LGR-001

The 001 is the first gravity racer that I’ve designed. It is designed with outright speed in mind, but does have some compromises that allow for cost effectiveness, ease of manufacture and also flexibility in terms of measurements to allow entry into different events that use different sets of rules. The wheelbase, track width and ride height can all be varied quite easily to suit.

Here’s the design so far….

Chassis

The chassis is made from 25mm mild steel box section with 1.6mm wall thickness. Mild steel is cheap, strong and easy to weld and although it is susceptible to corrosion it will be passivated and painted once complete. The chassis will have 4 longitudinal main rails, and 4 “bulkheads” – the front and back (the frame essentially ends where the axle joins) and then behind the driver’s seat, and also just forwards of the steering wheel.

The two central bulkheads will be larger than the smaller front and rear bulkheads, and the main frame rails will be bent to fit them – either by actually bending the steel under force before welding in place, or partially cutting the steel to allow it to conform. The first option will give a more flowing shape to the body lines, while the second will give a more angular shape. Which option I go for will be decided when I actually have the steel and can judge how much it will bend, and how easily.

Once the main rails have been welded to the 4 bulkheads, additional triangulation will be added for strength and stiffness. Additional bolt-in rollover bars may also be added in line with the central bulkheads to suit regulations where required.

Bodywork

Crossmembers

50mm dia steel tube front and rear with upright 50mm sections welded in. These would initially be bolted to the chassis using exhaust brackets rather than being welded in, and could be modified to add suspension in the future. Reducing or increasing the track width would be a simple case of bolting a new steel tube in position. The crossmembers could also be removed for easy transportation of the car.

Rear Hubs

The rear hubs would comprise an approx 100mm length of steel tube of sufficient internal diameter to snugly slot onto the ends of the cross member and be held in place with grub screws or bolts. A solid steel plug would be welded in one end, with a 12mm hole to allow for the wheel axle.

Front Hubs

Similar to the rear hubs, except the tube sleeve would be welded to a short piece of box section. The box section would be drilled top and bottom and have the vertical faces cut away to form the “mouth” to hold the kingpin and stub axle. The sleeve could be rotated back on the crossmember to provide ideal caster angle.

Front Wheels

20″ BMX fronts with 14mm axles
48 spokes
Slick tyres

Rear Wheels

Sturmey Archer X-SD hubs
w/70mm drum brakes & 12mm axles
36 spokes
20″ BMX rims as front
Slick tyres

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