Does anyone have an estimate on how slippery the alliance platform will be? I couldn’t find the specific material used for the platform other than that it is HDPE, which comes in many forms.
I am looking for either a comparison to another material with a similar coefficient of static friction or the coefficient of static friction for this specific material if you know it.
Thanks!
HDPE is 0.29
ABS is 0.5
Polycarbonate is 0.31
UHMW polyethylene is roughly 0.1-0.2
PET is 0.2-0.4
Polypropylene can be 0.1-0.3
Why do I know these things? I have no idea.
If anything like previous years - this material will be textured HDPE, which has a significant effect on coefficient of friction vs smooth.
841 got burned by this last year - I sourced smooth HDPE for our practice gear feeder chutes and the competition ramps were significantly faster.
The textured stuff is usually referred to as “Orange Peel”. I haven’t found that phrase in the specifications yet, but it could be under a different name.
I felt it at the NH kickoff, where they have the full field built. It is textured.
The specs say “matte finish” HDPE.
https://www.amazon.com/Seaboard-Density-Polyethylene-Finish-Length/dp/B00JPHTPCI
Did you happen to notice if it had any “stick”? was there any way that a robot with a mecanum or omni drive could get a good hold on it?
Coefficient of friction is not a physical property of any one material.
Having felt the field in NH, it is very similar to the textured bathroom stall plastic, I took a few close up pictures I will post tomorrow.
*Note to self, next year bring some sort of friction measuring device or some sample wheels to try on the field surfaces…
I wouldn’t describe it as sticky. The best way I can describe it was a smooth material made to feel rough because of the surface texture.
I don’t have a lot of experience with mecanum wheels or omniwheels so I can’t give you an educated guess on how they would perform on this material, sorry.
The cross-section image that Wikipedia uses to describe “Matte finish” appears to be a reasonable depiction of a cross section of the platform:
Here is an up close image of the texture https://www.chiefdelphi.com/media/img/f68/f6880a1041a0354993e460e0274bb5fa_l.jpg](https://www.chiefdelphi.com/media/photos/45677)
This looks like the stuff used for the platforms in 2015. I remember meccanum teams having little to no difficulty driving on it, if that’s what you’re trying to work out.
I was thinking this too…
The coefficient of static friction is dependent on the two materials interacting. And before someone tries to be clever and think it can be relative (i.e. two materials on HDPE will act similarly) you’re wrong. Weird stuff can sometimes happen between different materials. Basically, saying “well HDPE is slippery” isn’t EXACTLY a truthful statement since there could exist some material that has a very high coefficient of static friction with it due to some weird effects.
We used 8" Mecanums from AndyMark (the old style ones http://www.andymark.com/Mecanum-p/am-0083.htm ) in 2015 and had absolutely no traction issues on the scoring platforms. The slope on the ramps to those platforms I think is similar to this year, though IIRC they were a bit shorter .
BTW: We used 8" Mecanums due to already having them in stock – not because we felt we needed them for the game/field.
Good luck
Mike
I was just browsing through Inventables product line and noticed that they sell HDPE under their materials category, and it’s labeled as textured. The picture appears to indeed have some form of texture similar to the field on it. Considering we have a $100 voucher from them (included in the KOP), this might be a good thing to use it for.
I have not felt this years material yet, but I spent a ton of time in 2015 down on hands and knees feeling and retaping seams of what looks like the same material including the textured surface, the only difference I can see is the colors (blue and red instead of white from the pics I have seen, and the fact that it appears from the pics at least that they did away with the tape on upper seams, which was a hassle due to robots dragging at ramp tops and either stripping off or bunching up the seam tape creating a mess we just could not keep up with).
While it is fairly slick, the texture helps a bunch, and it does get scarred up a bit with use, our robot and many others were mecanum wheeled, very few had any issues with them either climbing or crossing, or traversing them. Those I saw that did were smaller wheeled, low less clearanced other wheeled longer type bots, that usually hung up on bunched up tape. We spent a ton of time cutting those areas out between matches and retaping the affected areas.
** This is not a rec. In any way to use mecanum wheels this or any other year, as I have seen the inate bias posted elsewhere here on CD that I do believe transfers to actual competition reality. Only, that if it is the same material this year as 2015, and if the ramps have a similar angle, mecanum worked just fine on those ramps and platforms.
Only you can choose what is best for you. I’m just adding the experience of seeing is believing.
