6WD: Which wheels to power?

[Mr_I]

We are very tempted to use the 6WD base that came in the kit of parts (simplicity, cost, agility, it's here now, etc.). The KoP frame, however, only powers the center wheel. I understand that a bot built this way can work (since the center wheel is hopefully always touching the carpet), but we're wondering about powering all the wheels.

Is working the details of chaining all six wheels worth the effort? Will powering only the center wheels put us at a disadvantage (pushing, for example)?

[Racer26]

Most teams using a 6WD base will link the wheels together with chains, gears, belts, or some other linking system I can't think of off the top of my head. Yes. I would highly recommend doing this.

[Akash Rastogi]

Yes you will want to run chains to all six wheels. Unpowered wheels are dead weight.

[Alan Anderson]

Ideally, you want every wheel that is touching the ground to be contributing to your motive force. Since your traction is intimately related to the friction on your driven wheels, and since friction depends on the weight applied through those wheels, every non-driven wheel with any weight on it robs you of traction.

[dodar]

The 2 most common ways I know how to power them is West Coast Style: you direct drive the middle wheel then belt/chain drive the other 2. The other way is to put the motor&gearbox between the middle and back wheel and then chain/belt to the back wheel and to the middle wheel and then the middle wheel sends chain/belt to the front wheel.(this way is more for redundancy, because you can lose your back wheels and still have 4 wheels that are driven and you can lose 4 wheels and still be driven by the back 2)(when i say lose i mean that they are no longer spinning, not that they have fallen off the robot lol)

[dodar]

Originally Posted by Alan Anderson

Ideally, you want every wheel that is touching the ground to be contributing to your motive force. Since your traction is intimately related to the friction on your driven wheels, and since friction depends on the weight applied through those wheels, every non-driven wheel with any weight on it robs you of traction.

Unless you do a drop center to help with manueverability.

[Jon Stratis]

FWIW, it's not terribly difficult to chain all 6 wheels together, unless you're trying to do it with a single length of chain! 6 sprockets (1 motor, 3 middle wheel, 1 for each of the outer wheels) and some carefully cut spacers to make sure everything lines up properly, and your set!

[thefro526]

Originally Posted by Akash Rastogi

Yes you will want to run chains to all six wheels. Unpowered wheels are dead weight.

Stogi's pretty much right on the money here.

Every 6WD we've ever build has had each wheel powered, usually using two chains on each side. The front and center wheels are chained together and the center and rear are chained together - we use this method to add a certain amount of redundancy to our drive so that we know we can throw one chain on each side and still have some degree of effective maneuverability.

[Chris is me]

Always always power every wheel.

[Ian Curtis]

Originally Posted by Mr_I

We are very tempted to use the 6WD base that came in the kit of parts (simplicity, cost, agility, it's here now, etc.). The KoP frame, however, only powers the center wheel. I understand that a bot built this way can work (since the center wheel is hopefully always touching the carpet), but we're wondering about powering all the wheels.

Is working the details of chaining all six wheels worth the effort? Will powering only the center wheels put us at a disadvantage (pushing, for example)?

Yup. In a perfect world, your weight (or normal force) is perfectly divided between each contact point with the floor. So a 6 wheeled robot has 25 pounds of downforce one each wheel. You only convert that normal force into tractive pushing force if that wheel is powered -- otherwise you might as well just stick a caster there.

(Imagine you have a really heavy piano. If you put it on unpowered wheels, it is easy to move. )

Ie, a 6 wheeled robot (in a perfect world) with 4 unpowered wheels gets 1/3 the pushing of a robot with 6 powered wheels. If you do the dropped center wheel, then its likely 1/2, since typically only 4 wheels are on the ground at any given time.

[MrForbes]

All of them!

[Rick]

Originally Posted by squirrel

All of them!

QFT

[roborat]

Remember that around the towers is a 1/2 plywood extending out under the carpet which could bring the center wheels off the ground if the front or rear ones hit it which would in turn loose traction.

[Teched3]

When using 6 wheel drive, we chain to each wheel for redundancy. You can lose 2 of the 3 chains on a side, and still drive. Worth the extra effort IMO.

In addition, try to center the CG over the center wheel.

[MrForbes]

Originally Posted by roborat

Remember that around the towers is a 1/2 plywood extending out under the carpet which could bring the center wheels off the ground if the front or rear ones hit it which would in turn loose traction.

That's on the "team" field, not the official field, right? The official fields will have 3/16" aluminum plate under the carpet?

But yeah, ground clearance is a good thing!