MOTORS AND SPEED CALCULATION

MOTORS AND SPEED CALCULATION

When you start designing wheeled robots start from the motors .
Decide the type of motor you are going to use .

According to gear arrangement DC motors can be broadly classified into

1. Motors with Internal gear's
2. Notors with External gear's

For beginners I would recommend using motors with internal gear box motor ,since they are easy to use(they eliminate the whole process of designing and fabricating the gear box ) .Internal gear box are available from a range of anywhere between 5 to 5000 RPM .And their speed can be varied either by

1.Varying the supply voltage or
2.Pulse width modulation (PWM )

After you choose the motor you can calculate the speed of the robot to get a rough idea about how fast your robot will go .(Never forget to do this while designing a robot ,otherwise you will end with a robot that is either too slow or too fast) .
The speed calculation doesn't involve big mathematical formulas .
Measure the diameter of the wheel (in meters) that you are going to use .Then multiply it with PI(pi = 3.14159265) .This gives you the circumference of the wheel .So you get a rough idea about how far the robot moves on one rotation of the wheel .

Circumference = Diameter X PI

Most cheap motors availabe never work to the specifics .The best way to find the RPM is trial and error .Apply the required voltage(remember to connect the wheel before applying the voltage) and start a stop watch for (say) 10 seconds and see how many time it rotates and then multiply it with 6 .This gives u the approx speed of your motor in RPM .And also mark a position on the wheel to make it easier to track it visually .
After getting the RPM of your motor multiply it with the circumference of your wheel .This gives u the approx speed of your robot in meters per minute.

Speed of your robot = RPM of motor x Circumference of your wheel (meters/min)