TO much traction??? (ifi wheels or AM wheels)

[Heretic121]

I was wondering if anynoe else who was using either the IFI or AM traction wheels were having problems with having TO MUCH traction... we were driving w/ our base *using the KOP gear boxes* and we were jumping back and forth while turning... *not good looking or sounding or for driving* and we have thrown around a few solutions but has anyone else found this problem??? and what are you doing to solve it...

we are trying to find a solution which will keep us still hard enough to push and not get pushed while still being able to drive easily.

idea 1 was using the tubing team 69 + 121 and a few other teams used in 2004 on thier wheels...

[sanddrag]

We had custom wheels last year with the wedgetop tread. 1.25" wide tread. Long robot. 6wd center ones lower 3/16" I'd say we had slightly too much traction. Even with a 6 motor drive. Anyway, we're not using that again. We're using smooth, small, and light Colson wheels.

[s_forbes]

How much does your robot currently weigh? My guess would be that it would jump less when it had a lot of weight on it and the wheels would twist on the carpet rather than jump up.

I've never had the opportunity to run a full size robot yet though, so I'm not too sure about that.

[Heretic121]

um we are at about 60 lbs but only 10-15 lbs of that weight is ABOVE the drive motors/transmissions and they are only slightly above the wheels *in hieght*

[Jared Russell]

Our team's solution was to mount casters to a pancake cylinder to "pop" the robot up 1/4" and allow smooth turning. With clever programming, this is transparent to the driver - the result is moving straight or sitting still gives the support of high traction tires and we can spin on a dime.

[Andy B]

We had this same sort of problem in 2004, although we used 4 large 8" diameter pneumatic tires. We just got some drain tube from the local hardware store and slit it and slid it over two of the wheels and it worked perfectly. The two uncovered wheels provided plenty of traction, while the two covered wheels were able to slide easily on the carpet. (I guess they were sort of cheap omni wheels made from regular wheels)

But, it all worked great. We were able to push around plenty of other robots.

[dtengineering]

We have a six wheel drive, long wheelbase configuration bot driven by two KOP gearboxes with four CIMs driving 6"x1.5" IFI wheels with roughtop tread using the KOP chassis. Testing on carpet did show that the robot was bouncing about a bit, but like your 'bot, we're only at around 60 pounds right now.

When we added some mass (namely a 130 pound student) to the robot (he was wearing a crash helmet... safety first!) the bouncing all went away and the robot turned beautifully.

Try adding some mass and things will likely smooth out.

Jason

[Joe Johnson]

This condition is a traditional problem with 4WD with wheels in the corner.

Grippy wheels want to roll, not move sideways (the direction along the axis of the wheel).

To think about why 4WD with the wheels in the corners is a possible problem, imaging your robot spinning about the center point of the wheels that are touching the ground. The relative velocity of the wheel with respect to the ground can be broken up into 2 components: one in the direction the wheel likes to roll (that is good) one in the direction of the axle (the direction that those grippy wheel does not like to move, which is bad).

Keeping with the mental experiment, you can clearly see that the problem gets better or worse as this ratio (L/W) gets smaller or bigger. That is longer wheel bases make the problem worse (i.e. force the wheels to have to slip sideway MORE) & wider wheel bases make the problem better (i.e. require relatively less sideways slipping).

There is no "official" number on what this L/W should be but the grippier your tires, the lower the number should be to avoid hoppy turns and hot motors. I recommend trying to keep the ratio to about .5, but I have always been a fan of 6 wheel drive so I am biased...

Joe J.

[jskene]

Joe is right - if you are using 4WD with tank drive, you want your robot to be short and wide. It will turn much easier than a long and thin robot.

Another common solution to this problem is to use 'omni-wheels' on the front that have much lower lateral friction compared to longitudinal friction.

You might try swapping your high-grip front wheels out for something with a smooth tread, or grind the tread off the front tires.

[Dennis Jenks]

In the early years with 254 we ran into this problem and solved it by mounting a caster wheel on a pneumatic cylinder at the rear of the bot to take some of the load off of the rear wheels. We would keep the caster down when we wanted to be maneuverable and pick it up if we got into a pushing match. You will need to experiment a bit to find the optimum height for the caster if you go this route, but with a little work it can be a very effective solution to your problem.