Hi guys,I m having problem with vibration as i m using on heli. How do filter out IMU data with minimum compromise. Or is there a way to minimise the effect??I am using 6DOF IMU, here is the test pic
RegardsPG
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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.
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.
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?
Replies
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.
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.
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?