speed current out in heat I²R efficiency
stall torque no-load Kv Km = Kt/√R

speedcurrentoutput powerefficiencyEverything here comes from two lines: V = I·R + Ke·ω and τ = Kt·I (in SI units Kt = Ke). Speed falls in a straight line as you ask for torque. Current climbs in a straight line with it. Power peaks at half the stall torque, and efficiency peaks much nearer no-load. Raise the voltage and the speed line moves up in parallel, and stall torque rises with it. The dashed lines are the motor at 24 V.