Anyone familiar with fiberglass as springs?

[John in CR]

I need to compress some large pouch cells with 4psi or so. Doing it with some kind of air bladder will take up too much room, so I'm thinking a large flat spring is the way to go. eg I slightly curved piece of thick fiberglass should do the trick. Put a "spring" on each end of the pack, and then drawing the upturned edges down flat should give nice even compression across the flat face of the cells.

Anyone have experience building fiberglass bows or crossbows, or anything else that turns fiberglass into a spring?

 

[fitek]

I just saw a guy using long pieces of polycarb for a 4 wheelers suspension at Maker Faire.

 

[rasputin1197]

John you are way more technical than I am.

Possibly vacuum bag the laminate to increase the fiber/glass ratio(very flexible with tons of strength)

http://www.nextcraft.com/vacuum_bagging_01.html

Not sure if this idea helps you. I learned vacuum bagging many years ago when I was employed building high performance boats. Now I ride a bicycle to work and walk the dog(trust me...the dog isn't impressed either)

 

[Metallover]

I'm a pole vaulter! The poles are made of fiberglass or carbon fiber. The poles aren't completely straight, they have a slight natural bend.

They can bend past 90 degrees all day long! And they always return to the exact shape. They do lose a bit of stiffness over the years, and a little after breaking in a new pole.

Fiberglass can hold a heck of a lot of energy! Letting go of the pole when it's bent is bad. I've had a pole fly 20-30 feet in the air, like in this video

[youtube]ghPZ7lSHAik[/youtube]

 

[Dauntless]

Leaf springs of fiberglas are gaining popularity. You know those powerrisers, the springy feet you bounce with? Is THAT the sort of spring you have in mind?

Never tried to make one, but various test strips were quite springy at the thinner end, so I'd say you just need to lay up a few layers on a surface with the curve you want. You create the shape you want it to return to, maybe bend it a little more after that.

You're actual spring will be an experiment, doubt there's any advice for the precise size and shape right now.

 

[Drunkskunk]

All I know is it works. I've rebuilt a fiberglass divingboard before. it's just a giant leaf spring.

But of more help could be wood. I had to build a lipo pack compressor to get my cells in the frame. I used a couple pieces of oak and some long threaded rod to make a vice. I was compressing the sides, not the top, but it should work the same.

 

[Tench]

As a temporary spring I am sure the example above convince us fibreglass is a viable material, I dont think it would be suitable to be held under constant tension though. The resins do continue to cure for a very long time so I am sure the tension will be lost and the spring develop a "set"

 

[zener]

As a temporary spring I am sure the example above convince us fibreglass is a viable material, I dont think it would be suitable to be held under constant tension though. The resins do continue to cure for a very long time so I am sure the tension will be lost and the spring develop a "set"

There are many different resins with a huge bandwith of characteristics. And threating the resin with heat can speed the full cure massive.
I guess with the right resin and technique its possible that it dont lose significant springing over 1000years.

 

[Harold in CR]

What are the dimensions that the springs will be?

As I told you before, I am using Tamarindo wood for my pouch compression springs. They can be made tapering on both ends so the center area can put compression across the whole board.

Today, I will lay up a pocket that will hold my cell groups and show the wood strips.

 

[John in CR]

Thanks guys,

I'm pretty sure that wood will lose it's ability to maintain compression over time, both from the change in size with SOC and temp, as well as our change in humidity between wet and dry seasons....The fit of house doors changes pretty significantly with season, so under tension I think it would be sure to warp the board.

I need 2 sizes to fit A123 amp20's as well as Nissan Leaf cells, so I'd be compressing surfaces about 6"x8" and 8"x9".

2 methods I was thinking are to wax up a curved surface and vacuum bag it; or as I saw someone doing with crossbow arms, make a mold and put wetted glass in and compress to squeeze the excess resin out.

Drunkskunk, for the diving board did you use cloth or single direction strands? All my past glass work was always to be a rigid, not designed in flexibility.

 

[Harold in CR]

I layed up a pocket mount today, and, will post photos once I get things ready.

This Tamarindo is as hard of wood as exists and it will never lose it's tension. My test piece is ¼" thick X 6" X 11" and I can barely flex it putting all my weight on each end over a dowel, laying on my work bench.

If you are worried about swelling, smear a couple coats of quick drying sanding sealer on it, to seal the grain. I'm not in the least bit worried, for my Leaf cells.

 

[John in CR]

You may not be worried, but Nissan sure does. The multi-piece steel plates with compound curves for extra rigidity that they use to maintain compression on their cells would make you think again before saying a 1/4" piece of wood is adequate. Without using an inflatable bladder, obtaining an evenly distributed pressure over the broad surfaces of these cells isn't as simple as it looks at first glance.

 

[mr.electric]

My compound bow has fiberglass springs that stay under tension at all times. They seem to last a long time. I see 20 year old compound bows for sale in working condition. For some reason people de-string traditional bows after each use. I am not sure if that is to protect the fiberglass springs or other parts of the bow.