Lyrebird Cycles

[Mark Kelly]

I can't give you an objective measurement, I talked to the fellow at ZFC about getting some testing done but his price for testing a few formulations would totally blow my budget. I'm thinking about building my own test rig but I have a few other things on my plate.*

I have some people doing some beta testing but no results yet.

* You may know I have been running a small business developing technology for the wine industry. I now have two partners and we have just been taken on by Australia's premier distributor of winery equipment so life may be about to get very busy, especially with the triennial Wine Indusry Technical Conference in a couple of weeks.

[Mark Kelly]

Wire Bike

You might have seen this pic before: as far as I can find out it was taken in the 1920s in England. I think the rider's name is Jimmy Cain, I do not know who built the bike (there appears to be a maker's name on the main tube it might be L Brian ? ).

I am however sure the bike weighed a metric $#!^ tonne and / or rode like a wet noodle because of the limitations of available materials.


Complete_2

Fast forward 100 years or so and a good deal of material science, I decided to have a go at something similar. A major impetus was being able to achieve clearance for 700c x 50mm tyres with a standard road crankset and >430mm chainstay length (horizontal) without resorting to dropped chainstays: I loathe dropped chainstays.

By design this frame has the same torsional stiffness as my old road frame, about 100 Nm per degree: I can't confirm this measurement until I rebuild my test rig (I decided to replace the framework which was creaking during fatigue tests).

I can confirm that is a lot lighter; just on 1.05 kg vs 1.45 for the old frame. It rides very, very well even by my standards and try as I might I cannot overpower the frame: when I stomp on the pedals in too high a gear up a couple of hills here in town the bike just goes.

I will keep riding it for a while before I build a second one: I can already see a couple of areas where I can improve the design but so far, for a wild longshot, this is working out.

[Chik]

Very interesting. What's the "wire" material and how is it attached to the frame so that it stays in place?

[Mark Kelly]

18 intermediate modulus carbon fibre 12k tows twined then rope laid*. The tows were impregnated with epoxy by running them through the part of the filament winder that does this. The ends of the rope were left unlaid and wrapped around the head tube then back onto themselves, the cured epoxy holds them in place.

The section that wraps around the seat tube top is on a carbon slip collar which was used to retension the stays once cured. I judged the tension required by ear and the collar was simply bonded in the new position.

There's a complication in that the rope is the same size on each side of the seatstays and "chainstays" as it is on the top stay and bottom stay. It's kind of tricky to explain how this worked if you've never laid a rope but I'll try.

I laid two sets of 6 twines each of 3 tows, then arranged these with a partial overlap equal to the distance required (eg around the BB, to and around the dropouts then to and around the seat tube). I then retwined the overlaps so I had a central section that was 6 twines each of 6 tows and two ends that were 6 twines each of 3 tows. The ends were retwined with each twine paired with one from the opposite part of the central section making 3 twines of 6 tows again.

The rope was laid from the centre sections out so I laid two ropes each 3 twines of 6 tows then the recombined ends laid as usual.

The net effect is a rope which starts out at 3 x 6, splits and doubles to two sections each also 3 x 6 then recombines to a single 3 x 6.

I didn't take any pics as this process took quite some time and I had epoxy on my (gloved) hands.

FWIW the sections weigh about 10 grams per metre length but have a calculated tensile strength of about 36 kN. Carbon is very good in tension. Also the frame holds my weight (90 odd kg) without the stays in place: I figured they might get damaged in use and I don't want the frame disintegrating if that happens.

One of the improvements planned is to armour the DS "chainstay" by making two boron fibre "C" sections and gluing them in place. Boron is more or less impossible to cut so this shoud mean the stays survive chain drops.





* I was a trainee aeronautical engineer in the Australian Navy but they still taught us ropework. It is surprisingly useful.

The key is always twine in the opposite twist to the rope lay. Since rope is generally S twist, the twines are Z twist.

[KonaSS]

Fast forward 100 years or so and a good deal of material science, I decided to have a go at something similar. A major impetus was being able to achieve clearance for 700c x 50mm tyres with a standard road crankset and >430mm chainstay length (horizontal) without resorting to dropped chainstays: I loathe dropped chainstays.

Fun. But seems like a long way to go to get around dropped chainstays. Is it just aesthetics? Is there something else about dropped chainstays that I don't understand?

[Mark Kelly]

It was a major impetus but not the only impetus. I was intrigued by the possibilities that open up when you can optimise design elements for materials and vice versa.

As an example, the tensile stays relieve the main tube of the need to take beam stresses so it can be optimised for torsional and compressive stresses. Combining carbon, boron fibre and wood works really well for this.

[RichTheRoadie]

That is mad as a box of frogs @Mark Kelly, but if I ever find myself in Beechworth I'll be tapping you up to take it for a spin! Very cool.

[darkmother]

Really interesting bike!

Is there a (practical) way to measure how much the cable frame members change in tension while riding?

[Mark Kelly]

Really interesting bike!

Is there a (practical) way to measure how much the cable frame members change in tension while riding?

Yep, just pluck them and listen.

Pitch is proportional to the square root of tension (all other things being equal). In post 244 I commented that this was how I adjusted the tension in the upper stays.

It's also how I build wheels, I've never bothered with a tensiometer. If I really needed a number I'd use my HP 5315A frequency counter but I usually just use a tuning fork.

[Blakey]

Mark, have you seen these:

I forget where I found this one, it was ~8yrs ago.


From a bike swap in Syd 2014, a McLachlan:


And a couple of art bikes
http://sonic.net/~ckelly/Seekay/artofmountainbike.htm

[Mark Kelly]

Mark, have you seen these:

No I hadn't seen them, thank you very much. Assuming the 1898 on that first pic is the date, the idea is even older than I thought.

Do you mind if I use that first pic?




Edit: I just noticed the footpegs on the front fork: I am assuming these are for coasting and that it is a fixed gear bike. Cool, but terrifying.

[Piledhigher]

Colourised version

[Blakey]

Do you mind if I use that first pic?

Not at all, I lost the source so can't give you a reference for it

[sk_tle]

Fantastic stuff Mark, would the same design be possible by making the chainstay rope removable in order to mount/replace a belt ?

[Mark Kelly]

would the same design be possible by making the chainstay rope removable in order to mount/replace a belt ?

Yes but the termination would need to change. Carbon rigging with termination to suit attachment hardware is now pretty standard in high end boating so it is doable.

[Mark Kelly]

Mid winter in Beechworth. Sucks, doesn't it.


In use_2

Thrashed the thing today on the first part of the course for the upcoming UCI gravel event (Gravelista) being held here.

Pic taken on the way home, exhausted from trying to find the limits of the bike on the hills. The limit is me.

[Colinmclelland]

Mid winter in Beechworth. Sucks, doesn't it.

Winter is easily my favourite time year here. We’ve managed to string three clear days in a row together, so here’s hoping.

I’ve just oiled my bike, and it’s satisfying in a way cleaning a painted bike has never been.

[Chris Chesebro]

I logged back in today after a long time away and this is the first update I saw - this is really, really cool.

[Mark Kelly]

Paulownia

Chainstay blanks in Paulownia.

At least two people at the Handmade Bike Show Australia suggested I try Paulownia, so I did. It's almost as light as balsa but is stronger and stiffer (and behaves more like wood than balsa).

I can buy Australian (plantation) grown Paulownia whilst all the balsa available is imported. I had to make a few changes to the way I do the blanks to accommodate the different material but I'm now happy with the process. The two sets shown are at different stages of fabrication: I cut the blanks to shape then make the channel for the carbon "jet" tube.

[Chik]

Mark, I think the date/clock on your camera is a bit off, unless you're bringing up a subject you dealt with 16 years ago. :)