Replies to This Discussion

ModeratorPermalink Reply by Morli on December 5, 2009 at 3:38pm

Any mechanical damping techniques applied? I am no good with Mr.Kalman and other similar people :) good luck

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Permalink Reply by automatik on December 5, 2009 at 4:19pm

Hi Pear,
I think that you need to provide a bit more information :
What's the magnitude of vibrations ( there is no y-axis scale ; perhaps you can edit/repost the picture). What is test setup ( is heli level on the ground with motor turned on or...)? Which 6DOF IMU are you using? Have you tried placing some kind of dampening material / techniques? - if so what?

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Permalink Reply by Pwar Gyi Sayar on December 5, 2009 at 8:16pm

Hi,
I am using 6DOF RAZOR board. I managed to get full resolution with 3.3V so 1024 full scale on ArduPilot. Although it is a bit of wire track cutting and routing from here to there.

This test is Half throttle motor speed and vibration is unbelievable. I did cusion a bit of foam between module and frame. It is level on the table. the problem is i cannot afford to put much weight on it. or i have to get bigger size heli.

the red line at the top is under gravity on its axis!!opposite G

Regards
PG

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DeveloperPermalink Reply by Randy on December 5, 2009 at 8:51pm

Hey Pwar,

This is the problem that everyone seems to hit when dealing with helicopters. I'm in the same boat and you can see some replies to my post on nearly the same subject although I'm using Spark Fun's 6DOF.
http://diydrones.com/profiles/blogs/my-uav-helicopter-vibration

The advice I've received is:
1. tune your helicopter as well as possible. It's helpful to breakdown where in the helicopter the vibration is coming from (perhaps multiple places). So try removing everything (tail blades, main blades, connection to the main rotor, etc), then add them back one-by-one to determine which components are contributing most to the vibration and then focus on cleaning those up (perhaps loosening or tightening links, balancing, repair bent shaft, etc).
2. add foam between the helicopter and sensor board. I put a massive 1 inch think piece of very soft foam (a sponge actually) under my sensor board and this made a huge difference (although I still have vibration problems)
3. make sure wires connecting to the sensor board are not flapping around - vibration can travel along the wires to the sensor board.
4. try a set of sensor's that aren't as sensitive to vibration. I've heard the Analog Devices gyros are the best but sadly they are very expensive and only come in a single-axis variety so you're back to having little boards sticking out at 90 degrees from your main board.
Analog Devices gyro & accelerometers from Sparkfun:
http://www.sparkfun.com/commerce/product_info.php?products_id=9058
http://www.sparkfun.com/commerce/product_info.php?products_id=9269
5. try increasing your sampling rate and perhaps adjusting it with your motor speed. I suppose it's theoretically possible that if you sample exteremely quickly you might be able to calculate a decent average even with all the vibration.

William Premerlani has done some work to adapt his board to work on helicopters and I've heard he's thinking of releasing a new version with better gyros at some point but not sure exactly when.

I'm actually thinking of designing a board that uses the Analog Devices accelerometers and Gyros but that's a big job and I'm not really a hardware guy. If you (or anyone) find an IMU that uses these gyros and accelerometers I'm very interested.

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ModeratorPermalink Reply by Morli on December 6, 2009 at 6:17am

There you go Pyar, you got pretty much there is to do for vib issues unless you want change the beast under the hood. Good luck and feed us back with your results.

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Permalink Reply by Heinrich Mueller on January 2, 2010 at 2:33pm

Hello we have tested a lot of different rate sensors. It seems that the ADXRS610 have the best vibration immunity.
The ST's sensors have an internal working frequency in the range of 4kHz. This is just the frequency that the rotors and motors generate. Filtering in the electrical signal path dose not help. The ADXTS610 has a frequency above 20kHz. The InvenSense sensors have also high frequency. Mechanically damping will sometimes help.

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ModeratorPermalink Reply by Morli on January 2, 2010 at 3:43pm

What about IDG500 Dual 500 degree/sec here , they seem to be cheaper here than ADXRS610 from same site

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Permalink Reply by Heinrich Mueller on January 25, 2010 at 10:31am

I think they will work to. We are going to test them next weeks.

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Permalink Reply by Jawahar balaji on January 25, 2010 at 12:18pm

i think this may help http://vrhome.net/vassilis/

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Permalink Reply by Gregg "Cabe" Bond on January 25, 2010 at 12:25pm

Thats pretty hard core.

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Permalink Reply by Andrew Whipple on February 14, 2010 at 12:45am

what were your results with the IDG500 Dual 500 degree/sec?

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