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#1
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Re: Recommended gyros that can keep up with fast rotation?
How fast does your robot rotate?
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#2
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Re: Recommended gyros that can keep up with fast rotation?
Depends on how fast we tell it to..
Honestly though, pretty fast if we spin at full power.Really though, even if we slow it down to cap at 300 degrees / second, there's the possibility of getting pushed around a bit by someone playing defense or something and losing track of where you're facing that way. I'd like the drivers to be able to turn quickly in teleop, but still have quick and easy "go to this angle" buttons for quick alignment. |
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#3
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Re: Recommended gyros that can keep up with fast rotation?
Your robot does probably turn pretty fast at full power, but you never need to turn more than 180degrees to snap to a location - can your robot really accelerate to 300 deg/s AND decellerate back to zero in 180degrees of motion?
I don't think I've ever seen a FRC robot that can do that. Do you have data that shows that you are hitting that limit? |
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#4
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Re: Recommended gyros that can keep up with fast rotation?
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An IMU will help with this issue, it will take inputs from other sensors (accelerometers, other gyros, magnetometer) on the same chip, and use them to filter the gyro signal to help minimize the drift. The NAV-X, Pigeon IMU, and ADIS16448 are all used by FRC teams successfully, and are pretty well documented. I think you will have a lot more luck with one of these IMUs than you would trying to find a better quality gyro. Even with an IMU there will be some drift over the course of a match. Inertial sensors in general do much better at tracking short term relative movements than they do at tracking position or orientation over a period of time. |
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#5
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Re: Recommended gyros that can keep up with fast rotation?
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That's likely enough to snap to a rough position - and if you want to use that for shooting, you'll need either vision or manual alignment anyways, so not being exactly exact isn't a problem. |
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#6
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Re: Recommended gyros that can keep up with fast rotation?
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#7
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Re: Recommended gyros that can keep up with fast rotation?
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) we've been getting around 2 degrees per match of drift. |
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#8
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Re: Recommended gyros that can keep up with fast rotation?
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It's rare that the actual rotation rate of the robot by itself will saturate the gyro. What's more likely is that collisions will. A short period of saturation can throw a gyro off by a substantial amount. That can usually be solved by giving the drivers the ability to rezero, or by making your calculations relative to something else, like a camera angle. |
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#9
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Re: Recommended gyros that can keep up with fast rotation?
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#10
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Re: Recommended gyros that can keep up with fast rotation?
We use a navX-MXP from Kauai Labs. It works pretty well I think, though we didn't use it last year so it hasn't gotten a whole lot of competition use.
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#11
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Re: Recommended gyros that can keep up with fast rotation?
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It's increadibly easy to set up, small, and has accuracy beyond belief. Gyros we have used in previous years all had some slight drift and we're some what complicated to use. First use out of the box we were able to drive around blind for a little and go back to where the gyro thought was 0 to within an inch or 2. Would highly recommend the navX, only slight con is that it takes up a USB port. |
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#12
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Re: Recommended gyros that can keep up with fast rotation?
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I am in no way disparaging the NavX. We've played with it and it works very well. However, I'm an engineer and I try not to make statements that product A is better than product B unless I have seen a marked difference in some measurable. Last edited by Tom Line : 08-02-2017 at 15:54. |
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#13
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Re: Recommended gyros that can keep up with fast rotation?
We've been using the ADXRS453 since the 2015 season. I'm not sure how our code lines up against the WPILib code for this family of Gyros, but ours has multiple years of execution time on it... bug free. https://github.com/Team2168/2016_Mai...c/org/team2168. In our implementation, comms with the sensor runs in a separate thread from the main robot. So timed events, like calibrating, don't block main program execution.
We have code kicked off from Robot.java which automatically detects drift while the robot is disabled (prior to match start) so if you've got a bad calibration (robot powered on and then moved onto the field - not stationary during initial calibration) it will get a new zero. This code is orig. stolen/inspired from 245's 2013? code, and we've improved upon it over the years. Last year we also spent some time with the BNO055. This is an IMU that's in the $30 price range. https://github.com/jcorcoran/BNO055_FRC Definitely a favorite of mine. Both of these have more than acceptable performance over the duration of an FRC match. |
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#14
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Re: Recommended gyros that can keep up with fast rotation?
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Pigeon specs are similar to navX-MXP/navX-Micro for 6-axis performance from a yaw drift rate, make sense as they use the same chipset which performs the 6-axis fusion onboard. The navX-MXP/navX-Micro firmware for calibration has improved over the two years, but it's likely safe to assume the Pigeon orientation angle accuracy after calibration is similar (sounds like it, according to published specs). Pigeon update rate is 100hz, navX-MXP/navX-Micro are 200hz, so if you want faster update rate the latter is superior. 200Hz is great if you want to drive rapid PID loops that manage the orientation of multiple wheels on the robot. We will have to see if there's any CAN bus contention limits the Pigeon IMU from consistently achieving update rate at 100hz, CTRE should be able to say on that. At 1mbps w/the PDP, 4 talons and a PCM all chatting on the CAN bus, and 100hz Pigeon updates there may be some contention starting to arise - that remains to be seen. However, in the configuration to connect directly a Pigeon to a Talon this would likely not be a concern. From a software perspective, the Pigeon docs indicate it provides yaw, pitch and roll - however the navX-MXP/navX-Micro also (perhaps because it's not limited to the 8-byte CAN bus data payload sizes) provide synchronized quaternions and a sensor timestamp as well. Timestamped Quaternions (and the fact that navX-MXP/navX-Micro have multiple simultaneous communcation interfaces) are being used effectively in the Sensor Fusion Framework (SF2) to correct for video processing latency, and create timestamped orientation histories. As a contributor to SF2, I can say that more features along this line are coming. Software is key to enabling more autonomous features. For newer teams the number of examples, the training materials and the large community that support navX-MXP/navX-Micro and help each other too are awesome. So in addition to orientation accuracy specs which I believe are very similar, there are several system and software level capabilities to also consider. |
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