3 Wheeler Initial Design
After the initial research, various sketches were produced to help decide on a style of vehicle. It was decided early on that the vehicle would be a single seater to reduce weight and design complexity. The aim was to keep the weight below 410kg which puts it in the same category as a trike. This is covered by the B1 class on a standard drivers licence. This class of vehicle was exempt until June 2003 from the SVA (Single Vehicle Approval) test that other kit cars require to pass before becoming road legal. As long as the car was registered with the DVLA before this dealine then it only has to pass a standard MOT test to be raod legal. This not only reduces the cost of the test but is less strict than the SVA test. The car was registered with the DVLA and allocated with a chassis number in May 2003.
To start planning the specific details of the vehicle, several methods were used. Firstly MS AutoCad was used to create a block sketch of the various components of the vehicle. Using a CAD package allowed for design changes to be made easily. To check the design, a full size 2D plan of the vehicle was made on the floor using masking tape (see below). This allowed various components to be laid out and for the driver to get a realistic feel of the size of the vehicle.
The size of the single seater vehicle was determined by the following factors:
- The first and most obvious factor is the driver size. The dimensions of the three team members were measured. A comfortable driving position was also recorded.
- Rear wheel and swing arm attachment are already determined from the existing frame.
- Engine positioning. Since the chain from the engine needs to be taught when going over bumps, the chain needs to be kept horizontal, limiting the engine position to in front of the rear wheel.
- For safety reasons it was decided to keep the drivers feet just behind the front axle, to allow for a small crumple zone.
- It was decided to use a rack and pinion and wheel hubs from a ‘donor’ vehicle. These would determine the width of the front of the vehicle.
- A ground clearance of 15cm was chosen, similar to that of a normal road car, suitable to clear speed bumps.
- The size of the drivers determined the minimum height of the vehicle, given that role bars were desired.
- It was desired that the driver’s arms would be contained inside the body of the vehicle; therefore this sets a minimum width.
3 Wheeler Detailed Design
Once the design had been agreed by all the team, a detailed model of the vehicle was created in AutoCAD. This would ensure that the frame was designed accurately and that everything would fit together before manufacture began. The CAD model would also aid manufacture considerably, allowing for accurate dimensioned cutting lists to be created for the space frame. It also allows for changes to be made to the design cheaply, as opposed to during manufacture where costs of design changes increase exponentially.