| The Daniel James Community School Race Team Web Site |
| Tips and lessons learned |
| There is no one way to build a kart, for at each stage you will always have several options. Any way that suits your school, your skills, your equipment and your budget. This is not meant to be a definative guide, but I hope it helps. Getting started: It is always a good idea to try and visit a race, so as to see what goes on and to see the karts in the flesh. Nowadays, you can even buy a complete Kit Kart from Greenpower or perhaps a better option would be to buy a second hand Kart. This would allow you to start racing very quikly, but be warned......you will not win many races with a kit-Kart......and you will probably end up selling it and using the money towards building your own Kart. Chassis: Mild steel tubing is cheap to buy, easily cut and welded and readily available. But do make sure that the tube you get is thin wall or your machine will be overly strong and overly heavy. Electrical conduit is also good to use. But many other teaps use GRP, aluminium, Carbon Fibre or plywood. The wider the kart�s track, the more stable it will be in the bends. Also, it is essential that you work from the most recent regulations. A good tip is to mark out on the floor in chalk the actual length, wheel base and track measurements that you are going to use. As we build all our Karts from scratch, in the past we built a wooden mock up of the chassis using 1�x1� softwood. This allows us to make all the mistakes in wood before we commit our selves to the steel tubing. It is also very easy for the kids to do . Layout: There are three layouts to consider. Each design has its own advantages and disadvantages. Autocar: A four wheeled vehicle. The Autocar layout shares the weight among four wheels, and is less sensitive to placement of weight within the vehicle.(obligatory layout if racing also in the �Greenpower Series�) But has the added complexity and weight and rolling resistance of the extra wheel. Tricycle: A three wheeled vehicle with one wheel in front. This is probably the easiest and the quickest design to build, as the steering needed is quite simple. The Tricycle offers a single wheel steering like a bicycle, and the opportunity to try front wheel drive, although usually one of the rear wheels is powered. this has the disadvantage of being the least stable layout when cornering heavily. You can simply cut and shut 2 bikes to have 2 bike back ends, mated to 1 front wheel�..chopper trike style��easier steering geometry, but watch the amount of scrub you produce, when cornering. Cyclecar: A three wheeled vehicle with two wheels in front. The Cyclecar steers with both front wheels, but requires a more complex steering system. Although it does force the driver to sit bolt upright, as the single rear wheel is in the way It offers a simple power train driving the rear wheel. Our most successful car has this layout, and many of the most sucessful cars in the American race series have chosen this layout. Steering: A big problem for us was getting suitable sized steering wheels�..sport wheels off a mini would do as would a go-cart�s or one off a tractor mower�or you could make one???�.we use ones of kiddies peddle cars�Very light ��you can use anything for the steering linkages�..rose joints�.little ball joints�mini trackrod ends��but do make sure your tyres a pumped up good and hard and that the tracking is bang on�make sure your brakes aren�t binding either�...your machine should sail across the workshop with just one little push�.(honest�.if it doesn�t, you will be no good)��.on this will hinge how good your race car is���.also use the smallest kid you can find as the driver�.it is my experience that if the builders know at the beginning that you need as small a driver as poss they don�t have a problem with it��.. And any old school seat will do. Wheels: Most competitors use spoked bicycle wheels. The largest diameter wheels to use in my opinion are 20� as used on kids bikes and BMX. (avoid the plastic wheels�they aren�t as strong as you think) But these wheels are not designed to take sideways loads��.so you must give your wheels a bit of camber. You can reinforce the strength of the wheels by wrapping the spokes with wire where they cross and twisting them or soldering them. A good bicycle mechanic can set you up with a very strong and light wheel. In fact, if you can find a cycle shop to help you, things will be easier and cheaper�Wheel chair wheels are worth looking at ( for the front wheels) as they have a heavy duty axle that is designed to only be supported at one end. Normal bike axles are 3/8� (10mm) diameter and will fail if not supported at both ends. Axles need to be 1/2" (12mm) if they are going to be suported by only one side. Get wheel covers if you can�.both for safety and for lowering drag. 20� wheel chair wheels and 20� BMX wheels can not share tyres as they have different rim sizes. Transmission: Nearly all teams use a chain drive adapted to fit a bicycle threaded rear wheel hub. Gear ratios are critical in tuning your performance and range, well worth making a system that incorporates a deraileur or internal hub gear. Almost any kart can acheive 80 miles in six hours...whilst even the least aerodynamic cars can reach the 100miles distance. 130 miles seems to be the maximum unless your car is very streamlined. (The best do nearly 200 miles) You will need to gear your machine for at least 20 mph�..(The National Champion is almost doing 50MPH) but do not be tempted to over gear (30MPH max). This is a common mistake amongst newer teams. All that happens is that your car runs fast for the first couple of hours but because of the current consumption, then hardly covers any milage in the second half of the race ��.You will find that type of gear ratios available when using bicycle components is not big enough�..so most people use a secondary shaft to get the required gearing One of the most frustrating problems encountered during a race is a derailed chain.. Motorcycle shops sell axle adjusters that allow you to align the wheel and tighten the chain together��. A good modification you can do is to sandwich your sprockets between 2 plastic discs�..this will stop the chain falling off, Another solution is to make a spring tensioned idler pulley to take the slack out of the chain but to me this seems like another thing to go wrong. We use a centrefugal clutch�..we are the only team I have seen using one�.but if you do, give me a call first as there are a few down sides and problems that you need to be aware of. Motor Control: Some teams use solid state electric�s to make an electric �carburettor��..I have avoided these like the plague as I have seen them fail far too often�.they can be very expensive and complicated ( although some teams swear by them). A much simpler solution is to use a 24v 80amp relay�.from your nearest lucas dealer (call me for the part number)�.or even simpler, is to use a foot operated solenoid type switch�..very simple, strong and cheap.....or even simpler a foot operated starter switch that does not even need a relay. I get my pedals from scrap yards�.metro and maestro accelerator pedals are great to use or make your own �.whilst there get your self a seat belt assembly��mine came from the back of an old escort. Quick release battery clips are a must. Bodywork: Bodywork is in my opinion essential�..for aero-dynamics (Above 15 mph wind resistance or drag is a major problem and all the front running Greenpower Karts are very aerodynamic). safety and as a place to put the race numbers�..it also covers a lot of mistakes�and it makes it look much more car like. Use a thin aluminium sheet for bodywork��ask at your nearest stock holders if they have any damaged sheets, or scrap an old caravan�..I then screw or pop rivet this to the tubing�..if you need additional forms �.eg�.wheel arches etc. I use 6mm steel rod and weld to it small plates every so often so as to have some where to put the rivets. Aluminium tank tape smoothes out all the joints and covers the sharp edges.(available from all motor sport dealers and available in a wide variety of colours) The roll bar is made from conduit, and covered in pipe lagging held on with cable ties. Testing: Testing must be a high priority, only by testing will you know that your car will stay the distance� and not fry the motor�..and that your gearing is right��it also makes your driver(s)more relaxed. When testing, be aware that the motor will do a lot more accelerating in a car park than it will do on the race track���and consequently the motor will get very hot .so try to position your motor in the air flow�..and think about some kind of cooling system�.and don�t fry it testing it around school��If there are problems such as binding brakes or wheels scrubbing�.the motor will destroy it�s self after only 20 or 30 mins |
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