I recently got SparkFun's 6 IMU board and played with it a bit. Basically I connected Arduino and Razor 6DOF board and ported DCM code. Code is ArduIMU v13 but just made to work with Razor board. I am not sure what to think about gyros on that board as it takes them a while to "warm-up". Below you can see run from cold start for over an hour and "zoom' on first minute or so (just raw ADC values). On the link referenced above, you can see same data plots for both gyros and accelerometers.




I also modified ArduIMU Labview code - mainly that "cube" is within main window rather then separate one. I haven't compiled the code but whoever has LabVIEW should be able to run it (developed with version 8.5)

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3D Robotics
Comment by Chris Anderson on November 5, 2009 at 5:37am
Nice one! Looks like it wants at least 30 seconds to settle down. That does indeed seem a bit long...
Comment by Tim Trueman on November 5, 2009 at 9:03am
This is where temperature compensation comes in…

Developer
Comment by Ryan Beall on November 5, 2009 at 1:14pm
Ahh the lovely temp comp problem!

T3
Comment by William Premerlani on November 5, 2009 at 3:40pm
Automatik,

The first 30 seconds has nothing to do with temperature. Its a startup transient in the electronics in the gyros and/or charging up a large capacitor somewhere in the circuit that you are seeing.

With the UAV DevBoard with its LISY gyros, I noticed a similar electronic startup transient, except it was over in 5 seconds. That is why I wait for 10 seconds to record the offsets for the gyros.

It looks like in your case, you will have to wait 30 seconds before you record offsets.

After that, I do not think that it will be necessary to do temperature compensation with the DCM code. The drift rate over an hour looks low enough for DCM to maintain lock.

But, you are going to have to wait 30 seconds to record offsets.

Bill

T3
Comment by William Premerlani on November 5, 2009 at 4:55pm
Automatik,

On a different subject, I wonder if you plan to do any vibration testing or electromagnetic interference testing on the Razor 6DOF board? I would be very interested in the results if you did.

We have found that the LISY gyros are subject to both vibration and electromagnetic interference. Since the gyros on the Razor are made by the same manufacturer, it is possible they would also be vulnerable.

In the case of vibration, the LISY gyros are ok in airplanes if you use moderate steps to isolate them from vibration, but they are not usable at all on helicopters.

In the case of electromagnetic interference, we found that operating a moderate power 900 Mhz Xbee too close to a LISY gyro will generate a large offset, so you have to be careful to keep the Xbee away from the gyros if you are using one for telemetry.

I am starting to think about the next generation of the UAV DevBoard. I briefly considered using the gyros used on the Razo, but because of the potential issue with vibration and electromagnetic interference, I will probably use Invensense gyros instead.

What do you think?

Bill
Comment by Faisal Shah on November 5, 2009 at 5:51pm
How about taking steps to mitigate EMI? Wrapping it in 3 layers, insulator + aluminimum foil + magnetic shielding (http://www.lessemf.com/mag-shld.html) ? And wrapping that up in two layers of foam, low and high density. Would that do the trick?

T3
Comment by William Premerlani on November 5, 2009 at 6:24pm
Faisal,

The team found the following combination to be effective in mitigating EMI:

1. Use a separate power supply for the Xbee.
2. Keep the Xbee at least 9 inches from the gyros.
3. Wrap the board that has the gyros in an anti-static bag, wrap that in copper foil.

As for me, I am not interested telemetry and ground stations, so I have not run into the EMI problem personally. All of my information is second hand.

Bill

Developer
Comment by Ryan Beall on November 5, 2009 at 8:33pm


Throw it in the oven at 170 deg F for 6-8 min and watch it......You will be amazed at how much it can be off. Ignore the 500 deg/s aspect of this graph and focus on how much 10deg will change the delta deg/s! Amazing...
Comment by automatik on November 5, 2009 at 10:17pm
@ Bill - sounds like a plan. I'l put them next to ZigBee and see what happens.

@Faisal - for EMI I usually try to follow basic rules: keep power and data lines separate, make sure there is good ground etc., and go from there. On system level (I guess in this case combination of all the various boards) it's good idea to have a good system ground, but to make sure you don't crate ground loops; and also depending on your components, to keep an eye on analog and digital grounds as well..Or you can go full bore and make Faraday cage
Comment by Surya Sharma on November 5, 2009 at 11:56pm
Is the connection pic (http://voidbot.net/razor-6dof.html) for the 6DOF Board and Arduino wrong ? I think he's swapped the 3.3V and the GND connections.

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