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The Servo Guide

Published on: | Author: Nedko Chulev | Categories: 2017a, Tutorials

1. Introduction and basic components of a servo motor
2. Weight
3. Energy consumption
4. Gear types
5. How far does the servo turn?
6. How does the servo move?
7. Digital or analogue
8. Servo project ideas
10. Additional information

 

1. Introduction and general components of a servo motor

What do your robot girlfriend rolling her eyes at you and an RC airplane have in common?
They both use servo motors! The only difference is that one uses them for motion and the other one for emotion. /ba dum tss

Jokes aside, servo motors are really useful and the limit to their use lies even beyond the sky! Through a well constructed Google search, I’ve discovered that servo motors were used by NASA and we know for sure that NASA is aiming way past the sky.

Now, before we jump into any freaky ideas, let’s understand what a servo motor really is.

“A Servo is a small device that incorporates a two wire DC motor, a gear train, a potentiometer, an integrated circuit, and an output shaft.”

Servo-Overview

Alright, now you go out there and make robots!… No, really, it may sound confusing at first but it really isn’t! Let’s dissect the above sentence to get a better understanding of what a servo is:

A small device – most of the time as big as a walnut but can be a lot bigger.
It incorporates a two wire DC motor – ‘member those toy cars you’ve taken apart for science when you were a kid? A two wire DC motor is nothing more than the motors those toys use.
A gear train – A cogwheel. A round piece with teeth. A toothed wheel if you will.
A potentiometer – This can be its own conversation but simply put it’s a spinning knob (like the ones you have on your oven for the temperature control or your audio system’s volume control) which can be used to control voltage or frequency. A servo motor uses the potentiometer to measure the position of the servo, which is controlled by the next component.
An integrated circuit – Another component that is a science in itself. You can think of it as the brain of the servo, which takes input (for example from an Arduino) and tells the motor to move. If you’ve been wondering why your servo has a 3rd wire other than the power and the ground ones – it is there to enable the communication between the brain of your servo and your Arduino.
The output shaft – The complicated way of describing the actual part of the servo that you’re going to use in your project – the hole with the part that will spin around.

That is basically what a servo consists of but you might want to learn a bit more about those nifty little guys.

2. Weight
A servo’s weight determines it’s category (at a corresponding price, of course) and what projects it can and cannot be used for. Do keep in mind that size doesn’t always mean everything, as servos generally consist of 2 types – those that are created for the purpose of speed and those that focus on torque. Naturally the first sacrifices torque and the second speed. Think of them as of athletes. Those that can run very fast are pretty skinny and thus cannot lift heavy weights. Those that can lift heavy weight are pretty bulky and can’t run as fast. Just to give you a general idea though – the very teeny-tiny servos weighs about 1.5g (0.05 oz) and the hulks among the servos can be as heavy as 80g (2.8 oz).

3. Energy consumption
Servo motors usually need between 4 and 6 volts. The very very small ones can run off of as little as 3.7V whereas the larger ones require between 4.8V and 6.0V. Another cool thing to know about servo motors is that they will consume as much energy as they need to move whatever it is that you have attached to them. So not only do they serve you great work but they are also energy efficient and thus care for our planet.

4. Gear types
Depending on the price you are willing to pay(and wether you want your project to be a total overkill) you are given a choice between a few different types of materials for the gears of the servo motor:

  • Nylon – the lowest price point servo motors (you probably thought that’s plastic anyway)
  • Karbonite – a slightly better option which offers more stability and longevity (can lift heavier than nylon ones and will likely last longer too); also generates less noise when operating in case that buzzing’s driving you crazy
  • Metal – will wear out faster than nylon but can withstand much heavier lifts
  • Titanium – very durable and robust – basically THE overkill for beginner projects but crucial if you need a near 100% reliable servo in your project

5. How far does the servo turn?
Something to keep in mind when using servos is their travel distance. They are usually built to turn in the range of 0° to 180° (in reality it’s from -90° to +90°) and are typically physically limited by the way the gears are built (it can be manually modified but don’t bother – it’s not worth it). Servo motors save even more energy by only investing their full potential when they have to move a long distance. For smaller movements they simply run at a slower speed also known as proportional control.

6. How does the servo move?
The actual movement of the servo happens after its “brain” sends out electrical pulses of different length to the motor. Imagine the range of degrees the motor can move as a scale for the duration of the pulses that are being sent from the integrated circuit to the motor. The integrated circuit checks the current position of the potentiometer against what is being sent and adjusts it accordingly if there is a difference from its current position.

7. Digital or analogue
The only difference between a digital servo and an analogue one is the frequency at which the impulses are being sent. Analogue servos have around half the “refresh rate” of a digital servo thus making the digital servo a more precise companion. Analogue ones send out impulses at a rate of 50Hz whereas their digital counterparts do so at 100Hz. The “only” advantage this has is for projects that require “smoother” or very precise movements.

 

8. Servo project ideas
That’s pretty much everything you might need for your first (or second) project. The only question that may remain unanswered is what to use servos for?! Fear not, I’ve compiled a highly scientific, futuristically innovative list of 13 ideas for your future project(s) below:

1. The self-turning door key
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2. The back-scratcher
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3. The toilet paper dispenser
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4. The beardcomb
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5. The nay-nay
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6. The candle lighter
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7. The meal-chooser
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8. The guitar player
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9. The “hold my beer”
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10. The GLaDOS
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11. The DeLorean
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12. The “Let there be light”
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…and of course…

13. The emotional robot girlfriend
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10. Additional information (did you notice yet?)
Of course there are countless places where a servo could be put to good use and this guide may not be of any help for your super-duper advanced project. If you’re curious how to integrate a hardcore servo motor in a NASA’esque project and travel light years through time and space…

…then all the information about servos you need can most likely be found here.

Happy tinkering!

linked categories 2017a, Tutorials

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