Speed regulator for accesibility step

[Hoppo]

hi all,
I am trying to convert a step that is fitted into the side of vans for disabled access from manual to automatic, Anyway i have converted the step to chain drive and am using the http://www.bosch-ibusiness.com/boaaelmoocs/category/CHP/283/product/803 bosch chp 12v Motor I am unable to find a motor that has the apropriate 5/6rpm, so i would like to stick to the motor present which brings me to my question, how could i bring the rpm right down without sacraficing torque i have tried using a 20a rated pwm but once wired up to a car battery the rpm could be achieved but looses all torque and can't succesfully lift the step! has anyone got any ideas on speed regulators e.t.c, my second question is as the nature of the step being driven on the pivot as the motor rotates the step is working against the motor until it reaches a certain point and then starts working with the motor speeds up and slams shut! is there anyway of regulating that! p.s there is not allot of room for gear reducions/increasement.
(pics of step https://flic.kr/s/aHsk4TgeyG)
many thanks
tom

 

[mfb]

Can the motor lift the step without any change?
If not, you have to increase torque mechanically, which basically means you have to find some way to fit in gears (there is some space between motor and axle).
If yes, an electric solution could be possible.

 

[Hoppo]

Thankyou for your reply,
Yes if the motor is powered directly off the battery it will swing the step shut with ease it's just a matter of trying to slow the motor down without loosing that important torque
Cheers
Tom

 

[mfb]

I still think gears are an interesting approach if they fit in somehow. They would also help to slow down the second part where the step moves downwards.
A velocity-dependent mechanical resistance could also help (in both parts).
Or switch off the motor with a very precise timing.