Gyroscope Filtering Discussion

[Electrobotz]

@jpearman

For this gyro that seems pretty good to me.

How/where is the gyro mounted on the robot ?

The gyro is mounted on the most stable part of the robot in my opinion, on rubber links. As far as vibration is concerned, I think that place receives the least amount of excess vibration on the whole robot.
Completely out of curiosity, in industry level work, are the gyros that are used more accurate or is the software they use more advanced, or both?

@kypyro

For platform tracking/positional awareness determination, you would normally either use more than one sensor system or perform a synchronization maneuver to synchronize and update your directional heading over time. It would be very unusual to use a single sensor system for that purpose for exactly what you’re seeing here: errors accumulate. For VEX you can sometimes use line sensing or ultrasonic sensors as another sensor system and perform sensor fusion to improve your positional awareness. However, aligning yourself with a synchronization maneuver is easier. One very simple such maneuver in VEX is driving in to a wall to absolutely square the sensor with the world. Then re-zero.

This sensor may never provide the accuracy you’d want for absolute positioning over two minutes while driving around in normal field conditions. This is not a complaint about the sensor; it really does a fine job. You just have to use it cleverly to wring a lot out of it.

It might be worth finding out how close you can get the constant if you believe it is contributing reporting error. That’s easily done. Zero the gyro. Pick up the robot and while holding it gently spin in place. Do this for at least five rotations without bumping or shaking the gyro. Ten would be even better. Gently put the robot down and square it up with its original position. Take the gyro reading. Use the difference in readings to determine whether your constant is correct. If it isn’t, calculate the updated constant using the data you just created.

Note that if you are using the standard gyro stuff in RobotC (I know you aren’t; other people will be) that it is helpful to set SensorFullScale to allow wrapping 12 or so times without sensor rollover.

You shouldn’t drive the robot in a circle to do this; the point is to measure the sensor’s sensitivity to rotation, not how it is affected by mechanical and electrical noise when driving.

And on that point, sometimes it is mechanical and electrical noise which are the greatest contributors to inaccuracy. That’s why @jpearman is asking how you have the sensor mounted. You can work on improving that and get lots of gain in accuracy.

Following that, the biggest gains come from occasionally re-zeroing when you know which way you’re pointing. Then, even a large measurement error can give acceptable results.

This is a great idea. I didn’t think about combining multiple sensors to measure rotation. I’m going to try to combine the encoder and gyro to see what I can get.

One more thing that I would like to ask, and I apologize for having so many questions, is some idea on how to handle collisions. Since the gyro reads vibration as movement, when the robot bangs into something, the gyro will read that as a large turn. Even if I add a lot of mass to one point of the robot and put the gyro there, collisions are extremely intense and will inevitable cause a lot of error. The only thing I can think of is observe the pattern of values the gyro gives when I collide the robot with something. Most likely it will be a sudden spike for a very short amount of time, and then when the robot detects something like that, ignore all that data and assume it was nothing.

[kypyro]

@The Electrobotz

The gyro is mounted on the most stable part of the robot in my opinion, on rubber links. As far as vibration is concerned, I think that place receives the least amount of excess vibration on the whole robot.

Mounting away from motors seems to be the most helpful thing, and sometimes to do that you have to mount in odd locations. In addition to rubber links, we’ve used both rubber band slings and anti-slip mat sandwiches to mount them. Both provide good vibration isolation. Maybe more than the rubber links.

Be sure the connector wire isn’t able to transmit vibration into the sensor board; we’ve seen that be a source of vibration transmission a couple of times.

Completely out of curiosity, in industry level work, are the gyros that are used more accurate or is the software they use more advanced, or both?

It’s a mixed bag. Gyros like this are used a lot, usually integrated into a small driver board which provides startup, calibration, and filtering. Pretty much the things you’re working on right now, it’s just that you’re doing it on the main processor. Often there will be two sensors of the same type providing input to the driver software, and it will then combine the inputs to derive a single integrated output. Again, exactly the kind of thing you can do if you use more than one VEX gyro.

There are, of course, many sensor packages available that have better accuracy and precision than the VEX gyro, but there’s no magic to them–mostly just good electronics design to eliminate noise and thermal effects. Then they incorporate small processors inside the sensor enclosure to perform filtering and sometimes multi sensor fusion. So instead of a small sensor board, they’re closed modules.

So, if you were designing a new system, you’d use one of those sensors. But lots of inexpensive devices use something exactly like the VEX gyro.

And for some purposes involving safety of human lives, the sensors are way more expensive, and way more reliable. The first programmable gyros I used in that kind of scenario cost more than a new car. They don’t cost that much any more, but $5000 is typical for a man-safety gyro. Space rated gyros can cost a good bit more. Anything, really.

This is a great idea. I didn’t think about combining multiple sensors to measure rotation. I’m going to try to combine the encoder and gyro to see what I can get.

That can work well.

One more thing that I would like to ask, and I apologize for having so many questions, is some idea on how to handle collisions. Since the gyro reads vibration as movement, when the robot bangs into something, the gyro will read that as a large turn. Even if I add a lot of mass to one point of the robot and put the gyro there, collisions are extremely intense and will inevitable cause a lot of error. The only thing I can think of is observe the pattern of values the gyro gives when I collide the robot with something. Most likely it will be a sudden spike for a very short amount of time, and then when the robot detects something like that, ignore all that data and assume it was nothing.

The impulse from a collision is very short-lived. I haven’t ever seen this be a problem with the VEX gyro. The sensor design takes some of that in to account, so it’s not clear to me you have to adjust for it. You should see whether you can trigger an erroneous turn this way. If you can, simple filtering will make it go away.