Team 1296 Mecanum Bump Test

[bcharbonneau]

We tested our mecanum wheels over a 4 X 4 to see how they worked. So far it looks good. Let us know what you think. http://youtu.be/jl8pHpCjQtY

[JamesCH95]

Originally Posted by bcharbonneau

We tested our mecanum wheels over a 4 X 4 to see how they worked. So far it looks good. Let us know what you think. http://youtu.be/jl8pHpCjQtY

A few things you'll want to change:

-ballast the robot to full weight
-a 'real' barrier overall dimensions at 4"x6"
-metallic bump material with radiused corners (I think this will really impact the wheels' traction)

Otherwise it looks good, plenty of ground clearance!

[wireties]

Originally Posted by JamesCH95

A few things you'll want to change:

-ballast the robot to full weight
-a 'real' barrier overall dimensions at 4"x6"
-metallic bump material with radiused corners (I think this will really impact the wheels' traction)

Otherwise it looks good, plenty of ground clearance!

Thanks for the input. We are thinking the extra weight will help but are worried about the "real" radiused metal bump. The bump being an extra 2" wide should not be a problem though as the opening in the middle of the robot is 21". The bot will have a nice ramp lowering device but we wanted to make sure it goes over the bump just in case.

We had quit a few folks say that it would not go over and some who thought it too dangerous (including me) but those super-duty mecanums from AM are really tough and the angled front edge helps - so much for the common "mecanums can't go over the bump" theory!

[JohnSchneider]

Im interested to see it with all the extra weight, because its going to change the force vectors on the angled wheel mounts.

[wireties]

Originally Posted by animenerdjohn

Im interested to see it with all the extra weight, because its going to change the force vectors on the angled wheel mounts.

True, but it will increase traction <fingers crossed>!

[Ben27Lacrosse]

Originally Posted by animenerdjohn

Im interested to see it with all the extra weight, because its going to change the force vectors on the angled wheel mounts.

I'm looking forward to more weight too, should make it easier more traction!

[JamesCH95]

Polymers as traction surfaces generally lose traction efficiency as normal force is increased. Search CD or any tire test data if you don't believe me. I would anticipate some specific traction (tractive force per unit weight) loss as you add on weight. You will have more total tractive force, but relatively more mass to move.

[pfreivald]

I'd be worried about repeatedly ramming my mecanum wheels into the bump... The AM HD's are quite nice, but they're not indestructible!

[wireties]

Originally Posted by pfreivald

I'd be worried about repeatedly ramming my mecanum wheels into the bump... The AM HD's are quite nice, but they're not indestructible!

The angled surface on the wheel assembly hits the bump first - it helps a little. And we don't plan to make a living going back and forth, just did not want to NOT be able to.

[wireties]

Originally Posted by JamesCH95

Polymers as traction surfaces generally lose traction efficiency as normal force is increased. Search CD or any tire test data if you don't believe me. I would anticipate some specific traction (tractive force per unit weight) loss as you add on weight. You will have more total tractive force, but relatively more mass to move.

Why would we not believe you?

Depends on the nature of BOTH surfaces of course but I'm sure you are basically correct and we have looked at the data. If we double the mass I expect a 25% reduction in the friction coefficient for urethane rubber. So I'm thinking the effect is (at worst) linear for the small increase in weight (and probably not that bad) and the bot will push its way over the bump at full weight - we'll see soon.

[pfreivald]

Originally Posted by wireties

The angled surface on the wheel assembly hits the bump first - it helps a little. And we don't plan to make a living going back and forth, just did not want to NOT be able to.

Right on -- I couldn't see that on the video!

[JohnSchneider]

Get to it Keith!

[mdiradoorian]

What I am worried about is that the wheels with lose its strength after hitting the steel bump a million times. Also you got over a wooden bump do you think there might be a difference between the steel and the wooden because they are two completely different materials?

[wireties]

Originally Posted by mdiradoorian

What I am worried about is that the wheels with lose its strength after hitting the steel bump a million times. Also you got over a wooden bump do you think there might be a difference between the steel and the wooden because they are two completely different materials?

We are thinking the wheels will hold up but the metal bump is worrisome.

[Kyler Hagler]

Man that robot looks sexy!!