omni wheel instead of mecanum wheels
 

assuming a rectangular robot chassis, could you use normal omniwheels (andymark type, for example) turned at 45 degrees like this:
http://www.charmedlabs.com/robot3.jpg
give the same functionality as 4 mecanum wheels?

if so, what is the advantage of using mecanums?

Thanks,
-Leav

Re: omni wheel instead of mecanum wheels
 

You have the wheels in line as opposed to at 45deg.

I--I
I--I
vs.
/-\
\-/
guess which is easier to build(and, somewhat more space efficient)

Re: omni wheel instead of mecanum wheels
 

yes you can, this is typically called a kiwi drive... the advantages of mecanum wheels come from the fact that they are still in a standard wheel orientation and can function as normal wheels or mecanum wheels while the drive system you are referring to only has 1 option of configurability. Both have different applications and both have been used in FIRST. It mostly comes down to preference.

Greg

Re: omni wheel instead of mecanum wheels
 

If i understand what your asking correctly i think your talking about a holonomic drive which looks like this
except on FRC not vex, which i believe can be done with the Andy mark trick wheels. they do more or less the same thing as mechanum wheels except with different methods, the only differences in function being that they are A) much easier to find and buy but are B) a possible disadvantage in this years game due to the issue of getting up the ramp with them(if i remember properly their was a thread on this issue) an issues that doesn't exist with mechanums.

my understanding of the basic idea behind them is that just like with mechanums they are designed to slip at certain angles which allows for lateral and diagonal movement of the robot. In actuality you are only pushing in the diagonal direction with a pair of wheels but the slip created by those rollers on them allows this to be converted into other directions

Re: omni wheel instead of mecanum wheels
 

First off, thats a holonomic drive (a "kiwi drive" aka a kilo-drive only has 3 wheels as opposed to 4-or any other number-), and it has its advantages and disadvantages vs. a mechanum drive.
The advantage is programming simplicity, in favor of an omni-drive. With a "fixed roller" mecanum system, you have a 50% efficiency loss, as you do with a 4-wheeled holonomic system (unless spinning in a circle, when you are using all motors, therefore have 100%, giving an advantage to an omni-system in a spinning situation). In a system where you can actively turn the angle of the rollers on a mechanum wheel you can obtain a much higher efficiency, but that creates very very great depths of complexity in design, and is nearly impossible with the motor, money, and time limits imposed on FIRST.
Id also highly advice you mount your omni wheels in the corners, possibly even tilted to acheive a much greater support base, reducing the chances that you will be tipped over.

http://www.chiefdelphi.com/forums/sh...ght=drivetrain
see that thread for many details about omni-directional and other systems.