Gumstix/Robostix

[clolson]

Hey, I was just wondering if anyone around here has played with a gumstix/robostix combination and been successful with servo control and reading servo signals out of an RC receiver?

I happen to have a gumstix/robostix in my possession right now (not yet even powered on) and I'm getting tempted to play with it ... so I'm trying to figure out if full blown servo code is available already, or if I'm going to have to start from scratch.

Thanks,

Curt.

[Unterhausen]

some of the guys in my group have built a balancing robot with gumstix/robostix -- prototype uses servo drive. However, they don't decode the radio. The code for decoding the radio would move over from the micronav project, correct?

[clolson]

some of the guys in my group have built a balancing robot with gumstix/robostix -- prototype uses servo drive. However, they don't decode the radio. The code for decoding the radio would move over from the micronav project, correct?

If I get a chance to sit down and start playing with a robostix, I might email you then.

The MNAV receiver decoding scheme is designed to parse out the single pulse train coming off the back end of the RF module. That's nice because you just have to run one wire, but it's a pain because you have to crack open your receiver and solder on it and that seems to inevitably reduce your range (maybe by a lot.)

I'd almost be interested in exploring the possibility of decoding each servo output seperately. That would require a bigger rats nest of wires, but would also support any receiver (2.4Ghz, PCM, PPM, etc.)

Regards,

Curt.

[cdrn]

Did you consider just using a radio modem to talk between a computer with, say, a joystick and the gumstix/robostix? It would serve the same purpose as the RC transmitter/receiver, and you'd probably want to put in a radio modem anyway for high-level programming, telemetry, etc.

edit: That doesn't really answer your question of servo control. The Robostix has an AVR (ATmega128, to be exact) as its core, and most of the pins on it, including the PWM pins, are simply breakouts of the ATmega128 and some from the gumstix. Now, I haven't yet obtained a gumstix/robostix combo (although I intend to in the near future), although it seems to me like the most robust way of using the Robostix is to load a custom program onto the AVR and then talk between the Gumstix and Robostix through SPI. In that case, you'd probably be writing C code for the AVR for the PWM control. There are millions of examples of AVR PWM code out there, so it should be easy to find an example. Make sure to read up the ATmega128 datasheet too, of course. One problem you might run into is that it seems like the ATmega128 only supports 3 independent PWM channels, so if you want more, you'll probably have to hook up another micro through I2C or a UART.