What makes six wheel drive so easy to manuever? is it the shortened wheel-base?
what advantages are there to having 6wd? I’ve seen a lot of veteran teams using 6wd and I’m just wondering as to why thats the most used drive train.
some advantages and disadvantages would be nice to know.
any pictures would be helpful.
thank you!
Often on a 6WD, the center wheel is lowered anywhere from 1/8" to 1/4" depending on the amount of rock wanted. Because of this, the robot only hase contact with 4 wheels on the ground at a time, resulting in less friction on turns. If the COG is dead center, then the bot wants to stay on those 2 center wheels, which allows for the easy turning.
Another method to make them easy to manuver is putting omni wheels on the ends. (See 488’s base from this year) This allows for the same traction as a rocker style 6wd, but the dropped center wheel is un-needed.
As for disadvantages, the only one I can think of is it can be heavy, but there are easy ways to fight this, such as using a 25 chain rather than a 35 chain.
Here is a classic case of search before you post! There are a bajillion threads on this topic…
However the quick answer you are looking for is that SOME (most?) 6WDs have a center wheel that is lowered more than the corner wheels. This essentially gives you 2 4WDs, but with the maneuverability of a very short wheel base.
here are a few posts to help you out:
http://www.chiefdelphi.com/forums/showthread.php?t=66009&highlight=6wd
http://www.chiefdelphi.com/forums/showthread.php?t=60074&highlight=6wd
Given the prevalence of the Kitbot from over the past four years (which supports rock), and from my unscientific survey of folks who’ve rolled their own frames I’d move the needle towards “most”.
Yeah i concur with that statement as well…i didnt want to make a blanket statement
Personally I think using omni wheels on the corners is a bad idea and I strongly advise against it. As a driver, whether on offence or defence, if I know that you have omni wheels on ur corners I will use them to my advantage. They may make your robt easy to turn… but that just makes my job a whole lot easier. i just tap ur corner and you spin like a top. I can pretty much push you where ever I want and you can’t do much to stop me.
From past experience the “rocker” is the best method of 6wd. if you can keep your CG rather constant (like not moving from front to back alot) you probabilly wont even notice a rock. Just be sure to keep the friction down on your corner wheels (i.e. only use 1" wheels if using high traction tread). This will still allow you to turn easily but give you enough traction so if pushed you still maintain control.
IMO…
We are able to set up our robot, with encoders, to actively seek the last input state. If the robot wasn’t turning and you try to spin it, it can automatically fight the rotation and hold its heading.
We don’t usually run the robot that way – it’s not worth the headache of tweaking and tuning the PID values – and we don’t really have many problems with people spinning us around.
Different strokes for different folks.
This works on ‘normal’ six wheel drive bots that have a dropped center as well. The way I look at it is this: If you build your robot so it’s easy for you to turn, then it will be easy for others to turn you, too!
In 2007 our robot was the standard 6wd, dropped 1/8" center, 6" wheel drive train. When people played defense on us, they could turn us no problem.
In 2006, the best defensive bot I’ve ever seen (1662!) had four 8"x2" wheels, all at the corners. Their robot had quite a bit of trouble turning, but when they wanted to stay in place, they stayed in place.
It’s just another one of those tradeoffs…
That is true but i have found that the little bit of resistance that you have on the corners can go a long way. We had 8"x2" wheels on our bot in '07 and defenders had a hard time pushing us, but when it came time to turn it was nearly impossible, especially in high gear. I guess there is just a fine line between good turning and strength against defence. Granted alot has to do with the game as to how much defence will be played and how maneuverable you want to be.