The Center Wheel

[Akash Rastogi]

If you are also concerned about the amount of teetering you're getting from a dropped center, make sure your outer wheels are as far apart as you can go. Its an obvious solution to a very minor problem once CG is maintained as close to the center of your robot as possible (barring any intentional CG changes given certain manipulators).

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[Cory]

From the experience we've had with a dropped center 6WD the rock has never been a problem. Not once.

Originally Posted by Cory

From the experience we've had with a dropped center 6WD the rock has never been a problem. Not once.

Same here.

[Eugene Fang]

Originally Posted by Cory

From the experience we've had with a dropped center 6WD the rock has never been a problem. Not once.

Same here, too. You don't need a lot of "drop" to get the effect you want. And that little amount of drop results in a barely noticeable rock.

[RoboTIP]

Originally Posted by squirrel

Don made a great suggestion (as usual), try some different things and see how it works.

And you can play engineer first, figure out what will happen using math and physics equations, then see how close your predictions are to your experimental results.

excellent idea! Anyone willing to share the relevant equations?

[Jon Stratis]

Whenever we've done 6-wheel designs, we've dropped the center wheel. In Overdrive, we had a forklift-like elevator that got up probably 10 feet high with dropped center wheels... and we never tipped over. We also had a giant steel plate on the bottom of the robot to lower the CG.

Dropping the center wheel a fraction of an inch does make the robot look a little unstable as it bounces between front and back wheels, this is true. But in reality, if your CG is fairly low, it introduces no risk of tipping while on flat ground (and even climbing ramps in Rack and Roll it didn't seem to matter).

You may want to create a small test bed to see the results and prove it to yourself. Create a standard robot chassis with 6 wheels, but make the center wheel's height adjustable for example, you could securely mount a screw vertically that, when tightened, pushed the axle downwards, giving you a dropped center wheel, assuming you're using dead axle's). Drive it around with both dropped center and non-dropped center, and see how it handles with each. Design some tests for stability to determine if that would be a problem. In short, get some data before you decide which way to go.

[Joe Ross]

Originally Posted by RoboTIP

excellent idea! Anyone willing to share the relevant equations?

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

[ajlapp]

How about making your drop adjustable?

Also remember that you can drop the center wheel or lift the outer wheel.

When making an adjustable setup it may be easier to lift the outer wheels that probably are not interfaced with your transmission directly.......depending on the rest of your design.

[RoboTIP]

Originally Posted by Joe Ross

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

thanks!

[jamie_1930]

It seems like that your problem with dropping the wheel is just because you think it will decrease the robot's stability, which in my opinion it will although I don't have an answer for you on how much, but if this is your problem I say go with your instincts and keep them at the same level. Although in order to gain some of the manueverabilty that dropping allows, make your outer wheels omni wheels and have your center wheel be traction.

On a different note and this is something I think we'll be trying in the offseason is, and we stole this from SparX (1126), do a 6 wheel with a 1/8" center drop, with the center wheel be traction wheels along with one of the outer sets. While having the other end be omnis, this will change the bot in a way that if you go in one direction, so all traction wheels are touching, you have more traction to the ground, or travel in the opposite direction, with one set of traction and one set of omni wheels touching the ground, which will give you more maneuverability