A DIY approach to realize one system to remotly pilot the hot screw of a CIK kart carburator+realize an electric choke for the air-box of a kart. The actuators are standard R/C servos. The microcontroller is the Parallax Basic Stamp. Run by a 9 Volts battery.
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100 cc CIK-kart racers have the tendency during races to choke the air-box during braking. Verbal tradition explains that they do that because they run the engine under a small as possible oil/fuel percentage. Choking the Air box during decelleration provide them extra needed lubrication and cooling. But, no matter why they do it but that is an unconvenient way to get into turns. FMK-karters have the tendency, also,to lean up the mixture during the first race laps. Further more, carburator setting is normally done by closing the hot carb screw by 1/8 of turn which can be some times confusing.
Few years ago when I was living in France I have started to develop an electronic choke-carburator control for a co-worker that was racing Karts (September 96). Just after having identified a concept and tested it for feasibility (November 96), I moved to Detroit, Mi, USA because of job related reasons. The move of continent delayed my testing but, finally during June /98 we maded for a full speed real life testing which went perfectly.
A triangular shape of foil of polypropilene 0.8 mm thick is fixed on the the servo shaft. The body of the servo is glued to a plastic piece. Due to this plastic piece it is possible to fix the servo on the air-box as near as possible to the air intake holes of the FMK-registered-air-box. 2 rubber elastic bands are used to fix the servo and his mounting to the air-box.
There are a certain number of Fmk-registered air-boxes. The system has been tested only with 2 types of these boxes. Holes on top (see photos) and Holes on the side (see photos)
The servos used for the air-box choke were 3.O kg.cm ones. So far even 2.0 kg.cm servos seem adapted to the task.
Different shapes and thickness for the polypropilene foil have been tested. Best results have been reached with a triangular shape of 0.7~0.8 mm of thickness.
One R/C servo is connected to the hot screw. One flange fixes the servo on the carb. A round electric box rubber foot is used to link the servo to the hot screw. Till now the system has been tested on two karting carburators: a Tillotson 304 and a Walbro WB-3A. Mounting for these 2 carbs have been hand-made. The system worked with 3 kg.cm (42 oz.-in.) servos. It is quite possible for some carbs that some 5 kg.cm (70 oz.-in.) servo would be required (see the Hitec catalog). The major problem encountered has been RFI due to the vicinity with the ignition coil expecially for rotary valve engines. The problem has been solved by using only some brands of servos that resist much better to RFI.
This is one of the mounting for the Tillotson 304.
A servo has generally only 180(I0(J of rotation avaliable. This system has, therefore, the possibility only to rotate the hot screw of half a turn, which means 4 times 1/8 of turn or 8 times of 1/16 of turn. Due to the possibility to easy mount/dismount the servo on the carb (2 screws), one previous carburator setting could be done manually, and the finishing could be done electrically during the last half turn of leaning the mixture.
It is simply a box with a button to actuate the choke and a switch to set-up the desired opening and closing angles. For more information read the following paragraph.
To drive the 2 servos are needed 1 microcontroller, 1 battery, 2 switches and 1 button. All is put into a box that can be fixed on the steering wheel, with the buttons possibly at finger reach.
When the button is pressed the ribbon go to the position closed. The degrees of the positions open or closed are programmable. The ribbon remains in position closed as long as the choke button is pressed.
The first switch on the box is a 3 fixed positions switch.To any of this 3 positions corresponds a position of the carb servo. This positions can be changed in any moment and the new position is kept in memory. The other switch has a central fixed position and two side temp positions. When this switch is pushed in one of these two side positions, the carb servo turns of 1/16 of turn (also 1/8 is possible depending on the software). So by these two switches it is possible to fine tune the carb in 3 differents positions. These 3 positions can then be recalled at any time by the 3 positions switch.
The open and closed positions of the ribbon can be modified. When the button is down, if the switch n.2 is pushed in one of the two side positions the ribbon closed position will change. For about one second after that the choke button is released if the switch n.2 is pushed this time the open position of the ribbon is changed and stoked in memory. If the same switch is pushed after this very first second after the choke button realese, it would be the carb servo that will turn of a 1/16 of a turn.
The battery used to power the all system is a 9 volt battery. If an alcaline 9 volts battery is used (it has about 550 mAh) it will last like for several races. If a rechargeable 9 volt battery is used (it has about 110 mAh) it will last like for a race.
The microcontollers used in this project have been so far a MC68HC11, and the basic stamps of Parallax. Among the 3 basic stamps the Basic Stamp D has been retained because even if a very small microcontroller it satisfy for the purpose, is cheap and programmable in BASIC. Potentially everybody can with this micro learn how to modify the software in an afternoon. The Basic stamp is not an automotive product as the MC68HC11. It showed some weakness to the RFI produced by the kart engine. During this testing the box used to enclose the system will be metallic to reduce electromagnetic interferences on the micro.
Link to Parallax Inc.
Since the begnning I prefered to use for semplicity some ordinary modelism servos. A problem was discovered during the first testing. A karting ignition system produces an icredible amount of interferences, something that is no longer possible to encounter in a modern car even if you mesure that on the skin of the ignition coil. About any R/C servo is controlled with a square wave of about 100 hz of freqency and in which only the lenght of the positive part of the square wave counts. A combustion engine produces interferences that are naturally similar to the square wave used to control the servo. Every servo is electronically protected agaist a certain amount of interference according to modelism industry standards. Among the servos tested the ones with the internal electronics made by surface mounted components performed much better then the others. The brand Hitec of Korea or the servos sold at Parallax (which are probably Hitec sold under another brand) are the ones that I tested.
Link to the Hitec page
Link to the Parallax servo page
So far the system have been tested on a Yamaha KT 100SC engine Kali kart, on a Haase kart with a Rotary-valve Parilla TT27 engine with a Motoplat ignition system and on a Birel Kart with a Comer engine WKA SuperCan Spec.
A computer-science school with a cool Karting Club that helped me out.
As long as I will not be back in Europe I feel that I can not support the final phase of this project as I should do. So I am looking for people willing to continue the project by themselves.
A HS-300 Hitec servo costs 17 US$ if purchased in the USA. A Parallax Basic Stamp D costs 34 US$ if purchased in the USA. Consider another 17 US$ for the metal box, switches and the harness. Consider a VAT (value added tax) of 19.5% added also to the shipment price if these items are bought in France.
If you are a karter, are familiar with electronics and want to develop such a system send me an e-mail, I can support you with prototypes. ATTENTION, I will ask for a participation to pay at least the hardware. A complete system has almost 100 US $ of hardware, and a system with only the choke or the carb control is around 70 US $. I will be also available for help and sympatetic to people that want to hand made the system by themselves.
A brief operating manual
Jimmy's Flow Bench
Grant Beattie Welcomes You......
Rebel Racing Main Page
Ferrari (96/97) steering wheel:
Description of Ferrari (96/97) steering wheel (in German):
if you go-kart race against him, you will probably see him only this way: