Control slot car with Arduino
It sounds like your powering the slot car directly from the arduino. Bad idea. Slot cars use a 120vac xformer to step down to 18vdc (Approx. dont really know the exact, look on your controller to see). By "normal power socket" I assume you mean 120vac wall power. Keep everything hooked up like it normally would (the slot car setup), then I would use the arduino to control a digital pot interfaced with the slot car throttle. You could have a slider control on the web site thats interfaced w/ the arduino dig. pot to control the speed. There are many other ways, but you being new to this, would be more complicated. Good luck.