Monday, December 26, 2011

Yet more musing on new velomobile

I did a bit more on my mock up to figure out the smallest size I could make it to fit me.

Here you can see the seat angle which is now pretty much about normal for a velomobile.  Well maybe a bit less that normal.   My shoulders just fit under the curved wood strip which is about as low as you can make shell.  I will need to add bumps for my knees and feet.  The nose still needs lots of improvement  which will happen as it develops.  I thought of making a CAD model with the measurements from the mock up but decided against it.  I prefer working with the actual shape as you can see and feel the shape develop and make changes.  Sometimes the shape just doesn't look right so I like to let it sit and just contemplate how to make it right.  A comfortable chair can be a valuable design tool at this stage.  I will build the basic shape and then use some pour foam to further refine shape.  The not so fun part of doing it this way is that making the second side match the first is quite tedious and seems to take forever.  This is where the CAD and CNC model has an advantage.  You just mirror the first side and the CNC machining has them come out exactly the same.  Even when doing this I am always tempted to further refine the shape as the computer model never seems to be exactly what you intended.    Most of the material in the mock up so far is left overs from converting the barn into a workshop. 

A top view where you can see how much the wheels cant in.  It looks pretty skinny so far.  The challenge will be in making the wheel wells so there is an acceptably turning radius and just enough room so I just clear them without touching.  Some careful shaping of the wheel well around where the wheels go when turned should get the clearance I am looking for.  They will end up looking a bit different from what found in current velomobiles.  There is also the possibility of being able to build the velo with different amounts of ground clearance using the same mould.   Not entirely sure if this will work but it is worth a try.  With this idea in mind I have decreased ground clearance to 8-9 cm. 

Wednesday, December 14, 2011

More musing on new velomobile

I built a quick mockup of the new concept.  One thing that became obvious sitting on it and observing the space required for pedaling is that the derailleur post and front derailleur stick up into your sight line with the seat very reclined.

 In the picture you can sort of see the recline of the seat.  It's about what the ultra marathon riders are using for their seats and about the angle I need to be at to sort of fit in the WAW.  I'll also try it with the seat in a more upright position.   If you have bumps for your knees and feet vision to the front and sides can be quite good as most the shell would now be a few inches lower than normal.  One big disadvantage of this approch is that you may need a couple of sizes of tops for different sized folks.  I am not too worried about this as I am making it to fit me.  Making a different top would make sense if there was enough demand.
The sawhorses with the foam clamped to them were to check shoulder width.  It's now 51.5 cm which just fits me but I will make in a couple of cm wider so I don't touch all the time.   Right now my base pattern is a bit too short in the front to get a nice nose shape.  I may have to extend it 10-15 cm.  If I do this I will shorten the tail by the same amount so the total length stays at 280 cm.  Even with this change the back end will be very aerodynamic.  There may have to be a bit of a bump for my shoulders.   Maximum width on the base is 71 cm with a track width of 78 cm.  Next step will be to mock up the wheels and imagine what the shape may end up being. 

Thursday, December 8, 2011

Thoughts on a new fast velomobile

The most sales of velombiles seem to be to folks who want to ride fast. This is not suprising as early adopters would mostly be serious cyclists and one of the primary reasons for considering a velomobile would be to go faster. What I am thinking of is something along the lines of a Milan/WAW/Evo K. It would have to have very good speed potential and still carry just enough gear to go touring. 

As for overall size it would similiar to the WAW.  With a shorter nose and a  longer pointer tail.  I would also have a bit more room for my feet, knees and shoulders. I am 6'2" and have size ten and half feet so I don't quite fit the WAW.  I could modify the WAW by putting in bumps for my knees and shoulders but it just seems wrong to do this to such a nice machine. Better that it eventually goes to some one who fits it properly. It should be possible to have a smaller frontal area than the Quest and still have enough room for gear.  From the bit I have ridden the WAW there is quite a bit to be said for its great cornering ability.  This comes about by its wider stance and front wheels that are canted in quite a bit.  Having you sit right on the floor helps too. 

It is very tempting to go with open wheel wells to decrease the turning raduis and make servicing the front wheels, brakes and suspension simplier.  Open wheel wells can be quite efficient provided that the wheels are nicely faired into the body with very little space around the tires.  The Evo K seems to verify that open wheel wells can be quite quick.  The best way to get this result may be to build the shell without the wheel wells and then glue them in afterwards.  Once the wheels are installed cut the opening to just fit around the tire. You could even adjust the size of the opening with an add on flat panel if you used bigger tires in winter and then switched to faster ones for summer time riding.  The big advantage is in how I would fabricate the bottom half as it is quite a simple part to vaccum bag or infuse without having to work around the wheel wells. Making the wheel well as a separate unit would also simplify making this part.  The risk of not having successful parts would be reduced. When you are vaccuum bagging or infusing you either get very good parts or junk you have to throw away.  What happens if you loose vaccuum at a critical point is  the part expands about 30% and fills with air.

My preference is for a head out velo but design it so a racing hood could be added for speed freaks.  I prefer the slightly bigger head opening so you can see inside the velo when riding with the roof on. The size I have on the Borealis seems about right.  This with a small foam cover for use in the most inclement conditions might be the best all round compromise.  The head  opening should be just large enough so you can crawl out of it if necessary. The size of the door section  should be large enough to make getting in and out easy.  Rather than go with a hinged door one that just lifts on and off is worth trying.  If it could just snap in place that may be ideal.  It should also sit on a substantial foam gasket so it doesn't rattle.  If it was just long enough so it could be made in different sizes depending on the height needed to clear your knees  you would have the option of customising the size of the velomobile a bit.  If you did the same with the section where your feet are with a removeable cover you would would gain easy access to the front derailleur, headlight and a bit more usefull storage space in front of the wheel wells.

Suspension on all three wheels.  While I would like to develop my concept for a carbon/basalt fiber spring front suspension it will most likey have the standard front suspension as found in other velos.  The time and effort to develop this is hard to justify when makes a very good unit.  Rear suspension should be an air shock  so the rider can personalize it to suit them.  The rear swing arm is best if not single sided so you have the option of using a Rohloff or rear hub motor.  Structurally  the double sided swing arm should be easier to implement.  If the rear swing arm can be pulled out of the bottom of the shell so changing the rear tire would be the same as on a normal trike.  One would have a removeable cover over this opening to clean up the air flow and keep everything clean. 

Ground clearance of around 10 to 12 cm.   Some cars are in this range for ground clearnace.  This will make it a very practical vehicle as it will handle most roads with ease.  Just the occassional speed bump that causes cars problems too may be an issue. 

Reverse gear would still be with at least one foot hole open. The mould would have  bumps for both feet so you then have the option of adding reverse or not.

Seat could be made easily removeable to make gear storage and cleaning the velombile easier.  If you can take the seat with you it would make the velmobile unrideable. 

This would be a monocoque structure with all the bike parts fitted to it.  There would be no separate frame except for the rear swing arm and a carbon front boom assembly.  Constuction would be out of kevlar and carbon fiber with some honeycomb or foam cores where necessary.  To get the most performance out of these materials the parts would be vacuum bagged or infused.  We have been looking into an epoxy resin system that seems safer to use than previous offerings.  It has very high elongation which would help to build a very tough shell.  There is a epoxy clear cost option that could add a very minimum of weight or even a paint that can be sprayed in the mould that would be lots lighter than gel coat.  In a few months there is an epoxy gelcoat coming from this manufacturer that can be bent into a one inch radius without cracking.  With any of these options spider cracks common in gel coat would no longer occur.   Target weight of less than 25 kg.  Cost is unknown at this point but it would be very competitve. Chances of this happening soon are quite low.