CAD/CAM Corner
Spring-Free Trampoline Coming to a Backyard Near You

Dr. Keith Alexander and the University of Canterbury develop the world's first spring-less trampoline using finite element analysis (FEA).
Dr. Keith Alexander and the University of Canterbury develop the world’s first spring-less trampoline using finite element analysis (FEA).

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Re: Spring free (not really, just not conventional)
Springfree   12/24/2013 12:23:11 AM
Hi Everyone,

Thank you for your comments on the Springfree Trampoline design.

This product launched to consumers ten years ago and there are literally thousands of happy families with Springfree Trampolines in their backyards all over the world.

We now sell and distribute into 29 countries including Canada and the US as well as Australia and New Zealand.

For those of you wanting more information and keen to see the product in action, our website contains a great deal of material and some good video footage presented by Dr Alexander. The following link will take you to the Safety Features part of our site where you'll see most of the design features in action.


Thanks again and I hope you have a chance to experience a Springfree Trampoline sometime soon. Our customer satisfaction and feedback is a real life testament to the difference that good design can make to the safety of products like trampolines.

Nichole Kelly

Springfree Trampoline Australia 

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Spring free (not really, just not conventional)
etmax   12/23/2013 11:57:30 PM
I think I've seen one of these, or one very much like it. My only question would be how much circular twist occurs during compression, and what it means to the user??

Mark Ravonsheed
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Re: Good group engineering project
Mark Ravonsheed   12/23/2013 2:40:31 PM
Please see below.

Ramesh Panday has given a clear explanation of this material.



Ramesh Panday

Hi All,

Glass-reinforced plastic

Glass-reinforced plastic (GRP),[1] also known as glass fiber-reinforced plastic (GFRP),[2] is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers made of glass. It is also known as GFK (for Glasfaserverstärkter Kunststoff), or simply by the name of the reinforcing fibers themselves: fiberglass.

GRP is a lightweight, strong material with very many uses, including boats, automobiles, water tanks, roofing, pipes and cladding.

The plastic matrix may be epoxy, a thermosetting plastic (most often polyester or vinylester) or thermoplastic.

Fibre Reinforced Plastics (FRP)

Fibre-reinforced polymers/plastics is a recently developed material for strengthening of RC and masonry structure. This is an advanced material and most of the development in its application in structural retrofitting has taken place in the last two decades. It has been found to be a replacement of steel plate bonding and is very effective in strengthening of columns by exterior wrapping. The main advantage of FRP is its high strength to weight ratio and high corrosion resistance. FRP plates can be 2 to 10 times stronger than steel plates, while their weight is just 20% of that of steel. However, at present, their cost is high. FRP composites are formed by embedding a continuous fibre matrix in a resin matrix. The resin matrix binds the fibre together and also provides bond between concrete and FRP.

The commonly used fibres are Carbon fibres, Glass fibres and Aramid fibres and the commonly used resins are polyester, vinyl ester and epoxy. FRP is named after the fibre used, e.g. Carbon Fibre Reinforced Polymer (CFRP), Glass Fibre Reinforced Polymer (GFRP), and Aramid Fibre Reinforced Polymer (AFRP).

The fibres are available in two forms

(i) Unidirectional tow sheet, and

(ii) (ii) Woven fabric.

The application of resin can be in-situ or in the form of prefabrication of FRP plates and other shapes by pultrusion. The in-situ application is by wet lay-up of a woven fabric or tow plate immersed in resin. This method is more versatile as it can be used on any shape. On the other hand, prefabrication results in better quality control. The manufacturers supply these materials as a package and each brand has specific method of application, which is to be followed carefully. Specialized firms have developed in India also, which take up the complete execution work and supply of material. It is important to note the difference between the properties of steel and FRP and it should be understood that FRP cannot be treated as reinforcement in conventional RC design methods

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bobjengr   12/23/2013 2:38:21 PM
 When our kids were small, we purchased a trampoline as a Christmas present.  They loved it.  It was the center of attraction for days to come, THEN, one Sunday evening I heard a blood-curdling scream.  Our oldest son lost his balance, fell and hit his head. Eight (8) stitches later, we returned home from the ER all the wiser.  He actually hit the supporting bar and not the springs.  I feel the springs are the lesser evil in the design.   If there was some alternative to that support I would love to see it.   

Mark Ravonsheed
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Good group engineering project
Mark Ravonsheed   12/23/2013 2:23:17 PM
The more I read and analyze the project, it seems that the inventor thought of the idea as another invention regardless of practicality or the cost for the end user.

See : http://en.wikipedia.org/wiki/Keith_Vivian_Alexander

The gentleman is an inventor and this unit has been available since 1999. Being in such a position, receiving grants and sponsorship is much easier for him than any high school teacher. As I mentioned earlier, this must have been a project for a group of young engineers.

Larger picture could be seen here:


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Re: Good group engineering project
paulzad   12/23/2013 11:43:42 AM
All of this engineering is well and good but has anyone considered the practicality of making those rods from fiberglas and the issue of sun exposure and breakage? Has anyone ever touched a ski pole made of fiberglas after it has seen a few years of use? I suggest you don't try it, because if you slide your hand down the length of a fiberglas rod after it has been used and flexed for several years you will embed hundreds of tiny slivers of fiberglas into your hand ---needless to say very very very painful and good luck getting them out....impossible. 

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Re: Dazed and confused
jlawton   12/23/2013 10:39:31 AM
The issue with vertical angular momentum is that a forward or back somersault (or a number of them) is one of the most common moves to be performed on a trampoline, and that requires that angular momentum occurs around one of the horizontal axes. If there is already angular momentum around a vertical axis (ie at right angles to the horizontal axis) then the net rotation would be around some vector sum of the angular momenta ie at some intermediate angle, which could be EXTREMELY difficult for the performer to adequately manage, and would make it almost impossible to do normal stunts at the competition level. Not promising at all.

Mark Ravonsheed
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Good group engineering project
Mark Ravonsheed   12/23/2013 10:30:09 AM
This seems to be a great design and as far as safety is concerned, if this unit reduces the total reported injuries to half, then there should not be any discussion about the cost (as long as it is reasonable)

Cost- when the final prototype is approved, then here we come China.

The article did not cover much, may be I missed a more detail one somewhere. It mentioned 3 areas of safety, but except the springs, nothing else was mentioned. Categories: 1- springs 2- metal frame, 3-ground all around.  Items 2 and 3 were left out.

Here are my comments and questions:

Fiberglass- durable, sturdy to a point, repairable, hard, brittle and could easily be shaped. I am aware of flexible type and some use isopthalic flex resin rather than acetone to achieve stronger, clearer and more flexible material, but what ever material they are made up, it must be subjected to tensile and stress test for such an application. (which I am sure it has been done)

What happens if one rod breaks? Will the pieces start flying or break and stay intact?

What would be the minimum bending angle or what is the length of each rod?

Have each rod sitting in it´s own ball/socket housing (fixed or removable) on the frame, doesn´t each require lubrication on the frame and under the mat?

If breakge is a problem, then have they invented a ball/socket housing that can rotate on another "whatever" that is free to move up to 360 deg. in X,Y and Z axis without breaking the rod?

How does rust and corrosion will effect the ball/socket housing? Steel and higher grade material could be used, then what about the cost?

To what distance to the frame will the rods support the mat? Another words, if the mat is sitting up 100 mm above the frame, then will the rods bend horizontally or lower?




I had a lot more questions and dissection to do, but decided to stop as I see this looks good as a project for a graduating student to learn a lot about safety, materials and effect of outside environment, but as final consumer product, well we need to wait and see.


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The reinvention of the "tramp"
shrimper53   12/23/2013 10:16:14 AM
Very interesting , and out-of-the -box thinking on the developer's part......... what we really need is VIDEO... to demonstrate exactly how this thing performs and reacts....

It would seem that the top surface would be subject to some rotation however slight, which would then cause the participant to acquire some rotatation also.   Talk about a whole new aspect to the adventure....

Sadly , this is also another illustration of the nanny-state mentality towards trying to eliminate all risk from everything....I do not wish to imply that such fundamental product improvements are not possible, and should not be pursued.  The several comments regarding how a net enclosure would work, and how the thing will actually propel you into the air, whether rotational or angular motion is introduced, etc. point out that often there are unintended consequences to a seemingly good idea.

Let's hope DN can find us some video..... I am very intriqued!

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Dazed and confused
jlawton   12/23/2013 9:47:44 AM
How this works isn't obvious to me at all, it looks as if the participant would be subjected to a degree of angular momentum around the vertical axis on each bounce, unlike a standard trampoline. Somebody please clarify how this thing works, will you?

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