Bridges and Mecanum Wheels

[burnzkid]

Originally Posted by Ninja_Bait

I'm more concerned with the key. That's an HDPE surface, and it's raised an 1/8", which is enough to turn mecanum bots into spin-my-noisy-wheels bots.

If this were reddit you would have all of my upvotes. Now, think though: I have no experience with Mecanum wheels, but would it be possible to tool-dip each individual little wheel or cover it in some kind of sticky rubber material to allow it for more grip, or would this hinder the side-to-side movement the Mecanums have?

[Ether]

Originally Posted by burnzkid

would it be possible to tool-dip each individual little wheel or cover it in some kind of sticky rubber material to allow it for more grip, or would this hinder the side-to-side movement the Mecanums have?

1) it would not hinder the mecanum's motion. the rolling motion of the rollers is what makes mecanums work, not sliding of the contact patch

2) even with better grip, there's still a problem. for a mec to work properly, all four wheels must be on the ground. once you lift wheel(s) off the ground, it can do weird things.

[burnzkid]

Originally Posted by Ether

1) it would not hinder the mecanum's motion. the rolling motion of the rollers is what makes mecanums work, not sliding of the contact patch

2) even with better grip, there's still a problem. for a mec to work properly, all four wheels must be on the ground. once you lift wheel(s) off the ground, it can do weird things.

Okay, so what you're saying is the second one wheel gets up on that 1/8" platform, one of the others will lose contact and the bot is gonna end up doing the Michigan Rag.

[jsmyth]

My question is, since rubber on poly will create much more friction then the bumps in break away, will this cause the wheels to stall up or slow down.

[Ether]

Originally Posted by jsmyth

My question is, since rubber on poly will create much more friction then the bumps in break away, will this cause the wheels to stall up or slow down.

Could you re-phrase the question please? I can't figure out what you are asking.

[jsmyth]

the bridge is made out of polycarbonate, the rubber on the mecanum wheels will most likely cause more friction on this surface. sense these wheels rely on a lack of some friction for forward movment, will this increase in friction cause your robots from moving across the bridge or possibly slow you down.

[Ether]

Originally Posted by jsmyth

sense these wheels rely on a lack of some friction for forward movment

This is a common misunderstanding. They do not rely on a lack of friction. See Post #12 earlier in this thread.

For more detailed explanation, there's lots of info here.

[zaphodp.jensen]

So can an experienced team with mecanum wheels on a bot test drive a bot over a mock up bridge with Polycarb, and on the HDPE key, and post the results?

[Djur]

Team 2084 just tested out 120-lb robot from last year on a full-scale, functional bridge a mentor made for us. We could barely crabwalk (move laterally) up it, but the robot is really imbalanced, so that's not as large of an issue. The bridge was also surfaced with fiberboard, which at after a rough test we determined to have about 1/3 the CoF as HPDE like Lexan.

We'll also be getting a 48"x88" HDPE board soon, so we'll resurface the ramp and run the test again, but I can conclude that mecaums won't have too much trouble on the bridge.

[maxwellt]

my team tested if mechcanum wheels could drive on the ramps which is made from white board material and all the wheels did was slide off of the white board so which means Mechcanum wheels will have no traction what so ever on the ramps, so they are not the way to go for the ramps

[372 lives on]

Originally Posted by Djur

Team 2084 just tested out 120-lb robot from last year on a full-scale, functional bridge a mentor made for us. We could barely crabwalk (move laterally) up it, but the robot is really imbalanced, so that's not as large of an issue. The bridge was also surfaced with fiberboard, which at after a rough test we determined to have about 1/3 the CoF as HPDE like Lexan.

We'll also be getting a 48"x88" HDPE board soon, so we'll resurface the ramp and run the test again, but I can conclude that mecaums won't have too much trouble on the bridge.

Originally Posted by maxwellt

my team tested if mechcanum wheels could drive on the ramps which is made from white board material and all the wheels did was slide off of the white board so which means Mechcanum wheels will have no traction what so ever on the ramps, so they are not the way to go for the ramps

could you two or other teams possible post a video so we can see. we do not have the resources to build a ramp quickly and need to see what it looks like.

[Djur]

Originally Posted by 372 lives on

could you two or other teams possible post a video so we can see. we do not have the resources to build a ramp quickly and need to see what it looks like.

Delivered.

The material is a fiberboard with ~3x less friction than HDPE. To be more accurate, we're getting a piece of Lexan to replace the fiberboard and test mecanums that way.

[ThirteenOfTwo]

We tested our old mecanum drive on the bridge after covering it with 2009's Regolith material (which, based on cursory testing, is slightly slipperier than the Lexan that will actually be on top of the bridge). The mecanum wheels move across it perfectly well, even from a standing start, although balancing with two mecanum robots was a little tricky and took about fifteen scary seconds.

I'm not terribly worried about the HDPE; people condemned mecanums over the bump in the field last year and that didn't mean anything. We'll try running some tests, but I'm fully confident that suspensions are not necessary to handle HDPE.

[Stimpy1901]

Our main mentor prototyped a mecanum base over the summer, so we were seriously thinking about using them this year. Due to all the concern, we obviously needed test them on the bridge with the polycarbonate.

Here is a video of three runs (and not a real driver controlling robot--just some old guy). You now have some evidence to ponder!

[zaphodp.jensen]

From what I can tell from your video (Thanks by the way!), you seemed to have enough traction on the polycarb to climb, but what about being pushed? If you were to have a pushing contest on the bridge, would you slide? I am worried about the traction if when balancing, and we get pushed a little too far, and fall off the other side...

As a sidenote, your motors were direct drive nanoboxes? And those were backdriving as you slide down the ramp?