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Gearbox and Torque

Most robot joints are driven by an electric motor through a gearbox that increases torque and reduces speed. The output torque is the motor torque multiplied by the gear ratio and the efficiency, which is always less than 1 because some energy is lost as friction and heat in the gearbox.

\tau_{out}=\tau_{in}\cdot N\cdot\eta

torque out of a gearbox

Symbols

$\tau_{in}$	motor torque into the gearbox	Nm
$N$	gear ratio
$\eta$	efficiency

Example

$\tau_{in}=0.6$ Nm, $N=100$ , $\eta=0.85$ :

$\tau_{out}=0.6\cdot100\cdot0.85=51$ Nm.

Do not forget the efficiency

\eta

– the real output torque is always a bit less than

\tau_{in}\cdot N

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Part of Robotics: Robot systems.