Gravity-powered Go-kart

This Instructable has this introduction and two more sections:

0. The Why-blurb (see below)

1. The How-blurb

2. The Pictures

I was motivated to build this gravity powered go-kart by the recent proliference of mini quad bikes and motorbikes in my immediate vicinity. Being interested in anything technical, I have nothing against them. However, they do seem to make quite a noise in our quiet village.We hatched the plan with the kids to build this cart last summer holidays, and as I agreed, there was no backing out this year.

The objective was to build something that does not use fuel, is quiet, gives the kids a the feeling of "driving" a vehicle, and thus ultimately, teach the kids basic driving skills - how to hold the steering wheel, use the brake pedal, and steer through a set of bends, around obstacles, etc.Furthermore, I managed to recycle many bits and pieces from my workshop.

It all sounds very we-shall-teach-you-while-you-play - which kids can usually sense and then try to ignore. Fortunately, they were willing participants and took part in the actual build themselves - so, many thanks to Tonička, Ondra and Stázka - 9, 6 and 5 yrs. respectively. The "kart track" is the half-kilometre grassy track leading gently down to our cottage - a safe, traffic-free environment for the kids.

This instructable does not provide exact step-by-step instructions because:

• A lot of recycled stuff was used - the source of most of it is impossible to identify.

• The instructable is aimed at those who have ideas of their own and are looking for ways of implementing them.

• I did not draw up specific plans - just the basic dimensions, and then added stuff as I went.

However, please feel free to ask if something is not clear. (I will be offline for a few weeks of summer hols)

So, to the basic dimensions, which you can change to suit the size of the kid (or adult. Yes, we all had a go):

There is a rough sketch in the "Picture section".

Length (includingbull-bar) 1500mm

Width 800mm Height (including seat) 8500mm

This is probably the most crucial dimension - Distance from brake pedal to seat back - 720mm (middle position of seat)

Wheelbase 1050mm

Track 660mm

Ground clearance (front) 110mm

Ground clearance (rear) 220mm

Steering wheel diameter 300mm

Front wheel diameter 310mm

Rear wheel diameter 400mm

The go-kart was partly constructed before the summer holidays, dismantled so the kids could paint it, then put together again. The length of the steering column and the seat position were then determined with the shortest and longest kid in-situ.

Basic construction

The chassis is basically a plywood monocoque from a 1350mm x 500mm sheet of 10mm plywood. This is screwed to two longitudinal 50mm x 50mm laths running along either side underneath. This base is then strengthened with three transverse plywood braces. The first one, at the front, takes the torsional forces of the front axle and locates the steering gear. The second brace forms the scuttle (with the triangular side pieces), strengthens the front bodywork and supports the top of the steering column. The third, rear, brace takes the torsional forces of the rear half-axles, strengthens the rear bodywork and also acts as a handle for pushing the go-kart uphill.

The swivel points for the front wheels are actually satellite dish clamps (rejects from a company where I used to work). They feature vertical tubes through which 12mm threaded rods are inserted to form the “king-pins” of the front half-axles. The front wheels (sourced from a car-boot sale) are attached to the king-pins with the help of U-shaped brackets formed from 30mm x 5mm steel strips, drilled to take the centre wheel fixings and with steering rods welded onto them.

The steering itself consists of a rotating drum on which (when steering) a cable from one front steering rod is wound, whilst the cable on the opposite side of the front axle is unwound. It is very simple, fast acting, with the oldest kid (Tonička) racing through the test slalom at fantastic speed. It does however need some modification as, due to the nature of the geometry, one cable (on the unwinding side) is slack at full lock. This is (relatively) well remedied through the fitting of a track rod connecting the left and right steering rods. However, I am considering using a Trabant steering box for next summer. The steering drum turns in bearings located in a metal housing which is bolted through lugs to the front brace. I have no idea what this housing was originally for – probably part of some farm machine or other.

The rear half-axles consist of frames welded (please do not study my welding too critically - I am an amateur) from 30mm x 4 mm steel strips with cross-pieces for bracing and for locating the brake callipers. The frames include welded lugs to hold the rear wheels (taken off an old kids's bike).

The brake callipers were among the few items bought specially for the kart – old-fashioned items, cheap and simple to fit and set up. The cables run (from the left wheel under the chassis, and from the right wheel along the side of the chassis) to the brake pedal on the floor. The pedal is fashioned from various bits and pieces of metal plate, linkage from an old tractor diesel pump, etc, etc. There is a foot brace bolted to the floor on the left. This is made from a piece of bent galvanized metal sheet.

The steering wheel is a belt pulley, from a decommissioned Whirlpool washing machine, and wrapped with foam pipe lagging. It is very comfortable to hold – almost F1-like.

The seat is made from an old 1960s chrome-framed chair, minus legs, with a plywood seat and back. The seat has three adjustable positions but we left it in its middle position according to the middle child (Ondra) and the shortest kid (Stázka) used a cushion on the backrest. We put it right back for "adult testing" but our knees were up to our ears (and our eyes wide open with fear).

So, one year later, the kids arrived for the summer holidays and we had to make some modifications to our go-cart. As I promised we would, we replaced the drum and cable steering with a rack and pinion steering box from a Trabant. We also replaced the original steering wheel (washing machine pulley covered with foam) with a real steering wheel, sourced at a car-boot sale.

The Trabant steering box is ideal for such applications - light, about 300mm long, and of simple construction. The only modifications to the "chassis" being the enlargening of the aperture at the front right wheel for the steering rod to go through and the drilling of two hole for securing the steering box itself. The steering wheel and column are supported by the original dashboard.

The result is more precise steering, more of a real-car feel to it, and a lack of vulnreable parts.