Quote:
Originally Posted by thefro526
Assuming that you are using off the shelf components a Mecanum drive is easier to make. Omni-Drives require precise angles (60° for a Kiwi and 90° for a Holonomic) and if you are not near perfect your robot will have some strange driving characteristics. Also it is much easier to climb ramps with Mecanums. To my understanding Mecanums are also more efficient in forward and reverse directions (like a normal wheel) while still giving you lateral mobility. Omni-Drives have a much lower efficiency (~50%) in all directions but they will give you true omnidirectional motion. Also Omni-Drives require much more skill to drive than a Mecanum Drive. Still, you should test out both drives to see what works better for your application and to suit the game.
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That's a lot of generalizations.
Mecanum drives require just a much precision to make as holonomic (omni/kiwi) drives, but instead of worrying about how to place your wheels radially, you have to place them in facing the same angle (if this is off, you will once again experience incorrect driving, unless you account for it in programming). In addition, like a mecanum drive, you can account for any imperfections in wheel placement in a holonomic drive with programming.
In general cases, Mecanums are capable of climbing inclines/steps/bumps better than most holonomic drives, but it is possible for holonomic drives to climb them given the right wheels and/or suspensions (and the size of the inclines/steps/bumps).
Mecanums and Holonomic systems aren't really any more efficient than eachother, they just function differently. Assuming a 45º roller placement on a Mecanum wheel (standard for FIRST purposes, used on the AM Mecanums), a Mecanum wheel delivers about 70%
([square root of 2]/2) of the force applied in both the "vertical" and "lateral" directions. Each omni-wheel delivers 100% of the force in the direction it faces, but the over-all efficiency of the drive depends on the number of wheels used, direction of travel, and rotational movement. Basically, a mecanum system uses angeled rollers and straight wheels to achieve the same goal a holonomic system uses straight rollers and angeled wheels for.
As for the driver skill, I fail to see how one would be harder to drive than the other (when programmed properly). A common control style is using a single joy-stick to control the lateral movements of the robot (using both the x and y axis) and either a z-axis or a knob (pot) to control the rotational motion. I have seen this system applied both to holonomic and mecanum drives (and have driven it with a holonomic....with ease).
Neither system is truly "better". They are very very similar systems, that function on the principle of vector translation. The programmers for either system should have a firm grasp on vectors and (preferably) kinematics in general. The efficiencies, torque, speed, traction, agility, cost, weight, size, and complexity vary greatly on the exact system you use (wheel choice, wheel placement, programming ability, etc.). Ideally both systems should have some form of suspension to ensure that all wheels remain in full contact with the driving surface, but teams have succeeded in the past with-out them.
I'd suggest you consult teams that have used each system for tips and lessons learned, as well as reading Ian Mackenzie's whitepaper on the kinematics of omni-directional systems.
http://www.chiefdelphi.com/media/papers/1836
Some existing threads on both systems:
http://www.chiefdelphi.com/forums/sh...hlight=mecanum
http://www.chiefdelphi.com/forums/sh...hlight=mecanum
http://www.chiefdelphi.com/forums/sh...hlight=mecanum
http://www.chiefdelphi.com/forums/sh...hlight=mecanum
http://www.chiefdelphi.com/forums/sh...hlight=mecanum
http://www.chiefdelphi.com/forums/sh...hlight=mecanum
http://www.chiefdelphi.com/forums/sh...highlight=omni
http://www.chiefdelphi.com/forums/sh...highlight=omni
http://www.chiefdelphi.com/forums/sh...highlight=omni
Programming emphasis:
http://www.chiefdelphi.com/forums/sh...ad.php?t=36205
http://www.chiefdelphi.com/forums/sh...092#post421092