Velomobile development drawings: Part 4

In Part 1 of this write up I said the steering geometry is based on the invention of Jurgen Mages and his Python recumbents:-

http://en.openbike.org/wiki/Main_Page

There has been a great deal of discussion and argument about the best steering angles for any size wheel in any application of the bicycle, road racing, track, mountain bike, shopping bike. All have their subtle variations in angles and trail, all to do with where the tyre meets the ground and pivots. Then along comes Jurgen who places the steering head behind the wheel, does not attempt any of the known rules and it works.

What Jurgen discovered was that at a steering head angle of +/- 65 degrees as the steered wheel is turned the frame rises. The weight of the rider pushes back down stabilising the system.

I refer to Python Projects Survey  http://www.python-lowracer.de/projects.html   where I find the trail figure for a 20 inch wheel is +/- 140 mm and a steering pivot angle of 57.5 – 71 degrees. Now I know this is for two wheeled vehicles and I am designing a three wheeled vehicle but you have to start somewhere.

At this point in this project I have developed a simple idea. I have looked at wheel sizes, axles, airflow, body shape by profile stacking, rotation, and extrusion. I have enough toys to play with.

Now is the time to measure the movement in the body structure to give a reasonable turning radius. To do this I use the original Chassis Bounded Volume set up with 20 inch wheels. The file is smaller and takes less generating time. It also allows me to check I am not entering any clearance borders.
Importantly it will also show where a chassis will have to reach to tie it all in to a structure. I take the axle and wheels and add a rotation block with its axis at the point where the 65 degree steering angle meets the ground.

I then place a circle at the origin (the centre of the 3 axiis) and make it a Component. The axle, which is a separate Component is then placed with the trail point at the origin, and tilted forward. Both components are then made a Group. When the Group is tilted back so the axle is level the handling circle is now at 25 or 65 degrees. When the rotation tool is applied the handling circle the axle rotates at 65 degrees to the horizontal. I then position the axle to the correct point on the body and rotate the axle. Axle and body are now combined as a Group. When the Group is rotated to get the axle level the body leans away from the turning direction.

At this point, I reversed the direction of the steering pivot, everything else remains exactly the same. The body now leans into the turning direction. By the findings of Jurgen the geometry is self centering so to pull the body back upright release the steering.

 

I repeated the process with the rendered body and the 26 inch wheels and straight axle to check for clearance, and this is what you get. I still have to carry on with the development of the one piece axle/nose and body bending design, but this is a good indication the geometry might work.

When I started out to design something I did not ‘see’ before, I did not expect this, but that is why you do it.

Velomobile skin on frame body from Cezar

Recently Cezar Totth from Romania contacted me with this message, and I have included it and the images here, as it is similar to what I am doing.

Hi Ken,

I just started a sketch for a simple and lightweight skin-on-frame velomobile hull.
Not aiming for that gorgeous streamline you made, I’m more into building simplicity and comfort, that means fatter & shorter, open cockpit, with fewer longitudinal tubes.

My current target is a light electric commuter delta trike with pedal assist.

I started a 1/2 scale model frame made of 11mm pvc tubest.

Thanks for your inspiring effort. As I mentioned, I find it gorgeous.

Keep having fun,
Cezar

v1

v2
v3

v3

v4

v5

IMG_20151219_203423

IMG_20151219_203446

IMG_20151219_203550

Yelomobile, velomobile, first trial run

 

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This was the first test of the Yelomobile, the first time the trike, and velomobile, had moved in over 2 years.
We had previously spent some time aligning the body to the frame for cycling clearances.
However between then and arrival on the track the adjustments had shifted again.

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All the data was collected on a Garmin sat. nav. and a heart rate monitor. Cadence could not be monitored, today.
Charles completed a couple of shake down laps and then started a flying lap of the 400 m cycle track in Bellahouston Park, Glasgow.
The same gear was used throughout.
He tried to maintain a speed he would normally use for long distance cycling of around 18 kph, +/-11 mph, for 10 laps.
This pace would be the target for +/- 50 miles a day for 100 days, +/- 5,000 miles.

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We then fitted the body.
Charles started from a standing start and then concentrated on producing the same cadence and effort.
He found for the same effort he was spinning out and his heart rate elevated trying to keep up.
This suggests a larger outer chain ring may need to be fitted, or reduce the effort for the same speed.

Yelomobile Test Results1

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Comparing the information at lap 5 the duration was reduced from 08:32 to 06:52 (-18%).
However the heart rate was 14% higher. Charles reported it just felt easier.
We then had to leave to meet an appointment.

It is way too early to early to draw conclusions but initial results are encouraging.

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Velomobile: Skin shrunk on

Front elevation

Front elevation

The skin was cut using the pre- shrunk pattern. I had to learn how to use a sewing machine to do this, so it is NOT perfect. It now has to be sealed and painted with acrylic mediums and paint. I use Golden acrylics.

Side elevation

Side elevation

The wheel covers are PVC Foam rims and hubs with Corex spokes covered withe Dacron.

Three quarters above

Three quarters above

The tail is covered by sewing the two halves along the spine,

Nose and wheel well

Nose and wheel well

The Dacron is heavy duty polyester sourced from Kudzo Craft. It is used for covering kayaks and small boats. I did not think aircraft fabric would hold up to being handled 200+ times on a long ride.

Velomobile body pattern wrap

The pattern is shrunk bubble wrap.

The pattern is shrunk bubble wrap.

This is the body frame covered in bubble wrap which has been shrunk to fit with a heat gun. The bubble wrap is about the same width as the final covering material, so this is a very accurate pattern. This gives a quick and cheap way of giving a surface to sketch ideas on to before committing to the final and harder-to-come-by Dacron. The red/brown lines are electrical tape which have been stretched on to give the cut lines.

Velomobile body construction progress

First position of the diagonals and the wheel well jig

First position of the diagonals and the wheel well jig

The forward half leaving the floor and the tail. Shut faces are PVC foam.

The forward half leaving the floor and the tail. Shut faces are PVC foam.

The diagonals interfere with the drivers knees on the first trial fit.

The diagonals interfere with the drivers knees on the first trial fit.

Checking for sight-lines

Checking for sight-lines

The floor is supporting the weight of the body but there are many clearance problems

The floor is supporting the weight of the body but there are many clearance problems. The diagonals have been moved. The hinges are tried in place.

The shut faces have been replaced by plywood for durability. PVC Foam is stiff but a little soft

The shut faces have been replaced by plywood for durability. PVC Foam is stiff but a little soft

One of the front body hinges attached to a 3D printed attachment point

One of the front body hinges attached to a 3D printed attachment point

Frontal aspect

Frontal aspect