Thursday, 7 September 2017

geared dc motors

By Ask Biomedical

*Geared DC Motors* - 


The geared DC motors are an advanced variation of the brush DC motors. They have a gear assembly attached to the motor. The speed of the motor is measured in Rotation Per Minute (RPM). The speed of the motor is reduced with an increase in torque with the help of gear assembly. By using a correct combination of the gears to motor the speed of the DC motor can be reduced with an increase in torque. This provides stability in the rotation of the motor and the motor can be stopped or changed speed in a controlled manner. 
 
The DC motors work in a specified range of the voltage and higher is the input voltage, higher is the RPM. For Example, if the motor works in the range of 6-12V, it has the least RPM at the input voltage of 6V and the maximum RPM at the input voltage of 12V.
 
The working of the gears in such motor is most interesting. It is based on the principle of conservation of angular momentum. The gears having smaller radius cover more RPM than the one with a larger radius. However, the larger gear will give more torque to the smaller gear and vice versa. The comparison of angular velocity between input gear (the one that transfers energy) to output gear gives the gear ratio. When multiple gears are connected together, conservation of energy is followed. The direction in which the other gear rotates is always opposite of the gear adjacent to it. In any DC motor, RPM and torque are inversely proportional. Hence the gear having more torque will provide a lesser RPM and converse. For controlling a geared DC motor, pulse width modulation technique is applied.
 
The torque and RPM of a geared DC motor depend upon the gear ratio. For example, suppose a DC motor may run at the speed of 12000 RPM and provide 12 kg-cm torque. By adding a 255:1 gear down, the speed of the motor can be reduced and torque can be increased. So, by adding 255:1 gear down, the resultant RPM is reduced to 53.3 (12000 rpm / 225) and torque is increased to 22.5 kg-cm (0.1 x 225). The motor now is able to move significantly more weight at a reasonable speed

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