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-   -   Gear Sliding down Ramp (http://www.chiefdelphi.com/forums/showthread.php?t=154125)

rlance 23-01-2017 11:04

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.

Ginger Bread 23-01-2017 11:14

Re: Gear Sliding down Ramp
 
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.

anthonyttu 23-01-2017 11:18

Re: Gear Sliding down Ramp
 
lexan is a name brand of polycarbonate

EmileH 23-01-2017 11:19

Re: Gear Sliding down Ramp
 
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.

rlance 23-01-2017 11:23

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by EmileH (Post 1635089)
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.

Yes, I realized we were not using the exact material, but the chart you referenced is showing a bigger difference in co-efficient of friction than what I was finding last night. We will obtain some HDPE and see what happens.

Billfred 23-01-2017 11:26

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by rlance (Post 1635090)
Yes, I realized we were not using the exact material, but the chart you referenced is showing a bigger difference in co-efficient of friction than what I was finding last night. We will obtain some HDPE and see what happens.

It may be easier/cheaper/faster to get some FRP (the white pebbly stuff you see in public bathrooms) from your local home improvement store. That's what's specced for the team versions of the field, and things slide very well down the one we have here at AndyMark.

Jon Stratis 23-01-2017 11:29

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Billfred (Post 1635093)
It may be easier/cheaper/faster to get some FRP (the white pebbly stuff you see in public bathrooms) from your local home improvement store. That's what's specced for the team versions of the field, and things slide very well down the one we have here at AndyMark.

Man, the one time I wish we still had some Regolith sitting around... :D

rlance 23-01-2017 11:38

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Billfred (Post 1635093)
It may be easier/cheaper/faster to get some FRP (the white pebbly stuff you see in public bathrooms) from your local home improvement store. That's what's specced for the team versions of the field, and things slide very well down the one we have here at AndyMark.

That is great to hear. I'll run and get FRP. Thanks.

rlance 23-01-2017 11:55

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Billfred (Post 1635093)
It may be easier/cheaper/faster to get some FRP (the white pebbly stuff you see in public bathrooms) from your local home improvement store. That's what's specced for the team versions of the field, and things slide very well down the one we have here at AndyMark.

The team version also has the angle 1.7 degrees steeper, which I assume is to account for the difference in co-efficient of friction between the HDPE and FRP.

dradel 23-01-2017 12:36

Re: Gear Sliding down Ramp
 
I have found the surface of a white board offers little friction. We tried the polycarbonate route and found it less slippery than plywood.

nuclearnerd 23-01-2017 13:46

Re: Gear Sliding down Ramp
 
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.

Robosparks2926 23-01-2017 13:56

Re: Gear Sliding down Ramp
 
Is there reflective tape on the peg/ platform for the gear placement?

cpapplefamily 23-01-2017 14:04

Re: Gear Sliding down Ramp
 
We had observed the same non-slide of the gear. A little spray of some dry lube and no stick.

Drivencrazy 23-01-2017 14:07

Re: Gear Sliding down Ramp
 
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.

mwmac 23-01-2017 14:08

Re: Gear Sliding down Ramp
 
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.

GeeTwo 23-01-2017 14:11

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Robosparks2926 (Post 1635161)
Is there reflective tape on the peg/ platform for the gear placement?

Yes, section 3.13 of the rules, details in figure 3-36.

rlance 23-01-2017 14:16

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Robosparks2926 (Post 1635161)
Is there reflective tape on the peg/ platform for the gear placement?

It is in the rules under Arena 3.13

s-neff 23-01-2017 14:18

Re: Gear Sliding down Ramp
 
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)

juju_beans 23-01-2017 14:51

Re: Gear Sliding down Ramp
 
We used some fiberglass and it worked pretty well but you have to be careful when cutting it.

Ronny Mohtar 23-01-2017 15:39

Re: Gear Sliding down Ramp
 
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.

SenorZ 23-01-2017 15:43

Re: Gear Sliding down Ramp
 
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 :]

Tanya & André 24-01-2017 15:25

Re: Gear Sliding down Ramp
 
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.

JesseK 24-01-2017 16:17

Re: Gear Sliding down Ramp
 
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.

Bruceb 24-01-2017 20:10

Re: Gear Sliding down Ramp
 
I just used b/c plywood with one coat of water based polyurethane then I sanded and put furniture wax on it. Works great

Fusion_Clint 24-01-2017 23:29

Re: Gear Sliding down Ramp
 
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.

cj3958 24-01-2017 23:48

Re: Gear Sliding down Ramp
 
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.

Donut 25-01-2017 00:18

Re: Gear Sliding down Ramp
 
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.

Bob Steele 25-01-2017 00:32

Re: Gear Sliding down Ramp
 
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?

Billfred 25-01-2017 09:12

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Bob Steele (Post 1635992)
STARBOARD....
hmm I wonder if they also have PORT?

That's for after ship day.

(I'm sorry I don't normally go off topic like this but I had to)

Pandaboy1293 25-01-2017 11:30

Re: Gear Sliding down Ramp
 
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.

jvriezen 25-01-2017 12:20

Re: Gear Sliding down Ramp
 
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.

Bob Steele 25-01-2017 15:14

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Pandaboy1293 (Post 1636124)
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.

Take a piece of FRP put a gear on it... lift it up on one end and record the angle at which the gear begins to slide. The tangent of that angle is the STATIC friction coefficient. That can be compared to other static coefficients. The static coefficient of friction is always greater than the kinetic coefficient of friction. Remember that these coefficients are based on two materials....so there is no "Coefficient of Friction" for FRP.... it would have to be FRP and carpet, or FRP and wood or something...

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.

GeeTwo 25-01-2017 16:54

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by Bob Steele (Post 1636210)
If anyone actually does this for both FRP and the orange peel HDPE I would be interested in seeing what that number is.

Not those numbers, but we did measure the CoF of a gear with an actual FRC (2015) carpet yesterday (laying flat) using the well-known ramp method, finding it to be 0.43*. Static and dynamic were indistinguishable; once the gear started it moved at a slow steady rate down the ramp. As the gear weighs 18.4 oz per the game manual, expect to have a frictional force of about 8 oz.

* 39" long piece of plywood backing, hand raised, tape measure measurements, so you might want to put around a +/- 0.02 on it.

MikLast 25-01-2017 16:58

Re: Gear Sliding down Ramp
 
We have some HDPE for our feeder station, took some video of the gear going down if anyone is interested in that. I apologize now for it being in a bad orientation, didn't pay attention at all when i recorded.

Unpushed
Pushed

Siri 25-01-2017 21:01

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by MikLast (Post 1636254)
We have some HDPE for our feeder station, took some video of the gear going down if anyone is interested in that. I apologize now for it being in a bad orientation, didn't pay attention at all when i recorded.

Unpushed
Pushed

Running these side-by-side, my perception is that your unupushed video is slower than field tour. Is that just because of the video angles (the field tour going out of frame soon)? I haven't tried to break it down frame by frame.

SenorZ 25-01-2017 21:04

Re: Gear Sliding down Ramp
 
Field tour vids make the surface look matte. This looks shiny?

Did you have "orange peel" HDPE?

XtremeFate 25-01-2017 21:10

Re: Gear Sliding down Ramp
 
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.

MikLast 25-01-2017 22:35

Re: Gear Sliding down Ramp
 
Quote:

Originally Posted by SenorZ (Post 1636363)
Field tour vids make the surface look matte. This looks shiny?

Did you have "orange peel" HDPE?

Dont know off the top of my head. Ill ask someone who knows tomorrow.
Natural HDPE.


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