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Traxxas ALIAS
- Ssayer
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I found out a long time ago that things don't fail as often when I have a lot of spares.
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- victzh
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- Ssayer
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- Ssayer
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- victzh
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- victzh
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The system has telemetry/presence, so TX knows that it transmits not into thin air, but to someone. At least battery level of RX is reported, may be some other info is sent back as well.
The packets are pretty simple - 16 byte packet, 2 bytes per channel, MSB first. Values are in the range 0x000-0xfff (0-4095), middle value is 0x07ff (2047). Zero corner for both sticks is left bottom.
No CRC, no frequency hopping.
The only unclear thing is how TX id is passed and how all the negotiation goes. It begins on one channel and RX seems to be transmitting some identifying sequence constantly, then transmission goes to another channel.
Still working on it, just wanted to report progress.
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- Ssayer
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- SeByDocKy
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- Machy2k
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- victzh
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I think, yes, it will. Why not?
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- Ssayer
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- victzh
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- PhracturedBlue
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- victzh
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- PhracturedBlue
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- victzh
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Attached are several SPI traces - one is just RX without TX being turned on, second is L and F switches, last is both sticks in several positions.
I figured from my own decoding that the packet structure is following:
16 bytes, 8 channels each 2 bytes MSB, last 4 bytes are always 7F007F7F. Values are between 0 and FFF, middle 7FF
Order:
1 ch - always 01FF or 07FF
2 ch - Elevator, 0 - bottom
3 ch - Aileron, 0 - left
4 ch - Rudder, 0 - left
5 ch - Throttle
6 ch - flags, default 010A, light 014A, flip 410A
7 ch - 7F00
8 ch - 7F7F
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- victzh
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- victzh
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- PhracturedBlue
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The SOP code and CRC seed are typically used (in conjunction with the channel). In the Devo protocol the data itself is also encrypted, but that really doesn't help much.
How does binding work with the TRAXXAS? Do you need to bind every time, or do you bind once and have it remember? Does the Tx wait for the Rx to become available before starting transmission?
Looking at the data you sent There are 2 channel configurations:
Channel 0x15 is used for Rx, 0x1a is used for Tx
CHANNEL 0x15: CRC=0x616a, SOP=dd 26 7c 50 66 cd 7c 50
CHANNEL 0x1a: CRC=0x2828, SPO=e2 f8 cc 91 3c 37 cc 91
The Rx reads the MFGID before doing anything, so it is likely that it is used for generation of at least some of the above parameters. In your case the MFGID is: e8 35 8f ae 67 fe
Before binding, we see that the Receiver sends:
03 e8 35 8f ae 67 fe 0e 00 01 02 00 01 0b 00 00 (which includes the MFGID)
Once it receives a packet back:
0b ff 07 ff 07 ff 07 ff 00 00 01 0a 7f 00 7f 7f
0b 0b 0b 0b 0b 0b 0b 0b 0b 0b 0b 0b 0b 0b 0b 0b
It transmits this:
04 02 00 01 0b 00 0a 07 10 00 00 00 01 0b 00 00
I believe that probably completes the handshake. Once that is finished, all communication happens entirely on channel 0x15
It then receives:
07 ff 07 ff 07 ff 07 ff 00 00 13 14 7f 00 7f 7f
07 07 07 07 07 07 07 07 07 07 07 07 07 07 07 07
And responds with the following which is likely temlemetry:
07 00 0a 06 10 01 00 00 00 00 00 00 00 00 00 00
CRC and SOP don't change for a given channel.
While we don't have a lot of information here, this protocol does not seem to use a key-hopping scheme (like DSM*). But we'll need a lot more info to be able to do much more.
Specifically, we'd want to see the Tx setup. what is the Tx MFGID?
Then it will likely be a case of emulating the Tx (or Rx) with the Devo radio/arduino and sending different packets during the binding phase, and see how the Tx/Rx respond.
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