Need I add tracking wheels for Odometry? Need I add tracking wheels for Odometry? Can I use only the IMU and the motors in the drivetrain for Odometry?
You should use at least 2 tracking wheels
Based on what I know, you don’t necessarily need tracking wheels for odometry, but it you’re going for accuracy its definitely a must. You can use drivetrain motor positions to act as your odometry but it never really works out to be as accurate. However, I would definitely invest in an IMU sensor because you’ll be able to tell your robot exactly which direction it is facing. You need at least two, one parallel to the drivetrain to track how far you’ve gone and than another thats perpendicular to the drivetrain to have the robot make corrective changes in the event in runs into an obstacle of some sort to fix its heading. Any questions?
You really should have tracking wheels, yes.
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Why is the drivetrain motor positions inaccurate?
Unlike optical encoders and rotation sensors, motors tend to have a bit of slippage. And if you gear your drivetrain motors, there’s more chance for values to be returned wrong for odometry. The encoders will only go as far as the motor will since the motor is powered and will hold positions, unlike the encoders. You’d rather have a free-spinning encoder that moves with the robot so that they determine how the motors should work rather than having the motors determine what they should do themselves. Does that make sense?
Depending on how much power you apply to the motors, the drive wheels can slip. The motor encoders are not aware that the robot slipped so they estimate that the robot is in a different spot.
Tracking wheels are merely following a long and they have no power to influence their measurement. The only concern is that they can’t lose traction. Teams often will use a mini suspension with rubber bands to apply downward pressure so the measurement is accurate.