How do you properly calculate the maximum allowable twisting force required on a lever of X size/weight when including the armature between the two points?

Hello all I tried this question over at /r/askphysics and I didnt get the help I wanted.

Im building my first Robot armature and Im trying to calculate the maximum allowable length (L) and weight (W) a lever can have at 90 degrees when a servo has (X) kg-cm of torque. Now I know that a 3 kg-cm torque means that the servo has a twisting force of 3kg at 1cm at 90 degrees but beyond that I dont know. does that mean at 2 cm the servo only has a twisting force of 1.5kg? That doesnt seem right.

Also when considering the arm, say I have a 3 kg-cm torque servo, I know at 1 cm I can have 3kg of weight or force on that single point, but when accounting the armature connecting that one point to the motor, how is the mass of the arm connected to those two points calculated against the 3kg twisting force and thus how does it reduce the allowable weight at 90 degrees at 1 cm?

submitted by /u/JSArrakis
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