Omni Directional Wheels
This is the page for Tad Goff's E5 final project, Omni-Directional Wheels
My goal was to build a device that moves omni-directionally using holonomic or 'omni' wheels. There will be four wheels arranged around the chassis such that there are two opposing sets. The device will be controlled by an analog thumbstick from a Playstation 2 controller, and will be programmed in MatLab. The final product is a “robot” that moves omni-directionally.
Segway's new RMP
I saw this image of Segway's new RMP (Robotic Mobility Platform) online and I though that it looked cool. I began to research these wheels and their feasibility as a final project. The programming and building of such an RMP, on a much smaller scale seemed within my ability if I could get the wheels. As it turned out I could not get the mecanum wheels but it did start me thinking about methods for omni-directional motion.
These mecanum wheels use rollers on a 45° angle around the circumference to allow lateral motion. When all the wheels spin forwards, the lateral forces created by the angle of the rollers cancel and the device moves forward normally. When the wheels spin in different directions, the forwards and backwards forces cancel and the device moves laterally, diagonally or spins.
Because I could not buy any reasonably sized mecanum wheels I chose to use holonomic wheels instead. Holonomic wheels (also known as omni wheels)have rollers perpendicular to the direction of rotation. This allows them to roll normally and slide laterally. By positioning them so they are not parallel they can move omni-directionally. My design uses two sets of wheels perpendicular to each other, but any no-parallel arrangement will work.
My design consists of two sets of wheels perpendicular to each other driven by servo motors. For control I took a Playstation 2 controller apart and used the thumbstick in stead of the two potentiometers in the "pot boxes" we used to control the arm. The script is very simple. It scales the potentiometer values from the thumbstick to add to the pulse widths for the motors.
For the power to drive my device I used continuous rotation servo motors.