Design Guide
The design guide has been written by and for those interested in having fun with gravity
The Bed Buggy
It begins with trolley making fundamentals, with sections on
wheels,
brakes,
steering
and
shaping
and conludes with two 'case-studies', which illustrate the building techniques used by
reigning Style-Meister Brian
Fangio
Smith and the Hilson family, who created the wonderfully simple
Bed Buggy
The derby is not simply a contest for speed-freaks!
Get seriously creative with your Trolley & Costume combination and you might drive away as Style Meister of the Hill
Fundamentals
If speed is your goal, the action of your wheels and their rolling resistance is the most important aspect to consider
Once you hit 40km/h, aerodynamics also impacts on your maximum possible speed
Of course, speed is useless if you haven't got control, so pay careful attention to your steering, brakes and structural rigidity
Keep your construction light!! Contrary to popular belief, weight is an enemy to every trolley
Shaping techniques are almost infinite, ranging from cardboard and sticky tape to carbon fibre - these can make the most basic trolley look like a speed demon
Remember, all trolleys must pass scrutineering
Wheels
Your choice of wheels determines your rolling resistance. This is the amount of resistance your wheels have to the inexorable pull of
gravity that is trying to make your trolley career down the hill.
The perfect trolley wheel is a compromise between weight, strength, contact area, braking performance, rolling efficiency and cost.
The lighter a wheel is the more acceleration it will have but a wheel must also be strong enough to withstand the forces of steering and braking.
The smaller the area of contact the wheel has with the road the less drag the road exerts on the wheel. This is great for acceleration but dire for braking - you see, it is all compromise!
Wheel bearings play a critical part in the speed of a trolley. Make sure your bearings are clean and use light oil.
Old wheelchair wheels are ideal as they have very strong axles and bearings. They can be attached directly to the side of the trolley.
These can sometimes be found at the
Nelson Recycling Centre.
Old 10-speed bike wheels make great, cheap trolley wheels providing they are pumped up hard. Unfortunately they must be supported on both sides of the axle
Old motor mower wheels are fine but don't usually have bearings
Pneumatic (air filled) and solid trolley wheels with bearings can be bought for about $40 a pair from Opel Industrial or Mitre 10 Mega (both near the airport)
Braking
Brakes are probably the most technically challenging aspect of building a trolley
Sam Laidlaw: designer of five Monarch of the Hill-winning trolleys
There are two common braking systems: Deadman and Active
Deadman braking
Deadman braking
Bed Buggy
Deadman Braking
Deadman braking is where the brakes are held in the 'brakes on' position by a spring, bungee or bike inner tube.
To race, the driver pushes the brake lever and the wheels are released.
This is a great system for young drivers as the brakes only stay off while the driver is in control ~ the instant they freak out and move their feet, the trolley slows down.
See the system used by the Bed Buggy
Footbrakes and/or handbrakes are not a good solution on a trolley with rope steering as it is crucial that:
-
The driver keeps both feet on the front axle
AND - Both hands stay on the rope
Active braking
Active braking
Brian Fangio Smith
Cars & bikes use an active braking system.
There are many ways to create rudimentary versions, for example:
- A large piece of car tyre rubber on a lever activated by the drivers foot
- A hinged lever carrying the foot pressure via a rod to the back wheels
For design ideas take a look at Brian Fangio Smith's suggestions
If you use 10-speed or wheelchair wheels, it will be possible to have brakes on all wheels.
If you have a fixed rear axle you can incorporate a bike disc brake.
Steering
Pivot Point
Fangio: Basic
Fangio: Advanced
Rope Steering
We are not big fans of rope steering, however, it is one of the easiest steering systems to create.
Because trolleys with 'old-fashioned' Rope Steering have proven to be dangerous (especially for younger and/or inexperienced drivers) Rope steering systems will be looked at very closely during scrutineering
Two important details to observe if using rope steering:
- Place the axle pivot point forward of the front axle.
This will allow the 'drag' from the front wheels to pull - rather than push - on the pivot point.
This is called castering.
Next time you are pushing a supermarket trolley, watch what happens to the front wheels when you pull the trolley backwards then move forward again - the wheels want to drag behind the pivot point and will rotate until they can. - Create a self-centering spring for the front axle.
Attach a piece of old bike inner tube (free from any bike shop) to each end of the axle then pull the centre of the tube to the rear of the trolley. The axle will then be resistant to pulling to the left or right.
Other steering systems
- See
Fangio
for combination rope-and-rigid and other common rigid systems
- See Bed Buggy for a simple, very much home-made, rigid system that is undergoing some improvements
Shaping
There are essentially two types of vehicle construction:
Blue Bullet - interior - rear
Blue Bullet - Braking and Steering
Blue Bullet - interior - front
Blue Bullet - exterior
The Everyman Trolley
- Chassis and Body
- A chassis and body structure has all strength in the chassis and the skin or body is cosmetic
- Monocoque
- In a monocoque design the chassis and body elements are combined to create a more rigid and lighter vehicle
Aeroplanes are an example of extremely efficient monocoque design
Both systems work well for trolley building as long as the weight and type of material is used not only to maximize performance but also to ensure the safety of the occupant, other drivers and spectators
For a monocoque design, 3mm - 5mm plywood makes a great overall skin structure, which can then be filled out with polystyrene, cardboard & brown paper.
A design that uses chassis and body construction can really take advantage of lightweight skinning materials.
With the rigid structure taking the weight of the driver and the stresses of the braking and steering systems you can use polystyrene, cardboard, sticky tape, PVA glue and paint to create an elaborate and aerodynamic skin.
Make sure you provide clear lifting points for loading on and off the trucks!!
Ensure any sharp or solid protrusions inside or out are well padded for yours and others safety.
For stability and reduced air drag, position as much of your weight below the axle as possible.
As all trolleys must be loaded on and off trucks at least 6 times during the day keeping trolleys small and light makes its easier to get your trolley back to the top of hill.
And remember, a light trolley is a fast trolley!
Good Luck!
