These are the wheels which you’ll be seeing on 258’s bot, if you’re at SVR.
Only three of the four wheels are actually visible in the picture. The other went out for a smoke, or something.
<Troy McClure>
Hi! I’m the tread! You might remember me from such other robots as 2002’s 254’s and 60’s robots!
</Troy McClure>
Can anyone specifically tell me whether or not the use of those 8-32 screws is legal? Bill’s been trying to convince me that our use of them is legal, but I’m still rather hesitant. We might have to switch them out for Nylon screws, or some such. Oh well.
I don’t recall where it states this exactly, but I believe in the rules it states that you are not allowed to have any metal at all touching the carpet. In previous years, the carpet has been ripped up pretty bad by various forms of wheels and metalic devices, so to avoid that, no metal is allowed to touch the carpet. Try epoxy for the wheels.
Did you guys measure a coefficient of friction for the “Team60Tread” (as we call it) on the carpet/HDPE/Wire?
We measured 1.2ish for both the carpet, and the wire. But I’m curious what other teams got.
I’m fairly certain use of screws in that manner is illegal. We ended up attaching our treads with liberal usage of Epoxy. I’m not sure though. FIRST has been very, confusing, in their answering of such questions. I believe the use you have is illegal in the wording of the rule, but legal if you obey the spirit of the rule.
Last year, we used both screws and epoxy to attach tread to our wheels, so we might have to do that again.
I’ll talk to Bill about the legality of the screw usage.
Thanks John! They ain’t as snazzy as some other teams’ wheels, but I think they’re nice.
We performed some rudimentary coefficient of friction testing on the HDPE (which we thought would be the most important surface to be able to grip to [take a wild guess at what we’re planning to do]) with the 254/60 tread and with two different variants of the tread we used last season (I can’t find a picture that really does it justice, but it was used by 192 in either 2001 or 2002 [faulty memory]). I can’t remember any of the values we got for the coefficient of friction for them, but I seem to recall they were about the same (keep in mind the fact that they were rudimentary tests).
We figure that if we ever get in a pushing match on the wire mesh, we’d definetly have to replace the tread on the wheels, if we use the tread we used last year (see this image’s description). However, we are going to have at least a few backup treads on hand, just in case this stuff gets torn up (see ChrisH’s post in this thread).
ajlapp: I’ll definetly have to talk to Bill about this, after seeing his post in the thread you linked…
Joe: Good points. I’ll be sure to perform some tests (press down on the wheel as hard as I can, and see if the screws touch the HDPE / carpet [which I’m sure they will, depending on how the belting walls bend]).
PyroPhin: I’m not quite sure what it’s made of (besides rubber and fabric), but according to a previosly linked thread, it’s made by Brecoflex, though I can’t find any online catalogs, on a cursory inspection.
And you can just buy some liquid rubber insulation stuff (I call it goop, you should be able to get some at an auto parts store) and just cover the screws with it, that should solve your problems I think.
*Originally posted by Johca_Gaorl * How did you make the wheels?
We have a girl on our team who is a senior, and her father is a senior ME at Northrop Grumman. Over the years her father has bought a CNC mill, a few manual mills, a lathe, etc. So they’ve got a machine shop in their 3 or 4 car garage. So Audrey used the CNC mill to carve the wheels out of 7" by 7" aluminum stock, then she and her father put the wheels on a lathe and made sure that the edges were round. Then they took out the necessary material to make an 1/8" indentation for the tread material to sit in, and drilled the sxle hole so it was concentric with the tread groove. Anything else you want to know?
<edit>
After all that was done, some other kids on the team (including Jim) drilled and tapped holes for 6-32 screws to attatch the treading.
</edit>
<edit #2>
At least I thought they were 6-32’s. Maybe I’m wrong.
</edit #2>
As far as I see it, those screw heads will contact the carpet and should be deemed illegal. Of course, sometimes FIRST has been very lax during inspections in the past… but I wouldn’t count on it this year.
Wheels look very similar to ours, but we wrapped tread around the side of the wheel and bolted in from the side in order to comply with the “no metal on carpet” rule.
*Originally posted by Mark Pettit *
**How’d you cut the belt? That stuff is pretty thick and rigid and doesn’t seem to cut very easily. **
Lots of time and persistence.
We bought a curve-bladed carpenter’s knife for this purpose alone, and Joe, who has cut the four current pieces of tread, has expressed at least a little malcontentedness at having to cut them, but apparently the smaller cuts are the hardest (the tapered angle cuts, and the ~1cm sideways cuts).
Mr. Van: Very interesting way of attaching the tread. As I said earlier, I’ll look into the legality of the whole thing later (Just about to leave the house to go to today’s robotics meeting).
Bill: I’m fairly certain that they were, in fact, 6-32 screws. Oh well, I’ll check, and edit the picture information accordingly, later.
