Summerlab was OK

I presented the plywood velomobile to on the Summerlab in Nantes. Watch the video. We tested the machine. The seat, the front suspension, the soft top and the chain guidance were failed or considered inadequate and than repaired and improved. Thank you guys!

We have thought about how the plywood sheets can be attached. Below you see a sample.

provisionally attached with staples...

glued with wood construction glue (foaming PU)

will we ever get these staples out again?

To get experience we tried to make a hard top too.

The chain is guided by four toothed chain wheels to reduce the losses up to the max. But it would easily derail from the rear sprocket because it could not be tensioned properly.

Jacques and ? (sorry I forgot your name) are adapting the wheel mount so the chain can be tensioned properly

Joris wanted to make a one wheeled trailer (remorque). I showed him my plywood design. Building a simple trailer was a fine way to learn (developing the sheet, bending the alu tube... )

Joris has made a mock-up to evaluate the shape and generate the development of the sheet

unwrapping the sheet

The edge at the top of the trailer will be reinforced with a tube. Bending it is not so easy. Because we did noty compensate for the elastic relaxation the tube did not get its definitive form directly...

bending aluminium tube Dxt 18x1

for the last turn we fix at a new position the tube so we can release the first par

oops ! We should have filled it with sand...

But not only details were studied. Scale models and a 1:1 mock-up was made too:

 

On the wiki you will find some more !

The summerlab was a very pleasant gathering of interesting people and thoughts. Although not presented at the summerlab and already written in 2004 to me the most intriguing was the philosophy on cyborgs of Natasha Roussel.

Cycloid drive

Miles Kingsbury reports a 90% efficiency on his cycloid drive:

"We have also found that although the drive is mechanically very efficient, physiologically it was not so good. We did a number of tests and found it was only about 90% as efficient as a circular drive. In the end we decided this inefficiency was caused because the main leg muscles were performing a 50% duty cycle compared with only about half that on a circular drive. Although it seems that this higher duty cycle should help efficiency, it doesn’t allow the muscles to recover and get rid of lactic acid build up, causing a severe burning sensation! ".

I will try to make a multi body analysis of this drive. It may be the problem is the kinetic energy of the thigh, calf and foot at the extreme positions. The cyclist has to do work for decelerating and accelerating his legs at the returns.

A page of Human Power, the technical journal of the IHPVA issue Volume 8 No2, spring 1990

Lineair drive

The conventional pedal rotates around the crank axle. In a velomobile with rotating pedals the feet are not only moving in driving direction but also up and down. Should the up and downwards motion be done away with the nose of the velomobile could be much lower. That may improve the aerodynamics of the body.

multi body of a human leg

Instead of a rotating crank we could use an oscillating crank. The pedals would move for and backwards while the crank rotates 60º only. The cranks could be connected via 2 sprag clutches to the wheels. But than the pedal speed would be almost constant. Only at both extreme positions the pedal speed would have to change very fast to the opposite direction. Is that comfortable and efficient?

motion of center of gravity of thigh, calf and foot [m]

To get an impression about the losses that could be created I calculated the kinetic energy of the thigh, calf and feet of a human leg while driving the lineair drive. At the returning positions they are 2 and 5 Joule. The last value is when the leg is stretched. Humans (animals too) are able to optimize their motion. It could be that we would stretch out our foot in the last phase to reach the most stretched leg position. In that case the kinetic energy of the thigh and calf would be recuperated. I think this is what we do while we are running.

kinetic energies Et: translation, Er: rotation

But in the most pessimistic approach all kinetic energy would get lost: 7 Joule at every stroke. At a normal frequency of 1.5 Hz that would amount up to 2*7*1.5=21 Watt. That is an enormous  amount. A normal bicyclist produces 75 to 150 Watt! It may be that the foot motion has to be decelerated and accelerated in a controlled way at the returns. This kind of loss may exist in the rowing bike too. Is there anyone out there who has done experiments with lineair drives? Paul Jaray developed a similar drive in 1920. Miles Kingbury developed an interesting alternative: the K-drive. The Human Power-team is experimenting with it too.

The motor

This is the kind of motor I would like to use in the velomobile wheels. It is a cam drive. The pistons make multiple strokes per revolution. This is ideal because the velomobile wheel rotates at low speeds (~ 500 rpm). The Hagglunds has to be scaled down a little. The smallest type weighs ~800 kg has a displacement of 15100 cc (15.1 liter) and produces 530 kW.

The Hagglunds Compact hydraulic motor

Efficiency of this machine is high but should be improved for the velomobile. Options for improving the efficiency may be found in reducing leakage, friction and optimizing the commutation. The velomobile motor may have a cam with 3 or 4 waves, 4 or 5 pistons and a total displacement of ~2 cc per revolution. The transmission ratio may be controlled by switching on and off the pistons with valves (see Artemis intelligent Power and this video). See also this page

 

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.

Introduction

A velomobile is something to have. But it is manufactured in limited numbers and expensive (I will name some makes: velomobiel.nl, leitra.dk, go-one, leiba.de, aerorider.com, sunrider-cycles.com, alligt.nl, dutchbikes.nl). Building it yourself is a good alternative and very much fun. This blog is dedicated to the development of a do it yourself velomobile.

The Alleweder Velomobile (photo Flevobike)

I was involved in the development of the do it yourself Alleweder velomobile at the Flevobike company in 1992. It was my job to improve and adapt the design of Bart Verhees. Bart Verhees is a very practical engineer and an experienced airplane designer. His Alleweder velomobile is build like an airplane: riveted aluminum sheet. At that time I saw the beautiful shapes that are possible using bent sheet only. And this idea never left me.

The electric machine

Together with designer Ronald Meijs we developed an electric car. It was made of an aluminum-polypropylene sandwich sheet (0.2-2-0.2 mm). This was a new material of Hoogovens named Hylite. It was aimed at the automotive industry.

Me and my first plywood car on a trip to Boulonge sur Mer

But my true love is human power and a year later I travelled to France in my first plywood velomobile. It was a 'head in' design and on that trip a learned that the fun of cycling is to feel the air flow along your head. But the concept of a velomobile of airplane plywood was proven. I made a new head out design which was build by Paddy Milford. It is has been hanging in my garage for 10 years now but recently Sjaak Bloemberg is working to get it on the road.

The De Havilland Mosquito: a plywood construction build in 1940-1950, (© FlightGlobal)

Wood is a very interesting material for velomobiles because of its low density. In the construction of the velomobile body the sheet stiffness is more important than its strength. The stiffness of the sheet is very much determined by its thickness. On stiffness relative to mass only sandwiches of alternative materials like carbon-aramid-epoxy with foam can compete with birch plywood. But building sandwiches is laborious and expensive and it is only recently that velomobile manufacturers offer bodies with sandwich sheet. For your information I will list some densities (kg/dm^3): birch plywood 0.7, aluminum 2.7, glass fiber 2.55, carbon fiber 1.75-1.95, polyester 1-1.45, epoxy 1.1-1.3.  Look at the site of Jan Hermhart for an example of plywood in aeroplanes.

My aluminum Alleweder was over 30 kg, my first plywood velomobile 27 and the second will be around 23 kg ! As soon as the second prototype has travelled its first 100 km I will get back to you. Let me know if you would like to be involved !

P.S. I'm not the only one: mosquito-velomobiles , gigomobile , Friend Wood, coronn