Effective Drive Base

[Shawyan]

Our team has mainly had problems with the KoP chassis while using 4 wheel drive. The robot consistently hopped 4-6 inches off the ground. This was done with high traction wheels, which may have been the problem. This hop was greatly reduced with a welded chassis instead.

The turning with a 4WD, in our team's opinion, has never been superb.8WD would be much more efficient, and easier to travel over the bump as well.

[Akash Rastogi]

Originally Posted by fuzzy1718

a page or two back some one said that 4 wheel drive is hard to turn with
2006, 2007, 2009 (with traction wheels added) our team turn just fine with 4 wheels... granted we were in the wide configuration, but it is actually better at turning than a typical 6-wheeler (don't quote me on the being better part, in our experiance it is better, which is limited to 2 chassis in the 6 wheel genre)

Simple physics and extensive experience with both types of drivetrains does not lie. Your wide orientation made the difference, by the way.

If you can't prove your logic to me then I highly suggest you learn the physics behind it and read this....

http://www.chiefdelphi.com/media/papers/1443

Note that the words "hard to turn" and "harder to turn" make a difference too.

Disclaimer: I am not taking into account possible varying CoF between the front and back sets of wheels.

[T3_1565]

I always found 6wd and 8wd to have a harder time turning then 4wd. more points of contact = more friction... making it harder to turn.

toss up between getting over the bump easy and driving easy.

[Akash Rastogi]

Originally Posted by T3_1565

I always found 6wd and 8wd to have a harder time turning then 4wd. more points of contact = more friction... making it harder to turn.

toss up between getting over the bump easy and driving easy.

6 wheel drive, drop center is the case in point.

On the matter of 8wd, I can't comment yet because I lack the experience in this type of drivetrain.

[MrForbes]

Originally Posted by Akash Rastogi

On the matter of 8wd, I can't comment yet because I lack the experience in this type of drivetrain.

but I think a lot of teams are going to know something about it by this time next week

[Akash Rastogi]

Originally Posted by squirrel

but I think a lot of teams are going to know something about it by this time next week

We'll be sure to post our results too*. I predict really slight differences in teams' 8wd set ups (slight elevations of wheels/drops/pivoting wheels). Should be fun!


* LOL at 8wd vs. Crab drive debates

[Brandon Holley]

Originally Posted by T3_1565

I always found 6wd and 8wd to have a harder time turning then 4wd. more points of contact = more friction... making it harder to turn.

toss up between getting over the bump easy and driving easy.

More points of contact with less normal force at each point of contact. Its not as black and white as you described it.

[T3_1565]

Oh, well I never said I was an expert on the subject, just never found it hard to turn with a 4wd bot

[GaryVoshol]

14-wheel drive anyone? http://www.chiefdelphi.com/media/photos/26312

[MrForbes]

We were talking about 14wd in our meeting today. We can't afford that many wheels.

[RoboMentorY]

Originally Posted by Madison

For the sake of discussion, I'm attaching a picture that shows an 8WD system going over the bump.

We just put these set of screen shots together with a 6WD, 6" wheeled system with a 0.25" drop center. As a powerpoint slideshow it shows the angle changes as the wheels change contact the bump. One can envision the crash at the tipping point on the down slope. Enjoy.

[Josh Fox]

Originally Posted by GaryVoshol

14-wheel drive anyone? http://www.chiefdelphi.com/media/photos/26312

That was one of the most impressive drive trains I've ever seen.

As a brand-new rookie drive going into the Detroit Regional in 2007 I was totally intimidated by the sight of that robot. It went anywhere it wanted whenever it wanted, and there was nothing you could do about it.

[J@GMFlint]

Some thoughts...

Does a robot "need" to go over the bumps to be effective in Breakaway?

Consider which potential scenarios would require you to "have" to go over the bumps. How often might they occur?

Would designing for bump crossing capability (as a priority) force you to compromise other perhaps more important attribues like scoring manueverability, or ease and speed in passing balls zone to zone?

[Chris is me]

Originally Posted by Shawyan

I believe the best overall drive train is either full holonomic or Swerve drive. This would allow being able to rotate the robot to face the goal, as well as drive in the desired direction. Swerve drive allow the team to keep more motors free for other activities such as a kicker, but still retain the "any direction i want, i go, no worries".

All the strafing of holonomic or swerve in the world isn't worth anything other robots violently push you across the floor (holonomic) or if your drive breaks (swerve)

My personal favorite for this year (not tied to any teams i'm working with) is a hang up between 3 different skid steer designs.

[Flyboy_u92]

Originally Posted by J@GMFlint

Some thoughts...

Does a robot "need" to go over the bumps to be effective in Breakaway?

Consider which potential scenarios would require you to "have" to go over the bumps. How often might they occur?

Would designing for bump crossing capability (as a priority) force you to compromise other perhaps more important attribues like scoring manueverability, or ease and speed in passing balls zone to zone?

I think this is a great point. I know that with our robot we've had some issues with scoring design because of our clearance. On another note for the tank treads. Couldn't you just use a dual sided timing belt? Say 3/8" pitch? and 3" wide?