A gear motor is a motor and gear assembly box . Users in the selection of the motor , often because the torque motor speed is too high or too small to meet the needs , this time , the choice of gear motors are the most appropriate and immediate solution. I produced a miniature DC gear motor selection of the most commonly used DC motors , gear boxes in diameter from 12 to 37mm, 48mm and large-diameter pear-shaped , etc. , applied voltage of 1.5 volts to 24 volts, 10 watts less power , speed in each Go to tens of minutes a turn , the torque in the broad areas of 30 kg cm below . Calculation of a geared motor . Speed ​​n = nm ÷ i (rpm) nm- motor speed , i- total gear ratio gearbox . 2 torque T = Tm × i × ηg ÷ 1000 (kgcm) Tm- motor output torque (gcm), i- total reduction ratio gear box , ηg- gearbox overall efficiency ( % ) . 3 gearbox overall efficiency ηg = η1 × η2 × η3 × η4 · · · η1- First Senior Vice efficiency gear , η2- second Senior Vice efficiency gear , η3- third stage gear pair efficiency · · · , each level Vice- efficiency gear about 95 %. 4 the input power P1 = U × I (W) U- voltage (V), I- current (A). 5 Output power P2 = T × n ÷ 97.5 (W) T- torque (kgcm), n- speed (rpm). 6 gear motor overall efficiency η = P2 ÷ P1 × 100 = ηm × ηg (%), ηm- motor efficiency . Structure and characteristics of the DC motor DC motor using miniature mass typical products , with good electrical and mechanical properties and consistency. Due to size constraints and brush commutator DC motor speed is generally in the 3000-12000 rev / min, a speed is increased , the operating life of the motor will decrease significantly