There are numerous styles of wheels and control of those wheels that can be used to create an effective robot. This year, we evaluated three drive systems for the competition robot.
Omniwheels utilize rollers as the tread surface to translate sideways when not rotating to cause forward motion. The wheels are placed perpendicularly to each other, such that motion occurs as a result of some wheels rotating and others translating, or some combination thereof. Theoretically, this design can achieve 41% faster speed than mecanum, with the same wheel diameter, motor, and gearing. The wheels are light and tremendously maneuverable, but the perpendicular orientation presents little resistance to being pushed away from an intended location. When one wheel departs the ground, control is essentially lost. Our practice with the omniwheeled prototype showed that it was very fast and could easily climb over obstacles, but that doesn’t overcome it’s pushover tendencies.Straight Omni Code Documentation
Mecanum wheels also feature rollers as their tread, but these rollers are oriented at an angle, while the wheels are set in the traditional rectangular pattern. As all of the axles are parallell, mecanum can be flexibly placed at outside corners, which helps to make space available within the frame. This flexibility comes at a price. The ability to place wheels outside of optimal crosses through the spin center, means that they have to overcome much more friction (rubbing) to create motion. This added friction gives mecanum robots more traction and an ability to push (or maintain their ground) better than their omniwheeled counterparts. However, non-orthogonal rollers and added friction make this design slower. Given the lack of quickness and the increased draw on the battery from the additional work done to move around, this was not a favored option.Straight Mecanum Code Documentation
Combining the two drive systems, omniwheel and mecanum, enables us to capitlize on the benefits of each, while reducing the drawbacks of either. The efficient speed of two omniwheels joins the space efficiency and ground-holding ability of two mecanum wheels. Our primary goal for the game is to pick up and place gears, which requires playing all over the arena. The combination drive allows the robot to resist pushing while possibly escaping being pinned via quick rotation. The front mecanum wheels are rotated axles-forward, to provide central space for any of our potential manipulators. Like the pure omniwheel base, the contact patches for all four wheels are balanced around the spin center, for easier control. Because omni and mecanum wheels are mechanically different in their drive action, the output of the omni wheels is scaled down for speed compatibility with the mecanum. This design provided the best balance for us, and allowed room for any of the proposed manipulators without the allocated volume in the critical front zone being impacted by drive motors.Hybrid Code Documentation