Gyroscope saturation?

[Tom Line]

We are planning on using the gyro angle to offset our cartesian coordinate plane so that when the operator presses the joystick away from himself, the robot always moves away from the operator regardless of robot orientation.

However, this years 80 degrees per second gyro has me a bit worried. It's tough to do by feel, but it sure seems like our robot can pull a 90 degree turn in less than 1 second by rotating.

Has anyone else had to deal with this, and does anyone think the robots can spin fast enough to saturate the gyro?

I considered purchasing last year's gyro but I can't find anywhere to do so.

[Kevin Watson]

Originally Posted by Tom Line

Has anyone else had to deal with this, and does anyone think the robots can spin fast enough to saturate the gyro?

Yes, it's possible. Two potential solutions come to mind: 1) write some code that will monitor and record the peak values from the gyro. If you find that you have a problem, you can implement a control loop that will minimize the chance that the gyro will saturate. 2) Purchase another gyro like the ADXRS150 or the ADXRS300.

-Kevin

[kaszeta]

Originally Posted by Kevin Watson

2) Purchase another gyro like the ADXRS150 or the ADXRS300.

We've had relatively good luck using 300 deg/s gyros. It's not fool-proof, however, since you'd be surprised the sorts of short-duration high-turn rate impulses you get from robot collisions. Expect it to still drift, especially in a game like this year's.

[ubergeek5075]

Last year for our dynamic braking system, we wanted a feedback loop from not only the optical encoders on the wheels, but also the gyros. However, I have experienced the same problems with saturation during collisions, and even when our robot turned fast enough.

I remember something from last year when i was researching the gyro from the KOP, that it was 150dps. Even with that we still had that saturation problem.

I agree with the solution of lower resolution gyros, but with the budget of a small team, it may take some convincing.

Also, what resolution on the controller end were you getting? How many values / dps rotation ?

[Tom Line]

Uber, we haven't implemented a testbed for this year yet, so I don't have any data. This was all hypothetical, because I was pretty sure you can saturate the 80 dps gyro pretty easily. I'll go with the 300.

Can collisions really saturate this gyro? How far off would that knock the reading? It seems to me most collisions don't spin robots at high rates.

[JesseK]

You could also ask your team the question of whether or not the robot should turn 90 degrees in less than a second for this game. Aside from sudden impacts that turn you, I doubt you'll ever have the need to experience a quick turn on a holonomic robot -- you could instead simply side-step an obstacle.

[ubergeek5075]

Yes, collisions can cause saturation of the gyros, even if they result in turning the robot slowly. It's all physics, the collision results in an extremely high, however very short turn rates. Graphically speaking, the turn rate spikes, then drops down when your turn rate is constant. This results in some very odd data sometimes, depending on how long that spike lasts, and if you pick it up or not.

[EricS-Team180]

We've experimented with the 75, 80 and 150 deg/sec yaw rate sensors, in the past, and have always concluded that we needed to purchase a 300deg/sec sensor, to keep up with the turn-rate capability of out 'bots.

I used to get them right from AnalogDevices, but these past 2 years, they show that they (their evaluation boards) won't be in stock until April

Anyway, let me throw this out for consideration. Can the yaw rate sensor in the K.O.P be "over-clocked" (for lack of a better word) - to measure a wider range? I'd be willing to experiment with giving up some sensitivity, to get 300 deg/sec for the K.O.P sensor.

Eric

[Tom Line]

I seem to remember that by placing a resistor across the leads you can modify the dps, but reduce other functions. Look up and thoroughly read the manuals for each sensor - I think I saw it there.

http://www.analog.com/UploadedFiles/...s/ADXRS150.pdf

I believe it's the portion talking about changing the scale.

[kaszeta]

Originally Posted by EricS-Team180

We've experimented with the 75, 80 and 150 deg/sec yaw rate sensors, in the past, and have always concluded that we needed to purchase a 300deg/sec sensor, to keep up with the turn-rate capability of out 'bots.

I used to get them right from AnalogDevices, but these past 2 years, they show that they (their evaluation boards) won't be in stock until April

There are plenty of other places to get Analog Devices gyros nicely mounted on evaluation boards. I've bought some nice 300 deg/s ones from Sparkfun.com, for example.

[EricS-Team180]

yeah..sorry... I should have said that I used to get them for $20 cheaper direct from AnalogDevices. I think I paid $70 for the SparkFun board last year. I also looked at a lot of yaw rate controllers from r/c aircraft catalogs. But they are controllers, not just sensors.

Anyone else take a look at what the r/c world has to offer? ...just curious
Eric

[FreakyAntelope]

My team has always been a little bit scared of doing this because of the gyroscope values drifting. Would one of these (300 dps) gyroscopes allow you to track your orientation over a 2 minute period without introducing too much error?

- Toby

[kaszeta]

Originally Posted by FreakyAntelope

My team has always been a little bit scared of doing this because of the gyroscope values drifting. Would one of these (300 dps) gyroscopes allow you to track your orientation over a 2 minute period without introducing too much error?

Team 95 has used gyros for years, and aside from the above caveat that you can pick up errors from collisions, the system has worked very well for us.

[billbo911]

Originally Posted by Tom Line

I considered purchasing last year's gyro but I can't find anywhere to do so.

I believe we have the same gyro as last year. If I am correct, it was also an 80 deg/sec gyro.

Try looking on SparkFun for a gyro. About $70 should get you a 150 or 300 deg/sec gyro.

Dang it Kevin, you beat me to it.

[Tom Line]

Bilbo, read this year's sensor manual. We have a new gyro. Last year's was 150 dps - so I wasn't terribly worried about saturating it with quick turns.

Thanks guys. I think I'll do both the code and purchase a higher dps one just to be sure. Better safe than sorry when it comes to the drivetrain.

Kevin, I'll admit that most of the words they're using on the specs page are foreign to me (mechanical engineer doing controls, go figure). Will the ADXRS300 simply "drop" in place of the KOP gyro using your same code?