independant 4 wheel drive

[Ryan F.]

I think the problem may lie in the pneumatic tires. We have a very simular 4wd drive system on out last years robot, and when we tested those tires on it, it jumped, and had horrible turning ability. I'm not sure exactly what we have...but we put some 9 inch wheels on, and that solved the problem.

[Astronouth7303]

Whoa! I may just be the programmer, but I know a complex drive train when I see one (besides, all our guys are seniors but me and Dan).
We just had a CIM and a drill for each side (CIMs facing opposite, drills same). They were linked together via chain and connect to both wheels directly. All chain. in the end: 2 motors, 4 axles, 4 chains, and 2 wheels. The only problem was that we kept breaking plastic gears (6 of them in all). The steel ones we had we're just too heavy.

[Pat Roche]

Also, by placing the idlers above the driven sprocket on one side and below the driven sprocket on the other side, we could have both our motors running the same direction (which is much more efficient than the worm gear solution posted above, since worm gear efficiency is around 70% at best, while sprocket efficiency is around 97%).

With worm gears the efficiency really depends on the maker (if commercially purchased or not...we used a Boston Gear worm reducers this year and the had about 80% efficiency. What would work best if you can find them is planetary gear sets. They have about a 97%-99% efficiency (depending on what you get).

[Astronouth7303]

You should hear Biff about last year's drive train. Drill motors through the drill gearbox and out a pair of worms TO EACH OTHER. All said and done, we had 100 mechanical watts. It did not drive well.

[Biff]

Originally Posted by ufa_mike

The problem with the 2 wheels move together idea is that to have good tunability your front wheels have to have less traction than the back wheels and slide when u turn. This means that your traction limit is lessened in the 2 wheels move together idea. WHat I really menat was to have each wheel move independantly from eachother so each wheel is at it's traction limit. Anyone know what I'm talkin about
Any help appreciated

.Are you talking about "crab" or "swerve" drive? There are drawings and info under those headings. And some teams that have people posting here can answer as to the complexity of the mech and programing. Most that I've seen have modules that swivel, truned with one chain per side. When looking at a swerve drive at Grand Valley, the team (sorry I forget their number) liked it but said it was a little over geared and tended to eat Fisher Price motors. I made a suggestion to put a spring loaded Z in the chain, on the outside of each "turning chain" and a piston or something on the inside so they could get the modules to form a O and do a tank style turn with out having to have the masses unballanced or be really geared down. I hope someday to be able to work with Students that have the machining (sp) skills to attempt a crab or swerve, for now I planning to stick with 4 wheel dirve and over power it to be able to turn.

[The Lucas]

Originally Posted by ufa_mike

The problem with the 2 wheels move together idea is that to have good tunability your front wheels have to have less traction than the back wheels and slide when u turn. This means that your traction limit is lessened in the 2 wheels move together idea. WHat I really menat was to have each wheel move independantly from eachother so each wheel is at it's traction limit. Anyone know what I'm talkin about.

Any help appreciated

Are you trying to "peel out" (raise the speed) the front wheels to lower friction for turning? Or are you trying to keep the speed of the outer wheels constant (front will want to move faster since it has less load) during a turn to reduce slipping?

[Grommit]

I'll avoid addressing items already mentioned and repeated, and state the following out of our team's experience:

Driving pairs of wheels on each side with one output shaft with chains going to each wheel in the pair, and having identical gearboxes on each side, has been successful for us. Fortunately, our motors wore down at roughly the same rate and it kept both sides at the same speed.

On the other hand, this year our drivetrain was a living NIGHTMARE. We had four individual modules, with all the gears mounted inside the wheel, and motors sticking out of the wheel suspended in $125 bearings (cha-ching!). All four modules rotated by way of a window motor on a chain that ran on the top of the robot, creating a mess that made mounting difficult. But the worst part was that the wheels broke down every so often, making them very high-maintenance. And did I mention that they were supposed to run at the same speed, but in actuality were quite a terrible mess? I'm not sure if this is electrical or mechanical, but half the time one of the four wheels was running slower than the other four and messing the bot up. Also, it is hard to align the wheels, and if your wheels are as wide and high traction as ours, you're dreaming if you think we can tank. Thus, I strongly recommend you consider carefully if you want a swerve drive next year, and no matter what, talk to people who have done it before, such as Bill Gold and Jim Gold on Sea Dawgs #258, who definitely can give you a good idea of what to do and what not to do with a swerve drive.