Can someone explain to me why everyone puts their rotation sensor on separate odometry pods instead of on a drivetrain axle? (something like this for example)
Because of gear slop etc. a separate odometry pod lets you accurately know how far the robot moved, not how much the drivetrain spun
Primarily because of wheel slippage and defense.
Since drive wheels are powered, they spin out/slip on the foam tiles during fast acceleration, which tricks the sensor into thinking you’ve moved further than you have.
Also, if another robot pushes you sideways, omni wheels will slide on their rollers without turning the drive axles at all. Unpowered, spring-loaded tracking wheels don’t slip, stay pressed to the ground, and will actually record the translation when you get pushed.
Simply put, your wheels won’t always be touching the ground, whether it be from defense or getting highsided on game pieces, and an odom pod ensures that the sensor’s wheel will be.