How RC Servos Works.pdf

7/27/2019 How RC Servos Works.pdf

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An RC servo

The anatomy of an RC servo

The servo with the guts out

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The block diagram of the

automation for an RC servo
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31/10/13 How RC Servos Works

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It would be very nice to have one type of universal connector that all

manufacturers would use, but this is yet not true. Although nowadays standards are

trying to be settled, still there are servos with different connectors and color codes.

Therefore, it is highly recommended, before you proceed connecting a servo or

experimenting with it, to check first what each wire does.

Following we have a table with some known manufacturers and the color code that they follow. Not that servos

have 3 wires that comes out: One wire that goes to the positive of the power supply, one that goes to the negative of the

power supply, and another one with the input signal.

Manufacturer Positive Negative Signal

Airtronics(Obsolete) RED BLACK (in the middle) BLACK, WHITE or BLUE

Airtronics / Sanwa(Obsolete) RED BLACK WHITE or YELLOW

Airtronics / Sanwa RED BLACK BLUE or YELLOW

Futaba RED BLACK WHITE

Hitec RED BLACK YELLOW

Japan Radio RED BROWN ORANGE

Tower Hobbies RED BLACK WHITE

Kyosho/ Pulsar RED BLACK YELLOW

If you cannot find your servo on the above table, or cannot find the manufacturer, you should get some help from

the following general information:

The vast majority of modern servos have the positive wire in the middle (just to avoid damaging the

controller in case of reverse plug insertion)

Most older Futaba servos use a "G" type plug.

Modern Futaba "J" connectors have a little polarization slot or tab

Some old Airtronics connectors have a gray or white strip on the positive wire

The old Airtronics connectors have three ridges on top

In general, BLACK or BROWN should be negative, RED should be positive and BLUE or WHITE or

YELLOW should be the signal

How to control an RC Servo

The power supply of servos is usually from 4.6 to 6 volts, and that could

vary between manufacturers and types. For maximum torque and speed

achievements, you should supply the servo with it's maximum nominal voltages.

As mentioned before, servos are controlled with a PWM signal driven to

their signal wire. A PWM signal has three parameters that characterizes it: The first is

the amplitude (or peak to peak voltage) of the signal. You should use from 3 to 5

volts for your signal, according to it's specifications. The second is the frequency. In

PWM, the frequency is usually fixed to a value. For analog servos the frequency is

30-50 Hz, and for digital servos it is 300 to 400 Hz.

The third and most critical value is the positive pulse with of the PWM, AKA "duty cycle". The width of the pulse

will have a direct result into the drive shaft position. In other words, to control the position of a servo, you should change

the duration of the positive pulse of the PWM signal driven to the signal wire of the servo...

The translation of pulse width to drive shaft position is not easily to be made. It depends on the manufacturer and

the type of servo. It is a good beginning to say that the pulse width duration for a full drive shaft move should be within

the range of 1mSec to 2mSec. If we take for example a rotary servo, a PWM with positive pulse width 1mSec would

cause the shaft to revolve fully left. A 2mSec positive pulse width would cause the drive shaft to revolve fully right.

1.5mSec pulse width would cause the shaft to turn to the middle of the revolution area.

There are of course manufacturers that have different min and max pulse width duration values. But those

differences slightly differs from the range of 1 to 2 mSec.

An RC Servo in the lab

And here is an example. Using a very simple PWM circuit, we will control an RC servo. This is the best circuit in

terms of flexibility and simplicity that i have came up with. It is able to change it's frequency, its highest and it's lowest

pulse width duration by just changing one component each time! With the addition of 3 potentiometers (instead of three

set-up resistors) the circuit can change all the above characteristics with just a screw driver!

An oscilloscope will be all the time visible so that you will see how does the angular position of the servo changes

in conjunction to the PWM duty cycle. Here is the corresponding video of this experiment:

Servo Motor Controllers

Servo Motor Basics

Long Range Video

Start Your Own Website

A very simple PWM servo

controller circuit to test our servo

in the labs
http://pcbheaven.com/scripts/imagepresent.php?filename=%2Fwikipages%2Fimages%2Fhowservoswork_1245416004.jpghttp://721352916.keywordblocks.com/Start_Your_Own_Website.cfm?&vsid=262244595394388&&hvsid=00001383222858516032854539435895&sttm=1383222858517&upk=1383222859.3736&dytm=1383222858871&kp=4&kbc=bd39e5d13af56bcee62d6664833c54bd.d2s&kt=234&ki=27043299&ktd=18940180&kbc2=101&fdkt=201&fp=wneKOkzoYPw%2FIzbf%2FotfqQ%2B3x%2BkUIdNyiqOWSyVR2LQcwW9%2Fn%2BGkK2tNlBodjX5Hkwbw%2FqlvuoVXVqas3rUdjyNoWj2YAT9zDQrTWyvfoK%2B2lvfaNcPm0a5Wk%2FcLbNmf&cme=FK9xhj58RE9UX4%2FclRx720hfi%2F%2Bb8E6oV899%2FE%2F1GjVXoS0ndW9VY%2Bsr2DpaHYOu6V1usdtv4JkqSTQHnChlLd1Sge50h3JuB6lLBpxxVc7bdbCmt2hAeXoGMXtm3OrbbiOAcALvCqA%3D%7C%7CN7fu2vKt8%2Fs%3D%7CFcl4VLL%2BIaIcsq%2BAjLmagceBwOWWE9DoWHsB1bLf3T0ZCGfaxzi3MoLFy0K1haNfC1Rbye7lEk8%3D%7CJf0d%2BWoAdPugZdiC0MCJNJau7I3ddLM8W8ylGHjbmIc%3D%7C2kUY5MRlnSc%3D%7C&cid=8CUZX8B20&crid=225226350&oRurl=http%3A%2F%2Fcdn3.media.net%2Fmediamain.html%3F%26esi%3D1%26cid%3D8CUZX8B20%26crid%3D225226350%26pid%3D8POS3M44A%26size%3D728x90%26cpnet%3DyVb1sHm%252B0KKoFeunLBVJxaXvbiW3ipSY45%252Bp%252BH53Alw%253D%26cme%3D%252BGrnje2DVSUEOXxUGC8xNiavel%252FfZ5Xsnz4bMh%252Blsr2y9cSqHE3VUyQktXJ1%252BfoMvtRtwN16AdqxG3QiEzO0j3PkHd8YmOzJRub3E4mQhME%253D%257C%257CN7fu2vKt8%252Fs%253D%257CFcl4VLL%252BIaIcsq%252BAjLmagceBwOWWE9DoWHsB1bLf3T0ZCGfaxzi3MoLFy0K1haNfC1Rbye7lEk8%253D%257CJf0d%252BWoAdPugZdiC0MCJNJau7I3ddLM8W8ylGHjbmIc%253D%257C%26cc%3DGB%26bf%3D0%26vif%3D1%26nb%3D1%26fvips%3D0%26ap%3D0%26pf%3D0&size=728x90&lpid=&tsid=4&ksu=70&chid=&acid=&fvips=0&http://721352916.keywordblocks.com/Long_Range_Video.cfm?&vsid=262244595394388&&hvsid=00001383222858516032854539435895&sttm=1383222858517&upk=1383222859.3736&dytm=1383222858871&kp=3&kbc=servos&kt=236&ki=17862764&ktd=18993428&kbc2=||l=1001||&fdkt=201&fp=wneKOkzoYPw%2FIzbf%2FotfqQ%2B3x%2BkUIdNyiqOWSyVR2LQcwW9%2Fn%2BGkK2tNlBodjX5Hkwbw%2FqlvuoVXVqas3rUdjyNoWj2YAT9zDQrTWyvfoK%2B2lvfaNcPm0a5Wk%2FcLbNmf&cme=FK9xhj58RE9UX4%2FclRx720hfi%2F%2Bb8E6oV899%2FE%2F1GjVXoS0ndW9VY%2Bsr2DpaHYOu6V1usdtv4JkqSTQHnChlLd1Sge50h3JuB6lLBpxxVc7bdbCmt2hAeXoGMXtm3OrbbiOAcALvCqA%3D%7C%7CN7fu2vKt8%2Fs%3D%7CFcl4VLL%2BIaIcsq%2BAjLmagceBwOWWE9DoWHsB1bLf3T0ZCGfaxzi3MoLFy0K1haNfC1Rbye7lEk8%3D%7CJf0d%2BWoAdPugZdiC0MCJNJau7I3ddLM8W8ylGHjbmIc%3D%7C2kUY5MRlnSc%3D%7C&cid=8CUZX8B20&crid=225226350&oRurl=http%3A%2F%2Fcdn3.media.net%2Fmediamain.html%3F%26esi%3D1%26cid%3D8CUZX8B20%26crid%3D225226350%26pid%3D8POS3M44A%26size%3D728x90%26cpnet%3DyVb1sHm%252B0KKoFeunLBVJxaXvbiW3ipSY45%252Bp%252BH53Alw%253D%26cme%3D%252BGrnje2DVSUEOXxUGC8xNiavel%252FfZ5Xsnz4bMh%252Blsr2y9cSqHE3VUyQktXJ1%252BfoMvtRtwN16AdqxG3QiEzO0j3PkHd8YmOzJRub3E4mQhME%253D%257C%257CN7fu2vKt8%252Fs%253D%257CFcl4VLL%252BIaIcsq%252BAjLmagceBwOWWE9DoWHsB1bLf3T0ZCGfaxzi3MoLFy0K1haNfC1Rbye7lEk8%253D%257CJf0d%252BWoAdPugZdiC0MCJNJau7I3ddLM8W8ylGHjbmIc%253D%257C%26cc%3DGB%26bf%3D0%26vif%3D1%26nb%3D1%26fvips%3D0%26ap%3D0%26pf%3D0&size=728x90&lpid=&tsid=4&ksu=70&chid=&acid=&fvips=0&http://721352916.keywordblocks.com/Servo_Motor_Basics.cfm?&vsid=262244595394388&&hvsid=00001383222858516032854539435895&sttm=1383222858517&upk=1383222859.3736&dytm=1383222858871&kp=2&kbc=b58cff038df16118fcb7d57c03d853d0.d2s&kt=201&ki=25761989&ktd=18940180&kbc2=0||l=1007||&fdkt=201&fp=wneKOkzoYPw%2FIzbf%2FotfqQ%2B3x%2BkUIdNyiqOWSyVR2LQcwW9%2Fn%2BGkK2tNlBodjX5Hkwbw%2FqlvuoVXVqas3rUdjyNoWj2YAT9zDQrTWyvfoK%2B2lvfaNcPm0a5Wk%2FcLbNmf&cme=FK9xhj58RE9UX4%2FclRx720hfi%2F%2Bb8E6oV899%2FE%2F1GjVXoS0ndW9VY%2Bsr2DpaHYOu6V1usdtv4JkqSTQHnChlLd1Sge50h3JuB6lLBpxxVc7bdbCmt2hAeXoGMXtm3OrbbiOAcALvCqA%3D%7C%7CN7fu2vKt8%2Fs%3D%7CFcl4VLL%2BIaIcsq%2BAjLmagceBwOWWE9DoWHsB1bLf3T0ZCGfaxzi3MoLFy0K1haNfC1Rbye7lEk8%3D%7CJf0d%2BWoAdPugZdiC0MCJNJau7I3ddLM8W8ylGHjbmIc%3D%7C2kUY5MRlnSc%3D%7C&cid=8CUZX8B20&crid=225226350&oRurl=http%3A%2F%2Fcdn3.media.net%2Fmediamain.html%3F%26esi%3D1%26cid%3D8CUZX8B20%26crid%3D225226350%26pid%3D8POS3M44A%26size%3D728x90%26cpnet%3DyVb1sHm%252B0KKoFeunLBVJxaXvbiW3ipSY45%252Bp%252BH53Alw%253D%26cme%3D%252BGrnje2DVSUEOXxUGC8xNiavel%252FfZ5Xsnz4bMh%252Blsr2y9cSqHE3VUyQktXJ1%252BfoMvtRtwN16AdqxG3QiEzO0j3PkHd8YmOzJRub3E4mQhME%253D%257C%257CN7fu2vKt8%252Fs%253D%257CFcl4VLL%252BIaIcsq%252BAjLmagceBwOWWE9DoWHsB1bLf3T0ZCGfaxzi3MoLFy0K1haNfC1Rbye7lEk8%253D%257CJf0d%252BWoAdPugZdiC0MCJNJau7I3ddLM8W8ylGHjbmIc%253D%257C%26cc%3DGB%26bf%3D0%26vif%3D1%26nb%3D1%26fvips%3D0%26ap%3D0%26pf%3D0&size=728x90&lpid=&tsid=4&ksu=70&chid=&acid=&fvips=0&http://721352916.keywordblocks.com/Servo_Motor_Controllers.cfm?&vsid=262244595394388&&hvsid=00001383222858516032854539435895&sttm=1383222858517&upk=1383222859.3736&dytm=1383222858871&kp=1&kbc=b58cff038df16118fcb7d57c03d853d0.d2s&kt=201&ki=25762000&ktd=35717396&kbc2=0||l=1007||&fdkt=201&fp=wneKOkzoYPw%2FIzbf%2FotfqQ%2B3x%2BkUIdNyiqOWSyVR2LQcwW9%2Fn%2BGkK2tNlBodjX5Hkwbw%2FqlvuoVXVqas3rUdjyNoWj2YAT9zDQrTWyvfoK%2B2lvfaNcPm0a5Wk%2FcLbNmf&cme=FK9xhj58RE9UX4%2FclRx720hfi%2F%2Bb8E6oV899%2FE%2F1GjVXoS0ndW9VY%2Bsr2DpaHYOu6V1usdtv4JkqSTQHnChlLd1Sge50h3JuB6lLBpxxVc7bdbCmt2hAeXoGMXtm3OrbbiOAcALvCqA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4/11

The circuit

Following, i have added the above circuit schematic diagram.

As you can see, the circuit is a 555 connected as astable multivibrator. The servo is controlled through a

2N2222 transistor directly connected to it's signal wire. You should add a resistor if your RC needs lower signal voltage,

and also you should take care about the supply voltage of your servo. If it is powered with lower than 5V, you should

add a zener diode accordingly.

There are 3 componnents, three resistors in the circuit that have no value, the R1, the R2and the R3. Those

components are the ones that changes the characteristics of the output signal. The resistor R3is the one that will change

the PWM frequency. In my test circuit, this resistor is 470K, and this results in an oscillation of about 35Hz.

The second resistor is the R1. By changing the value of this resistor, it results to the lower positive pulse duration.

In my test circuit, this resistor is chosen to be 6.9K(two resistors in series, one 2.2K and one 4.7K) and as a result i get

about 0.6mSec minimum pulse duration.

The third and last resistor is the R2. By changing it's value, it results to the maximum positive pulse duration. I

have chosen a 33Kresistor. The maximum pulse duration that i get with this resistor is about 2.5mSec.

As you can see, this is a very flexibly circuit. If you change the R1 and R2 resistors with a rheostat, then you will

be able to change the minimum and maximum angle of the drive shaft by simply changing those rheostats. Isn't that

something for such a simply circuit!

Relative pages

555 theory of operation

Basic transistor circuits

Learn how dimmers work

PWM signal theory
http://pcbheaven.com/wikipages/PWM_Modulation/http://pcbheaven.com/wikipages/Dimmer_Theory/http://pcbheaven.com/wikipages/Transistor_Circuits/http://pcbheaven.com/wikipages/555_Theory/http://pcbheaven.com/wikipages/How_RC_Servos_Works/


5/11



Peltier coolers (TEC) theory of operation

Learn about the WiFi interferences to the human body

How to make a PWM fan controller / LED dimmer using a 555

Dr.Calculus: LED resistor calculator

Dr.Calculus: Standard resistor values calculator

Op-Amp IC Pinouts

Learning PICs @ PCB Heaven On-Line Book

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At 30 August 2013, 9:48:05user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@Robert Sisco It all has to do with quality (==price). You cannot exchange a servo with stepper nor a stepper

with a servo. They are designed to do different jobs. Get a good (and expensive) servo and it will not fail.

At 27 August 2013, 14:24:40user Robert Siscowrote: [reply @ Robert Sisco]

I am concerned with the reliability of the potentiometer (variable resistor) in the back of the servo. I have

repaired many old Radios, where the volume control becomes noisy after a few years. Would the stepper

motor and gearbox arrangement be more reliable? Regards, Robert

At 14 August 2013, 4:27:17user Innaswrote: [reply @ Innas]

Hi,

Could anyone please help me in finding a Radio Control circuit (transmitter and receiver circuits) to control 4

servos and a small DC motor.....anything to help will be greatly appreciated.

Cheers

At 17 July 2013, 15:29:18user Pete Langerwrote: [reply @ Pete Langer]

Hi, Can I use a AirPlane Servo in a Buggy or will it burn it up? Spektrum offer an A6020 which I purchased

by accident. They also offer a S6020 for surface. the torque and speed specs are the same and they use the

same gear set and casing, but someone told me the dead band is different and could burn it up if I use it in my

Buggy on the surface.

Electric Linear Actuatorswww.linearactuator.co.uk

and screw jacks , bevel gear boxes Designed For Industrial Machines.
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6/11



best regards,

PJ

At 27 June 2013, 6:40:48user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@eemjay They are both ceramic.

At 25 June 2013, 17:05:30user eemjaywrote: [reply @ eemjay]

I think I figured it out. I was using ceramic capacitors. I need to get the polarized Electrolytic Cap. I justordered the 100nF (0.1uF) capacitor. is it necessary to get the 0.1nF cap in Electrolytic? I dont think they

come that small...


@eemjay Futaba has some good servos. Check first if the waveform is stable though with an oscilloscope.

At 17 June 2013, 4:10:52user eemjaywrote: [reply @ eemjay]

I have a similar problem as David. My circuit works, I have attached a potentiometer and can rotate the servo,

but it is jittery and hums. It seems like the little motor in the servo is working even when i am not altering the

signal, and it is heating up. My servo is a cheapy, so do I just need to invest in a better servo? Any suggestionson brand or model. I'm trying to keep it small


@David Eriksson Yep, if the waveform is ok, then the problem is the servo encoder (potentiometer inside the

servo). Cheap ebay servos have this problem usually

At 4 June 2013, 8:41:16user David Erikssonwrote: [reply @ David Eriksson]

Hi,

Thanks for the incredible informative post! I have built your circuit but instead of going to one particularposition, the servo jitters back and fourth. On the oscilloscope the waveform locks as you describe. There is a

voltage drop of around 1V (from 6V to 5V) when I connect it, but that should be ok, or?

Could this be because of the servo I am using?

David

At 23 May 2013, 12:56:27user Pliniowrote: [reply @ Plinio]

Hi Bernt,

You can amplify the signal from your PT100 and introduce it into an error amplifier circuit using an operational

amplifier. ALthought it seems complicated, it s very simple and I would be glad to help. The solution I think

consists on an amplifier that receives the weatstone bridge signal and produces a proportional, amplified DC

signal. The second one could compare the setpoint you have with the actual temperature, producing an "errorvoltage" that could be applied into the 555 in PWM mode. My e-mail is [email protected] Regards.

At 22 May 2013, 23:13:30user ARM AVRwrote: [reply @ ARM AVR]

Hi Bernt

You can use differential gain amplifier.

At 9 May 2013, 16:13:36user Pliniowrote: [reply @ Plinio]

Nice post! Nobody told me that an analog servo could use a PWM signal. As the name analog, I thought it

was a comparator with an H brigde....So, stupidly, I tried to tie potentiometers, variable suppliesvoltage/current.....and nothing worked.....Back to the bench....Thank you!

At 4 February 2013, 23:04:28user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@Alan Jacobs Remove first the power from the 5V, and then remove the PWM signal. this might work.
http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27plinio%27%29/http://replytouser%28%27arm%20avr%27%29/http://replytouser%28%27plinio%27%29/http://replytouser%28%27david%20eriksson%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27eemjay%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27eemjay%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/


7/11



At 2 February 2013, 17:10:16user Alan Jacobswrote: [reply @ Alan Jacobs]

Here's an unusual servo question regarding turning OFF a standard analog RC servo motor. I am an amateur

astronomer with plenty of good test equipment ( scopes, logic analyzers, meters,etc ). We are building a crude/

cheap grating spectrograph for a telescope. The light weight grating film is sitting on top of an RC servo motor (

shaft vertical ) which rotates the grating less than a few degrees. There is NO TORQUE LOAD on the servo

motor since the shaft is vertical. We rotate the grating with the servo and then turn off the power to reduce

EMI.It works well. Unfortunately, most hobby RC servos seem to have a capacitor which discharges to rotate

the shaft to a fail-safe home position on power off. We need the grating to stay in position when the power to

the servo is turned off. Is there a way to defeat the fail-safe home position feature....maybe remove the

electrolytic capacitor in the motor ? If you reply send an email to: [email protected] & thanks.

Alan Jacobs

Green Bay, Wisconsin, USA

At 25 January 2013, 12:09:16user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@H Chris Spreckley It will not be simple Chris, you will need a microcontroller. I suggest that you check out

Arduino which has simple servo solutions.

At 23 January 2013, 5:48:36user H Chris Spreckleywrote: [reply @ H Chris Spreckley]

Dear George, My promulgated web site not currently active.

I am wanting to create as simple a circuit as possible to drive a 5v servo motor in order to operate model rail

points and semaphore/arm signals. The motor needs to be instructed to turn 90 degrees, say left and halt and

then 90 degrees right and then halt with the halts being from a few seconds to infinity. Currently signals in use

are operated by way of nomentary switches and magnetic solenoids which are entirely successful but not

prototypical as they are very quick in operation. The servo works at an appreciably slower speed which I

deem to be more in keeping with reality.

Can you help me or point me in the right direction please. I am currently building your servo test circuit but

don't expect to be able to operate the signals and turn outs from it.

Cheers,

Chris Spreckley

At 21 November 2012, 7:19:04user wkteywrote: [reply @ wktey]

Nice post!

Until now only I get a well understanding on RC servo motor.

Good job!

At 20 November 2012, 4:09:42user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@Ivan depends on many parameters like resistance etc. Normally, with a proper set of resistors it will work

At 19 November 2012, 7:36:07user Ivanwrote: [reply @ Ivan]

If I set bend sensor instead of potentiometer... does it work normally?

At 8 October 2012, 3:32:18user Billwrote: [reply @ Bill]

I am not even into RC vehicles but have been offered a opportunity.

Is there controls available to run a full size Jet ski?

I am going to need 12 units.

Any help would be appreciated.

Bill

At 18 September 2012, 2:16:20user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@krishna nope, you need , - and position

At 18 September 2012, 0:44:06user krishnawrote: [reply @ krishna]

can a servo be controlled using only two wires?????
http://replytouser%28%27krishna%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27bill%27%29/http://replytouser%28%27ivan%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27wktey%27%29/http://replytouser%28%27h%20chris%20spreckley%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27alan%20jacobs%27%29/


8/11



At 16 September 2012, 8:19:34user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@Pellas basically you mean "variable duty cycle" and not "frequency". What you want to make is certainly

possible and easy to make. Replace the pot with a set of resistors, each one taking place only when a limit

switch is achieved.

At 16 September 2012, 0:44:03user Pellaswrote: [reply @ Pellas]

Hello from Greece!

I would like to make a very compact servo controller with a three position switch (by using different resistors)

and adjustable frequency, upper and lower positive pulse. Basically like the one you did but with a two or three

(or more) position switch instead of a rheostat.

Is that possible?

At 13 September 2012, 19:58:11user Jacqueline wrote: [reply @ Jacqueline]

@akshay The rate of change of switching pulse[duty cycle] will vary the speed of servo movement. The

different duty cycle is just telling the servo which angle to turn to. Decrease from neutral may means turn anti-

clockwise while increase from neutral may means turn clockwise.

At 8 June 2012, 7:02:24user edwardwrote: [reply @ edward]

hello!ive built a rc bulldozer that uses a gas engine to power a 24 volt generator that powers all the 24 volt

motors to make it go.i have 24 volt batteries in parallel to absorb voltage spikes to protect the esc.im using

system voltage,through a servo testor,to control a servo to set my engine throttle.in theory,and in practice,it

should sense current draw and adjust engine speed to keep voltage at a set point regardless of load,and it

does.the problem i have is at partial loads,the voltage drops to far below battery voltage.at no load and full

load it works well,keeping voltage around 28 volts.im powering the servo testor with a seperate 6 v battery,the

signal(hooked to 3rd leg of pot on testor)is system voltage through a standard diode,then a 24 v zener,470

resistor,100 cap to ground and another resistor.the servo is linked to the throttle so that as voltage goes

down(signal)the throttle opens more and vice versa.any ideas on why my half load conditions cause low system

voltages? thanks ed

At 17 May 2012, 17:51:46user Conan Hwrote: [reply @ Conan H]

Thanks for the details on the different servos. I am doing some research on repairing rc cars and this was quite

helpful. Keep up the good work.

At 28 April 2012, 23:11:51user Giorgos Lazaridiswrote: [reply @ Giorgos Lazaridis]

@Andrew Yes it does indeed, and this is the idea. You put the 100K pot and then adjust it by the R2 to

achieve the min and max PWM duty cycle, since the potentiometers do not come in a wide value variety as

resistors. The same goes for R1 as well. So, with R1 you can set the minimum potentiometer value (when it is

rotated to 0 ohms), and with R2 the maximum value (when it is rotated to 100K).

At 28 April 2012, 14:13:46user Andrewwrote: [reply @ Andrew]

Hey Giorgos

Great article! I just have one question -- I notice that you clamped the variable resistor range by bridging its

outside pins with R2. Doesn't this affect the taper? Any thoughts on how to get around this if you *need* to

use a 100K variable resistor?

Cheers

Andrew

At 30 November 2011, 6:48:12user Robertwrote: [reply @ Robert]

I am doing a project on dc servomotor and have started by saying the application for my servomotor is in an

industrial air con system without fully understanding this is this a viable choice ? i may change the application to

R/C vehicle to enable me to use lower voltage (6-12v)where can i find PCB layout drawing and parts list andspec. Any pointers would be greatly received

At 20 October 2011, 14:47:02user danielwrote: [reply @ daniel]

great page, very good info, and well explained. thanks a lot!!
http://replytouser%28%27daniel%27%29/http://replytouser%28%27robert%27%29/http://replytouser%28%27andrew%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/http://replytouser%28%27conan%20h%27%29/http://replytouser%28%27edward%27%29/http://replytouser%28%27jacqueline%27%29/http://replytouser%28%27pellas%27%29/http://replytouser%28%27giorgos%20lazaridis%27%29/


9/11



At 24 September 2011, 10:50:04user Kammenoswrote: [reply @ Kammenos]

@Dangerous If i understand correct, you want this circuit to operate 2 servos. Id this is the case, then you can

operate them directly by connecting them in parallel

At 24 September 2011, 7:26:52user Dangerouswrote: [reply @ Dangerous]

@Kammenos

ok Is there a point on the circuit board like the reverse of frequency of the servo you can put another motor for

example? OR

Do you know a way you can put 2 motors on one channel without using the Y-cable and you have to switch

between the both of them, doesnt matter if its one is going Clockwise and the other CounterClockwise. I dont

need a ECS because im not worried about how fast just need the signal to change between them

At 24 September 2011, 0:35:55user Kammenoswrote: [reply @ Kammenos]

@Dangerous i cannot understand your point. Can you send a design to the forum?

At 23 September 2011, 11:49:17user Dangerouswrote: [reply @ Dangerous]

hey Kammenos I got a great question for u

if you have two solenoids you want to make it for one servofor example on the transmitter if you turn the stick to the left servo move Clockwise, if you moved the stick to

the right the servo to rotate CounterClockwise. can I put one solenoid one the wire for the motor and the other

solenoid + wire on the 2N2222 to make one stop and the other one to start?

At 16 August 2011, 11:53:45user Kammenoswrote: [reply @ Kammenos]

@Michal the period [T] is the reverse of frequency [F].

T = 1/F

So, as you say, period of 50Hz is 20mSec etc. Of course, the period depends of the frequency of the servo.

Regarding the fast servos with the 400Hz signal, i have never test them, but i do not find something strange if

the signal has 2.5mSec pulse duration and the angle setup is from 1 to 2 msec... Sounds ok to me, although i

have never test it.

At 15 August 2011, 14:00:08user Michalwrote: [reply @ Michal]

Hello,

I know the duty cycle is usually between 1-2 ms. But what about signal period? In case of 50 Hz servo, should

it be 20 ms and in case of 30 Hz servo 33,3 ms? Does signal period depend on servo frequency? If yes, what

about digital servo with frequency 400 Hz? In that case, period will be 2.5 ms what compared to duty cycle 1-

2 ms just doesn\'t seem right to me. Could someone explain this to me, please? Thank you for any information

you can provide.

Michal

At 13 August 2011, 5:50:57user kushik bharadwajwrote: [reply @ kushik bharadwaj]

which type of servo motor was used in this video?

At 12 August 2011, 2:51:28user Kammenoswrote: [reply @ Kammenos]

@dannyman3819 with the PWM module. Something similar i have done here:

http://pcbheaven.com/projectpages/Servo_Actuated_Door_Keylock_Hack

At 11 August 2011, 16:00:32user dannyman3819wrote: [reply @ dannyman3819]

Could you do this with the pic16f88 if so how

At 6 May 2011, 22:19:49user Samwrote: [reply @ Sam]

An easier version of this controller uses a 556 ( two 555 IC in a single package). Set the first 555 to operate in
http://replytouser%28%27sam%27%29/http://replytouser%28%27dannyman3819%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27kushik%20bharadwaj%27%29/http://replytouser%28%27michal%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27dangerous%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27dangerous%27%29/http://replytouser%28%27kammenos%27%29/


10/11



astable mode permanently at 50hz and run the output into the trigger of the second 555. that 555 will run in

monostable mode with its Capacitor and variable resistor ( potentiometer) tuned so that at max resistance the

High wave will be be 2 ms long and as you decrease the potentiometer the high wave will shorten to 1 ms.

At 12 March 2011, 12:07:47user Kammenoswrote: [reply @ Kammenos]

akshay i think you got something wrong here. The duty cycle on a servo has nothing to do with the speed. The

speed on a servo is fixed to a standard value. The duty cycle controls only the position. 1msec positive pulse

means most left position of the servo, and 2msec means most right position. the middle is at 1.5 msec. read the

document once more to make this clear.

At 11 March 2011, 5:20:46user akshaywrote: [reply @ akshay]

kammenos- sir , i am talking about the servo shown in the video. when the potentiometer is turned i could see

the pulse width decreasing and the servo motor was gaining speed. but generally if we increase the pulse width

the speed actually increases and here in the video i see the opposite. please forgive me if i am asking questions

which seem very basic and stupid. i am only a beginner.

At 18 February 2011, 2:07:30user Kammenoswrote: [reply @ Kammenos]

Yes Vaju, it is, but it requires a lot of test. I would never do this with a 555... Better i would use i

microcontroller. Otherwise, replace R1 and R2 with potentiometers.

At 17 February 2011, 7:52:26user Vajuwrote: [reply @ Vaju]

Hi again, thank you for your help Kammenos. Just wondering is it possible to scale down the position. for

example a 10deg turn on the pot correspond to 5deg turn on the servo? Thanking you in advance

At 5 February 2011, 10:39:09user Kammenoswrote: [reply @ Kammenos]

That is easy Vaju. The pot has 3 wires, one in the middle and two on the sides (right and left). You only need

to exchange the side wires, the left with the right and vice-versa.

At 5 February 2011, 8:46:33user Vajuwrote: [reply @ Vaju]

Hi, I've got the circuit working however its working the wrong way round. I mean when the potentiometer is

turned right the servo turns left and vice versa could you please help me? Thanking you in advance

At 19 January 2011, 7:11:05user Kammenoswrote: [reply @ Kammenos]

akshay, what speed? for which topic are you talking about?e

At 19 January 2011, 6:34:45user akshaywrote: [reply @ akshay]

sir if we increase the pulse width the speed of the motor must increase. but in the video when u decreased the

pulse width the speed of the motor is increasing. how come

At 15 December 2010, 22:48:51user Kammenoswrote: [reply @ Kammenos]

Hi George,

The RC servo i got operated at 5 volts. So it is impossible to run at 12. First of all, you need to get a servo

able to run at 12 volts. Also, you may need to add a 100 ohm resistor to the yellow connector of the servo, the

one that starts from the emitter of the 2n2222.

The 555 will operate normally, but the frequency may change - this is normal if the voltage change. The R3 is

responsible for the frequency. Current circuit has about 35 Hz. You need to test t be sure.

You should not need other changes, except R1 and R2 that sets min and max angle of the servo, but that has to

do with the application.

At 15 December 2010, 11:55:07user Georgewrote: [reply @ George]

Hy, I would like to use the circuit that you showed, with the same values that you did. But i plan on using it on

an 12V servo(in a car; 12V to 14.4 V). Due to the fact that there are 12V to 14.4V instead of 5V, should i

change anything in your circuit. Sorry if I bother you with this question, but I\'m quite a beginner with these
http://replytouser%28%27george%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27akshay%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27vaju%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27vaju%27%29/http://replytouser%28%27kammenos%27%29/http://replytouser%28%27akshay%27%29/http://replytouser%28%27kammenos%27%29/


11/11


things. Thank you!

At 21 November 2010, 7:55:50user Berntwrote: [reply @ Bernt]

sounds like a good plan, thanks.

At 21 November 2010, 7:33:07user Kammenoswrote: [reply @ Kammenos]

You will need to experiment with the values. Make it on a breadboard and test it with potentiometers. Then

measure the pot value and replace with resistors.


Thanks, (that was quick) with the 100K pot you get 6,7K to 24,8+6,7K. If I use an NTC with 1,255k @80C

and 0,51 @110C. How can I make that work ??

Bernt

At 21 November 2010, 6:13:18user Kammenoswrote: [reply @ Kammenos]

The only way to make it work properly is with a microcontroller, because there are too many parameters to

take in mind. In any case, the 80-120 degrees is not to small, if you use a proper PTC (or NTC) sensor. Youcan adjust it by R1 and R2


Hi

This is what I have been looking for, great! I\'m trying to construct a mechanism to control the airflow over the

engine in my model aero plane. So I figured I could just replace the potentiometer with a temperature sensor

(PT100....), but the difference (80C - 110C) is too small to make it work.. any suggestions?

Bernt

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Documents

How RC Servos Works.pdf