Raspberry Pi as robot controller

[StevenB]

The Pi itself is pretty lame as a robot controller. The GPIO pins are all 3.3V, and there isn't any analog IO. That's not to say you couldn't build a cool shield/cape/extension board that would give you a lot of robot control functionality, and people are working on it.

The idea of having my robot be a full-blown Linux box is pretty appealing. I think I'd take the new Vex ARM9 controller (which also runs Linux) over the Raspberry Pi when it comes to robot functionality, but it's hard to beat $35.

[ToddF]

Lots of people in the Raspberry Pi forums are working on this. I bought three Pi's to play with, and am progressing a little at a time, adding functionality necessary to make a Pi a viable robot controller. (I'm a mechanical engineer, not a software guy.) I hate to advertize my future plans, because the web is full of people announcing big plans with no follow through. But, to date I have been successful in using the Raspberry Pi to control a Jaguar and a servo using a joystick as an input device. With no additional hardware, you can control up to 8 PWM channels. Adafruit sells a $15 accessory board from that lets you add 16 PWM channels at a pop. And it's only a matter of time before other inexpensive boards hit the market allowing for analog and digital I/O.

Video of joystick control here: http://www.youtube.com/watch?v=0ODQY2mDYR0

[Ether]

How are you generating the PWM signal to the Jag and servo? Is it one of the following, or something else?

- does the Pi have built-in hardware support for generating PWM signals on the GPIO pins so all you have to do is configure the period for each channel and then provide a pulse width for each channel?

or

- continuously poll a clock and turn GPIO on/off for each of the two PWM channels as appropriate based on the respective joystick inputs

or

- use a fixed-period interrupt with a counter and a state machine to turn GPIO on/off to turn the GPIO on/off

or

- use a fixed-period interrupt (at the desired period of the PWM) which turns the GPIO on and then enables a one-shot interrupt to turn the GPIO off

or something else?