weight distribution

[kDude]

So we're finalizing our chassis design, and we are going to have 2 powered wheels (6") in front and have 2 omni wheels (6") in the back. But we're not sure where to place our electrical components, battery, gearboxes, etc. Should we have the weight evenly distributed, or have the weight shifted to a certain end?

Another question, our team is going with a fast and small robot and our chassis is 25 1/2" x 35 3/8", but we aren't sure how tall to make construct it. Any insight?

[MrForbes]

If you're not going to have any ball handling "stuff" on the robot, then you probably want to make it as low as possible (remember you'll need a part that sticks up 51" to mount the flag).

We're trying to get our center of gravity (to use the old term) as low as possible, centered on the robot front/rear, and to the left side of the robot as much as practical.

[sanddrag]

If it isn't too much trouble, I'd recommend running chains to those omni wheels so they are powered too. You'll get more pushing force.

[David Brinza]

If you plan to make fast left turns, you might want to put more weight on the left side of the base of your robot. Especially if you have any sort of arm, forklift, etc that might be carrying a ball. You don't want your CG to get outside of your right wheels when you're turning; if you do, you'll tip over.

[kDude]

Originally Posted by sanddrag

If it isn't too much trouble, I'd recommend running chains to those omni wheels so they are powered too. You'll get more pushing force.

Would that mean putting in two more gearboxes?

[MrForbes]

No necessarily, you can drive the front wheels off a different sprocket on the same transmission that drives the rear wheels. There are lots of different drive arrangements, you might want to spend some more time looking around here at pictures of various robots.

[Otaku]

Originally Posted by sanddrag

If it isn't too much trouble, I'd recommend running chains to those omni wheels so they are powered too. You'll get more pushing force.

Really good pushing force won't be a deciding factor this year, I predict.

Originally Posted by kDude

Would that mean putting in two more gearboxes?

Not particularly. Extra tensioners, more chain and maybe a few more sprockets. Double sprockets on one of the normal wheels, one to drive, one to the omni's. I wouldn't suggest it, though.

[kDude]

Originally Posted by David Brinza

You don't want your CG to get outside of your right wheels when you're turning; if you do, you'll tip over.

Well since our robot has a greater width and length than the height, I don't think it would tip over, right? Which brings me to the possible height of our robot. We're just talking putting the electrical boards, battery, and gearboxes in it, no mechanical arm or pneumatics so it should probably be around 24" tall?

[EricH]

Originally Posted by kDude

Well since our robot has a greater width and length than the height, I don't think it would tip over, right? Which brings me to the possible height of our robot. We're just talking putting the electrical boards, battery, and gearboxes in it, no mechanical arm or pneumatics so it should probably be around 24" tall?

Remember the flag rule...but that mast for the holder shouldn't affect the CG too much.

[JesseK]

For weight distribution, you'll want your stable center of mass slightly in front of or slightly behind your center of rotation (which looks like it's the exact center of your bot). If it's a low-profile bot, center of gravity doesn't look like it's of too much concern; just put your flag-holding device slightly left of center.

[kDude]

What about if the robot had 4 omni wheels, one on each corner, and the two power wheels on the middle of either side. That would give us a much tighter turning radius.

[AdamHeard]

Originally Posted by Otaku

Really good pushing force won't be a deciding factor this year, I predict.



Not particularly. Extra tensioners, more chain and maybe a few more sprockets. Double sprockets on one of the normal wheels, one to drive, one to the omni's. I wouldn't suggest it, though.

more pushing force = better robot driving performance....not necessarily just pushing other robots.

[Justin M.]

Originally Posted by AdamHeard

more pushing force = better robot driving performance....not necessarily just pushing other robots.

Yeah more torque means more pickup, you'll be able to get to top speed much quicker.

[IbleedPink233]

Originally Posted by kDude

What about if the robot had 4 omni wheels, one on each corner, and the two power wheels on the middle of either side. That would give us a much tighter turning radius.

It sure would give you a tighter turn radius, allowing you to spin in place about the center of your robot, ie tank drive. If you did this, then putting the weight in the center of the robot would probaby be your best bet. That way, you won't have weight on the outside to swing around and slow you down (at least, that's what basic physics would say, I don't know about the real world) and you would have more weight on the traction wheels, where it does the most good.
Somehow I don't think that placing weight on the left side would help you make fast left turns in this wheel configuration (if so, then it could slow you down if you need to go around the Track in reverse), but I could be wrong.

[MrForbes]

If you look at the relationship of CG relative to where the wheels contact the floor, and then you look at the forces acting on the robot going around a turn at speed, you might find that locating the CG over towards one side will indeed affect the speed at which you can make a corner bofore the robot falls over. Although if your CG is low enough, then you will loose traction long before this becomes an issue!

24" sounds way way too tall for a robot with no ball handling stuff, I'd shoot for 8" or less overall height, not counting flag holder.