Effective Drive Base

[Tom Line]

Originally Posted by Akash Rastogi

The kit bot rolls over the bump with ease because of the large wheels, it does not bottom out on the top of the bump. However, turning with 4wd is a pain. The robot "jumps" as it counters the friction while turning with skid steer.

Try actually adding some mechanisms to that kitbot frame. The COG is so high that it gets scary pretty quickly. We've done a lot of testing the last couple days, and 6 wheel bots long, 4 wheel bots wide, and even 6 wheel bots wide are all pretty darn scary on that bump - the smallest twitch makes them flip over. We're moving on to more exotic drive systems =). You absolutely CAN NOT decide on a drive train without at least building a small trial-bump to play with and see how your bot is going to react.

[Jstack14]

Originally Posted by hipsterjr

We designed these articulating drive pods back in 2005 and have been waiting for a game like this to use them.

How heavy is it? and how well does it turn?

[MrForbes]

Originally Posted by Tom Line

6 wheel bots long, 4 wheel bots wide, and even 6 wheel bots wide are all pretty darn scary on that bump

We didn't test any of those, our first prototype is 8wd. I sure hope it works! We had to figure out what wheels to use on it, then order them, so we won't have it going for a couple more days

[MrForbes]

We put some old 6" rover and Bayer kit wheels on the 8wd chassis, and rolled it over the bump (human powered, not motor powered)....looks pretty good so far. Nothing too scary.

Hopefully we'll get the drivetrain and electronics going and drive it over by Friday.

[fsgond]

Originally Posted by Michael Ogden

On mecanum wheels: I saw a video of one team (who will remain anonymous) having issues steering with a mecanum drive. If that doesn't turn your mind away from mecanum, AndyMark is coming out with a lighter version of mecanum wheels on Jan. 22.

Mecanum when programmed, design and driven correctly have great agility and maneuverability, arguably as good as swerve. Obviously the video that you saw was not a good representation of what good mecanum can do.

Originally Posted by fsgond

Mecanum when programmed, design and driven correctly have great agility and maneuverability, arguably as good as swerve. Obviously the video that you saw was not a good representation of what good mecanum can do.

A properly built Mecanum system is one of the most impressive drive systems out there. That being said, it has absolutely no pushing power. If your team rates maneuverability over brute strength, Mecanum is the way to go. However, a large majority of teams don't utilize a Mecanum's trues strength: Translating and rotating at the same time. It takes a skilled programmer and a very aware driver to really use a Mecanum system to full effect.

[Chris is me]

To some extent, every mecanum bot I see makes me second guess my own engineering decisions. I made a thread about that. To another extent, every mecanum I see makes me grin, knowing that my team's robot is best equipped to harass them to no end.

[J93Wagner]

Well, to combat lack of pushing power (we use omni-wheels), we decided to use a drop-down, traction wheel covered in roughtop.

[Daniel_LaFleur]

Originally Posted by J93Wagner

Well, to combat lack of pushing power (we use omni-wheels), we decided to use a drop-down, traction wheel covered in roughtop.

We did almost the same thing.

We started with a skid steer high traction drive and added a dropdown kiwi holonomic drive.

[PAR_WIG1350]

4WD only "jumps" when all 4 wheels have a lot of traction (side friction) switching 2 wheels to slick wheels will fix this.

Also, drop-center 6wd is not true 6wd because you really only have 4 wheels on the ground for most of the time. 6wd doesn't give you more maneuverability, a shorter wheelbase does:

If you wanted to turn a robot about its own axis (the center of the wheelbase) easily, draw a circle that is centered on the axis and intersects each pair of wheels at the wheels, do this for each set of wheels. The closer the wheel is to being tangent to that circle, easier it will be to turn. The circles drawn must be concentric for this to work. Using this method, it can be seen that wheelbases that are wider than they are long will have wheels closer to tangent than longer wheel bases.

Now, change the center of the circles to the center of the force applied by the wheels during the turn. Now, the higher traction wheels should be closer to tangent than the lower traction wheels, this is good. lower traction wheels can slide sideways more than high traction wheels. If you find your drive train, when drawn out with this method, has high traction wheels placed really far off line with the tangent line at the point of intersection, it might not be a good wheel choice for that location.

Edit: I don't think this works well (at all) with swerve, mecanum, or holonomic drive trains