speed limiter for playground

hI ive just red the post on speed limter play ground ,pls im working on the same course work , play ground with speed limiting device, postion of bearing seatings,limit and fits required at the bearing seatings,size and shape of the centre support column and seal arrangements, the revolving top plate which is a gap of only 300mm. the speed will be no more than 8rpm approx and the total weight including Children of the revolving top will be between 300Kg/400Kg . pls is their any calculation behind this and any possible sketches/ drawing .Thanks