When estimating motor torque, which factor should be considered in addition to the torque constant?

• A. Gear ratio as needed.
• B. Battery voltage and current.
• C. Wheel diameter in the gear train.
• D. Ambient temperature.

Answer: (A)

Torque from a motor is set by the current through the torque constant, but what actually reaches the wheels is that torque transformed by the drivetrain. The gear ratio multiplies the motor torque (and conversely reduces speed), so when estimating wheel torque you must include the gear ratio (and an efficiency factor). The other items influence performance in different ways but don’t directly set the wheel torque the way gearing does: current determines motor torque, wheel diameter affects how torque becomes ground force, and ambient temperature has a more minor, secondary effect. So the gear ratio is the essential factor to include alongside the torque constant.