Pitch and roll measuring

All questions related to the configuration tool and groundstation

Moderator: lukasz

Re: Pitch and roll measuring

Postby Gears » Fri Mar 01, 2013 8:36 am

Hello again Tom,

Thanks a lot for your help so far. I still ponder about two problems though:

1) When you're at an angle, taking a corner - how can you know the exact angular velocity of the corner (to calculate g-forces), as the gyro axis along which you measure is now under an (unknown) angle.

Do gyro's always measure from a fixed plane? If so then the above problem would be solved

2) When you know the actual driving forces from your GPS/speed + angular velocity, how do you know to substract them from the accelero data? You don't know what direction the forces are applied, so you don't know how to substract them from the accelero data in order to have only gravity direction remaining.
Gears
 
Posts: 8
Joined: Fri Feb 22, 2013 12:51 pm

Re: Pitch and roll measuring

Postby Tom » Fri Mar 01, 2013 10:05 pm

1) Assuming you always know the current roll and pitch angle (as it is an iterative calculation), so the combination of 2 gyro's + some algebra would give you the current angular velocity for the corner you're taking

2) Same as the above, you assume you know the current pitch and roll data to make the calculation

To satisfy these assumptions, the calculation should be done as much as possible, mostly 50 or 100 times per second.
User avatar
Tom
Site Admin
 
Posts: 1016
Joined: Fri Nov 13, 2009 6:27 pm
Location: Belgium

Re: Pitch and roll measuring

Postby Gears » Fri Mar 08, 2013 11:18 am

I don't quite understand. You take angle data from a gyro, which is assumed inaccurate. With this inaccurate data, you compensate for lateral forces to aquire the same angle from an accelerometer, which then in turn compensates the gyro angle again. Doesn't this stack error upon error upon error? Is this not the definition of drift, the continuous stacking of errors?
Gears
 
Posts: 8
Joined: Fri Feb 22, 2013 12:51 pm

Re: Pitch and roll measuring

Postby Gears » Fri Mar 08, 2013 12:36 pm

I have the feeling I'm trying to do age-old work which I'm never going to be able to do as good as solutions out there. I can find plenty of IMU's and alike that have everything 'integrated'. Example of this would be the MPU-6050 from InvenSense.

I don't nessesarely need to figure out the algorithm myself. Aren't there simple small chips available for a reasonable price that simply output pitch, yaw and roll angles in analogue / digital format so it can be read straight away by a datalogger?
Gears
 
Posts: 8
Joined: Fri Feb 22, 2013 12:51 pm

Re: Pitch and roll measuring

Postby Tom » Thu Mar 14, 2013 3:22 pm

Sure there are quite a lot: just make sure you get one with the GPS integrated.

Nice reference: http://paparazzi.enac.fr/wiki/Sensors/IMU

I would use the CHIMU for low-cost and good quality. As I explained, you will need to send the vehicle speed to the module in order to get correct calculations. See manual: http://www.ryanmechatronics.com/public_ ... _REV_E.pdf
User avatar
Tom
Site Admin
 
Posts: 1016
Joined: Fri Nov 13, 2009 6:27 pm
Location: Belgium

Previous

Return to Software

Who is online

Users browsing this forum: No registered users and 3 guests

cron