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Author Topic: Carbon fibre ‘jump stilt’ springs  (Read 1435 times)

synthpunk

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Carbon fibre ‘jump stilt’ springs
« on: 27 October 2020, 07:43:00 pm »
Hello everyone!
My first proper post, apart from the introductory one, so ive done some homework and used the search function and failed to find an answer first so here goes-

Has anyone used the leaf springs from ‘jumping boots/jumping stilts’ as CK springs? Im referring to these-
[/url] https://motorcycleaccessoriesuk.co.uk/adult-pro-jump-cz-series-cz110-springs-pair/ [/url]

Or these
https://motorcycleaccessoriesuk.co.uk/adult-pro-jump-m-series-m110-black-spring-1pc/

Which are available in a range of strengths from 60 to 120 kg and appear to have some useful looking holes already in place for attachment points.

Has anyone had a play already? any good? Theyre 50Ł a pair, so reasonably priced... id quite like to know the dimensions, im going to ring the shop tomorrow.
Cheers,
Rich

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RhysN

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #1 on: 28 October 2020, 05:05:04 am »
Great "out of the box" thinking, please share dimensions.
A number of folks have been discussing composite springs over the years, but talk is all we did. I would give some a go, depending on the dimensions.

TheGiantTribble

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #2 on: 28 October 2020, 07:57:38 am »
Oh they could be oh so useful.
Great find.

synthpunk

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #3 on: 28 October 2020, 10:47:59 am »
Cheers chaps! Pleased to open up something new for discussion but in all honesty this is an idea that I saw mentioned on the blog www.cyclekartdesign.com - one of the Michigan ice racing kart chaps suggested them.

There are also the F series springs that are for children’s stilts, that go up to about 60kg - they’re also smaller, cheaper (35Ł) and look even more like the traditional buggy seat spring- pairs of holes at each end for mounting eyes/brackets..
I was thinking last night about what sort of strength would be required- I’m planning a wooden chassis for my kart, in the style of a G.N., with quarter elliptical suspension. If the kart weighs  about 120 kilos say, and I weigh 80, then 200 kilos divided by 4 wheels is 50 kg. Do you think maybe 60 kilo springs will be a good first try? If they do end up too springy I might be able to repurpose them as drivers seat suspension springs and get some heftier adult springs for the front end...

I’m at work right now but I’ll ring the shop at lunchtime.

TheGiantTribble

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #4 on: 28 October 2020, 01:37:09 pm »
A couple of thoughts, a CKs weight is manly at the back.
If you assume 50KG and your springs are 60KG you are
Not allowing much for hitting rocks, boulders,  bounce factor
if you will. Of course this is mostly pure guesswork.

ChrisS

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #5 on: 28 October 2020, 01:41:43 pm »
What does 60kg mean? Does anyone know how it is measured? I'm happy to try and measure my springs to provide a comparison.

RhysN

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #6 on: 28 October 2020, 01:42:44 pm »
hi Bill, the only fault in your logic is that these folks sell about 20 different weight variations, up to 120 kg. I'm waiting for dimensions too! Of course I have a few sets of steel springs here to compare with.
« Last Edit: 28 October 2020, 01:45:02 pm by RhysN »

synthpunk

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #7 on: 28 October 2020, 01:54:12 pm »
Okay i spoke to Sarah at the shop, who very kindly went and measured a pair on the shop floor for me. She measured some adult ‘M’ series springs- they are 81cm from eye to eye, and 88 followin across the arch as it were... so theyre about 31 inches long. The child sized ones are about 2/3 the size, so about 24 inches, which sounds about perfect. THe junior size goes up to 69kilos.
My thoughts are that this ‘spring strenth’ is the total weight of the person using the stilts. Each spring has to be able to deal with the total weight of a person running at 25mph and doing 7 foot high strides, so the force it has to take at the point of impact is going to be alot more, due to gravity and inertia and stuff, and these ratings are almost certainly factored with a massive safety margin as presumably you could seriously hurt yourself if a stilt broke in use... massive lawsuits etc...

So anyways, im going to take the plunge and order a set of 69 kilo child springs, as the 1st major purchase of my build... ill report back!

Chris Brown

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #8 on: 28 October 2020, 02:11:53 pm »
All sounds very interesting, I did a little bit on polyester glass composite spring blades, but other things got in the way of taking it further. If this works out it'll save a lot of effort in making them!

synthpunk

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #9 on: 28 October 2020, 02:20:11 pm »
Right- order complete! A pair of F68 springs and two bottom brackets that I thought quite useful looking, all for 54 quid, postage free.
I spoke to Sarah, and the shop is Ghostbikes in Preston ( ghostbikes.com ). If it all works out ask for her and she’ll know what you’re on about- I sent her off to YouTube to look up some cyclekart videos...

synthpunk

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #10 on: 28 October 2020, 03:27:39 pm »
I’ve had a thought about testing springs- if anyone has a pair of proper ones for a comparative test- clamp the spring in the middle, with a measured amount of distance to the free end and then hang weights off the free end, and measure the deflection from normal (unloaded), ie maybe 1/2 an inch at 5 kilos, an Inch at 10kilos or whatever.... If I clamp mine up at the same distance from one end I can do the same and report back.

RhysN

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #11 on: 29 October 2020, 07:37:29 am »
Comparing with an existing spring makes an assumption that I have been questioning myself about. That the current spring is an appropriate stiffness right now.
 I have 2 sets which I'll test
« Last Edit: 29 October 2020, 07:39:23 am by RhysN »

RhysN

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #12 on: 29 October 2020, 12:14:24 pm »
So, preliminary with a US buggy spring  which is what most US folks use.
Photo shows the method. From the clamp to where the "weight bucket" is attached is 300 mm
Measurement from the straight edge to centre of the spring eye
No load        135mm
3 kg             128
5 kg             125
10kg             120
15kg             110
17kg             103
21 kg            98

I have more weights, just currently don't have the equipment to weigh them!

synthpunk

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #13 on: 29 October 2020, 01:25:25 pm »
Oh cool!
Ill try and rig up something similar. The springs have arrived his mornin, ive just popped home for lunch and given them a measure

They are 23” end to end across the span
1.25” across their widest point
Slightly under half an inch thick
When placed on the ground theres 5” of arch.

They also appear to be VERY stiff. I got 68kg weight, i think they might be too stiff at this weight. Ill clamp em up and see just how much too stiff later on, but size wise theyre pretty much spot on.
Exciting stuff!

RhysN

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Re: Carbon fibre ‘jump stilt’ springs
« Reply #14 on: 29 October 2020, 08:08:06 pm »
I suspect they will be MUCH stiffer than the US Buggy, and I'm questioning whether they are too stiff!