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Carbon disk wheel DIY, pancake wheels

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runcyclexcski View Drop Down
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    Posted: 11 July 2017 at 5:17pm
Been researching DIY carbon disk building. Superficially, it seemed easy: get deep Alu rims, get a carbon fiber honeycomb panel of thickness matching the width of the rim... say, 20 mm,, with several layers running at various angles, cut, sandpaper, epoxy. I like the honeycomb idea b.c. panels of decent quality are mass-produced, and thus are relatively cheap. However, most commercial disks do not appear flat: they get wider at the hub, so they are technically wide cones, not disks (just like spoke wheels). Can the flat pre-made honeycomb idea still work?

If the flat honeycomb idea works, I had an idea to take this further. What if one stacks 2-3 wheels together, by bolting the panels together, and makes a double/triple "superwheel" with 2-3 tires? Think a stack of pancakes, or rear truck wheels. The length of the road hub is at least 3x bigger than the rim width, so no new hub needs to be invented. Individual wheels can be removed/added on as needed (e.g. for racing I can leave one pancake in). The point would be to increase the gripping surface in side winds and in slippery conditions. If one loses a tire to a flat, you do not go down instantly, as there is another one next to it to get you to a safe stop. This is on a tricycle, not a 2-wheel design, obviously. A
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Yanto View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 9:01pm
The flat honeycomb works well on 20" wheels see build here http://www.bhpc.org.uk/Constructors/Kingsbury/bubble-and-squeak.aspx

A double wheel has also been tried by Velomobile.nl but they found that stones became wedged between the tyres causing punctures.

Tyre grip in sidewinds is not a problem, being blown over is if you resist the side forces.
Ian, not so ex racer but still of dubious capability
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runcyclexcski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 10:13pm
Thanks for the tip on 20" wheels!

I also thought about the stones being wedged... one could space the wheels apart by ~2 inches. Or more. At some distance, the stones to be wedged would have to be so large that one should question being on a road with so many large stones to begin with. :) I say, if one stays away from dirt roads, there should be not many 2" stones around.

The pancake stack idea works for large trucks/lorries. While driving from a triathlon race yesterday, from Germany, specificaly paid attention to the spacing between the tires -- looked about 10 cm or so, i.e. quite large. Did not notice any rocks wedged in between. Would not have to be that wide on a velo, 2", I think, is sufficient.
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runcyclexcski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 10:29pm
Regarding being blown over: the pancake wheels were to test if one could take the heroic aspect of riding in rain and side wind out of the equation. Or at least to reduce that variable 10 fold.

When I set out in my car on a rainy windy day, I do not think much about it (well, unless there are trees falling ). In contrast, with velos and recumbents it's dodgy. While riding in crappy weather, I do not want my brain CPU to be used up for not being blown into oncoming traffic.

My current design thus avoids flat vertical side surfaces, i.e. it's a nearly perfect water droplet, with a round cross-section. The idea of the pancaked wheel came from the fact that cars and motorcycles have fatter/wider tires, hence more contact with the road. Motorcycles are heavier 3x than velos (with rider included), but they also have sh*ttier aerodynamics. Attaching a motorcycle or a car wheel to a velo is a non-starter, weight-wise. But stacking together 3 Alu rims achieves the same surface contact, only increases the weight by 1.5 kilo (at 500 g per rim, plus disk), plus the added bonus of redundancy in tire blow-ups.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Yanto Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 7:18am
When you have drawings, and i mean engineering drawings rather than stylised sketches please post them so we can have a look at them, I'm interested how you would keep a low CofG when using a a fully 3D teardrop shape, this alone has more effect on not tipping than tyre width. 

What track width are using?

Wheels external to the body on out-riggers?




Ian, not so ex racer but still of dubious capability
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Post Options Post Options   Thanks (0) Thanks(0)   Quote atlas_shrugged Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 10:00am
I have seen a tube made by Schwalbe where there are 2 inner chambers. When one chamber experiences a puncture the other chamber keeps the tyre on the rim.
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runcyclexcski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 11:17am
Yan -- most definitely. I am putting together a design based on T-slot Alu extrusions, so that I can test and change the parameters you mentioned (width, length, center of gravity) in one rig, before committing to moulding the shell and committing to thinner/lighter CF tubes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoyMacdonald Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2017 at 3:26pm
Its not the wind pressure on the side that's the issue on a round section but the vacuum on the non wind side that's the problem. The Dutch Quest riders stick strips down the length of the Velo to break up the flow and fill in the vacuum to some extent. Mike Burrows in the latest version of the club booklet "So you want to build an HPV" mentions the flow across a tube and how to disrupted the airflow that creates the vacuum effect.
I had to instigate the repair of a tower block where in a storm the vacuum created on one side of the building sucked out the brickwork infill forming the wall of the bedroom and then proceeded to suck out everything in the room including the tenant in his bed. Fortunately for him he had a large wardrobe that fell across the opening and stuck and his bed jammed against that. Never underestimate the power of a wind created vacuum like the brickies who thought that wall ties weren't important on a small wall so left then out.  
 
If you just place rims alongside each other without some kind of diff I would expect a large increase in rolling resistance and tyre wear. Might be worth taking a look at the QuattroVelo. More rear tyres would solve the issue of rear wheel spin on trikes.
 
All the best.
 
Roy


Edited by RoyMacdonald - 15 July 2017 at 3:27pm
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runcyclexcski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2017 at 4:52pm
Very interesting, Roy. Are there any rough estimates/simulations for different wind speeds and forces generated?

If one ignores the head room -- suppose one makes the cross-section ellipsoid shaped, with the long axis of the ellipse parallel to the ground -- would that help? I note that most Velos have the ellipse long axis perpendicular to the ground.



I am thinking to simulate this by printing shapes on my 3D printer, sanding them, and placing them in a wind tunnel (put together with a blower). Have an anemometer to probe wind speeds. Test 10-20 different shapes. Record the wind speed at which tipping took place. Take a few points for each conditino. Compare with published/existing velos.
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runcyclexcski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote runcyclexcski Quote  Post ReplyReply Direct Link To This Post Posted: 15 July 2017 at 4:54pm
BTW... I used to live in a high rise, 24th floor, with an open balcony. If this vacuum effect was so strong, people would get sucked out of their balconies, like, all the time. But I have never heard of this. I am sure a terrfying death like that would make local news. Was that a hurricane that destroyed that brick wall?

Edited by runcyclexcski - 15 July 2017 at 5:03pm
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