A hypothetical Mecanum drive-train and chassis was researched and designed during the early summer of 2008. It was never built, due to high cost (it could not be satisfacorily built on reduced scale) and other priorities. It is included here as to not lose this information.
Some key points:
- (4) 8" diam AndyMark Mecanum wheels are used
- Each wheel is driven by a CIM motor with a Bainbots 2-stage planetary gearbox with 16:1 reduction
- Each wheel is independently suspended via a pair or thermoformed polycarbonate springs
- Center-of-mass is low.
- The center of the chassis is entirely open for scoring systems
- Provisions exist for encoders on each wheel.
- Chassis frame must be welded Al
- Mass of Chassis (as-shown) is 48 lb
View the pdf-format drawings
View the Microsoft Excel BoM
on smaller scale
We've built a number of Vex based robots that use the omni-wheels in cross setup. Since they are not true Mecanum setups, they vary from the predicted efficiency:
- Less grip due to the 90% angle of the rollers
- Not a true "right and left" wheel to help amplify the forces
Testing did show that the wheels performed better when they were equidistant. Long or wide bases did not have the maneuver skills of a square.
In a two night effort a tri-wheel, triangle based drive train was build. With the wheels at a 30 degree angle to each other, the rollers we able to get some additional traction. There are two things that should be improved if we try this again:
- A better, more rigid frame. The three wheel setup puts a lot of strain on the frame. Building out of a heavier material would help.
- The control system needs some work to move more power to the motors. The original holometric code was revamped, and it inserted some imbalance into the movement.
This ommi and mecanum drive presentation by Ian Mackenzie has a very good description of whats going on. He does a great job on describing the force vectors.
This swerve drive spreadsheet is a way to see how the pivots should react.
(This page needs additional work)
2008 Drive-train Development