How do servo motors work? | Teardown and explanation beyond the pulse.

I did a teardown of a servo motor to see what it is made of and how it works. Inside the casing is the DC motor, gears, a potentiometer, and an integrated chip.
I couldn't find great data sheets for the chips in my particular hobby servos. Instead, I looked up some popular RC servo chips. They all seem to have the same basic components - a potentiometer hooked to a voltage regulator and one shot generator, which converts position of the armature to a PWM pulse. This PWM pulse is compared to the original one sent by the microcontroller. This logic board finds the difference between the pulses, which is called the error. The magnitude of the error is sent to a pulse stretcher and the direction of the error is send to a flip flop to be stored as a high or low. The magnitude of the error is stretched out by the pulse stretcher. Then both parts of the error are sent to the output driver, which is probably an h-bridge. Most servos are 50HZ, which means this control loop is happening 50 times every second until the error is "zero". The dead band for the pulse stretcher sets a minimum pulse length that it will stretch. Anything below this limit is considered zero error.
There is also a resistor goes between the IC and the motor. The back EMF from the motor is used to dampen the control loop. I didn't feel like I could explain this well enough so I left that out of the video.
Let us know what you are building and have a wonderful day!
Servo chip part numbers:
KC5188 -- The chip on one of my servos
NE544
Mitsubishi M51660L
AA51880 -- www.agamem.com.tw/productPDF/A...
References:
-Build Your Own Quadcopter: Power Up Your Designs with the Parallax Elev-8by Donald Norris (Chapter 7)
-Analog Circuit Design Volume 2 by Jim Williams; Bob Dobkin (Chapter for pulse stretcher)
-DC Servos: Application and Design with MATLAB by Stephen M. Tobin (Appendix)
-Modern Control Engineering by Katsuhiko Ogata (read but too advanced for this video. A servo is actually a control loop where you are minimizing error over time)
-Practical Electronics for Inventors by Simon Monk and Paul Scherz (amazing book!)
-www.seattlerobotics.org/encode...
-sound.whsites.net/articles/ser...
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[@PBOZAI]

A channel that actually explains how a servo works, rather than just explaining how to control it with an Arduino. Thanks!

[@Socratica]

Wow, this is something we took for granted but never really thought at all about how it actually worked. Thanks for a great video!

[@joehopfield]

😂 most of my servos "don't work anymore" for similar reasons. Thanks for this, you have saved several more servos from horrible deaths

[@jamesthiel2628]

Thank you! I've been trying for days to find out what chips are used to control servos. All the other videos I've watched talk about controlling with an Arduino. You're the first to actually open a servo up and document what's inside. Glorious!

[@KjartanAbel]

Hi. Thanks for teaching how servos works. You have a great way of explaining.

[@nihadkhadraharkat575]

I've been looking for a good explanation for a while now and the one in your channel is the best thank you for the informations provided they re berry useful

[@AnthonyFrancisJones]

Great explanation! Well done! Such a simple looking device hides some rather complex concepts!

[@BioBush]

This will sound silly, but I feel like those little ICs are magic, like they can't be comprehended. But you broke the code and showed that it's just a series of logical steps in physical circuit form. It was fun to see!

[@SciJoy]

It doesn't sound silly at all. That's how I felt when I started learning electronics. That's how I still feel about most things. Bit by bit I'm figuring out how the magic works. Thanks for the nice comment.

[@BrackstonesTravelAdventures]

Great video and best explanation on youtube. Most do not explain the difference from input PWM and the potentiometer PWM etc: thank you

[@larrydaponte1708]

Loved your Servo video. I wanted a deep dive to understand how these servos worked so I could explain it to a class building the EZ Robot Arm. Thanks!

[@excelisfun]

So rad = the way you answered a question, thought about it, and made a great video!!!! : ) Thanks for the cool video, SciJoy : )

[@excelisfun]

PS your video rocks with the animation and close ups and many other cool things : )

[@SciJoy]

Thanks so much

[@DreThePlug]

Yessss girl get it 🔥🔥🔥 nice explication over the motors

[@NitishYadav-lb7zc]

amazing explanation!!!!!!

[@RobsPlaceFL]

Sweet! Great video!

[@snaprollinpitts]

very well described, thank you

[@Enigma758]

Good explanation!

[@DreThePlug]

Nice video I love it!

[@ljay0778]

What a treat! That great explanation and you pretty face! can't beat that! Thank you_

[@paulmeynell8866]

Awesome thanks

[@bvbtron12ka44]

Great 👍

[@childofthemosthigh5485]

Omg you are so smart

[@donaldhenke2750]

smart. i love you.

[@carbon273]

this is intense.

[@messybench974]

great video! such a good explanation ... but i have a question... What is the working voltage of the mini dc motor in the case of that 9gr servos, How much voltage is going out from the board to the motor? thank you so much! cheers

[@ganeshpingle.8423]

thank you for sharing knowlge. i am try to make a big servo using 775 DC moter but using potentiometer and other servo componts. so can you please guide me, please.

[@nickkowalski7979]

Nice video! Can you also explain how the potentiometer wiper is limited to the ~270 deg range of motion (if it has to be)?

[@smartwazihsw]

Whence can I get the servo ic ?? Can you make a video on converting dc motor to servo motor using this ic ?

[@envisionMagic]

I have a question, I hope someone can answer it, it’s a simple question. I need for a simple servo to just turn either direction about a quarter inch or less, nothing exact. I have been able to do this by simply connecting some of the three wires to enable battery and I see the server working perfectly as I wanted to but am I doing the right thing? Am I damaging the servo? I’m using a 9 V battery and it looks like when the power surge of the 9 V going to the servo, it causes it to move exactly how I want it to. So my question is is there a better way? I just need to push my remote control button and have it move about a quarter inch or less., Thank you all in advance.

[@farmerdave7965]

The motor inside the servo uses on/off control and on/off control requires deadband AKA hysteresis.

[@moslimalking8619]

can you explain operation feedback to servo motor and thank you

[@NERO-ez1mn]

so how to program a servo with a m51660l ?

[@gok_dogan]

I want to understand how the voltage that comes from potentiometer are converted pulse. In video you say one shot pulse generator. Do you mean one shot pulse generator as same for timer555 one shot generator ?

[@embeddedmicrocontroller]

very good explanation really knowledgeable i have one question in servo they use KC 5188 supply to motor from pin 3 and 6 and pin 1 and 8 going to transistor if i take that pin output and attach to 2 Channel DC 5V Relay Module with Optocoupler Low Level Trigger Expansion Board and with relay attach high volt motor and motor shaft fix with potentiometer will it work actually for high torque servo motors and drivers are very costly i want to control only direction speed not required in my project waiting for you response i subscribed your channel waiting for your notification thanks

[@EngRiadAlmadani]

Wow

[@SciJoy]

Took a look at your channel. What projects are you working on now?

[@EngRiadAlmadani]

@@SciJoy mind wave sensor with arduino

[@EngRiadAlmadani]

@@SciJoy kzbin.info/www/bejne/eWKwnnV7lMyVabs

[@martales8563]

all that for 3 DOLLARS , amazing