Requesting motion-algorithm help

UFAnders · Joined: 13 Apr 2005 Posts: 36 Location: Michigan

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I am using a tri-axis accelerometer with a PIC 18F2520 in hopes that I can eventually calculate velocity and displacement from the ADC results. Has anyone done this sort of thing?

I'm not looking to save myself effort, but moreso time - does anyone know of any algorithm resources that could help point me in the right direction?

Thanks for taking a look!

Anders

Ttelmah · Guest

Question, is do you have the system gyro stabilised, or a seperate compass?. Three axes, do not maintain a position fix, unless you have data about the direction of the axes at any time, or keep the axes in a constant direction.
If the axes are stabilised, then you can sample at a fixed time interval, and simply sum the accelerations in each direction, so you maintain an integral of acceleration, which directly gives you velocity. A second integral, gives the actual position.
If the axes are not stabilised, you need to take a direction term as well, and then generate a sin, and cos from this, and use this to generate the sums. This is assuming that your vertical axis is stabilised by gravity. Otherwise you need a term in this direction as well.

Best Wishes

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

Ttelmah, are you a teacher in real life?

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

Hope you are not building an IMU for a cruise misile.

If you decide to go with gyros, check out Analog Devices' iMEMS gyros. These are, probably, the cheapest one s you can find. There are 2 warnings about the MEMS gyros, though. (1) You can damage them with vibration. (2) Readings drift with temperature. You can keep the gyros at a constant temperature, and/or you can compensate for the temperature (the gyros have an on-chip temperature sensor for that).

Nick