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Gear Sliding down Ramp
I built a player station this past weekend and was trying to get the gear to slide down on its own. I realize I was using polycarbonate and not HDPE like is actually used, but I could not get the gear close to sliding on its own. I wouldn't think the HDPE is that much slicker than the polycarbonate and the specs I found appear to show that HDPE is a little slicker, but not much. Has anyone else run into this problem with their player station?
The angle in the rules says it is 72 degrees from vertical, which is what I am pretty sure I am using. |
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My team made this out of wood and the gear has a great deal of friction even when we put lexan on top of the wood to simulate the field.
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lexan is a name brand of polycarbonate
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Polycarbonate and HDPE are NOT the same. HDPE has a coefficient of friction of 0.28 according to this chart, whereas standard polycarbonate (lexan) has a CoF of 0.38.
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I have found the surface of a white board offers little friction. We tried the polycarbonate route and found it less slippery than plywood.
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We have HDPE sheets on our wooden chutes. It's not the same texture as the field versions (they use something called "orange peel", which is not commonly available here), but the gears still slide much better than on wood alone. That said, the "static" friction is still high enough that the gears will stick to the chute until you give them a (very) little push. I wonder if the real field has the same behaviour.
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Is there reflective tape on the peg/ platform for the gear placement?
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We had observed the same non-slide of the gear. A little spray of some dry lube and no stick.
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We had some orange peel HDPE from the scoring platforms in RR. Significantly faster slide than the plywood and polycarb. If your designs are sensitive to the exit trajectory of the gear, I'd get some.
Have not compared to FRP. |
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This product worked well for us in 2015 to serve as the feed chute surface for totes.
https://www.woodcraft.com/products/slick-strips-3-width This year, given the width of the loading station and the size of the gear, it made more sense to us to use the frp alternative. |
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Sorry, but those actually are completely different plastics for the application.
The coefficients "look similar", but going from 0.28 to 0.38 [as quoted earlier in thread] is a 30% increase in friction! Textured FRP or textured ABS are both much better choices than smooth polycarb, if you can't get HDPE in either smooth or "orange peel". Consider bringing the gear to the store to test your substitute-of-choice before buying? (Our smooth HDPE works great, I haven't tested our textured ABS) |
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We used some fiberglass and it worked pretty well but you have to be careful when cutting it.
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Code Orange cut off a piece of FRP that they used so we (SMbly Required) didn't have to order it. We both used it for the ramp and it works very well.
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Practice with something as close to the real thing as possible. If your robot is relying on the gear slowly plopping out of the chute because you designed around a wooden chute you'll be really upset at comp... unless you do floor pickup. Then whatever :]
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Upon searching some reference material, we found that Formica has a similar coefficient of friction to HDPE. If someone on the team has recently renovated an old kitchen, perhaps you can find a piece large enough. We find it works well for us - no problem with sliding.
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In a similar-to-but-not-exactly-related vein:
Adding a bit of duct tape to the bottom of a gear and then sliding it across the school's tiled (linoleum?) floor was approximately the same friction as a plain gear sliding across carpet. Just keep adding tape until they 'feel' the same. |
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I just used b/c plywood with one coat of water based polyurethane then I sanded and put furniture wax on it. Works great
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Or just spend $13.25 plus shipping and get HDPE to line your chute.
https://www.mcmaster.com/#8619k426/=1625apw This is working great for us. |
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Imho everyone should just acquire some HDPE from Mcmaster. Its not that expensive(~20$ for a 2'x3' sheet) and it allows you to get a very similar experience you will get on the real field. If you find something at your local shop that has lower friction than the HDPE it is equally as bad as using plywood or polycarb. At the end of the day you want something that acts like the real field will act.
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Grainger also has HDPE for slightly less and no shipping cost if you can pick it up at a local branch:
https://m.grainger.com/mobile/produc...searchBar=true Once we found out our school district had an account with Grainger for the facilities group we have started leveraging it, better vendor for plastics on both cost and shipping if you usually rely on McMaster. |
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We found that a material that is called "Starboard" which is used in marine applications among others is actually HDPE with the orange peel surface. We found it at TAP plastics.... it is SIGNIFICANTLY easier to slide the gears....on our practice version.... the gears actually slid all the way down without any push on the part of the human participant.
Regular HDPE is significantly different in that it has a noticeably higher coefficient of friction. We are covering our retrieval stations with it... 1/4" pieces cost about $35 or so. (We picked it up at the store) All told for 4 pieces it cost us $160 or so.... that was 4 pieces... STARBOARD.... hmm I wonder if they also have PORT? |
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(I'm sorry I don't normally go off topic like this but I had to) |
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Does anybody know what the CoF of FRP? My team is using and I'm concerned that it might not work for what we need it to.
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I have no idea how it compares to the real thing, but we put on a layer of 1/8" hardboard, smooth side up, and it slides pretty well on that.
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good luck!! If anyone actually does this for both FRP and the orange peel HDPE I would be interested in seeing what that number is. |
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* 39" long piece of plywood backing, hand raised, tape measure measurements, so you might want to put around a +/- 0.02 on it. |
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Field tour vids make the surface look matte. This looks shiny?
Did you have "orange peel" HDPE? |
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We just took some fine sandpaper to our polycarbonate and it slides very well. Seems that the glossy surface was sticking to the gear somehow.
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Natural HDPE. |
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