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Hi all,
I have introduced myself in the right place.
Can't resist jumping in and having a go at building a roller type slingshot as I've seen from JoergSprave.
I'm an old engineer but never built anything like this before, let me know if this could work.

I'll explain and try and do a sketch later.

I was thinking of the 'W' design.
Centre handle but either side constructing ladder frames. Two parallel flat bars.
Instead of just one V groove roller on the top, as JoergSprave's H, I was thinking of putting another below within the frame.
If I connect the band behind the frame just below the top roller, then under the bottom roller and through the frame, then up and over the top roller.
So, if you can see it, the band would form a U with the bottom running through the frame, then up the front and over the top with little or no band continuing past.
My concern would be as the band contracts it may be snagged on the frame where it passes through the frame under the bottom roller?

If it could work I would have a long 'draw length' slingshot.

The main reason I've thought of this is because I have no access to welding kit and it would be difficult to keep the rolers in the clear.

I'd be interested in your thoughts. ..... Hope you can see what I'm thinking, as I said I'll try and sketch it out later.
 

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One serious problem is to keep the bands on the rollers. They will want to slip of when you pull out. I solved this with my "Limit":


Keep in mind that you do not need a draw length increase that exceeds 30 cm (butterfly style) or 20 cm (normal draw). You can stretch the rubber to 500%. If you go ahead of 30 cm, then even in full butterly your arms are too short to draw the bands out in full.

Jörg
 

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One serious problem is to keep the bands on the rollers. They will want to slip of when you pull out. I solved this with my "Limit":

Keep in mind that you do not need a draw length increase that exceeds 30 cm (butterfly style) or 20 cm (normal draw). You can stretch the rubber to 500%. If you go ahead of 30 cm, then even in full butterly your arms are too short to draw the bands out in full.

Jörg
Hi Jorg, good to meet you.

It is your videos that have inspired me, thank you!

Keeping the band on the bottom roller will be no problem I think. It passes through the ladder frame so will not slip off.
The rollers will be V grooved as your H so hopefully the thinner band will be kept to the centre and away from the frame when drawn. Should work?
The top roller will also be of the V groove type.

Thanks for the info on band lengths, I will design it in accordance with those figures. Probably on the shorter side as I will no doubt draw to the same anchor
point as my bow, for consistancy.

I have a lot to learn but will enjoy the process.

When I eventually get around to builing it and post progress pics I would appreciate your input if you don't mind?

One of the reasons I would like to increase draw length is because I have a fused left wrist and have little palm shelf on which to take the pressure. I may have to design a brace to aid me also.
So getting extra power is better for me by increasing the draw length.
I can't hold with the other hand as I have low grip strength between thumb and fore finger with my damaged hand and drawing could be awkward or even dangerous if I loose grip on the draw.
So I must keep pressure lower than most can deal with.

Do you ever accept commissions to build a slingshot or do you do it only for your own gratification? .... I would be very interested in something like the one you've just shown me.

Cheers!
Steve.
 

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Steve, I never sell slingshots, this is just a hobby.

But I am happy to assist others in making slingshots!

If you need a brace anyway AND you want to draw to, like, the corner of your mouth, then I recommend making a starship slingshot. This means you simply forward extend the fork. This requires braces (which are illegal in Germany), as without braces the slingshot "wants" to turn around in your hand.

A forward extended frame is easier to make and more effective, as there is no friction. More power and longer band life (chafing is an issue).

Jörg
 

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In addition to tracking problems, engineers should also consider rotational friction and angular inertia. I looked at this a bit when I considered trying to increase speed through cams or pulleys.
Right now, I enjoy the elegant simplicity of basic bands. You'd be surprised how much speed is available.
 

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Discussion Starter · #8 ·
Steve, I never sell slingshots, this is just a hobby.

But I am happy to assist others in making slingshots!

If you need a brace anyway AND you want to draw to, like, the corner of your mouth, then I recommend making a starship slingshot. This means you simply forward extend the fork. This requires braces (which are illegal in Germany), as without braces the slingshot "wants" to turn around in your hand.

A forward extended frame is easier to make and more effective, as there is no friction. More power and longer band life (chafing is an issue).

Jörg
Ok thank you Jorg,
Yes I agree a starship would be more efficient, easier to build from what I've seen and I may certainly have a go at one.
I just love engineering stuff though and I'm after something I can pop in a backpack easily.
I'll post pics of my progress when I get at it.

Cheers!
 

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Discussion Starter · #9 ·
it wont snag if you have the right bands and smooth rollers and corners
Cheers! And Hi,

Great, I will of course round and smooth all edges. The rollers will be good needle race if I can get them.
I'll go and have a gander at your blog.

I have much to read up on, terminology etc etc.
 

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Discussion Starter · #10 ·
In addition to tracking problems, engineers should also consider rotational friction and angular inertia. I looked at this a bit when I considered trying to increase speed through cams or pulleys.
Right now, I enjoy the elegant simplicity of basic bands. You'd be surprised how much speed is available.
Hi, thank you.

Now your stretching my old brain, ....
Moment of inertia, angular momentum. .... I need to get back to Uni.
........... I think I'll just be doing the practical stuff nowadays and see what happens.
Yes I guess the straight forward KISS priciple will yield good results. But, I do like to fiddle ........... I wonder if incorperating springs would be interesting. Compressing a spring mounted roller on the draw? ... Oh dear I'm off, got to stop my racing brain before I try to re-engineer the wheel !!!

Cheers!
 

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Discussion Starter · #12 ·
Styks, we all go through that phase... and end up making normal frames.

I am eager to see what you come up with!

Jörg
Yes I'm sure, full of enthusiasm am I ...
... I'll calm down after a while and no doubt be doing as you say, thanks for the check Jorg.

Actually, I'm not going to read up too much, sometimes comming at something new with an empty mind can produce interesting results.
Or not .. ha ha
 

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I like Vlastimil Zuska's masterpieces. Some of them use springs in addition to the rubber.

http://www.melchiorm..._vlastimil.html
Well I say, I love this guys mind!

And not a welding torch in sight!

How do you expand on that I wonder?
Add coil springs in the rotating heads also?? ..

Darn it, just spotted that in his "Roto Swingshot" but minus the front spring.
Using rubber band attached to pullys at the bottom is essentially the same as having coil springs in the heads?

I can see where you got some of your inspiration in several designs.
 
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