3 wheel vs 4 wheel vs 6 wheel

[Rob]

Depending on your strategy, 3 wheel drive may be appropriate. The obvious problems with this concept are stability issues and less powered wheels on the ground. Advantages are higher manuverability and a lighter drivetrain than say a 6 wheel design.

In 1998 my team used a 3 wheel design, 2 powered wheels in the front and a caster in the middle back. In order to maintain stability we had .5" of ground clearance. In addition, we put small delrin skids on the bottom of the back corners in case they contacted the ground. As far as less powered wheels goes...We wanted to be quick and manuverable for that competition. While we had virtually no pushing power, we could escape from defensive machines using our manuverability.

My point is the following:
You should identify what qualities you want your drivetrain to have, and pick your design around them. List the advantages and disadvantages of each design. See if the advantages fir what you want, and see if you can come up with effective solutions for the disadvantages.

Remeber that people on your team will have vastly different ideas about what to do. Look to past robots from other teams for some inspiration on your ideas. Finally, compromise is sometimes the worst solution, you may have to give up on your idea, or convince others to commit to yours. It helps if you have some math or experiment results to back up the claims you make about your design ideas.

Good Luck,

Rob

[dhitchco]

Brandon,
as others have suggested, the optimal drive design is a big "it depends".

There are many examples of real-world 3-wheel (or overhanging) designs such as engine lift cranes for automobile repair, or drum lifter cranes for 55 gallon barrels.

More importantly, it is vital that you and the team come to some concensus on your design and then put your best foot forward. By far, the biggest problem will be if you do NOT stick to some pre-determined strategy. You know that !#@$% will happen, but at least you can stay that you chose a design wisely and then executed flawlessly....win or lose.

[locohammerhead]

well the team im on wants a arm that can turn 360 digrees and the 3 wheel desighn that they have in mind is really narrow and thats a big prob.

[Gary C]

Originally Posted by locohammerhead

well the team im on wants a arm that can turn 360 digrees and the 3 wheel desighn that they have in mind is really narrow and thats a big prob.

Why not go ahead and build a circle for that matter.

[Jeffel]

treads are slow and they suck for quick turning and overall they suck and casters are horrible too. Its better to just use 4wd!

[663.keith]

Originally Posted by Jeffel

treads are slow and they suck for quick turning and overall they suck and casters are horrible too. Its better to just use 4wd!

treads can be very fast and easy to turn if done correctly. We have a robot that is by far the fastest we have built and he uses treads. conversely, one of our 4wd robots was terrible at speed, and could barely turn (it used a wonderful "Bounce turn"). I believe that treads work better than 4 wheels in many cases.

[Jeffel]

sorry but i'd still like to disagree on that one... i just dont like how the whole robot bounces around while turning on treads. sorry, never was a fan

[elknise]

We did a three wheel chassis last year, two powered and a caster. We had no problem with tipping even when we went to raise yourselves up on the center bar.

4WD is good, but 6WD is better, if you have time and resources to pull it off.

[NoodleKnight]

Originally Posted by 663.keith

treads can be very fast and easy to turn if done correctly. We have a robot that is by far the fastest we have built and he uses treads. conversely, one of our 4wd robots was terrible at speed, and could barely turn (it used a wonderful "Bounce turn"). I believe that treads work better than 4 wheels in many cases.

That depends on how you build it, if you drop the center portion of the tread (much like most 6wd designs with their center wheels), then turning on a tread drivetrain can be better than a 4wd platform. But if your treads are just 100% level, then there's a whole lot more side-friction to overcome compared to a 4-wheel drivetrain.
As for speed, that depends on your motors, gearing, and drivetrain efficiency.

We also had that problem with our 2003 robot, where would hop side to side when it would turn. It had too much traction and only weighed like 90 lbs.

Personally, I like 4wd, its a good balence between drive systems. Plus the kitbot is set up to do so.

EDIT: When I read 3wd, I actually thought you meant an actual 3WD robot with only 3 wheels, kinda like a kiwi drive platform. But if you're talking about a 2wd caster bot, I've always had bad experiences with them, but with some modifications, it can be good.

[MFS766]

6-wheel is the best, but make sure the middle wheel is slightly lower (1/8 ish). This blends the 2wd and 4wd, all your weight is going to wheels with power so you should have good traction. It also centers more wieght on the center, oppose to the edges (farther from the turning point) of 4wd. This means 6wd takes less force to turn the robot. Also the wheel base is shrunk since amost only 4 wheels will be possible to signfigantly press into the ground. 4wd of the same shruken wheelbase are not stable. I saw many tip last year. Hey with 6 wheels, if it has problems, you can throw of wheels until you have 4wd of 2wd with a castor or two. It is easier to take away then add.