Re: [Autopilot] PCM versus PPM

[Trammell H. <hu...@sw...>]

On Tue, Mar 23, 2004 at 07:55:08PM -0600, Francisco Lobo wrote:
> Does autopilot uses PCM or PPM?

The GPLed software that makes up the autopilot project uses PPM,
either Futaba or JR.  The commercial uavpro software that Rotomotion
sells with our flight controllers and UAVs uses PCM.

We've found that PPM has unacceptable noise on gasoline engines and
the lack of any checksums makes it dangerous in the event of bad
reception.  There are heuristics that can be applied to lessen the
impact of noise, as others have mentioned, but they do not have the
same level of assurance that PCM offers.

Coert's work with reverse engineering PCM is very impressive, although
I am not certain of the legalities of using an unprotected chip.
I believe that my work is a true clean room implementation that
does not have any encumberances (other than the patent, perhaps).

I would like to produce a specialized receiver that has PCM, a
serial port and current/voltage monitoring.  To that end, I am
currently talking with a receiver manufacturer about licensing
our PCM code.

Trammell
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