Thread: New Product Walkera DEVO 10
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Old Mar 14, 2012, 03:11 AM
FDR_ is offline
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Quote:
Originally Posted by i812 View Post
I'm new at the RC protocol, but from what I've recently read, the only difference between 2401, 2601, and 2801 is the number of pulses being transmitted, where essentially the width of the pulse indicates that particular channel's stick position.

A 2801 TX has ALL the capability of talking to all 3 types of RX's. To the best of my newbie knowledge, during Model Setup when we program our 2801 which "mode" to transmit in, all that happens is the "extra" pulses for the channels (stick/switch positions) that won't be transmitted are simply "dropped" from the serially transmitted pulse train. The stick/switch positions are re-measured, the pulse train is updated and re-transmitted 20? times per second.

For instance every 20? seconds, this many pulses are transmitted:

8 channel mode = 8 pulses, with each pulse having a width that corresponds to a channel's "stick" value between MAX and MIN. From what I remember the pulsewidth is a "universal" Servo standard: 1.5 msec +/- 0.5 msec, where 1.5 msec = mid "stick"

6 channel mode = 6 pulses

4 channel mode = 4 pulses

The RX circuitry simply demodulates the pulse train off the RF (microwave) carrier, serially "strips" the pulses off the "train", and sequentially switches the pulsewidths to its appropriate "channel".

Apparently before Devo, if a 4 channel RX received 8 pulses in a "serial" train, it would get confused, so the TX had to be programmed not to transmit extra unwanted/un-used pulses.

Maybe the new Devo RX's have better circuitry, are able to disregard the extra unwanted pulses, and therefore don't need to have the TX pre-programmed to operate in a specific mode?

Someone told me (guessed?) the only reason Devo TX isn't backward compatible is because it waits to receive valid "handshaking" data to be transmitted from the telemetry unit in the field, before the TX completes the initialization routine with the RX in the field. If this is true, and if it was possible, a User could use the Model Setup to pre-program the TX to operate in a certain "mode" (2401, 2601, 2801 just like the old days), and if in that mode, the TX wouldn't require Telemetry validation/handshaking to sucessfully complete initialization, and wouldn't transmit extra unwanted pulses.

Once again, I'm sure this "chat" is OT, and doesn't belong here in this thread. It is probably too basic and "intro" TX stuff to be posted in the "hacking" thread, and I probably won't get any knowledgeable responses posting it anywhere else, so I'll keep on "threading" along in this thread since it currently has "hacker" eyes looking at it.

I think I've reached a plateau where there's not much more mechanical stuff for me to learn about RC Helis, so I'm at a point in my RC training where I'm trying to get a deeper understanding on how the electronics works.

From what I understand, one of the biggest differences between one manufacturer's RC transmitting protocol and another's is whether the pulse trains are transmitted upside down or not, and the ordering of the pulses. Regardless of which protocol is used, the pulsewidths are all universally understood to represent the same value.
It might be quite far from truth...
Here are the findigs of rcH4x0r about the simplest 4ch Walkera protocol (24xx):
http://rch4x0r.com/walkera_4_ch_packet.html
http://rch4x0r.com/walkera_freq_hopping.html
Have a good read!
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