Chief Delphi - Getting A Bot To Turn

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Re: Getting A Bot To Turn

Quote:

Originally Posted by Evan Austin

Here is another question:
I know that some teams with 4wd robots will use 2 standard wheels on one end and use 2 omni wheels on the other end to enable them to steer easily. I wonder if anybody is using 6wd has done something similar with the 2 standard center wheels and omni wheels on all 4 corners? I know of one team which used a 2wd center drive and had small omni wheels on all corners, and they were very maneuverable and stable. However, they were not powering these wheels on the corners. If this would work, you would not have to lower the center wheel, thus keeping a flat footprint.

FRC Team 40 did this in 2004.
Perhaps they can relate their experiences with it's performance.

Re: Getting A Bot To Turn

The robot my team (1072 last year) built had a similar problem like this. We had six wheel drive, with the middle wheels 0.250" lower. Before we had the elevator mounted, the robot was generally balanced over the middle wheels, so it would rock back and forth a lot during turning. However when we put the elevator on, the center of gravity moved forward, so only the front 4 wheels would touch the ground during turning. Thus, our robot wheel base was only half the length of the robot, and made it very easy to turn. Then when we accelerated, the robot leaned back and rode on the back four wheels. From what I have noticed, I guess it helps to have your CG forward or backward, so its not close to the middle wheels. That way it is harder for the robot to bounce around when youre turning, since the weight of the robot opposes bouncing more.

Re: Getting A Bot To Turn

Did this years game require a high traction power bot? Did any team make it to the finals with a power bot and a defensive strategy? At our regional robots that were highly maneuverable and fast tetra placers won. Your teams choice of 6 grippy wheels indicates that your team thought that power and pushing ability was most important and that turning was an after thought. May be your team needs to review your design process. In the off season you could review some drive strategies for different game play. What's best for maneuverability, for pushing and king of the hill, what to do for ramps and steps ? Its very difficult to get a drive system perfected that is excellent for all game play requirements.

Re: Getting A Bot To Turn

Quote:

Originally Posted by KenWittlief

omniwheels!

Mecanum!

Speed, agility, what more could a robot want? And it looks really cool.

Speaking of which, it is kindof unrelated to 6 wheel drive, but the turning part applies. Mecanum wheeled robots turn verywell because of the 45-degree rollers. Instead of slipping your wheels, the rollers on your wheels spin, so you do not burn out your wheels.

Re: Getting A Bot To Turn

Quote:

Originally Posted by Andrew Blair

Today I was brainstorming drive train ideas, but I was struck with a problem we encountered this year and never fixed really. The problem is, we have extremely grippy wheels on a 6-wheel layout. This works fine on a low bot, and it turns rather well, but with a tall, heavy mast like we have, we encounter a strange phenomena when we turn. The robot will begin to violently rock the more we turn. The things like a train when it's going straight, but when it turns quickly it's occasionally in danger of completely tipping. Any ideas for it or for a new 6 wheel bot with a high mast? thanks, this is an interesting problem.

The thread seemed to focus on the drive train, but I think you need to look at the entire robot. Part of your problem appears to be a high center of mass. It is unclear if the mass was over the center of the wheelbase. Perhaps you should rethink the design of your mast to help lower the Center of Mass. For "FIRST Frenzy, Raising the Bar", we used 13" tires to allow us to climbs the steps. But we worked very hard to make our arm light and mounted heavy parts as low as possible. As a result our CoM was very low and we were very stable. I just want to point out that you should try to think of the whole package and how it works together.