Motor Gearbox 12V 70 RPM - Find Radius to Lift 0.5kg

[faymalaka]

I have a motor

http://www.megabuy.com.au/gearbox-w...04324.html?utm_source=getprice&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

 

[Danger]

The specs of the motor are irrelevant, since they can't take into consideration external influences. The output of the gearbox is what matters. All that I can suggest, without breaking the forum rules about helping with homework, is that you should think of your "circular thing" as a lever arm.