Friday, November 10, 2006

Carbon High Racer construction.

I have been cycling on a recumbent bike for 2 years now and it is time to move to a lighter and stiffer bike.
A carbone High Racer as we called them is a recumbent with 2 x 26' wheels. They are not as fast as Low racers (20' x 26') but they are good for training. They are also higher than low racers and you can ride more easily with normal up-right bicyles.

1-The first stage is to design the bike frame on CAD with a 2D software such as Autocad. The shape is up to you but you must bear in mind that the chain line must avoid the frame and the brakes.
If you don't have any knowledge about structure then avoid small x-sections because carbon can't always make miracles.

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Basic dimensions: (main section 96mm x 65mm) . After the first ride, I noticed that the chain was too close to the rear break and a pair of lug were required. The seat is now a bit higher than shown on the drawing.
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2-Once you are happy with your drawing, transfer the file on a USB key and bring it to your local printer. (print cost about 8euros)

3-Then buy extruded polystyrene sheets ( 2 x 1250 x 600 x 20mm thick-blue styrodur is best but pink is acceptable, avoid yellow foam) in a DIY shop.
4-Bond sheets together with propiatory glue (make a test first!).
5-Then use 3M spray adhesive (for pictures) and glue paper drawing (precisely cut with scissors) on the foam.
6-Use a hot wire to cut the foam. Avoid saw where possible as it gets messy in the garage.
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Split rear fork through thickness.
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7- Rebond rear fork in a curved shape. (use a template to fit hub width of 135mm)
8- Drill bottom braket hole (34mm) and steering column (34mm)
9- Cut foam to desired X-section. Use a small 'Sur-form' and sand paper (80 and 400 grit)
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10- Build a template frame to maintain frame with perfect angle during lamination ( foam is not very stable with heat variation); you can prepare every template on CAD and buy precisely cut MDF.
11- Prepare single skin rear luggs , 5mm thick max.
12- Fit foam core on template frame and bond premade rear luggs.
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13- Laminate the steering column pole with 2 x carbon +/-45-300g/m² and epoxy resin about 80mm longer than pole. Slide the foam core over the pole ( tape the top end of the pole to hold carbon while slinding done the core) and fold the extra carbon length (40mm each side) on the outside of the foam. Reapeat this operation for the bottom bracket. Finish with a layer of peel ply which will level the overlap bump. Let it cure.
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14- Check foam core for any unwanted renin drops.
15- Prepare carefully the carbon layers to cover the bottom part of the frame. Basic specification in my case: 1 carbon UD300 at 0°,1 carbon UD250 at +45°,1 carbon UD250 at -45°, 1 carbon twill 300 at 0/90°.
16- Wet out foam core where you expect to place the carbone and add 20mm alround.
17- Laminate carbone with long working time epoxy resin (8H should be Ok) on a plastic film. Pour some resin on the plastic film then drop the carbon on to it. Use a squeeze to force the resin throught the carbone. Apply more resine if require. Use the squeeze to remove excess resin.
18- Place carbon layers one by one the the foam core. It is important to remove every air pocket trapped under the carbon. A second personn is very helpful at this stage.
19- Finish with a layer of peel ply and use your hand (always use latex or rubber gloves with epoxy) to squeeze the carbone and remove any air bubble.
20- Let it cure at room temperature. I recommand to laminate when temperature starts to go down in the afternoon because air pockets can kick in if temperature rises. Avoid direct sun light.
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21- remove peel ply and use a grinder to smooth carbon/foam transition.
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21- Laminate second half of frame.
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At this stage, the frame weighs 1900g (this includes the boom)

22- fill and fair.
23- Check assembly before painting.
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24- Modification: After 200Km of testing, it is time to make a couple of improvement before painting. The major problem was the chain ragging against the rear break so the rear wheel support has modified. New single skin plates were bonded and laminated. The clearance is now 20mm between the chain and the break when riding on the big ring.
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I made a carbon tiller over the WE. I used and aluminium stem, a bit of polystyrene and 1 layer of carbon cloth 300g/m².
this is the tiller before laminating. the aluminim bit is on the left hand side and on the right handside, you can see 2 single skin E-glass plates (4mm). The tiller and tilt up and down.
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24- Paint with 2 pack paint (car paint) and finish with a varnish.


Anonymous Normandie-bents said...

Genial :)

12:49 PM  
Blogger richard said...

This is a great bike--is anyone going to make and sell it? I don't have the necessary tools to build it, but I'm interested.

Let me know please

4:37 PM  
Blogger Speedy said...

This bike is very likely to go under small production very soon. The front end of the frame must be changed so it can be adapted to different riders. If you want one, leave a message and I will contact you.

8:27 PM  
Anonymous Anonymous said...

Very nice!

7:28 PM  
Anonymous evan said...

Hi Speedy, that's very nice work and thanks a lot for the detailed description!
Why did you laminate the bottom and then the top of the frame? To be sure, the PS foam will stay straight? Did you cover the frame by fabric all around as well (or just as you wrote first bottom halve and then top halve)?

3:21 PM  
Anonymous Paul said...

Instead of modifying the front end (sliding boom?), perhaps it would be better to add a seat mount that adjusts horizontally for different riders. Excellent work. Please post pictures of the finished lowracer.

4:05 PM  
Anonymous Anonymous said...

Really nice work. I plan to try something similar for my next bike. Can you give some details of how you attached the idler wheel to the frame? The construction images don't give any hints.

4:56 AM  
Blogger Speedy said...

To Evan,
The main problem is to keep the foam core straight and it is easier to laminate the skin in two hits with an overlap on centreline.
I also built a track frame (normal bike) with a foam core and Low temperature prepregs (80degC) and you can laminate in one shot.

To Paul,
Yes, moving the seat is one option if I want more people to use my bike. I will soon build this bike with a sliding boom so it should fit almost very body.

To Eric,
I bonded a chunk piece of E-glass laminate on the side of the frame (30mm diameter x 10mm thick). I overlaminated with a light cloth (0/90 300g/m2 weaved) then I drilled this reinforced area and inserted a stainless steel thread. (also called Elicoil: looks like a spring).

2:10 PM  
Blogger Hollywood said...

I have been designing my own carbon fiber recumbent and was happy to find your blog! I really appreciate the information that you are providing here. I do have a lot of questions though. First off I was wondering where you get your knowledge of how carbon fiber works mechanically? I haven't really seen any solid information on how to calculate how many plies of carbon to add to a frame and how to orient the weave of the cloth. It seems that you are using less material on your lowracer than on your high racer. Is that due to things you learned while building the first bike? Are there any books or websites that explain this stuff in a less technical manner?
Also, I was on a more specific topic I was wondering what material you made your dropouts out of and how thick they are? I have seen a few designs that use aluminum but some use .125" and some use .25". Thanks.

3:53 AM  
Blogger Speedy said...

To Hollywood:
I am working as a structural engineer and the fiber placement/direction is only driven by logic.
Unidirectional fiber (UD) are place in the main direction of tension and compression. When a beam is bending, one side is in tension and the other is in compression. Between these two forces, there is a shear force going at +/-45deg so we need some fiber with that direction.
when the beam is in torsion, we also get a torsionnal shear force at +/-45deg.
The general rule is
40% UD at 0deg
40% at +/-45deg
and 20% at 90deg (whoop stress) to avoid any section colapse. Foam core is good to avoid that.
I don't think there is any book or website to explain the construction of a bicycle frame. simple rule: if the frame is stiff enough (you will know straight away) then it will be strong enough.

My lowracer frame has been reinforced so I have about 30% more material forward of the fork because the foam core is only 50mm thick when the high racer uses 60mm core.

To calculate how many layers of carbone you need, you can either start from an existing aluminium frame. A carbone frame should be 30% lighter so if you know the area of the tube then you know how many layers of carbone you need. ie: 300g of carbon + 300g of resin = 600g/m2-thickness = 0.34mm

My dropouts are made of carbon (5mm thick) but the derailleur lug is a classic removable lug bolted on the outside with 3 small screws.

It is difficult to bond aluminium, you must use a bonding adhesive such as Araldite. It is safer to bolt. I build my dropout with my offcuts and clamp it between two plates to get a fat plate.

good luck with your project. (send me a picture)

5:15 PM  
Blogger Sam in TN said...

This is fantastic! Thank you very much for sharing this experience with us and your knowledge of carbon fiber construction. I would like to build a LWB recumbent using carbon fiber and this provided much needed information. Can you recommend any sites or books with more information on the material?
Thank you again,

7:09 PM  
Blogger Timmi said...

Bonjour de l'autre côté de l'étang... à Montréal! :-)

Good job and congratulations on the final product!

Malric, did you use anything to dissolve the foam core afterwards, or is it still inside?

How did you calculate the necessary frame geometry, and how does the bike handle? Any shimmy or speed wobbles?

I'm also wondering how steering is, with the chain+wheel overlap? Have you gotten used to it or how is it? Did you check your front/rear weight distribution, and how hard can you brake before the rear wheel lifts off the ground? (I'm just wondering, as I was surprised to go over the handlebars of mine during emergency braking to avoid a car who's driver thought you can just ignore bicycles.)

I noticed you host your images on another server (and some don't load). Would you like some hosting space? (free) I pay for histing and have way more than I can use. I'll be launching in 2009, and you'll be welcome to have a section if you like.

Best regards,

12:27 AM  
Blogger Salil said...

Hi Speedy

great looking bike .. I also dream about making such a nice looking functional bike ... take a look at my handmade bike ...


12:44 PM  
Blogger cycleguy said...

Hello Malric,

Really beautiful work on your CF recumbent. I currently use a FWD recumbent from Great bike, but a bit too heavy for the hills in Massachusetts, so I am designing a CF version. 2 questions:
1. Would you ever trust a DIY fork? Since this is a FWD model, the front end is really the rear triangle brought up front. The fork needs to be wide enough to accomodate the rear cluster. A standard fork won't do. And to clarify your droputs: The rear dropout, is there anything reinforcement necessary between the carbon, or is that just a hole drilled through the built up carbon? And the hanger is also just held on by bolts through the carbon?

Thanks for this great work!

1:41 AM  
Blogger Speedy said...

To: Sam in TN
I am sorry, I don't know any book that would explain the built process. Before building the entire bike you better off trying on a small part and work with someone who has already built something. Wear gloves and goggles!

To Timmi:
I kept the foam in the frame to provide a skin stability a reduce noise. I designed my own geomtry based on my experience from the low racer. The frame is stiff and does not show any shimmy. The bike is very long and does not have any longitudinal stability problems. I never stopped hard enough to lift the rear wheel. The narrow tires tend to slide before lifting the wheel. The front wheel only touches the tire if I turn hard to the right. I have no problem turning right.

To Cycleguy:
I would only trust a fork if I build it myself. I built 2 sofar and it is a difficult job. You better off buying a normal carbon fork and chopp the bottom ends to rebuilder wider ones. That is quite easy. I drill directely into the carbon in way of wheel axle. The hanger, i have two methods. I either extend the lugg down then drill and tap the derailleur into it or I screw a normal aluminium lug on the outside. In the first case, the lugg mus be vertical and that is difficult. You can buy a repair thread to place into the carbon from VAR. I am also preapring the Forward wheed High racer. they could be the futur of long distance bikes.

11:06 PM  
Blogger daves said...

Excellent help! Thank you for this great tutorial!!
website development

8:35 AM  
Blogger cristina said...

I am helping to do a book for a non profit foundation( in Spain). It is about bikes and engineering. I really love your bike and I would be very pleased if you sent me a high resolution picture of your bike to include it..(I would obviously name you..

2:26 AM  
Blogger michaelvk said...

This comment has been removed by the author.

11:16 AM  
Anonymous Conversion Analysis Report Optimization said...

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12:01 PM  

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