A friend and I built a small motorized racer years ago.. seems to that we used a chainsaw engine with centrifugal clutch. drive was a chain around a drive sprocket near one rear wheel. Brakes were actually pretty neat. We welded ( he welded.. I have only just recently learned to weld.. ) a spare tire hub on to the axle, and used a belt.. leather or rubber converyor belting, wrapped around the wheel, going to a pedal operated cam, using a 1/4 inch steel rod for linkage. Pressing the brake pedal, cammed the linkage over, and drew the belt around the rim, stopped pretty good. An earlier version merely had a round metal drum.. cut from some 4" od pipe.. we found that sometimes the belt/brake would come off.. then you were scr*w*d... instead of adding lips to the pipe drum.. we used an old rusty rim of similar diameter to the front/rears... worked great.. belt never came off.
Stopping was good EXCEPT when it got wet..( mudpuddle ) then brakes went out, a sthe leater spun on the bare metal drum.
Our final improvement to the brakes was taking a strip of bias ply tire ( dating myself here... ) and ?riviting it to the rim.. so the leather strap pulled against tire....worked excelent.. though wore the leather good.. that was when we went to a conveyor belt strap that went around the hub.. etc...
By then I think we had also swapped out the power unit with a small gas motor from a roto tiller that actually had a cable operated clutch... very very nice... cable was also routed to a foot pedal using a long choke line as I remember...
That was fun.. untill the clutch cable broke once...
That was when we then added a 'kill' switch the operator could pull to kill the engine. Up untill then, this thing was more or less a team operated deal, as you wanted to be setting in it and have someone else start it, etc, as even the first generation with the chainsaw clutch wanted to freewheel a bit. ahh.. the memories.
Now that I've been remembering this, and with the thread about the other guy building a tractor.. now I feel like tinkering again.... wifes gonna kill me..
Soundguy