Re: [Gumstix-users] Expansion/mother boards - RoboStix - Autonomous Air Vehicle

[Dave H. <dhy...@gm...>]

Hi Mike,

> It looks like going with a third-party GPS unit will give me more choice and
> should be easy to integrate.
> Looking more closely at the capabilities of the RoboStix...
>
> The ADC is (only) 10bit - Ignoring any improvements possible with dither, on
> a +/- 10g IMU, the precision will be only about 0.2 m/s^2 (quite poor
> relative to the accuracy of the accelerometers themselves). Is there a
> practical way of increasing this precision. If not, i will have to consider
> using an integrated digital IMU (something i wanted to avoid for cost and
> because I wantered to implment my own filters on the Robostix), or
> alternatively an auxiliary ADC (I assume one can buy such a thing).

Yeah - you can get i2c or spi based ADC units that are 14-16 bits

> Additionally, I noticed that the Robostix has 6 dedicated PWM terminals. Can
> I program the other GPIO pins to perform the same function (whilst carrying
> the power direct to the servos).

The 6 PWM outputs are the only ones that have power routed through the
board. These also have the PWM generation in HW. i.e. once you setup
the hardware it take no CPU load to continue to generate pulses. You
can use any of the other GPIO pins to also drive servos, it's just
that you have to generate the pulses in software. You'd also need to
route the power serparately.

> At this point I can wondering if the RoboStix is really giving me anything
> useful, or if indeed I am going down the right route with hardware.

It's hard to say.

How many servos do you need to control? What additional
hardware/sensors do you need to interface to?

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/