Quote:
Originally Posted by vamfun
Tom, the approach you describe may or may not work depending upon the requirements you are trying to meet. What is the max rate you expect to see and for how long? Lets say the bump transient is .1 sec constant rate upset... if the upset is only 90 deg we are talking 900 deg/s then what you have is probably ok. If its only 500 deg/s then I would choose a 100 deg/s fine gyro and say 500 deg/s coarse gyro.
The CRIO a/d's have a 5mv resolution without oversampling. For the 5150 this means about 7.5 deg/s resolution. Also, this is really a 6000 deg/s gyro with the amplified output at 4x. The noise density is .175 deg/s/(sqrt(HZ). I believe this is at 1x so with the 140 HZ BW the the 4x noise is 4*.175*sqrt(140) = 8.3 deg/s rms. So you have a total rss accuracy of about 11 deg/s. This could be reduced with oversampling , but even without this it isn't too bad for a .1 sec interval. But what may kill you is the nonlinearity error of 1%FS= 60 deg/s. So you might be off as much as 6 deg here from the .1 sec transient so the compass is looking better.
If however, you could live with the (fine,coarse) = (100 deg/s,500 deg/s) you could probably beat the compass.
The adj regulator would be fine, but you could save a resistor if you just bought a 3v fixed regulator.
I would also sync the long term average of the coarse gyro to the fine gyro average to mitigate the drift. This is easily done with a low pass (10 sec time constant?) on the error between the two gyros whose output corrects the coarse gyro input.
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Unfortunately, estimating the duration and impulse of an impact of FRC robots would be quite difficult - how they hit eachother and what angle would all contribute to the amount the robot spins and how quickly. That's why I took a shotgun approach. A good solid gyro for my 'fine' and the highest dps gyro I could find for my coarse.
The quick calculations you performed are exactly where I need help. If you want gear ratios or bending moments or torques I'm your man.... but I absolutely hated system design, fourier, etc. and I'm afraid I blotted it out of my mind rather quickly after school
A benefit of the 500 dps is that it runs on 5V and the voltage regulator could be eliminated.
Just so I'm clear - the higher rate gyro is going to drift more, so you're suggesting using the lower rate gyro to correct the higher rate one. Essentially, saying that when the lower rate gyro isn't turning at a rate that's above it's maximum, you would constantly update a correction factor to minimize the high dps gyro's error from zero. Is that right?
Regarding the compass: what are the rate sensors used for in the compass? Wouldn't they be knocked off-kilter just as much because of a collision?