What are the best solutions for odometry wheels? 1 forward and 1 sideways or 2 forward and 1 sideways?
Also, how should they be positioned on the robot? Is it ok if they’re at, say, the back of the robot? It would still measure movement travelled.
1 forward, 1 sideways, and a gyro to measure rotation. It doesn’t matter where they go on the robot.
The only real difference between 3 wheel and 2 wheel odom is that 3 wheel allows you to calculate the rotation of your robot along with position. This was mostly used before the release of the v5 inertial sensor, as now the inertial sensor is generally more accurate, so most teams use 2 wheel.
As for positioning, the wheels can be basically anywhere on your robot. Just make sure that they are attached securely and both wheels are perpendicular to each other. Keep in mind though if the wheels aren’t lined up with the center of rotation of the robot they will move when the robot turns in place, messing up odom, so you need to do a little extra math.
In general you want to have some rubber band tensioning to slightly push tracking wheels into the floor and mount them far from each other to reduce tracking error and jitter.
This topic has a lot of pictures and advice on making good tracking wheels for odometry: Position Tracking Wheels Mechanism
For example, the back view of the 5225A robot:
240P’s robot design was a very well thought through application of tracking wheels:
And this was an example of packaging tracking system in a very tight chassis: