I would seriously consider some cross bracing between the front and rear wheel supports and cross ways.  It will be a far more efficient design and much easier to keep stiff and eliminate weak points.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

No shame in requiring a wheelchair, one of best mates is a wheelchair user and he lives a fulfilling and active life, we even built him an adaptive waterski !

Not sure which one 1.8pcf equates to as all the work I have done with Nomex used 29/48 or 64 grade

29 being VERY soft and pliable 48 being the standard default core almost and 64 mainly for flat sheets/light curves

Mainly used in ALI cores but also avalible in Nomex you can get over expanded cores or flex cores which aren't hex cells but various shapes designed to aid flex

Looking at your sketch rather than separate front and back legs cant you incorporate them into a single piece ?

brainfart san,
Warren san,
ChrisR san,
f1rob san,

Thanks for advicing!



>brainfart san

>As a way to reduce cost may I suggest building all the parts during the experimental/development stage with glass fabrics and foam cores.

ah...That is good idea!




> These parts have to absorb considerable shock loads

a heavy load is focused on a small area of the leg.
so the leg need to be strong...but as a result,the leg might not absorb shocks...
I think its better  to improve the leg.




>What do commercial wheelchair manufacturers use here?

I am attaching  some images in next post.please check them out.




>All the places where bolts go through the laminate will require strenghtening

I will  fill the honeycomb with the microbaloon and resin.
or I will use a dense foam core  instead of honeycomb.




> Warren san

>I would seriously consider some cross bracing between the front and rear wheel supports and cross ways.

I think so too..why I choose this type of shape
is that I want a compact and easy to build wheelchair.
but,a heavy load is focused on the leg, I think it might be better to give up this type of leg.



>ChrisR san

>honeycomb of any material is NOT the right solution for a core

yes. I will get a dense foam core.



>just make sure you know where the load is going!

I have simple simulator (Autodesk simulation mechanical)
It is almost impossible to simulate precisely anisotropic(composite)material though,
I can simulate isotropic(metal)material.maybe sometimes that will help me.



>f1rob san

>Looking at your sketch rather than separate front and back legs cant you incorporate them into a single piece ?

I choose this separated leg because it looks easier to build.
but I think it might be  not a good idea.

to be honest.
I have been plannig different type of wheelchair,too.

>>>>
Before that,
I would introduce a very popular comercial CFRP wheelchair.
 


This is the lightest wheelchair in the world.
made in Sweden.
weight is only 2.1Kg(4.63lbs).super light!. and  4.2kg(with rear wheels)
price is about 10000 dollars.

it looks that it is made of pre-preg CF and autocrave technique is used.
 Full monocoque frame.
it has 3 sections, right side frame, left side frame and crosmember.
each frame is baked in autocrave then connected.
back rest can be folded.




I tried this CFRP wheelchair.But I was NOT satisfied with its function.

because...
1st, the wheelchair is not stiff enough.I could easily bend the frame when I tilt my body.
     I guess only light weight may be  first priority.
2nd, its frame size variation is limited.it was too big for me. riding position was too high.
3rd, (like most wheelchairs) seat is something like Hammock.it is unstable.
     and my legs must be painful when I use this wheelchair for a long time
4th, legs are sometimes obstructive when I take the wheelchair into my car.
 

    

ultimately, I believe that this type of wheelchair has a serious problem.
that is...its center of gravity is too high.
unlike motorcycle,wheelchair is not more heavy than human body.
so total(wheelchair and human) center of gravity is very high especially super light wheelchair.
to addition, its center of pitching and rolling is too low.
(precisely,the wheelchair has NO suspension system.that makes the wheelchair more unstable.)

as a result, it is easy to pitch or roll over.
to solve this problem is one of my dreams.





Here is my second idea(plan2).
This has suspension system like a MTB.



in this case(image),
the suspension system lifts up wheelchair`s center of pitching.
if  center of pitching is close to the center of gravity,
the vehicle is more stable.

If the suspension system is add to the wheelchair,
a load is sustained by the suspension and shock is absorbed by the suspension, too.
That makes  easier to develop the frame because the direction of load can be controlled.



Anyway,
I need to design a new frame shape again and I will post it.

I would be happy if any comment or advice.

As said, just pay careful attention to all your frame triangulation.  It is key to load distribution and keeping it light.  It would be real easy to make an over engineered wheelchair, but it would be over heavy too. The beauty of an already light and stiff material like carbon, is that even with over engineering, a slightly heavy carbon part is still lighter by a long way than a similar metal part and thus can still meet the persons needs, however when pushing the limits of svelte design you need to be a bit more precise and plan it carefully.

Do that and im sure you will create a awesome wheelchair.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

> Warren san

Thanks!

I am re-designing CFRP wheelchair now.
maybe I will report it after proto-type is built.

You have a blank sheet of paper,you can do what you want but now comes the hard part-you have to think outside of the box !

I have spent the last 30 years watching people make everything from bikes to tables to toilets !

90% of these people have tried to do a direct copy and make what they already have in carbon with usually very poor results but the other 10% make the product using the best aspects of the material and look and perform nothing like the original

few examples (I would put direct links but im a computer idiot !)

1-Lotus Chrid Boardman bike

2-Established & sons carbon table by John Barnard 4mts long and 2mm thick !

3 Skelletron guitar

4-splinter works bath

5-Madfibre carbon wheel

good luck

>f1rob san

Thanks!
I searched the 1-5 CFRP items.
The CFRP furniture is so stylish!

I think I should continue to design the CFRP wheelchair.
I believe that I can improve wheelchair.

I will post again if my design is finished.