16ms to fully accommodate the data from 8 channels (8 * 2 = 16ms).
Now comes an important element: the Sync Pulse. It needs to be wider than all other ones to indicate the start of a new PPM train. Any 8 channels system based on a 20ms has room for a 4ms pulse (16 + 4 = 20ms). Even with all the channels at 100% a system like that still gives you a perfect sync pulse.
That's the BIG problem with FRSKy CPPM. If you start using some switches and knobs you are pretty much risking to lose the sync on your autopilot. Because the sync pulse is squeezed until having the same size of any channel.
I hope they can fix that with a firmware update sooner, because I believe it's not acceptable.
Until that, you cannot use it on your autopilot without risks. [Note #1 below]
[ NOTE #1 ]
This is far away from the ideal, but there is a cheat to eliminate the risks when using just 6 channels by suppressing CH7 and CH8 from CPPM.
At least on a ER9X or ERSky9X radios there is this way:
By changing your model's setup to use a Proto PPM 6CH it will not output CH7 and CH8.
(The frame space (300uSec) though is just ignored. I did not see any changes.)
I've verified on Oscope. It works!!! The CPPM was outputed from RX without CH7 and CH8.
Is still a shame and disappointing using just 6 from 8 channels. But that seems to eliminate the risk.
[ NOTE #2 ]
Jani, from jDrones took this issue to FRSky's GM/CEO and got a response from them. They are now baking a solution to release a new firmware. Probably the new CPPM frame period would be 27ms (the next available number dictated by the hardware's clock division).
[ UPDATE ]
Yesterday (28th September) Jani came up with a beta firmware from FRSky. It does output CPPM frames at 27ms. So far we have some positive feedback from DIYDrones dev team's tests. I'll not update this post anymore. A new post instead will show some results followed by a mini updating tutorial for those CPPM capable receivers. Stay tuned! ;)
[ UPDATE ]
This post shows how to fix it.
--Sandro
Comments
@ David Baker, thanx for reply:
yes, all FrSky CPPM used to have an 18ms period. However, the new firmware is out to make it 27ms so it will work fine with all 8 channels on your D4R-II, all you need to do is upgrade it. The D8R-XP is also supported at 27ms period with the new firmware in CPPM mode. All other FrSky Rx's that do CPPM will remain at 18ms. Note that this new firmware does not affect the non-CPPM operation, other than it removes the "HS mode" previously avaliable on the D8R-XP.
I don’t actually have the D4R-II yet, it was the one I was planning to replace my V8FR-HV with.
is there any firmware for the V8FR-HV that would enable CPPM @ 27ms?
Are these firmware for the V8HT TX module or the RX? I cant find any 'how to' on FW updates on any of these units.
@Mark, I don't, but probably can get one after they return from holiday... Many in China are on vacation this week as I understand it, following their "National day" on Monday.
@David,
Do you have schematic for D8R-Plus? One of mine has stopped working, I need to find out why 3.3v is only 3.0v and not passing to ST32. I may have applied +5v to TM sensor ports but not intentionally..
Cheers
I belive the D8R-II can be upgraded to output CPPM. I did it to a D8R.
@David, many thanks for the information. I just starting with APM and I thought that my FrSky Tx module maybe could be connected to the PC by an USB cable (like that used for upgrading its firmware) and thus not requiring a another wireless system like 3DR radio.
And no, you can't connect the D8R-II plus to your PC...it will only talk to an FrSky Tx module.
@Eladio, the D8R-II Plus can be used by wiring it discreetly to the APM via 8 PWM servo cables as normal. What you can't do is 8ch CPPM, as that model doesn't support it at all. In other words, there is no 27ms CPPM firmware upgrade for the D8R-II plus.
So could I use my D8R-II plus RX as wireless connection between APM 2.5 and my PC if I upgrade its firmware?DPLUS 2.4Ghz 8CH ReceiverDiD8FrSky D8R-II PLUS 2.4Ghz 8CH ReceiverR-II PLUS 2.4Ghz 8CH ReceiverFrSky D8R-II PLUS 2.4Ghz 8CH Receiver
@Dale, yes, all FrSky CPPM used to have an 18ms period. However, the new firmware is out to make it 27ms so it will work fine with all 8 channels on your D4R-II, all you need to do is upgrade it. The D8R-XP is also supported at 27ms period with the new firmware in CPPM mode. All other FrSky Rx's that do CPPM will remain at 18ms. Note that this new firmware does not affect the non-CPPM operation, other than it removes the "HS mode" previously avaliable on the D8R-XP.
is this problem with all Frsky CPPM? I was about to switch to useing this for my quadcopter useing a D4R-II RX
with my Frsky modded 9x with er9x F/W
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