Re: 4wd vs 6wd?
 

If you have a 4WD bot that is made for pushing, and you add on two more wheels, and the middle two are dropped, you're not going to be pushed around easily by the same people you could push before.

Re: 4wd vs 6wd?
 

Team 42 (P.A.R.T.S.) has used a 6-wheel drive system for several years now. The center wheel is dropped (as I recall) 1/4" and we drive all 3 wheels on each side.

If you don't drop the center wheel enough, then the extra friction from the outer 4 wheels can make the current draw really spike up when turning.

We have found that your choice of wheels also can make a big difference. A robot that would barely turn at all on carpet without browning out a couple years ago turned just fine after we changed the corner wheels back to solid core instead of the pneumatics we had mounted for extra traction. There can be too much of a good thing...

For the last 2 years we have used slightly deflated pneumatics as the center wheels and solid cores on the corners. That gives us a nice balance between traction and turning ability.

Re: 4wd vs 6wd?
 

Few questions. How many teams that have done 6 wheel design only dove 4 wheels. which ones did they drive and why. Also a nice 6 wheel design from last year is 233S roccobot very nice. I am only saying this because I got a up close and personal look at there components and transmission. o second question how much weight does an average 6 wheel design run? Any teams that have done 6 wheels for a while.

Re: 4wd vs 6wd?
 

This, I think, is the most pertinent and useful information you'll find in this thread so far. There is nothing intrinsic to the use of 6WD systems that make them superior in turning. Instead, current draw during turning is affected by friction and wheelbase dimension, essentially, and 6WD systems with a lowered center wheel are preferred over a shortened 4WD wheel base only because they are more stable. The 6WD system is, after all, nothing more than than two shortened 4WD systems that share a common wheel.

The other benefits that people seem to associate with 6WD systems, such an increased traction, seem to be related only anecdotally. For once, though, I'm going to leave the beating of that poor horse to some other people.

This Whitepaper by Chris Hibner is a great resource when trying to figure out if you're robot will turn.

Re: 4wd vs 6wd?
 

In 2003 we had a 6 wheel bot with only 4 of them being driven. The front two wheels had steering. We did this becuase we thought it would allow us to accomplish many tasks. Looking back it would have been nice to have had all the wheels driven.

Here are some pics:

1

2

Re: 4wd vs 6wd?
 

2 years ago, we had a woefully underpowered 4wd bot that just didn't want to turn (as the breakers kept popping). The wheels were essentially in the corners of the base, with long chains connecting the 2 wheels on each side. Our problem was that we had such a long wheel base that the drill motor we were using on each side just wasn't powerful enough to get the job done. To turn, we finally took the wheels off the bot and took them to the router, giving a rounded face to the edges of the wheel.

Last year, we went with a 6wd, drill/CIM drive. We got lawn-mower wheels (the hefty black rubber ones with the white steel hubs) and used those. We trimmed the corner wheels with the router as we had the previous year, but we left the middle wheel alone, and we never dropped it. We never really had issues with being pushed around, or any turning problems.

What I really want to know is: what were the heaviest things in a 6 wheel drive train that caused the most weight headaches, because they were essential?

Re: 4wd vs 6wd?
 

are you asking any 6wd heavy component? or heavy compared to others such as treads or 4wd?
because many heavy components would be necessary for any kind of drive system. ex) batteries.
well if you're comparing, lets start a list
extra wheels (compared to 2 or 4 or 3 or 5?? wd)
more sprockets or w/e you use to power the exra wheels
chain or belt or w/e you use to tranfer power to all the wheels
bearings/bearingblocks
axles
bolts nuts of course


please add on

Re: 4wd vs 6wd?
 

Team 492 http://www.titanrobotics.net has been using 6wd with lowered center wheels since 2000 and team 360 (the first team I was associated with ) used it in 1999. AFAIK we were the first as I didn't see any 6wd robots at either San Jose or Epcot, that year. Since then, they have become pretty popular.

Benefits: 100% traction no matter what the contact is (hills, valleys, flats, going over barriers), fluid, low power turns. In 2004 we were able to run 6 finals on one battery. The motors only got "warm", never hot.

Disadvantage: more complex, somewhat heavier, *harder* to drive straight and easily knocked about: the reason? Because the robot is pivoting on two wheels, there is very little restraining force. That is why 4wd robots drive so straight: they resist mightily any turn! They also burn up the motors...

In 2004 team #492 solved the disadvantages by using active servo to control wheel velocity. We used very grippy tires (3" beadlock) and used torque estimation to limit current draw when in a shoving match (no need to smoke motors!). Finally, for autonomous mode, we used a gyro chip for heading reference (the encoder feedback from the servo for distance) and never failed to hit the target ball - even after being hit by another robot one time!

Typically we aim for a 15-18 fps top speed, but use the servo to limit speed to something less (say 10 fps). We use the servo for control rather than gearboxes. It hurts our ability to push, but, fortunately, 2004 wasn't totally about pushing. A maneuverable robot that was fast & controllable could still dominate.