Calculate Torque, Speed & Radius for Motor Gearbox

[faymalaka]

I have a motor

http://www.megabuy.com.au/gearbox-wi...utm_medium=cpc

and i want to attach a spindle, like a circular thing directly onto the shaft.

the circular thing has to have a radius, such that it lifts 0.5kg but does not lift 1kg,
i do not know how to find the radius so it lifts 0.5 but not 1! please help


]2. Homework Equations
F=ma, Torque=F*r



3. The Attempt at a Solution
i am having trouble as i don't think these formula's are the only ones i need. also the unit for toque is in a weird form and i don't know how to aplly it.

if i try to sub what i know into Torque=F*r, it doesn't work out.

 

[Marioqwe]

Link is down.

But if you think about it, you just need to find F for 1kg. And if torque is given, you can find R. Then you can say something like: "r has to be r<R."

Same for 0.5kg.