Manual Clutch for Horizontal Shaft Motor

[Steve O'Hara]

Greg,

In 1991, my first full season in Toyota Atlantic, I set the lap record in the race while finishing 3d at Trois-Rivières. During the course of the race I discovered that I was faster in the sharp left hander under the arch if I did not go down to 1st and stayed in second and just lightly clutched on the exit to keep the engine from falling into the "gurgle zone".
In those days the Atlantic motors were still carbureted and if you applied full throttle anywhere below 7k the motor would stumble just a bit.

Too bad I didn't figure it out in qualifying... might have finished a bit higher if I had started closer to the front.

Danny's clutch looks very cool and if it can be controlled adequately it can produce the same or better results than a centrifugal clutch but the problem is in the details of the control. If electronics are added to make the control programable based on feedback then you have some interesting potential but the technology is way too much for karting.

In the Atlantic car the centrifugal clutch concept was entirely motivated by winning the starts but the development process exposed some other benefits that I had not really been looking for when I built it.
The biggest gain was the effect it had on the handling of the car in tight hairpin corners. Atlantic cars use one of several different types of torque biasing differentials and there is a trade off between getting the power down through both rear wheels and the understeer caused by the " live axle" effect of a locked up diff. I preferred the handing of a cam and pawl diff that basically locks up when torque is applied in either direction and that means when the driver comes off the brake and rolls into a very tight corner the engine braking keeps the rear wheels turning the same speed leading to understeer. We eventually found that we could tune the centrifugal clutch to release at the right rpm on corner entry to let the car coast rather than slow from engine braking and the elimination of torque in the diff would let the car roll through as though it had an open diff. The car could enter faster and turn in much better which set it up for a much better exit. Add the benefit of the engine being up in the power band once the throttle was applied and we had a big advantage over the competition in the hairpins. We saw the biggest gain from the system at Long Beach in 1994 where I ended up 2nd to Richie Hearn even though I spun early in the race while trying to pass for the lead and lost 10 spots.
With the big advantage in the Queens hairpin we were able to gear the car taller in 1st and 2nd than everyone else and not lose ground coming off the corner but when we hit 3d we had around a 600 rpm smaller drop in revs so we had a lot more power and could just drive by the competition down the long straight.
Those were interesting days... we had a fraction of the budget that the big teams like Players, Ralt America, Galles and Lynx had but we lots of ideas to help offset the cubic dollars and some of them worked.
I hope Danny will keep working on the design.... I would like to see how it could be used in conjunction with a jackshaft to facilitate direct drive karting without the problems of having to push the kart to start it.
Steve O'Hara