Comment by Andrus Kangro on October 26, 2009 at 2:06pm

Hi, IMU 6DOF Razor uses high-pass filters on gyro outputs, which is ok for sharp and sudden movements, but not ok if you want to measure long-lasting movements like turn rate of circling aircraft. Therefore, I would short circuit capacitors C1, C2 and C19 befor using Racor board for IMU, i.e. it looks like its not usable for autopilot "as is".
Ardupilot board seems to use low-pass filters only.

Comment by Ryan Beall on October 26, 2009 at 3:26pm

The Razor uses high pass and low pass. They are set up correctly to operate in the aircraft dynamic range. The highpass amplifies freqs in the .5 Hz range and deweights everything in the upper freqs. The big thing about this unit is its completely analog so you have to see if the ardupilot has that many a2d channels

Comment by Chris Anderson on October 26, 2009 at 5:04pm

People are confused about the difference between a pure IMU and an IMU+AHRS (Attitude Heading Reference System). This is just an IMU, which is to say just the sensors. You need to do a huge amount of processing to make any sense of it. The ArduIMU is an IMU+AHRS, which is to say the sensors plus an onboard processor running the code to interpret them. There is a big difference between them--basically a PhD's worth of math!

Comment by Nan on October 26, 2009 at 8:07pm

Will ArduPilot Mega use this flat IMU sensor layout? It is much more crash/pet/kids proof.

Comment by Chris Anderson on October 26, 2009 at 8:09pm

Yes, it will use a flat layout.

Comment by Faisal Shah on October 26, 2009 at 8:38pm

Chris, will ArduPilot Mega use these exact sensors? i.e this circuit will be copy/pasted to the new board with signals directly routed to the adc?

Comment by Darro Lin on October 26, 2009 at 10:07pm

I have the 4DOF version of this. Where is the best place to power it from a ArduPilot system? GPS adapter board? shield board? It needs clean 3.3v I think. (opps I ordered the shield without the 3.3v regulator)

Comment by Chris Anderson on October 26, 2009 at 10:21pm

No, this IMU is not related to the forthcoming ArduPilot Mega. This one was developed by Sparkfun, not us. Ours will be based on our own design.

Comment by Andrus Kangro on October 26, 2009 at 11:07pm

Hi Ryan, high-pass filters on Razor filter do not amplify anything, as they are passive elements, but filter out any movements below 0.5HZ range. This is why its called high-pass filter.
Meaning, that if my aircraft is in constant turn (cirles around waypoint), then gyro itself will deliver constant output voltage, but Razor high-pass filter output will gradually drop after 2 sec until it indicates zero movement. And, if aircraft comes out of the turn and gyro output drops to indicate zero movement, then high-pass filter makes it look like 2-sec pulse in opposite direction.
So yes, these filters operate ok in dynamic environment like with game console, but with ap's we want to know about long-lasting (static) movements also.

Comment by Faisal Shah on October 27, 2009 at 5:42pm

Assuming I had a good ADC converter, would the measurements out of of the sensors on this module be as good in quality (with the intent of making an AHRS system) as the ArduIMU ? I just want to compare the output of the sensors between the two.

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