Input torque doesn't match output torque

I want to have a precise output torque (or force) but when I input some torque of around 0.3 N.m with a pulley of radius 0.05 m, I can lift a weight of 1.7 Kg hanging directly with a cable connected to the pulley, doing some math:
1.7kg * 9.81 = 16.8N
16.8N * 0.05 m = 0.839 N.m
input << output
0.3 << 0.84

why is that? how can I relate my input torque to output torque - then force - accurately? I’m using D5065 270kv motor.

Hi there! We’re discussing this on the Discord, correct?

Yes, this question was posted before starting the discussion there. Anyway, I will keep this post, once I find a solution I will add the answer for reference.