Tank Drive Alignment w/ Gyro

Technical Programming
1

I am curious how some teams use a gyro to align a tank drive for vision. Could someone explain how I could implement a gyro to align to a target for vision?

2

Why would you need a gyro? Does your vision system give you degree offsets?

3

I’m trying to figure out how to align in vision, and I saw that many teams have implemented a gyro and calculate the relative angle of the camera then use a PID loop to align.

4

There are a couple different ways to handle this problem:

  • If there isn’t much delay between your camera and your robot code, you can just try and point directly at the target every robot loop.
  • However, if your camera->robot system has a lot of latency, or images take a long time to process somewhere, what you can do is stop moving for a moment, get the information from your camera (e.g. “the target is 10 degrees to the right”) and then use PID and your gyro to point at that target.
5

I’m using an NVIDIA Jetson co-processor so latency/speed isn’t an issue. I understand in theory how to make the alignment system. I just don’t understand how to apply different values to both sides of a tank drive to make a smooth alignment. Like how to you maintain moving forward will rotating one side to fast align?

6

Got it. You’ve got some options, here are just two:

  • Treat your drive like an arcade drive, and hand the “rotational” aspect of it over to the alignment PID, while performing whatever overall forward/backward translation however you want.
  • Given your targeting data, figure out where you want to be compared to where you are right now, and use the new WPILib kinematics libraries to calculate a trajectory and follow the path there.
7

Thanks! That makes sense I’ll look into it.

8

Check out the Limelight docs, they have a lot of useful information there. They even have one for aiming and getting in range at the same time! Hope this helps.

9

wow these limelight docs have everything I need thanks!

10

I found it on Chapter 11 Case Study: Aiming and Range at the same time: https://readthedocs.org/projects/limelight/downloads/pdf/latest/

11

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