Basics of Electronic Torque Control (ETC) and Torque Measurement

Some Basic of Electronic Torque Control (ETC)

ETC, or Electronic Torque Control stages as example

Electronic Torque Control utilizes advanced sensing and control capabilities of a Brushless DC (BLDC) Motor to precisely regulate current going into the motor.  Specific torque at each Stage was tuned according to the brushless motor specification, gears/impact mechanism, current and timing.  It is similar to a car gear shit table.

Torque vs Tension

While there is good reason we use “Torque” (force x length) to relate to pivoting force with tool of different lengths, However, it is an indirect measurement of force on a bolt.  The direct measurement of force on a bolt is “Tension“, the force applied along the bolt.

On the Electronic Torque Control (ETC) tool, the device measures and controls the current to a preset level and the motor would deliver a specific rotational force (not “Torque” by definition).  The higher the Stage#, the higher the current allowed to motor, and thus, the higher twisting force to the bolt. and the higher “Tension” applied to the bolt (or pressure on plane as a reactional force). But this is NOT exactly “Torque” (force x length) by definition

Measuring Torque Using Torque Tester

On the torque tester, it translates the “Tension” on the bolts to “Torque” with below relation.  While the ETC tool created a specific tension regardless the bolt size, the measured Torque will nevertheless varies depends on the bolt size, “D”, in below relation.

T = ( K * D * P ) / 12

  • T = Torque (ft-lbs)
  • D = Nominal Diameter (inches)
  • P = Desired Clamp Load Tension (lbs)
  • K = Torque Coefficient (dimensionless, includes friction, heat dissipated … and the like)


Due to above Torque and Tension relation, the torque delivered at each ETC Stage and bolt size will look like blow chart

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