Gyroscope for Tricopter

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#1
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Dear forum,

I'm searching for information concerning the stabilisation using only gyroscopes and an AVR for a tricopter.

From the different forums read, most implementations are for 5,6 or even 9 Degrees of Freedom (magnetometer readings, alas!) which typically involve an accelerometer and a gyroscope. Kalman filters are proposed to perform a correction estimation for the measured data, taking covariance matrix operations into account.

As I understand, an integration is made over time between consecutive samples to find out the rotation on one of the axes.

My first question is: Using only a 3-axis gyroscope, would it be possible to use a simple filter (i.e.: lowpass) to filter out the noise?
Second question : How would the cutoff Freq be calculated? The copter itself uses motors with 750rpm/Volt @ 3 Volts.

Any input would be much appreciated.
Cheers.

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After searching around some more, the short answer is that one needs a gyro for each of the three arms of the tricopter, it is much simpler than processing data coming from perpedicular axes of only one gyro. The arms of the copter are only concurrent, yet not perpendicular.

Regards.

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It's not one gyro for each arm, it's one gyro for each axis. That is independent on the number of arms.

You may want to look into the KK multicopter. It has three gyros and controls up to 6 motors. As it happens, it is based on an Atmega328 and the (assembly) source code is available online. So is the schematics.

Sid

Life... is a state of mind

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You're right! - each arm is an axis in the model.
I'll try and write the C code and make it public, I found the *.hex file at Sparkfun, loaded it into AvrStudio and got the assembly.

I want to integrate it with a RFM12 radio transceiver, which is why I prefer C.

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You're missing the point. The axis are pitch, roll and yaw - not arm1, arm2 and arm3.

Sid

Life... is a state of mind

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I need to read more! ;)
Thank you for your help.

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The rate gyros output a rate in degrees per sec that must be accumulated to get an angle. Its hard to tell when to reset the integrators when not rotating. If the accelerometers indicate no accel in any axis, the integrators can be reset to level. I think.

Imagecraft compiler user

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Some of the older gyro chips by Murata will output a Vref voltage that will work with ADC on mega chips.
I have one here that works like a potentiometer.
Too easy. But it doesn't have high resolution like some of the new gyro chips.
(as in, degrees per second)

I've just ordered ITG3200 gyro to play with recently.
Still waiting for it to arrive. This is for a helicopter though, but similar idea.
I found them for $15 on ebay vs $50 on SParkfun..

If I manage to figure out how to use it I'll post some code.

HEre this guy has one in his multicopter setup.
http://www.rcgroups.com/forums/s...

if (Learning_AVRs)
{
DOH();
}

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If you just want to play with it you could buy this one. It has 3-axis gyro, 3-axis accelerometer, LCD, Atmega324PA and an ISP header. At $30 it's a bargain.

Sid

Life... is a state of mind

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Speak of the devil and he shall arrive!

if (Learning_AVRs)
{
DOH();
}