Quote:
Originally Posted by EricH
Some other things to take into consideration: how easy is it to push you? Omni's are a little easier (two-wheel drive in any given direction save diagonal). Mecanums may be set up in two orientations ("easy-spin", which looks like an X, and "hard-spin", which looks like an O) and are harder to push because you have to fight all four wheels.
Ease of building: Mecanums are easier to build. Given four AM planetaries, a set of mecanums, and a kit of parts, it is possible to put one together other than programming in about an day. Omni's need a custom(ized) frame.
Maneuverability: there is a slight difference (I think). Mecanums may be programmed to allow turning while strafing, enabling large arcs. I'm not sure an omni-wheeled robot can do that without spinning.
Traction: Most teams that use mecanums have relatively high-traction rollers (often rubber). Most teams that use omnis do not (often plastic). It's a little harder to push a mecanum robot partly due to this and partly due to four-wheeled resistance.
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A mecanum is really a form of holonomic drive (as mentioned earlier), but instead of angeled wheels with straight rollers, a mecanum has angeled rollers on straight wheels. Instead of applying a large portion of the force from not a large number of motors, mecanums apply a smaller portion of force from more motors.
As for your notes:
Pushing:
Assuming both sets of wheels have identical traction, it is really the same. You can push on each from angels where you will get partial resistance from all the wheels, or locations where you will ignore 2 wheels (as you will be pushing along the rollers) and fight the full resistance of 2 wheels.
Ease of build:
Mecanums will adapt easier to a "traditional" (kit of parts) frame than a holonomic system. AM Planetaries would be a poor choice for a drive train though (given current rules). The AM CIM motor planetary is more for manipulator use, with a 181:1 reduction.
Maneuverability:
Both Mecanum and Holonomic drives can drive in arcs, spin in place, translate in any direction, and "frisbee" (rotate while translating in a straight line) given proper programming.
Traction:
In general, neither system gives a great amount of traction (because of the general principle of rollers), and each wheel has a direction it can be pushed by (in theory) only overcoming the rolling resistance of the rollers. AndyMark sells both plastic roller omni-wheels, and the "trick wheels" (which you can have rubber and neoprene rollers, with higher traction).