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The Human Powered Challenge 2006

Constructing your Vehicle

Home Rules Design Construction Testing

What? Me build a vehicle?

Surely, building a fast and fancy vehicle requires lots of equipment and high technology.

Umm, actually no.  Many people have built fully functional vehicles in their garages, and some have even done it in their bedrooms. 



Materials

 Vehicles can be built out of all sorts of stuff.  However, some things are more convenient than others, as you will see from the following.

Steel

 This is one of the most convenient materials for making HPVs.  There are lots of reasons why:

Advantages
 Disadvantages
Steel is strong. You don't have to use fancy alloys; even mild steel is strong enough for an HPV.
It's easily available - you can get suitable steel tube and other parts from "donor" bikes from garage sales or recycling centres or bike shop junk.
If you need longer or bigger tubes, exhaust pipe from a muffler shop works well.  If it needs to be bent into a special shape, the muffler people will usually do that as well.
Easy to work by hand or with handheld power tools.
Easy to join by welding, although thin-walled tube can sometimes be a bit of a challenge.
Easy to join by brazing - brazed joints can also be softened and adjusted if something didn't go right the first time.
Easy to make changes to a design once it's built.  Just bend it a bit to make it the right shape. Cut a chunk out to make it shorter.  Weld a chunk in to make it longer.
Steel is heavy, if you use too much.
It has to be coated to stop it rusting, but, hey, you'd want to paint your marvellous machine anyway...



If you can get access to a welding or brazing plant, then steel is probably the ideal.

But steel is not the only choice...

Aluminium
This is also good for making HPVs:


Advantages
 Disadvantages
Quite strong, but bulkier than steel for the same strength.
Lighter than steel for the same stiffness.
Easier than steel to work by hand, but not so easy to work with ordinary power tools.
Doesn't need painting and won't corrode.
It's possible to use bolts and screws to fasten the frame together, and not need to weld at all.

It's more difficult to weld than steel.
It can't be brazed like steel.
It can be glued with epoxy adhesives, but the joints need to be carefully formed. Otherwise they will crack too easily when under load.
Harder to make changes to an aluminium frame once it's built.  You can't just bend it like steel without risking cracking
It's more expensive than steel.  Ordinary aluminium  can be a bit soft for frames, so aluminium alloys are usually required.  You can't just cut chunks off old bikes and use them.


Wood



Advantages Disadvantages
Easy to work with, no fancy tools required.
Can be quite strong if used properly.
Not expensive.
Easy to glue, and easy to make very strong joints.
Can be quite light if used properly.
Still have to have some metal parts such as steering tubes, bottom brackets, wheel mounts.
Bulkier than steel or aluminium.
Hard to change a design once it's built.


Carbon Fibre Composites
The fancy stuff.  Think of Sarah Ulmer's bike. Think of Americas Cup yachts.


Advantages Disadvantages
Very light and strong, if used properly.
No fancy tools required for manufacture.
Smooth flowing shapes possible.

Requires flammable and volatile chemicals and resins - need good ventilation and protective clothing.
Fibre cloths and resins are expensive.
Very difficult to change a design once it's built.
Forms razor-sharp edges when it breaks!


Cardboard
Not for frames, of course.  For fairings! A fairing is a streamlined shell that helps your vehicle slip through the air with less drag.


Advantages Disadvantages
Really cheap.  Get fridge and TV cartons from recycling wastetakers for nothing.
Lightweight.
Easy to work with.  Strong glued joints are easy.
Several heavy coats of acrylic paint makes it fairly weatherproof.  Any colour you like.
Not very durable, especially if it gets wet.  But then, how long does it have to last?
Can't do smooth compound curves.



Once the fairing design is worked out in cardboard, you can always build a long-term durable version out of Corflute.  It's often called Corboard or Coroplast as well.  This is the lightweight polypropylene plastic that signs are often made of.  It's available from signwriters and plastics suppliers (maybe as free scraps from old signs, if you don't mind some writing on it).  For HPV use, 3mm is plenty thick enough, and even 2mm thick is usable.

Wheels, Pedals, Cranks,
etc
These can be bought new, if you are feeling rich, but usually, these will come from donor bikes.  You can get donor bikes from garage sales or recycling centres or bike shop junk.  You can start with basic wheels and fittings and get the basic vehicle working, and then replace these with better quality wheels when you find some.

Equipment

 You don't need any fancy equipment to build a vehicle.  Here's a basic list of things:

Pretty well essential
  • Workbench and vice - a Workmate is a reasonable alternative.
  • Tape measure and set square.
  • Spanners or socket set for dismantling donor bikes.
  • Good quality hacksaw, since nice square cutting will make construction much easier.
  • Metal files to do the fancy shaping for joints.  You should have at least a large flat file, a medium to large half-round file, and a small round file. 
  • Hammer - an engineer's hammer is best, but a claw hammer can be used if that's all you've got.
  • Electric drill - a mains powered one is best; a battery powered one will run out of charge too quickly.

Handy things but not necessary
  • Angle grinder - much faster than hand files for shaping steel, and more exciting, but no good for aluminium.
  • Welder - for welding steel, a basic electric arc welder is enough, although an oxy-acetylene welding set is nice, since you can braze instead.  For aluminium, you need a TIG welder, or you need to know someone who will do the welding for you.  With the welder, you definitely need all the safety stuff: mask, gloves, etc.
  • Calipers, for measuring tube sizes, etc. - a cheap plastic one for less than $10 will be good enough for most measurements.

Plans
Do your plans full size if you can.  It's very handy for seeing just how big (or small) your vehicle will be.  You can lay parts out on it to check the fit, and take measurements directly off it.

The back side of old vinyl wallpaper is excellent stuff for drawing full size plans on.  It's cheap (try decorating shops for leftover rolls) and it's tough.  You won't want heavily embossed paper, of course.




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