Look at the design page for info on the plywood velomobile construction.

Friday, 31 December 2010

Front axle

McPherson wheel suspension
This is the front axle. It was simplified to the maximum. The polyurethane foam element is spring, damper and bearing. The McPherson suspension is a well accepted design but is it the lightest alternative ?
In the first comment on this post Bob Stuart, the designer of The Car-Cycle X-4, 
argues that the McPherson is one of the lightest options. In our design of a micro electric car (Elite) we used an alternative construction. It is a sort of torsion beam suspension. Because the distance between the wheels is so little, this construction may be lighter than the McPherson. Another advantage is that it incorporates the anti-roll function.

This drawing shows the wheel suspension of the Elite micro electric car. It was mounted to the body via silent blocs

The McPherson construction distributes the wheel load over six distant points on the monocoque. Large torque loads will be transferred as small forces in these points (braking, cornering). This seems all very beneficial but the McPherson construction urges us to strengthen the monocoque at places where we really don't need it to be strong at all, would we not have this suspension. When we use a McPherson suspension we are forced to add material at the mounts of the longitudinal arms and vertical columns. We also have to increase the lateral rigidity, for instance with an u-frame between the front wheels. This may increase the body mass. The torsion beam axle connects to the monocoque at the front side of the seat. This is a place where we need it to be strong and stiff anyway...

Torsion beam suspension

About mass

Mass distribution of the first prototype. Total mass 27 kg.
13 years ago I determined the mass distribution of my first prototype (see here). Although it was larger and a 'head in' design it is still illustrative. The total mass of the first proto was 27 kg. The second proto is 23.3 kg. The mass reduction is due to leaving out the heavy polycarbonate window and the rear wheel suspension and also due to the smaller size and improved body construction.

Mike Burrows Windcheetah, the archetype of a tadpole trike, is 15 kg. Based on my figures this would mean that Mike uses 5,4 kg for frame and seat. In the first prototype 3,5 kg is used for wheel suspension which the Windcheetah doesn't have. We can conclude that a velomobile of 23,6 kg is still 23,6-15-3,5=5,1 kg too heavy. Although one might argue that the mass of a coat and two bags should be added to Mike's (beautiful) design...

Wednesday, 15 December 2010

On the road !

Until I've got a better picture this will do. The black cover is fixed temporarily.
Lots to be done but I can ride it !
The second prototype is (almost) ready. I improvised a seat and made a short trip. Very much fun! Although some details can be improved I think the general concept is proven: It is possible to build a very light velomobile with plywood.

I will sum up the main specs and add a better picture as soon as the weather allows me to take one: Two front wheels with McPherson suspension, one unsprung wheel with Rohloff 14 speed hub behind. Two side sticks for steering. Monocoque body (No frame inside!). Drum brakes in front wheels. Size: 2750x720x750 mm (LxWxH).  Cost estimation: 300 euro (body materials only). Total mass 23.6 kg.

23.6 kg is very competitive...
Who's going to take the development further? Come and see our machine. Learn from our mistakes and and build your own! Please send me a mail if you are interested in building my plywood velomobile design.