# Do Pulleys Really Increase Speed?



## JacobL (Jan 10, 2018)

I've been considering design some kind of high-tech slingshot, with designs like spring loaded forks to pulley equipped ones.

I've heard that things like the classic Combow shot fast and were a good design, though at the same time I've heard that it was due to the light tubes, not the pulley system.

I've also seen Joergsprave use pulleys to great success, only to tell everyone that they aren't worth it.

One of the coolest things I've seen was a post in the Arbalist Guild. A guy used a pulley setup and rubber to shoot an arrow. At 60 pounds of draw it didn't make a difference, but when he took it past that things changed. With 150 pounds of rubber and the pulley setup, he got an arrow speed of 400 FPS with a lightweight arrow.

Pulleys increase speed but halve force, unless I'm wrong, and the guy who made the crossbow used more rubber for more force, and lightened most of the middle section by using a bowstring.

So after reading about all that, I'm thinking about making a pulley slingshot with a light pouch and string for the center.

I'm not sure if it's worth it, though.

Anybody out there know about this?


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## M.J (Nov 1, 2010)

The Combow didn't use pulleys. It had wheels at the front of the forks that let you mount bands at the back and pull them over the wheels, effectively increasing draw length. The wheels didn't multiply force.
The whole idea of pulleys and whatever all sounds like a whole lot of work for very little return, but I know some people just like to build things. Don't expect to revolutionize the slingshot with it, through.


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## JacobL (Jan 10, 2018)

I never expect to revolutionize anything, I just want to see how fast pulleys are. Slingshots dont need a revolutionary change, or any real optimization. Pulleys are just wheels, which is what the combow has, and all I want to know is if it makes the shot faster compared to the same draw length on a normal frame.

The setup I'm talking about is pretty much just the combow.


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## JacobL (Jan 10, 2018)

Also when I said force I meant power. Using a weight of 40 pounds and putting it on a pulley sort of halves the weight and so on.


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## ash (Apr 23, 2013)

I thought the same thing some time ago and always intended to build something, but recently did some calculations to work out what was possible and found that to beat the speed of ordinary tapered rubber, the pulleys need to be turning at enormous rpm. On the set-up I was looking at, the pulleys would have spun at 142,000 rpm just to keep up with heavily tapered Theraband Blue. That speed at that load is a recipe for self-destruction, even if the inertia and friction didn't eat so much of the power.

With something as heavy as an arrow you have the luxury of more leeway with weight to allow for bigger pulleys and reduced rpm, but to be fair, you could still do that with plain old tapered rubber and draw length.


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## Ordo (Feb 11, 2018)




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## romanljc (May 26, 2014)

I thought about making one like spray did but i decided not worth the effort for the little speed you may get. If you hunt and want more power there are just simpler ways to get it bigger bands and ammo or a starship .


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## JacobL (Jan 10, 2018)

Ash, there's the reply I'm looking for, thank you. I seen Joerg say that the pulleys didnt turn fast enough and that makes enough sense to me. I mostly just want a high speed slingshot that last longer than tapered tubes.

Ordo, I've always loved that one he made. He ended up actually removing the bearings and using teflon rod, which was apparently faster then any rollers. I might look into that maybe. I also like his little magazine, very cool.

Romanljc, that's true. I actually made a HUGE starship a while back which gives what is more than a butterfly draw length and it devastates everything LOL, it's just very large, and I want something small.

Thanks for the replies everyone, I'm starting to see that I should just stay focused on my latest project: a bullet crossbow for steel balls. I'll be sure to post here when I'm done, currently working on the string.


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## romanljc (May 26, 2014)

JacobL said:


> Ash, there's the reply I'm looking for, thank you. I seen Joerg say that the pulleys didnt turn fast enough and that makes enough sense to me. I mostly just want a high speed slingshot that last longer than tapered tubes.
> 
> Ordo, I've always loved that one he made. He ended up actually removing the bearings and using teflon rod, which was apparently faster then any rollers. I might look into that maybe. I also like his little magazine, very cool.
> 
> ...


 you want to work on something inventive come up with a collapsible Starship that you can fit in your pocket now that would be cool


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## JacobL (Jan 10, 2018)

I thought about that a while back, sort've be like one of those folding .22 carbines. I might do it, but meh I kinda got obsessed with a spring loaded slingshot so I might go through that first haha


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