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EQUATIONS

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LOAD TORQUE

     The torque requirement for an application can be calculated, measured directly using a torque measuring device (torque watch), or measured indirectly using a DC motor. When using a motor, measure the current draw of the motor under load, and calculate the torque using the equation below:
          T = (I - INL) x (KT x N x h)

Where

I = Current
T = Torque
KT = Torque Constant
N = Gear Ratio (Equals 1 if there is no gearbox) h = Gearbox Efficiency (Equals 1 if there is no gearbox)
INL = No-Load Current

     Please be aware that this equation approximates the true load torque and does not take thermal conditions into consideration. The results are reasonably close and suitable for most purposes.

HORSEPOWER OF A MOTOR

     A motor's Hp (Horse Power) is calculated using the following equation.
          Hp= (T (lb-ft) x N (rpm)/5252. This gives the Hp at a rated speed.

RATED SPEED

     The output speed for a motor or gearmotor is given by the equation below:
          w = [VS - (I x Rmt)] / (KE x N)

Where

w = Speed
VS = Supply Voltage
I = Current (Obtained from previous equation) Rmt = Motor Terminal Resistance
KE = Back-EMF Constant
N = Gear Ratio (Equals 1 if there is no gearbox)

     Maximum continuous (rated) current can be obtained from the previous equation and used as the current value to obtain the speed at the maximum continuous (rated) torque.
     Please be aware that this equation approximates the motor speed and does not take thermal conditions into consideration. The results are reasonably close and suitable for most purposes.

Manufacturer of Highly Engineered Motors and Motion Control Products
SL Montevideo
2002 Black Oak Ave., Montevideo, MN 56265 USA

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