Re: Effective Drive Base
 

Would four wheel drive be effective, would it be able to make it over the bumps, how would the turning be?

Re: Effective Drive Base
 

can someone explain to me how the serve/crab drive will not be an effective climber? I don't understand how the fact that a swerve is complected would matter when climbing. Climbing is all about traction and a swerve with the right wheels would have the same traction as other systems.

Re: Effective Drive Base
 

It depends on how you build it. If you make a typical swerve with small wheels, then have fun going through the tunnel. But if you use larger wheels and put them directly in the corner of your robot without any frame to inhibit contact between the wheels and bumps, then I would say that you have a very good chance of getting over the bumps.

Mecanum would seem like a very poor choice this year, especially with such a small area to get through the tunnel. But some will do it and someone will do a great job with it. There always is at least one good team with mecanum!

Re: Effective Drive Base
 

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.

Re: Effective Drive Base
 

Sir, you should perhaps examine the official field drawings for the bumps that will be on the field. The chamfer on the rib that supports the bump happens to be 10 1/4 high and 10 1/4 wide. Simple trigonometry tells me that the bumps FIRST is going to be building will be at an angle of 45 degrees.

Re: Effective Drive Base
 

Madison,

You should put a CG marker on your sims, things get more interesting when you start looking at where your robot starts tipping, and where you end up after you tip.

Re: Effective Drive Base
 

Thanks, Kevin... before I read your post I was thinking... "NOOoooo... we didn't screw up when we built 45 degree angle bumps... did we?", and actually went and re-downloaded the drawings to check.

I've attached the relevant image here.

45 degrees is correct... and wow... it sure looks scarier in person when you see an actual bump first hand than it does when you look at the drawings.

On a seperate note, a student drew up some drawings very much like Madison's this afternoon... and while I don't think ground clearance will be an issue, so long as teams plan for it, CoG is certainly going to be.

After watching teams like 254 climb the ramp, drive sideways across the ramp, basically jump off the ramp and show off what a low CoG can do in Aim High, however, I'm pretty convinced that we can build an even lower CoG for this game. In fact, I wouldn't be surprised if some of those old Aim High robots have already made it over the bump....

I think the really maneuverable robots this year will not only be able to "get air" off the ramp, but to climb a flight of stairs.

Jason

Edit: And as for making a 4wd robot with big wheels turn... AndyMark might be able to help out a bit http://www.andymark.biz/am-0104.html

Re: Effective Drive Base
 

Madison's 8wd picture is looking pretty good...and similar to what we came up with when comparing 6 and 8 wd bots going over the bump.

You can get the CG way lower with 8wd than you can with a 4wd bot that clears the bumps. And playing with raised end wheels does neat things to steering ability.

Re: Effective Drive Base
 

Actually, the kitbot does not roll over the bump with "ease". The tough-boxes bottom out on the top of the bump, and unless you are moving with speed you will get stuck there.

I’ve confirmed this both in CAD and testing.

Of course you can mount the T-boxes on top of the frame, and solve this problem.

Interesting design feature AM... :rolleyes:

Re: Effective Drive Base
 

That's how we have them set up. I figured teams would have figured that out when trying out the kit base. Also, the kit base's "slick wheels" help a bit with turning the 4wd.

We are most likely going with 8 with the front sets raised slightly, I think it will be a common design among experienced teams.

Re: Effective Drive Base
 

Given that my model is symmetrical in two planes, the CG is right in the middle. The robot will obviously behave differently going over the bump if the CG is very far forward or aft, but my model isn't complete enough to capture that yet.

8WD may send the robot "higher" on its way up the bump, but the same behavior that causes that also prevents the end of the robot from falling quite as far as it might on a 6WD system. I am under no illusion that the robot will ever stop successfully on the flat top of the bump and understand that it's going to dive hard into the ground on its way down in all cases, though.

It's also possible to implement 6 or 8WD systems wherein the wheels are not equidistant from one another and see some altered behavior from that. In 8WD, moving the center wheels closer makes the system begin to approximate a 6WD frame -- so it won't ride up as high while climbing, but falls correspondingly further on the trip down. It's all about trade offs, obviously, but I am more concerned with minimizing the force of the giant thud that'll happen on the way down than I am with tipping to 45* on the way up.

Re: Effective Drive Base
 

Half-tracks, anyone? Short tank treads in the back, powered omnis up front. Power to push & climb with the addition of maneuverability...;)

Re: Effective Drive Base
 

Try mounting the transmissions on top of the chassis.

Re: Effective Drive Base
 

Could 4 wheel crab steering make it over the bump?
Our team is looking into either that or standard 4 wheel skid steering.

Re: Effective Drive Base
 

I would love to see a version of 2004-71 style swerve.