How to turn better with four wheel?

Technical Technical Discussion
1

My team is currently using the lift kit so that we can get over the barrier in the middle of the field. We have never done four wheels before, but because of the brackets we are trying it. It is very hard to turn, is there anyway to turn better?

We are currently using 4 independently driven wheels that are at http://www.andymark.com/product-p/am-0514.htm but we have tried 2 wheel drive with all 4 of those wheels, along with 2 wheel drive with the other 2 wheels from the 2011 game. We have also used 4 of those plaction wheels with 2 gearboxes only. None of these systems seem to get even decent turning. Any ideas to help the turning?
Thanks,
WarriorRobotics

2

Add omni wheels at 2 of the corners or add 2 wheels in the center and drop them an 1/8th inch for a 6 wheel drive. Both will reduce frictional forces that oppose turning.

3

Try using the slick wheels that they gave in the KOP for 2010. Or tr using omni wheels in the front or rear of the chassis. These will greatly aid in turning.

4

Buy two more wheels.

5

4 wheel Crab drive.

6

If you are using the kit frame chassis you will notice that the hole for the center wheel is dropped by 1/8 of an inch. This is there so that you can put a 2 more wheels in your drivebase taking if from a 4wd to a 6wd setup and the chassis will rock between the front and back wheels and will greatly improve your turning ability. You can use the 2010 slick wheels or omni wheels on either the front or back to make your 4wd setup turn, but those wheels won’t have a lot of traction if any.

You can either buy two more wheels, or use the 4 plactions in the back with 2 8in kit wheels in the front.

7

But seriously for a second, take a good look at your design.

You have 8" wheels. You do not need a lift kit. You can very easily modify the kit chassis so that the wheels in a 6 or 8 wheel drive are exposed in the front and make contact with the barrier to get over. You don’t need the lift kit.

8

I second what akash said, with some slight modification you can avoid the lift kit.

If you want to improve your turning then omni wheels or slick wheels are the way to go. With the slick wheels you could find yourself spinning out if you accelerate too quickly but it is very similar to the plaction wheels you already have so the adjustment would be easier. One piece of advice I would have if you decide to go with the omni wheels is for you to put two of them with alternating rollers for each wheel you replace so that you always have an omni wheel roller contacting the ground.

9

Add one to two wheels on both sides and drop the center ones a little to allow for a rocking drive train. This should significantly help out with turning.

10

Is there a way to turn better without adding an extra wheel on a wide chassis, or without changing to omni wheels? We would be doing this with 4 wheels, not 8, however.

11

Moving your wheels closer together or making your bot much lighter is the only thing I can think of.

12

Our team did a 4 wheel driven with “conventional” wheels (not omni, mechanum, or swerve) two years ago and… It didn’t work. We used the smooth ones from Lunar Lunacy on the front, and the event I drove (post season, I joined late) I ended up having to go backwards and swing the robot to the left (there was too much weight on the right side!) in increments to get it going the direction I wanted. It was not fun.

Now, if you can’t buy omni wheels (either the more expensive omni wheels or two pairs to mount interlaced), which are probably the best solution, I can understand. Our team is so poor we’re running out of nuts and bolts! In this case, I would highly suggest you switch to a two-wheel driven design, where the front is powered. The rear wheels should be slick, such as the Lunar Lunacy wheels; if you don’t have access to those, I’m sure a local team might have some for you to use, or you could try ripping the treads/rubber off of some other wheels (not sure how they’re bonded, though, might not work).

Another option is casters. I’ve heard them being trash talked on CD a bit, but if you trail them, the wiggle from direction change will be nonexistent and only show up when reversing (to remedy, use smaller wheels). This might not be as cheap as the slick wheels.

Of these options, our team is currently on the first alternative, using lunar lunacy wheels. They will be in the rear, with the front having this year’s treaded wheels being driven. We were also making sure to put most of our weight over them (this could also help while balancing three robots, we imagined). Based from my terrible experience with our past robot, this will work much better than having them in the front… We were eventually wanting to switch to casters, but we don’t have a way to make them.

If you wish to drive four wheels, and end up using the slick wheels on one side, I would highly trying to drive them at full tilt to break traction during a turn – I never got a chance to try this, but I think it would have worked on that one terrible robot we had (I just never had time to implement it, long story).

13

We have had luck using a double set of rubber wheels at the front, and single slick wheels (like from Lunacy in 2009) on the back. This gives you good grip up front but lets the back end of the robot swing around easily. Worked well for us in 2007 and 2011 for positioning to hang tubes, but may not be what you’re looking for.

http://www.chiefdelphi.com/media/photos/27552

14

What’s keeping you from REMOVING 2 wheels - you know, segway style?

:slight_smile:

15

This is crazy enough to work.

16

Gravity. Friction. The usual, though this does give me an idea:

Dean Kamen created the 2 wheeled segway.

Team 256 will now invent the 1 wheel segway! With 3000 gyroscopes and over 6 lines of code!

17

That’s interesting…we’ve had a 4 wheel drive robot at 119.9 pounds before on 6 inch andymark plaction wheels with no problems turning…are you using 4 CIMs in you’re drivetrain? If not, this extra torque could aid in turning.

18

We are using all 4 CIMs. We actually aren’t experiencing problems since we haven’t tested yet (Testing tomorrow, can’t wait! :D), however we wanted to know if there was anything we could do to prevent any problems.

19

Ah, then I’d bet you’d be fine! A 6 wheel drive narrow chassis breaks up the wheel base into 2, 28 x 19 rectangles (roughly), which is a ratio of 1.47:1. With a wide chassis, you have one wheel base that is a rectangle of 38 x 28 (roughly), which is a ratio of 1.36:1. Now short of vector analysis, that’s easy math that can show you the turning abilities should be somewhat similar; don’t expect any major changes.

20

Thanks!