The basic structures of Greenpower cars have been made from a huge range of materials, some more suitable than others. There's no perfect material as they all have their pros and cons so which you choose will depend on budget, available facilities and the skills/experience at your disposal. Before choosing a material be sure to read the current Greenpower regulations as some areas have specific materials requirements and exclusions. Consideration must also be given to the material properties, their suitability for your intended application and to appropriate safe working practises. Please research these aspects before commencing your project.
Natures own composite material, easily worked with the most basic of tools, light weight and inexpensive. The most commonly used form is plywood but always make sure to use a good quality marine or birch ply which will offer high strength as well as being resistant to damage by water. Wood is perfectly suited for making a monocoque structure, but may also be used to cover metal spaceframes. Overall, wood offers the best balance of cost, workability and weight.
Medium cost, lightweight and almost as easy to work as wood but does require more specialised tools, especially if you intend welding any joints. Available in a wide range of profiles and sheets so Greenpower has seen aluminium monocoque chassis, space frame chassis and everything in between (see the SG1 project). The easiest way to join aluminium is by riveting which is quick, cheap, and easy; bonding works well with the correct adhesive. Welding is possible but needs a TIG welder and plenty of skill, it's probably beyond the scope of many school teams.
Low cost, reasonably workable, very strong. Plenty of cars use a steel frame but it needs to be well designed if weight is to be kept down to acceptable levels. Steel is much easier to weld than aluminium, MIG (metal inert gas) welding gives good results even with limited experience but it is also possible to use arc welding down to about 1.2mm material thickness. It is now possible to buy inverters for well under £100 that make it much easier to obtain decent results from arc welding.
Medium cost, strong, slow to work with. Can be used to make a monocoque or a lightweight, aerodynamic shell to cover a metal frame chassis. To do the job properly is a long and messy process, firstly you must produce a “plug” which is a solid copy of your finished part but usually made out of wood and filler, secondly a mould of this is taken by covering with a thick layer of GRP and separating when cured, finally your part can be layed up. The advantages are good strength to weight ratio and the ability to produce complex shapes. Disadvantages are potentially messy, time consuming and the attention to detail required to produce a good finish and structurally sound component.
High cost, high strength, requires experience. At first glance the use of carbon fibre appears to be very similar to GRP but in reality is far more complex. The raw materials are 5-10 times more expensive than GRP, most components will require expensive core materials, and for best results it must be “vacuum bagged” whilst curing to ensure the best possible combination of weight and strength. For an experienced team looking for every possible gain then carbon fibre will have its uses, but it's an unnecessary complication and expense for the vast majority of cars.
|
|
Wood (ply) |
Aluminium |
Steel |
GRP |
Carbon Fibre |
|
Cost |
Low |
Medium |
Low |
Medium |
High |
|
Strength |
Medium |
Medium |
High |
Medium |
High |
|
Ease of Use |
Easy |
Moderate |
Moderate |
Difficult |
Very Difficult |
|
Weight (typical use) |
Light |
Medium |
Heavy |
Medium |
Very light |
|
Specialist tools required. |
None |
Few |
Medium |
Medium |
High |
|
Overall Suitability for typical school |
Very High |
High |
Medium |
Low |
Very Low |
The materials above have all been used as the main structure for Greenpower car chassis' and monocoques. The following are commonly used for additional panels and fairings.
Lost cost, high impact absorption, easy to work. Styrofoam is extruded polystyrene foam, usually blue, pink or grey in colour, and not to be confused with the white material comprising expanded beads. Its use is mandatory for the nose of a Greenpower car but it can be used more extensively to create lightweight aerodynamic fairings and panels (see the SG1 project). The most efficient method of cutting is with a hot wire bow but can also be carved and sanded.
Lost cost, easy to work. Typically used in sheet form for such items as instrument panel fairings and wheel spoke covers. A wide range of sheet sizes and thickness are available. Both materials have a tendency to be brittle but are inexpensive enough that regular replacement is possible.
Low cost, easy to work. Thin sheet (2mm – 6mm) extruded polystyrene but much lower density than Styrofoam, most commonly seen in small, slot together gliders. Works extremely well for wheel covers and fairings when combined with vinyl film.
