# Teflon: Improving on Sprave's failed roller slingshots



## ShockleysWW4Slingbows (Jul 3, 2014)

SS discovery of the year!
















Joerg Sprave says that he gave up on his roller slingshots because the speed gotten from the extra leverage was largely nullified by what he thought was "friction".

Well, I asked Mechanical Engineer Franco Normani, who has this cool physics website http://www.real-world-physics-problems.com and had previously explained to me the "cushion effect" in a "W", and it turns out that it is mostly roller INERTIA, not friction that nullifies leverage.

He says that "the band, during release, turns the rollers without slipping between the two, so as the band releases, it unstretches and in doing so it turns the rollers [at] high rotation speed caus[ing] a large energy loss, which increases with the square of the rotation speed."

And so I decided to eliminate the roller inertia by using teflon tape instead, with great results.

Here's a video of me shooting it with triple Bill Herriman tubes which are very smooth and have very little friction. Even if the chrono connect in my phone is in general reading all shots too fast, notice that it measures about 20 feet per second more here than the "Big W" with flat (theraband gold) bands (see previous vid I posted).

Since small tubes are slower, this can only be explained by a successful implementation of greater leverage.






I have just ordered a prochrono and will be doing further tests with this and other of my slingshots.


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## ryguy27 (Nov 8, 2013)

Looks Interesting. How Is Band Life, And Where Do They Tear When They Do?


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## ShockleysWW4Slingbows (Jul 3, 2014)

ryguy27 said:


> Looks Interesting. How Is Band Life, And Where Do They Tear When They Do?


I just made this one this evening, I haven't used it long, but these are Bill Herriman's tubes. Tubes last longer than bands, so I think quite long. And the pouches I use are supple double shoulders leather, so that ain't breaking. If you're asking what friction with the teflon does to band life, my guess is almost nothing. The stuff has the lowest coefficient of friction of any material
http://en.wikipedia.org/wiki/Friction#Coefficient_of_friction


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## ryguy27 (Nov 8, 2013)

I do like the looks of that low friction. 
I think you're comparing apples to oranges when it comes to speed tests as you are changing multiple variables to the point where it isn't a controlled experiment.


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## ShockleysWW4Slingbows (Jul 3, 2014)

ryguy27 said:


> I do like the looks of that low friction.
> I think you're comparing apples to oranges when it comes to speed tests as you are changing multiple variables to the point where it isn't a controlled experiment.


I've ordered a prochrono with (the incredibly overpriced) indoor lighting system. I will be conducting more experiments soon.
These are the 3 other slingshots I shot with the same distances and phone placement


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## TheNewSlingshotGuy (Oct 11, 2014)

For once, I think that engineer guy of yours actually made sense! It ain't pretty, but you are on to something Mr. Shockley! I still don't like your views or general attitude, but I'm not gonna lie, it is a great idea.

Edit: Also, you could have done a better job naming this thread. Jeorg's rollers may not have worked well, but he still brought the whole concept to the table.


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## ShockleysWW4Slingbows (Jul 3, 2014)

Also, notice that I'm getting the same leverage of a starship without even using a wristbrace!


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## jazz (May 15, 2012)

Seing you wearing protective glasses realy made me happy!

cheers,

jazz


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## wll (Oct 4, 2014)

I think the use of teflon tape is a good idea.

Another material that we have used for years in the archery business for bushings is Delron. it has very low coefficient of friction and I believe can be purchased in tubes, it is great stuff.

Good luck and keep experimenting, just because it has not been done before does not mean anything, sometimes the simplest of ideas are overlooked for one that is more technical .... I know, believe me.

wll


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## Charles (Aug 26, 2010)

This concept has been around for a while.

http://slingshotforum.com/topic/37125-the-sling-thing-speed-shooter/

The sling-thing does not use rollers, but relies on low friction between the tube and the fork.

But for a much more elegant and better engineered design that uses very small rollers, have a look at Robert Blair's combo-sling.

http://www.combowslingguy.com/INDEX.html

http://slingshotforum.com/topic/9384-combo-sling-speed-shooter/

http://slingshotforum.com/topic/10292-com-bow-sling/

Cheers ..... Charles


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## The Gopher (Aug 25, 2010)

"(the incredibly overpriced)"

I find the irony in those three words almost too much to bear!

Didn't ZDP use strips of teflon tape under his flatbands? someone did anyway, nothing new.


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## Alfred E.M. (Jul 5, 2014)

*Didn't Sprave ban you from his forum? Isn't that why you're hellbent on putting him down? Your psychological needs are transparent and creepy and that is the true elephant in the room. All technological issues aside, you ooze arrogance in all of your presentations and to prohibit commenting on that does a huge dis-service to 'keep it real'. You are so unaware of how you are perceived but always insist that you're right and everyone else is wrong. To say 'personal attack' is like saying 'profiling' because one doesn't like liver and onions - it's inappropriate to the over-riding issue. *


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## VWscooby (Oct 18, 2012)

You want to see creepy? Check out dear old Johnny and his views on women in this video


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## Tentacle Toast (Jan 17, 2013)

VWscooby said:


> You want to see creepy? Check out dear old Johnny and his views on women in this video


Shockley=pol...which explains a lot...


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## shew97 (Feb 13, 2014)

Do you not have a place outside we're you can shoot?


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## ShockleysWW4Slingbows (Jul 3, 2014)

MNipples, a technical improvement is not a personal attack. Chill.


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## Bill Hays (Aug 9, 2010)

I'm thinking this idea may have merit... now to devise a fair test and check it out for myself!


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## ShockleysWW4Slingbows (Jul 3, 2014)

Bill Hays said:


> I'm thinking this idea may have merit... now to devise a fair test and check it out for myself!


Cool, if you're using eyebolts, add some epoxy to completely close the circle before adding the tape


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