Going over 6 inch step with 12 inch wheels

[Al Skierkiewicz]

Originally Posted by Joe P

The set of front wheels go over with no problem but the back set of 12 inch wheels get hung up and start spinning a lot. We eventually get up to the top of the platform but it takes great effort for the driver to get up there.

Joe,
I think if you watched closely, the robot front tires are actually being pushed into the step edge. The resulting force combined with the turning ability of the tire results in the tire climbing the edge. The robot front wheels would climb even if they weren't powered. (Think of a bike going up a curb.) There is just more point friction on the front tires. Lowering the air pressure in the rear tires should help quite a bit. Some teams have added some friction enhancers, i.e. teeth or grippers, to the tires. These grip the edge during climbing and do not allow the tires to slip on the platform edge. I have seen grippers mounted right on the tire and on a wheel attached to the tire.

[Grommit]

I'd like to point out that the 12" wheels are actually 12.5" wheels, which makes a slight difference. But more importantly, it requires a very low center of mass to drive one of these things. I watched Kehillah Jewish High School, Team 1043, with Patrick as driver (over two years of experience), in practice, and even he had problems with the robot tipping over. The robot had a large arm mounted upon it to hang, and it wasn't particularly heavy, but consider the following:

Diameter 12.5" implies a maximum wheel base of under 24 inches, probably 20 after the protection in the front. Under these rather optimal conditions, with one wheel up on the step and the other down, we have an angle of nearly 18 degrees. With a center of mass that is high enough, the momentumof the base might flip you over before your other wheel reaches the step.

[Matt]

We actually have the 9 inch wheels. We have a belt drive system. When going up the step our belts are being pushed on the plat form and pulling us up the ramp. With this we have the ability to climb the 6 inch step with no power and with no ramming speed.

[Brandon Holley]

I don't know if you guys have any type of arm, but thats the key. In NJ, our robot would bounce and bounce and bounce for about 40 seconds until it got up the ramp, and then we had to do it all over again...wasn't pretty. This way was with the hook in the back. Next match we turned the bot around and extended the arm in front of our robot, we were on the top step hanging in 15 seconds...the start of our success.....try it with an arm if not...might i recommend zip ties and pneumatic tubing....

[Combat Chuck]

If you guys can get the front wheels on easily and are having trouble with the back wheels, have you considered using a small piston on the back end to lift the rear of the robot enough to clear the platform. If you lift the back of the robot, you can pull the robot forward with the front wheels until the back wheels are on the platform, then retract the piston and continue on.

[Joe Ross]

We also use 16" wheels, and had a little trouble getting up the step. We added some weight to the front (on the bottom) and now have no trouble. A lot of the other suggestions are good too, if you don't have weight to spare.

[OneAngryDaisy]

My team quickly realized that so much can happen on the platforms. (tested out our tread drive subsystem and flipped every time) What I would suggest is add another 2 feet to your arm/hanging mechanism so that you can hang from the floor. We have a light (4 lb) 12' telescoping arm, the extra 2 feet was well worth it for us. I realize this might not be possible, but just tossing another idea out.

[Solace]

for all teams that have problems with turning and the like - in the future, use 6 wheel drive. all your problems will be solved

[Joe P]

Originally Posted by Al Skierkiewicz

Joe,
I think if you watched closely, the robot front tires are actually being pushed into the step edge. The resulting force combined with the turning ability of the tire results in the tire climbing the edge. The robot front wheels would climb even if they weren't powered. (Think of a bike going up a curb.) There is just more point friction on the front tires. Lowering the air pressure in the rear tires should help quite a bit. Some teams have added some friction enhancers, i.e. teeth or grippers, to the tires. These grip the edge during climbing and do not allow the tires to slip on the platform edge. I have seen grippers mounted right on the tire and on a wheel attached to the tire.

Thanks for all the replies from everybody.
You Guys are the best.

Joe P