Traxxas ALIAS

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09 Jun 2014 17:32 #23995 by victzh
Replied by victzh on topic Traxxas ALIAS
I will look into a possibility to solder to TX, I initially soldered to RX because it was much easier.

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09 Jun 2014 17:35 #23996 by victzh
Replied by victzh on topic Traxxas ALIAS
Also, answering your questions about binding - TX and RX bind every time as far as I understand - no special binding procedure. TX "feels" presence of RX - it behaves differently, and reports RX battery.

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09 Jun 2014 17:53 #23997 by PhracturedBlue
Replied by PhracturedBlue on topic Traxxas ALIAS
The 1st byte seems to be the state byte. 0x01 is a normal transmit (from Tx). 0x07 is a request from the Tx for telemetry. 0x03 and 0x04 are related to binding.

I see 2 likely cases here:
1) There are some steps missing in the binding procedure. In this case, my guess is that the Tx/Rx remember the previous Tx/Rx and if they see the same as last time, skip some of the binding process. For instance, the Rx never receives the mfgid from the tx. If it recalled it last time, this would be possible, but it doesn't explain how the Rx would ever see a 'new' tx.
2) The entire binding session is dependent solely on the Rx. Every Rx will transmit on channel 0x1a with a CRC of 0x2828 and SOP code of e2 f8 cc 91 3c 37 cc 91. The Tx does some math and determines the proper channel/SOP/CRC to transmit with. If this is the case, it is especially annoying because it means we need to figure out the math to bind. replay attacks will be impossible.

Either way, we definitely need to see the Tx traces. It is likely you'll need to try to send different Rx codes to the Tx to see if it responds differently.

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09 Jun 2014 18:35 #24001 by PhracturedBlue
Replied by PhracturedBlue on topic Traxxas ALIAS
I found this:
latrax.com/pdfs/6639-KC1952-R00-Transmit...ing-Instructions.pdf
Which indicates there is some 'model memory'. But as the Rx has no binding mode, this means (2) above is probably more likely.

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10 Jun 2014 01:41 #24006 by victzh
Replied by victzh on topic Traxxas ALIAS
Latraxx transmitter is a nightmare - I just desoldered the cover over the radio chip. I don't know how people handle it without Chip Quick.

While I'll try to solder to the TX, I observed one more interesting fact - the TX and RX bind to each other in any order and if you turn on/off any of them they bind anyway. I don't know how you can ensure control by your selected TX for your model in such a scheme. I only can think of physical proximity during binding and low power binding signals.

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10 Jun 2014 02:54 #24007 by PhracturedBlue
Replied by PhracturedBlue on topic Traxxas ALIAS
I suck at removing shields. I usually just cut them off with an x-acto and a lot of patience :) I need to get some Chip Quick.

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10 Jun 2014 05:16 - 10 Jun 2014 05:20 #24009 by victzh
Replied by victzh on topic Traxxas ALIAS
I would have cut it, but:
1. I had Chip Quick
2. There is no access without danger to cut the traces

Attachments:
Last edit: 10 Jun 2014 05:20 by victzh. Reason: Added reduced size image

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10 Jun 2014 06:02 #24012 by SeByDocKy
Replied by SeByDocKy on topic Traxxas ALIAS
ChipQuick is on my short list "next thing to buy" but I didn't find a good europeen retailer not doubling the price with shipping fees.
Here hard to find it below 25 euros when you know you can pick up it for 8-9 USD in US ....

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10 Jun 2014 07:01 #24013 by SadSack
Replied by SadSack on topic Traxxas ALIAS
as a replacement "ChipQuick" which has a normal price or re branded...
Low Melt Solder 70 degrees
www.anticsonline.co.uk/533_1_1671854.html

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10 Jun 2014 11:34 - 10 Jun 2014 11:46 #24015 by blackmoon
Replied by blackmoon on topic Traxxas ALIAS
This one is a low melting solder paste 138°c, it's euro located and only 8€ shipping, plus accepts paypal. Same composition Sn42Bi58 (42/58) as chip quick btw

www.tme.eu/en/details/asnbin_35/solders-...nc-sn42bi58t387-35/#

And the 500gr, all your life stash : www.tme.eu/en/details/asnbin_500/solders-pastes/amtech/#
Last edit: 10 Jun 2014 11:46 by blackmoon.

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10 Jun 2014 12:36 #24016 by PhracturedBlue
Replied by PhracturedBlue on topic Traxxas ALIAS
Back on topic, is the MCU visible somewhere? or is it on the underside of the board that is soldered sown to the sticks? You could tap those vias, but it is annoying. I thought I'd check the FCC-ID, but a search didn't match the number on the board

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10 Jun 2014 13:35 #24017 by victzh
Replied by victzh on topic Traxxas ALIAS
At the bottom of the photo you can see a piece of LCD raised above the main board approximately 1cm. Underneath the LCD is the MCU, absolutely unreachable. I will try to solder to vias, it's much more realistic.

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10 Jun 2014 15:21 #24022 by PhracturedBlue
Replied by PhracturedBlue on topic Traxxas ALIAS
Have you considered removing the LCD? It is very likely that everything would work fine without it. I don't know if you have plans for the Tx once you're done.

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10 Jun 2014 18:45 #24023 by victzh
Replied by victzh on topic Traxxas ALIAS
I have considered it, but my photo does not do the justice to all of the complexities of this design. The board with soldered LCD is in turn soldered to another board with stick potentiometers mounted on it. I can only cut LCD, not desolder it. I do not have big plans for this transmitter, but I'd like to have a correlation between RX battery level and presence info with SPI trace. Moreover, the chip under the LCD is high pitch - 0.5mm, which makes it no easier to solder to than the vias.

It's a ridiculously elaborate design for a cheap transmitter. Even the antenna was supported in shape by custom plastic piece.

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01 Jul 2014 20:04 #24339 by Ssayer
Replied by Ssayer on topic Traxxas ALIAS
(just quietly lurking and waiting) :silly:

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11 Jul 2014 18:38 #24529 by Ssayer
Replied by Ssayer on topic Traxxas ALIAS
@victzh: Obviously not high on your list, but have you had a chance to look into it any more yet? :unsure:

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12 Jul 2014 02:35 #24535 by victzh
Replied by victzh on topic Traxxas ALIAS
True, and Real Life does not help either ;-)

Traxxas is two-way protocol and I need to solder to TX and analyze it as well. While soldering to RX was relatively easy, TX is not such piece of cake. I will try over the weekend, and probably with the generous help of PhracturedBlue we'll have it.

There is another thread about Traxxas which has more recent info.

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12 Jul 2014 20:46 #24547 by Ssayer
Replied by Ssayer on topic Traxxas ALIAS

victzh wrote:
There is another thread about Traxxas which has more recent info.


Can't seem to find the thread? I searched using "Alias" and then using "Traxxas". :blink:

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02 Aug 2014 19:22 #24983 by Ssayer
Replied by Ssayer on topic Traxxas ALIAS
Just checking again to see if there's been anything new. :whistle:

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08 Aug 2014 07:00 #25092 by victzh
Replied by victzh on topic Traxxas ALIAS
I'm on vacation and far from my helicopters. I almost soldered to the TX just before, but some wires fell off and I did not have a chance to do it again. As soon as I'm back I will repeat the attempt.

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