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-   -   omnidrive vs. kiwi (http://www.chiefdelphi.com/forums/showthread.php?t=47204)

slent thndr 08-05-2006 16:29

Re: omnidrive vs. kiwi
 
So which of the two ways is best? what are the trade offs? In the system in the video, all 4 motors can be powered for straight motion, so there is more raw power, but a lot of it is wasted because the wheels are at an angle to the way you want to be going.

Lil' Lavery 10-05-2006 22:16

Re: omnidrive vs. kiwi
 
Quote:

Originally Posted by slent thndr
Oh, the 4-wheel omni drive in this video functions differantly.



It has its wheels laid out as northwest, northeast, southwest, and southeast, and northward motion involves all 4 wheels spinning forward. Having the northwest and southeast motors on, and the northeast and southwest motors motionless would produce northeasternward motion.

I suppose that there are just two ways to set up a 4 wheel omnidrive?

It actually functions exactly the same. Just imagine that one of the corners of the bot is north, instead of a flat face. I just used a motor to represent "North" for ease of explanation.
And you can orient the wheels in any fashion you want. It doesn't have to be directly aligned with a "cardinal direction", or 45 degrees to it. Your vector equation to control it just changes whenever you move the wheels' orientation though.

Quote:

Originally Posted by slent thndr
So which of the two ways is best? what are the trade offs? In the system in the video, all 4 motors can be powered for straight motion, so there is more raw power, but a lot of it is wasted because the wheels are at an angle to the way you want to be going.

As I mentioned in an earlier post, unless spinning (where the more motors does equal more power), both systems result with an effective power of 2 motors. 66.7% efficient 3 wheel drive, and a 50% 4wd. So, the 3 wheeled acheives the same power for most applications with lesser motors, wheels, and weight required. The 4 wheels grants a larger conservative support polygon, or "footprint" and you are therefore more stable. Additionally, a 4 wheel drive only requires right angles, while a 3wd takes 60 degree angles, which are much harder to contruct acurately with a vex kit.


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