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View Full Version : Bridges and Mecanum Wheels

Red_Storm_509
07-01-2012, 17:02
I wasn't able to get a good look at the material of the bridges at the kickoff, does anybody know if mecanum wheels would have enough traction to get up the bridge?
JaredSanMiguel
07-01-2012, 17:05
The surface at competition will be HDPE (High-density polyethylene)

I'm not sure how much grip that will provide but I think mecanums will be able to get up and over.
USSMISSOURI
07-01-2012, 17:07
I do not think that those wheels will work on the bridge very well, i would recommend either the KOP wheels or bigger versions of them.
Donut
07-01-2012, 17:29
As mentioned it is HDPE, as many ramps and platforms have been in the past.

Nice video with closeups of the bridges on the FRC youtube page:
http://www.youtube.com/watch?v=-AMaqqmoLgQ&list=UUHA7zyPRS3VPDvl4ehss-zw&index=3&feature=plcp

Answered an important question for me, balls can't get stuck underneath and the bridges return to center with nothing on them.
lcoreyl
07-01-2012, 17:32
There were teams that used mecanum with no problem on the bumps in 2010 breakaway.

The only difference in traction for mecanum is they will reach their max (friction force) before a regular wheel of the same material. This would be a consideration for pushing contests, but not climbing the bridges.
Ninja_Bait
07-01-2012, 21:12
The bumps in Breakaway were carpeted, so it was easier for the mecanum wheels to grip.

The bridge is surfaced in polycarbonate, if it makes any difference.

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.
CrashTestPilot
07-01-2012, 21:54
Nice video with closeups of the bridges on the FRC youtube page:
http://www.youtube.com/watch?v=-AMaqqmoLgQ&list=UUHA7zyPRS3VPDvl4ehss-zw&index=3&feature=plcp

Answered an important question for me, balls can't get stuck underneath and the bridges return to center with nothing on them.

Thanks for pointing this out. There is a lot of other usefull information related to this years game if you watch all other episodes. Was this shown during todays kick off? Somehow I missed this.
jason701802
07-01-2012, 22:01
I don't expect many high functioning mecanums this year without a quality suspension.
EricDrost
07-01-2012, 22:07
I don't expect many high functioning mecanums this year without a quality suspension.

I don't expect many high functioning mechanums any year :P
Mr_I
07-01-2012, 22:12
There is a lot of other usefull information related to this years game if you watch all other episodes. Was this shown during todays kick off? Somehow I missed this.

These were not shown during KickOff. It would have been very helpful if they were. (Suggestion for next year?)
burnzkid
07-01-2012, 22:34
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
07-01-2012, 22:41
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
07-01-2012, 22:54
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
09-01-2012, 20:12
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
09-01-2012, 20:18
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
09-01-2012, 20:22
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
09-01-2012, 20:25
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 (http://www.chiefdelphi.com/media/papers/2390).
zaphodp.jensen
10-01-2012, 18:14
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
10-01-2012, 20:26
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
10-01-2012, 22:31
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

::rtm::
372 lives on
10-01-2012, 23:43
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.

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

::rtm::

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
11-01-2012, 00:15
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 (http://www.youtube.com/watch?v=tHQuOS7yu6U).

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
11-01-2012, 00:45
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
11-01-2012, 02:49
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 (http://youtu.be/XaKFklyzQ9w) of three runs (and not a real driver controlling robot--just some old guy). You now have some evidence to ponder!
zaphodp.jensen
11-01-2012, 08:43
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?