10kw Carbon build possible????

[richdeloup]

Thanks for the boost
Here's my thinking that making the frame somewhat solid, wont actually add too much to the weight as cabling will take up at least 50% of the space, just need to fill the gaps and hope that it strengthens it somewhat.



Unlike resin, Alumilite is water thin when mixed and dried hard in around 3 minutes, so only get one shot at it but it can then be ground, drilled, sanded etc.

 

[speedmd]

I have seen some great work with expanding foam in cavities. First you do your epoxy / fiber fill at the inner wall sections you are looking to strengthen, than insert a bladder into the center of it all while it is still tacky ( plastic or thin rubber bag) and fill via a open end with expanding foam (Great stuff) to help compress the structural composite lay up to conform tightly against the inner frame walls. They make it in a few variations. For your app, the stiffer / more expanding the better. Gorilla glue works well also in small areas.

You can go without the foam and just use air pressure in the bag (bladder) to help form and compact the inner reinforcement layer and fill later with foam if you desire. This way you can do it in stages if you decide on adding more fiber / epoxy if you find more flex in the structure than you desire.

 

[richdeloup]

That's a great tip, never hear of that but do use foam to stick houses together and apparently its really good for making moulds. Cut it to shape, sculpt it, fill with car body filler and sand it down. Many uses, great stuff indeed

 

[Chalo]

PU foam isn't structural; it's only used as sealant and insulation. It will fill spaces in your frame, but it won't make the frame significantly stiffer or stronger. it can only add the structural integrity that a foam piece the size of the void in your frame would have by itself. You might as well fill your frame full of pancake batter and bake it.

 

[speedmd]

Tell that to surf board and boat builders.

 

[richdeloup]

PU foam isn't structural

Ye, Im making a 10kw foam bike :lol:

 

[Chalo]

Tell that to surf board and boat builders.

A thin, flat fiberglass skin needs positional support to carry loads. A tubular space frame doesn't.

Pressurized soft drink bottles have a lot of structural integrity that they lack when they are open. That doesn't mean pumping up your bike frame will make it stronger.

 

[speedmd]

Chalo my good friend. You make lots of good points. Unfortunately they mostly are directed in a negative fashion. You would be a powerhouse at helping folks trying to do the near impossible if we could get you to knock the chip off.

Even soft foam drastically changes the buckling characteristics of thin walled tubes, vastly improving their structural integrity and impact resistance. You should know this. In the case you brought in with the reflector going into / breaking the tube on the trek, it would have greatly benefited from foam fill. May still have failed, but having seen first hand what foam cores can do with thin walled carbon poles, it is like night and day. Certainly all foam is not the same, but some of the canned compositions are relatively stiff and would be very good for inflating blind core areas that are being repaired/ reinforced as this frame will be. As you know, it is near impossible to get into some areas and aid the needed compression of the resin/ fiber to the outer wall which is the key hear. Lighten up a bit as you experience could be a big help if you just try to be helpful. Costs you relatively nothing.

BTW, pressurizing a bike frames larger tube diameters would certainly pre-stress them into tension and could make them significantly stiffer. I am not suggesting you do it, but structurally speaking it would be a interesting analysis in how it changes the feel of a lightweight carbon frame.

 

[Rix]

Chalo my good friend. You make lots of good points. Unfortunately they mostly are directed in a negative fashion. You would be a powerhouse at helping folks trying to do the near impossible if we could get you to knock the chip off.

Even soft foam drastically changes the buckling characteristics of thin walled tubes, vastly improving their structural integrity and impact resistance. You should know this. In the case you brought in with the reflector going into / breaking the tube on the trek, it would have greatly benefited from foam fill. May still have failed, but having seen first hand what foam cores can do with thin walled carbon poles, it is like night and day. Certainly all foam is not the same, but some of the canned compositions are relatively stiff and would be very good for inflating blind core areas that are being repaired/ reinforced as this frame will be. As you know, it is near impossible to get into some areas and aid the needed compression of the resin/ fiber to the outer wall which is the key hear. Lighten up a bit as you experience could be a big help if you just try to be helpful. Costs you relatively nothing.

BTW, pressurizing a bike frames larger tube diameters would certainly pre-stress them into tension and could make them significantly stiffer. I am not suggesting you do it, but structurally speaking it would be a interesting analysis in how it changes the feel of a lightweight carbon frame.

Speed MD, I am with you. Chalo is making some great points, and in a classy manner, even though somewhat on the "this can't be done" side vs the "how do we do it" side. I hammered on Chalo on another thread before for being so negative, but this is a pleasent persuasive argument he points out. @ Chalo, whats up man? How does one building a CF frame get around the issue you have identified?

 

[Sean9002]

Tell that to surf board and boat builders.

Bicycles have forces applied to them in a different manner to both a boat and a surfboard. they either sit in or on a material that they are buoyant in, they exploit surface tension of water to stay rigid and displacement to make them float. Tap on a surfboard while on the beach and you get a hollow sound lay it on water and tap it you get a dense sound. Bicycles cant really be compared in the same manner. They have two very small contact patches and neither of them increases the rigidity. Chalo nailed with the pressurized vessel comment. Different conditions, different results.

 

[richdeloup]

All comments are helpful, even the ones on the 'not possible' side

From what I gathered, Speedmd's suggestion about using foam in a bladder, was more about using the expanding qualities to compress the layers of carbon in hard to reach internal areas when laminating and not really about any structural qualities of the foam itself.

I would have thought though that if a frame is trying to twist and turn whilst riding, any internal fill would be of some benefit acting as internal support.

When I removed the rear triangle, I tried to gauge it's strength by pushing to two dropouts together, until I started to hear the fibres trying to crack. I opened it up and filled it and now I can try flexing it until my hearts content, with virtually no movement or cracking noises.

 

[richdeloup]

You could take a hammer to this post now and wouldn't get far

 

[richdeloup]

Update on how this build is progressing.

After researching mid drive solutions, I've realised that this initial build is more about testing out frame strengthening ideas and that I would do things slightly differently for a dedicated mid drive ride. I.e add motor support brackets, use different cranks, extend dropouts back further and better etc.

So as not to delay this build, Im going to stick with my original plan of strengthening all the key areas using the plastic fill technique as in the picture above. Then I'm going to test with an HS3540 and if all is good, I'll then bolt a Crown on to test at 6kw+.

From what I learn with this, I'll then start a mid drive build along the same lines; lots of ideas, One of which is taking a mould of this frame and making a cast plastic frame with all the cables and maybe batteries cast in place and then wrapping it with carbon to stiffen ???.....

 

[richdeloup]

Bicycles cant really be compared in the same manner. They have two very small contact patches and neither of them increases the rigidity.

Can you expand on this as sounds interesting. Do you mean that either end of a tube has a contact patch, generally onto another tube? or were you talking about the tyres contacting with the road surface?

From what I remember from my basic schooling, A cylinder under direct compression is the strongest form, and along with the traditional double triangle bicycle shape, makes for a pretty strong overall structure. The sort of torque we are putting through frames, mainly leads to more twisting, especially if being flicked around at speed through a fast trail ride etc. Battery box /pivot covers are the obvious path to increasing rigidity, however I'm trying for a tube fill technique to try to get similar results...

 

[speedmd]

So much of the structural dynamics gets confused here, so be careful extrapolating statements as general rules. Failure modes must be analysed to properly understand what exactly is needed to stay safely away from failure. In the bottle example, they most definitely are a much stronger structure when full. This concept is used in fuel tanks for rockets as well. Chalo claims to have worked in the field, and he can possibly bring in his structural analysis rather than just saying it is or is not stronger when pressurized than using a soda bottle example to poke fun at a real mechanical engineering solution on large composite structures. The large tank structures when made as light as possible would buckle easily without internal pressure as would a surfboard with out the fill. Large Thin walled tubes act much the same way, resisting buckling much better when filled with non compressible or even compressible substances to a much less degree. A bicycle with small diameter tubes can not be properly compared to a large diameter tubed composite frame. The smaller diameter thicker walled metal tubes are much less susceptible to wall buckling and more limited as has been mentioned by the end attachment method. When stressed to failure, they will break at the weld unless they are butted / lugged or filleted to a large degree.

The stronger the material in general, the less it flexes/ stretches before it yields and subsequently fails. Good quality Steel bike tubes are in the 8 - 10% elongation region, while most HM composites are 2- 3%. This is a critical difference and most definitely makes a difference in how the thin walls need to be supported. They will only flex a small distance before they give up. Support is critical, no matter how it is achieved. Rare they would fail in tension or at the well radius-ed and thickened butt ends.

 

[richdeloup]

The process to key in the headset tube to the top tube and down tube.

The fork stearer was covered in release spray and installed with some old bearings. All the cable holes were taped up and Alumilite was poured to create a solid internal 3 way plug thing. The forks were removed just before full setting and the hollow will be greased to take the forks....
This is more like cooking than frame building

 

[speedmd]

A well known and respected fighter jet uses high tech plywood as a core/ filler for its composite wing spar. Dam near unbreakable and super light. Most composite sail masts are filled with various materials also and super strong for their weight. It is a well proven method to keep tubes and other structures from loosing their shape and buckling/failing prematurely.

 

[richdeloup]

 

[richdeloup]

Testing packs for fit.
Ive done away with some of my initial plans. Firstly my carbon rod idea didnt happen when I realised that the plastic fill that im using is actually as tough if not tougher than the carbon rods that i purchased; so no need for them as the filling alumilite holds eveything together well from what I can gather.

Secondly, I was going to wire everything up to a series/charge disconnect/connect plug but as im only running 4 packs in series, it was easier to just have access to balance leads and disconnect pack series for charge.
Also It was important to be able to quickly take out and replace the packs if wanting to go on a longer journey (6 miles with spares in a back pack etc. Ive got this down to less than 5 mins, hopefully less once Im used to it

 

[richdeloup]

Arrg, Cycle Analyst fried! must remember not to connect full pack voltage to throttle red

 

[richdeloup]

Hmm, nice colours and useful as a speedo and temp gauge but not much else!

 

[richdeloup]

A well known and respected fighter jet uses high tech plywood as a core/ filler for its composite wing spar

I saw a youtube clip of a similar thing, making huge spans with perfect CNC cut plywood, mortise and tenon joined into crazy shapes before being covered.

Hmm bamboo and carbon frame?

 

[richdeloup]

Easily distracted for new build ideas

 

[richdeloup]

 

[richdeloup]