Fuel leaves behind a thin film

Technical Technical Discussion
1

I have noticed that the fuel leaves a film on anything that it slides against, and each piece of fuel adds to that layer until eventually there is a pale yellow plastic film covering everything!

This film seems to reduce the effectiveness of shooter wheels by reducing their coefficient of fiction, and reduces the grip of rollers and polyurethane belts.

Our plan is to simply scrape it off after every match with fingernails and non-metal tools. stretching the polyurethane belts a bit by hand also seems to loosen up the film.

What are your thoughts on this Polyethylene film menace?
How do you plan to remove it?
How long before the fuel loses so much mass that it shoots differently?
Have you found any wheels that naturally shed this film?

2

It looks like the challenge was even more challenging than we anticipated.

How do you plan to remove it?

We are not doing fuel, so we won’t worry about it.

How long before the fuel loses so much mass that it shoots differently?

I think that is the least of the worries for teams that are playing with fuel.

Have you found any wheels that naturally shed this film?

No. But haven’t looked, either.

3

Wheels that shed the film will be the same wheels that have an even lower coefficient of friction, particularly fluoropolymers, such as FEP, PTFE, and Viton. Silicone may work though.

4

Our team was suggesting that we spool up our flywheel shooter, and touch some high grit sandpaper to it for a few revolutions.

5

We are going to be doing a bit of experimentation on techniques to remove the film but honestly we are probably just going to be buying a ton of wheels and replacing them up to a few times an event.

6

Yep, chances are the fuel is going to be cracked and/ or broken before the weight becomes a serious issue. The residue is a menace, but each individual ball is leaving behind very, very little.

7

Embrace the residue. Let the residue become part of your shooter wheels. Then you never have to worry about cleaning it off :wink:

8

That would be okay if it weren’t polyethylene.

9

I disagree our robot has shown significant decreases in ball speed when the residue builds up. After shooting about 150 to 200 balls our grey flywheel is a nice high visibility yellow color!!!:ahh: :ahh:

10

I saw the same thing with the FTC particles while mentoring last year. It looks like it shouldn’t cause much of an issue if your shooter wheels are moderately compliant, and in contact with the fuel for several inches of travel.

My best guess is that it happens with the initial acceleration, where the fuel is grabbed after about 2 rotations, and it’s not causing an issue after it is at speed.

If you plan to be shooting a lot, either plan around it or be prepared to remove it after each match. In FTC, I found that it’s easy enough to grab with your hands.

11

Sounds like you might want to make your shooter so it works well after you shoot 200 or so balls with it. That’s the point he’s trying to make…if you set up your shooter so it can just barely make the shots when the wheel is new, then you’re going to have trouble. You want to set it up so it shoots too far when the wheel is used and has turned yellow, and dial it back a little.

12

We have not seen this in any of our testing.

13

I suspect this starts cropping up when you move from gravity feeding into a shooter wheel to controlled conveyor feeding. If you don’t get the spacing right, the conveyor is still holding the fuel when it contacts the shooter wheel, and the shooter wheel slips until it gets enough grip to rip the fuel out of the conveyor. At least, that’s my experience from multiwheel frisbee shooters.

Basically, anything where physics is going to force the wheel to slip at high speed on the fuel for a prolonged time is probably going to melt some of it off.

14

Try acetone or benzene.

15

This is an issue for every single kind of shooter wheel, intake mechanism, etc. that we’ve tested. Some tips:

  1. Coarse sandpaper, with pressure and motion applied parallel to the axis of rotation (i.e. left to right) will quickly (albeit, not easily) strip off this material.

  2. Some material retains their traction qualities better than others when coated with this clear stuff. Think about the different factors that cause adhesion beyond just if the rubber is grippy or not, such as compliance. Big hint there.

  3. Get the RPM right for your wheels. The more slippage between the ball and the wheel, the worse the wear is going to be. Everyone who did Frisbees in 2013 knows this. So if you’re relying on over-driving your wheel open-loop and just taking the speed loss, you’re doing it wrong.

  4. Load the shooter as fast as your mechanism can justify. The less speed differential between your ball speed at the indexer and your ball speed at the shooter, the less material gets stuck due to lower slippage. (Of course, there may be more material on your indexer surface, but that’s less of a big deal)

  5. Pick kids for pit crew who love sanding things.

16

I will definitely be looking for this now. Though i do have our infeed running the same speed as our shooter feeder rollers, so maybe we won’t see the extended contact…

17

Is there any prolonged effect of the polyethylene buildup on the shooter wheels even after scraping it all off every match? How often are we all going to have to replace our shooter wheels?

From testing shooter prototypes in the snow, even a little bit of ice or water buildup reduces shooter speed far more significantly than I ever would have thought.

18

We have not seen this in our testing either. Our compression is fairly low so that could be part of it.

19

QFT. If you can get a student who’s excited about maintenance in your pit, the’ll make sure it gets looked after between each match.

20

This entirely depends on your kind of wheel, your shooter dimensions, your motor power, etc. and is the kind of thing every team has to figure out themselves, unfortunately.