Robotics tool kit series - servos & motors

We continue to our toolkit series and today we will talk about servos and DC motors.

A motor is often used to turn the wheels of a robot whereas a servo is used for angular movements often precision related like robotic arms.

Example - For a robot like SID2 we use a DC motors for wheel movements whereas for a hexapod like MK6 we use servos to control the legs.

So what's the difference for a starter for a motor and a servo?

Motors are a much simpler component which spins with the current. They work on pulse width modulation (PWM) and the RPM varies with the PWM provided.

Servos on the other side rotate a shaft to a degree and is a combination of dc motor, potentiometer and a gear unit. Here the movement is regulated by the time of the current provided.

The current flow is not same and is based on the PWM signal based on the duration. So a duration 't' in PWM will drive the servo shaft at position 'p'.

The other difference is motors like a DC motors will have two wires - one ground and one positive. You use a motor driver bridge to drive the PWM and control the RPM and direction of the revolution.

For a servo, you have three wires - signal wire that releases the PWM 't' and the positive and negative. For control of servo's especially, if there are many like in MK6, we use a servo controller board.Servo also comes with servo horns in various shapes which are used for angular control.

Both servos and motors can be used with by single board computers or micro controllers.

One thing to keep in mind is that no servo and motor is fit for all robotics needs.

Example: You would need to factor in the weight of your robot to calculate the torque/rpm you need from your motors. Whereas for a servo you would need to know how much accuracy, the degree of freedom's you are looking and decide the cost of servos you wish to buy.

If you have just started then try the normal cheap servos and motor to control them using simple codes and drivers. Then you may wish to more expensive motors and servos.

Common DC motors: These look something like above and are called as BO motors. These come with the most entry-level robotic kit as well.

Common servos: These are called as 9G servos and looks something as in the picture above. These are a bit noisy and comes with plastic gears. Excellent choice for starters before moving to the more expensive and durable metal gear based servos.

Servo tester | Robotics blog | Start with robotics

Servo tester: A very cheap module as below is very handy for checking servos. This comes at $2 dollars and highly recommended when you end up with loads of servos and need to test them easily and fast. Hope you found this tool kit suggestion useful.

Guest blog on robotics | Robotics blog

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