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Guidance
Notes PDF Format. Download Here
Lots more
useful info at the the British Pedal Car
Championship website The guidance note on this page will hopefully be a useful reference to those intending to build their first car. There's no better way of picking up good knowledge though, than talking to those who've already done it. You'll find some useful numbers to call on our Contacts page. For inexpensive parts, the BPCC have established their own components website offering all sorts of quality goodies, such as wheels fitted with hub brakes and other ideal bits and pieces. A discount is available to New Milton competitors. Just contact the New Milton Race Director for details.
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Guidance Notes on Pedal
Car Construction |
Steering
The way in which the front wheels are attached to the frame will, of course, be dictated by the way in which they are supported. There are basically two ways in which this may be done. The first method is to support the wheel by means of a stub axle from one side of the wheel only. This method is perhaps the most elegant but inevitably weaker way than the second method of supporting on both sides by means of forks. (Figure 3) These could be forks from two bicycles cut down. For anyone with limited machining facilities, I would suggest the 'forks method' of supporting the wheel is the one to go for. The next decision is the means by which the wheel is 'hinged' to the frame. In the case of the one-sided hub arrangement, then this swivel would be incorporated into the hub/axle. In the case of the 'forks' arrangement, the forks themselves can be attached to the frame via two stem heads from two bicycles. The next principal is to grasp the Ackerman steering. From the illustration in Figure 4 you will see that the only time the front wheels should be parallel is when they are pointing dead ahead. When they are turning into a corner they should turn by different amounts, the sharper the corner, the greater the difference with each wheel following a different arc. Fortunately, the way this wheel alignment is achieved is straight forward. The first method is one adopted on soap-box carts with the front axle swiveling about the central chassis. The second and more convenient method is by the use of track rods. The angles of attachments are calculated as follows. (Figure 5) Begin by drawing a straight line between the point at which the front wheel touches the ground and the centre of the rear axle. Repeat this process for the opposite side. Selecting a point 150mm or so back down these lines will be the point at which the steering would be linked. If arms are now attached to the forks which terminate at these points, they may be linked together with swivels at each end and the wheels should now stay in track. All that now remains is to design some means of moving the track control arm from side to side and the steering will be almost complete. This is normally achieved by means of a steering column held in a cycle drop tube. The steering column has an arm attached at 90 degrees. The length of this arm will decide the steering ratio and is the final variable in the whole geometry. Trial and error will be the simplest way of deciding on the final arrangement, but as a guide it will be found that 100mm track rod ends and a 100mm offset on the steering column, will be a good starting point for further experiment.
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Transmission As mentioned earlier, there are two basic ways in which to arrange the transmission for your car. The first is to use a rear axle with a centrally located cog which accepts its drive directly from the front sprocket. Although it may need some form of jockey wheel to guide it beneath the seat and take up the tension in a long chain, it is a direct, and therefore an efficient means of getting power to the back wheels. The lucky scavenger may even be able to find an adult sized rear axle from a tricycle, which will incorporate a differential and frequently a three-speed or even derailleur type gear attached. The next and more popular layout is to use a lay shaft to transfer drive from the centre to the outside of the car. (Figure 6) A front chain sprocket drives a chain to a five-speed freewheel and a derailleur located below and in front of the seat. The freewheel is attached to one end of a shaft as a cog attached in line with the rear wheel. A simpler and equally effective arrangement is to have a lay shaft with fixed cogs at each end, but utilise a Sturmey three-speed hub in the driven wheel. A chain between these completes the drive mechanism. All that remains then is to couple the gear changing to a selector. Bodywork, Brakes, etc A certain amount of bodywork must cover the front and sides of the car. There must be sufficient paneling to allow the car number to be clearly displayed front and back. Design is purely down to the individual and original ideas are always welcome, but NO DANGEROUSLY PROTRUDING PARTS due to safety issues.  Efficient
braking is essential and
the most popular arrangement is the use of
cycle
caliper brakes mounted to both rear wheels. The brake levers are mounted on the handlebars with the shortest possible run of cable between levers and brakes securely attached to the frame. In some cases it may be worth while having the brakes operate on the front wheels, but only if they can be fitted successfully.
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The best way to design a frame is to sit on the garage floor. With legs outstretched, mark out with some chalk where the base of the seat is to go and the furthest point to which your legs will reach.
It will therefore be found that the pedal crank will have to be mounted at a height of around 300mm above ground level. The two simplest alternatives then are to mount the pedal crank above the chassis line or mount the wheels below. (Figure 2)