Gyro emulation using two accelerometers

The only problem with accelerometers is that they will also sense acceleration of the vehicle, which is probably not what's wanted and difficult to compensate out. Have been doing some background work on a solid state horizon and have collected books and other docs on inertial nav along the way. The nasa tech reports server is a really rich resource in particular and much of it is in pdf for download. Do a search on inertial navigation and you get tech reports going back to the sixties, when it really hard work and stretching the state of the art in just about every way. eg: microcontroller power or less flight computers. istr, there is a report covering just what you are trying to do as well as early work on improved direction cosine algorithms etc. Books which you might find usefull are:

Titterton and Weston: Strapdown Inertial Navigation Technology

Collinson: Introduction to Avionics

Both the above are fairly recent.

Savant, Howard, Salloway et al: Principles of Inertial Navigation

Parvin: Inertial Navigation

(Early 60's timeframe, missile applications etc)

You can usually find the above on ABE books at a fraction of new price as well. Just plug in the Author or title...

Chris

First you should do some error budget calculations. For inertial guidance you are doing double integrations, which require tremendous absolute accuracy of the basic measurements in order to get even mediocre end results. For example, calculate what happens if one of your accelerometers is even 0.1% off zero. That's an error of 0.01 meters per second. That's an acceleration of 4.5MPH per minute. After ten minutes your device thinks it's going 45MPH when it's actually standing still. After an hour it's beaking the sound barrier while just sitting there.

I don't think you can make a useful IMU out of $5 components. The best Honeywell laser gyros have been in development for 30 years, cost $70K each, and only promise 1 mile per hour drift.

READ THIS!!! Inertial Navigation Sytems. Very Good !!!

For a gyro, look at AD22304

For IMU info, search on Alonzo Kelly, a researcher at Carnegie-Mellon Robotics Institute.

Thank you all for your answers.

In fact I think using a GPS to aide the low cost IMU. GPS module these days are cheap (< 20$). your comments about the accurracy of cheap accelerometers made me doubt about the faisability of such IMU even with a GPS. GPS can correct evey second when it's outdoor. But when the GPS is OFF the low cost IMU error can be greater than 1000 meters after 1 minute !!!. What kind of accelerometers are used in commercial IMU ? About my equation. It's wrong. I found this very usefull paper about Gyro-Free IMU:

If we want to simpify the computations using 6 accelermeters we must choose a suitable position for each accelerometer.

My GPS works fine indoor but sometimes it take one hour to fix if not aided. So my IMU can be usefull if the error growth don't exceed 500 meters after one hour. If it cann't meet these performances then i'll not call it IMU. If the main source of error is the accelerometer offset then it can be cancelled during calibration. If it's a zero mean noise then it will zero mean error in the position (right ?). If it's a drift then we can do nothing because we integrate (and don't differentiate Helas).

Sincerely

Look at

The error of a GPS can be close to 100meters when you are in an area with a lot of buildings.

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On a sunny day (Wed, 27 Dec 2006 08:53:17 GMT) it happened snipped-for-privacy@puntnl.niks (Nico Coesel) wrote in :

100 euro for a cable?

mmm

Don't forget the noise and offset of the output. Plus there may be a dependency on supply voltage and temperature.

Rene

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Yes, the cable is the show stopper. Whatever the other items are priced, they appear as overpriced as the cable. Rather not sell the cable at all.

Rene

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FYI:

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