Hi Folks, thanks for making this forum.
There's loads of great advice here. 

I've been making 60 cm diam rings by bending 5mm carbon rod , setting the ends inside a cuff and sewing these inside a dacron sleeve.
This puts the carbon rod under a lot of initial stress. So much that vinylester rods break randomly in the night. I should use epoxy.
From here they are compressed even more by 6 lines on a tensile torque transmission system. 
This is a very weird project making a flying wind turbine... https://windswept-and-interesting.co.uk

I'd love any suggestions or advice on how to make these rings better. ..I can't afford a bike wheel for every ring in a stack
Is there anywhere which makes a set pultruded coil which I could cut and set as a ring?
Is there anyone makes a prepreg packing or sealing gasket I could wrap around a large cylinder?
Should I just make corner blocks and use straight rods?

Thanks in advance

Sounds like you are right on the limit of what the rod can bend to.  Can you use a smaller diameter rod? or is the strength insufficient?

If you could find a tube of the right overall diameter, you could hand lay up carbon fibre to make pre-bent rings.  They would not be as neat as a pultruded rod, but with care you could make a neat and fairly consistent carbon band. I would probably look at using carbon tow to help improve the hoop strength. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Do the rings have to be carbon fibre? The fibreglass pultruded rods would be more resilient than the carbon for the same size.

Or a slightly smaller dia carbon rod or a better grade or carbon ??

Or as suggested layup your own if you can find a large piece of metal tube that would make a good mould to use, then they could be wet laid or pre preg and even a sandwich structure. Layup a piece of it and then cut this into the rings.

Thanks for the advice Fasta and Warren,
I'll do better research on the minimum bending radius of epoxy 5mm rod first before trying to lay my own version.

I'm a little concerned now that the Vinyl Ester pultruded rods may actually have a better ultimate tensile strain rating 1.4% than the epoxy 1.1%
So Vinyl Estsr should be able to withstand the bending strain
Vinyl Ester
https://www.azom.com/article.aspx?ArticleID=2001
Epoxy
http://www.goodfellow.com/A/Carbon-Epoxy-Composite-Composite.htmlhttp://www.goodfellow.com/A/Carbon-Epoxy-Composite-Composite.html
How to calculate minimum bending radius
https://www.reddit.com/r/engineering/comments/5y2mcp/question_maximum_bending_of_a_carbon_rod/
Thing is ... If my rod is 5mm and the bend radius is 320mm (64cm dia 2m length rod)
Then I'd have thought my max strain level (seperation / radius of curve ) is only 2.5mm/320mm = 0.0078 or 0.8% ish so my rods shouldn't be snapping.
 It's only the odd 1 or 2 which pop 
and by 2 different methods either a straight snap or a crushed delamination
I may have to start making my own custom gear

Very interesting, good job and thanks for sharing such a good article.

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