Thanks for the tips Andrei

I had a look at the accelerometer unit you are using, it's a switchable range (up to +/-6g) 12 bit unit. I was hoping for a 14bit solution, but who knows if I can find one that is affordable. I believe that it is the precision of these types of units that will be the determining factor in the performance of the IMU. May I ask what kind of success you have had with it? Are you using it as part of a complete integrated system including GPS? If so, have you managed to estimate the overall accuracy you have achieved? Are you using your sensors for stability augmentation?


08 January 2007 18:55:52
Andrei Rylin (

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

--- Mike Whincup <> wrote:
> 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).

I use 3-axis accelerometer with digital interface:
It's not (much) more expensive than analog ones.
There's also 3-axis digital magnetometer:

I wish I could find inexpensive digital gyros,
but in the mean time I'm using 2 of these
connected to the ADC on Robostix.
Remaining ADC inputs are used to measure power supply.

> 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).

There's a couple of PWM on the Gumstix, but
they are 3V, in any case 6 PWMs is enough for me:
2 for ailerons, 1 flaps, 2 to the tail and 1 for ESC.
What else is there to control with PWM ?

You definitely can try software PWM with any GPIOs.

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