The Difference between Analog and Digital RC Servos
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- เผยแพร่เมื่อ 5 ม.ค. 2020
- In this video we take a look at the differences between analog and digital servos.
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If I were to grab a bunch of digital and analog servos, ripped the labels off and asked for you to hand me only the digital servo's, it would be very challenging. The reason is, there really isn't a difference between digital and analog servos on the outside. In fact, there really isn't much of a difference on the inside either. Both types of servos contain the same gear train, same 3 wire lead to the Rx, brushed motor, case, and even potentiometer to determine the servos position!
The large difference between the types of servos is in the circuit board. We explain this in more detail during the video as well as listing out the advantages and disadvantages of each.
Is it ok if my digital servo makes noise when there is no control input or external forces acting on the servo? The quick answer to this question is yes. It is quite normal for a digital servo to sing to you. The reason for this is because of the high frequency pulses that get sent to the motor within the servo. You are in fact hearing these high frequency pulses that the motor is receiving. Listen in near the end of the video to hear this. - วิทยาศาสตร์และเทคโนโลยี
The pulse to the analogue servo is a requested position not an "on time". Small movements result from a small change in the duration of the on time not a small on time itself. You need to be clearer between the signal to the servo circuit board and the signal from the servo circuit board to the servo's motor itself.
seems like this channel benefits from youtube hiding the dislike count. the content in this video strikes me as very shallow, or maybe it's just dumbed down...
Thank you so much for this video! I am just getting back into R/C after about a twenty year break and I am dusting off all of my monster trucks and restoring them back into running order. My head was spinning with all of the advancements made in the R/C world while I was away all that time. I was so confused about the new digital servos but your video made everything so clear and simple.
As for my trucks, I'll just stick to the affordable analog servos. One thing that I have discovered is that the approximately 20 years added to my age during my vacation away from R/C did not help my driving abilities at all. Thus, I highly doubt that I would notice the differences if I spent the cash and replaced all of my monster trucks' analog servos with digital ones. This is one case where getting older actually (unintentionally) helped me out!
Thanks again for the video!
Thank you for the comment!
Good to have experts like you in the RC hobby.
Thanks 👍
I just bought my first real super high end servo and it screams like a banshee and it scared the hell out of me I thought I ruined it somehow, Thankfully you just calmed me down and put my fears to bed, Thank You Sir!
Just bought a BNF plane set up with digital servo’s and one sings to me continuously (should say shouts at me). It’s too loud to work on in the house! But, the manufacturer (Horizon) tells me it is normal, probably right by what Mark reports.
Very well explained. Thank you.
Glad it was helpful!
Thanks dude! This is great info, straight to the point.
Can't wait to ruin whichever one I order!
Thanks for the comment Kimchi Robotics.
Haven’t watched the video but I can already tell it’s a great topic! Love the videos and content man!
Awesome video man, 11:34 is a question I have had for a long time but never really found an answer to. Very helpful video and super informative
Thank you! I'm glad this video was able to help!
RCexplained it was super helpful actually, the servo noise always gave me anxiety, but now I think of it as singing to me :)
Thank you for creating the content, your videos have been eye opening.
Right on!
That's Awesome. Really good to hear!
I've always wondered what the differences were, and now I know! Thanks!
RIght on! I'm glad the video helps!
Thanks for the advice. Great video keep up the good work.
Thanks, will do!
Do you happen to have any suggestions for a very silent servo?
Thanks a lot mate, you've cleared up a lot of my questions. Cheers!
Glad to help!
Thanks for explaining the differences clearly. I'll just add that the chatter/whine of digital servos, particularly high torque ones, drives me bananas. Made the mistake of putting a real brute into my rock crawler and because I'm usually up close while driving it, I don't really enjoy driving it. Live and learn.
Some of the high-end servos don't make the high pitched noise when you try to move them. I've been trying to find out why, but no one seems to have any idea. You happen to know? Is there a stat in the description you can look for when purchasing one to ensure you get a quiet one?
Thanks for the explanation!
No problem!
thx for this information, good explanation !!! thats what i need to know
Glad it was helpful!
savox servo's don't whine, they scream.
True
Love you channel! So if my digital servo whines after turning say, left and right, then stop, then it continues until I wiggle the wheel (tx) or apply some throttle. I have endpoints adjusted properly ( I think) so it is not reaching or straining. So this whine is ( mostly) fine? thanks.
The wine is fine.
@@RCexplained whine , not wine . CoolwHip , not coolwip .
Another great video, thank you !
Ps : Are the digital servo's more likely to give out or receive interference to/from esc's , vtx, etc ? Cheers
Hi Mark, in my experience digital servos have not transmitted or received interference from other RC components. The difference in the frequency band is quite significant. Example - 2.4GHz or even vtx @ 900MHz vs
@@RCexplained Awesome thank you for getting back to me =)
Great vid. With 6 digital servos on my glider, it sounds like an orchestra!
Thanks for the comment. It sure does make a lot of noise! Some digital servos are much quieter than others.
Thanks for the video. I don’t know why they call the digital servos ‘digital’ to be honest. They are just higher frequency analogue servos.
I’m new to the hobby and from an electronics background. I assumed a digital servo would use a digital encoder to give the output shaft position. But they still use an analogue pot ! Oh well, you live and learn. Cheers. 😊
Digital servos use digital signal processing to control the servo motor. Where analog servos use analog circuitry to control the motor.
Thanks for the very detailed tutorial, much appreciate.
IKEA art!
Thank you!
You're welcome!
Awesome video thanks alot👌👍
Thank You Justin! Appreciate the comment!
Thank you so much. This is so helpful. I connected a analog servo (I have no idea about this before watching this video) to my Noble NB4 (default setting digital servo) which did not work. Finally figured out. By the way, very good speech in the video. I am a TH-camr too. I always have my thinking slower than talking. So lots of "ah" & "um" in videos. But your video is great.
Thanks for the comment Jimmy. I'm glad the video is able to help.
Excellent use of your nouns, good sir. You cannot use them too much, where ‘it’ is over-used.
Thank you for all the content man you always explain everything perfectly and I'm quite illiterate lol thanks a lot
Hey Richard, thank you for your awesome comment!
i realize Im kind of off topic but does anyone know a good place to watch newly released series online ?
@Aiden Pedro Flixportal xD
@Cesar Devin thanks, I went there and it seems like a nice service :D I appreciate it!!
@Aiden Pedro you are welcome :)
I'm smarter now compared to 12 minutes ago. Thanks!!!
That's excellent! Thanks for the comment!
Hey bro may i have a question
Why is it my digital servo works only when using a servo tester. Doesnt work when im connecting it to my receiver?
I would like to use a servo as a thermometer pointer (a hangar-type wire). However, I can't have the whine as this is in my living room. Accuracy is very important (to me). Will an analog servo be accurate enough? Can any digital servos not whine? Thank you.
I can't visualize what you are trying to do. There are some digital servos that wine less.
@@RCexplained Similar to this; however, much more accurate, larger and nice looking. I just need zero whine. Thank you. th-cam.com/video/cl-w2wkeINs/w-d-xo.html
I would try a decent quality analog servo.
Asking program able servos ? How do the work and what is the difference
I moved over to a brushless servo. No more jitter or ‘singing’.
I had a low profile SAVOX digital coreless it was so loud it was crazy.
My obligatory comment "first!"
Keep up the great info about the RC hobby.
Thank you for your comment LusoiHarware!
Thank you very much.
Thats a really nice shirt! :) :)
So Will all digital servos whine? Can I use that as a test? Like if I buy some inexpensive servos from Ali express which claim to be digital, if they don’t whine that means they are actually analog?
The best way to test the digital servo is to use an oscilloscope on the output to the motor within the servo. I have digital servos that do not whine like the ones in the video. One could mistaken the noise for the noise an analog servo makes.
its clear now... thanks..
I'm glad, thanks for the comment!
Do you have a video for cat packs?
Hi Dex. To serve what purpose? I have a video outlining what you should do if extending ESC battery side leads. Was this what purpose you were looking for?
I think he meant cap packs. To store power I think? Would like To hear you explain also
Hey Justin. To store power for what RC purpose? There's a couple. Here's a video I have done to help with one: th-cam.com/video/QIp8JZ-B8S4/w-d-xo.html
Hi. Is it possible to convert an analog servo to a digital one? Because i once dis-assemble both type of servo and could not find any difference visually (i think the only difference is the 8 legged IC). Perhaps if we could find the digital IC, flash it, and solder to the analog board, we could get a cheap digital servo alternative.
hello sir, can we get some code for testing this.
Possibly, you'd have to find some one who has the code.
@@RCexplained Thank you for the swift response, I think I meant if you happened to have the code since I am currently trying to program a digital servo and after watching your video I am not sure If I should be driving it the same way I drive the common analog motors. Thank you.
@kevinkipkorir3132 no I don't have the code you will need.
@@RCexplained Thank you, sir, I really enjoyed the video. Second time watching it this year.
Can a analog servo tester operate a digital servo motor?
That sound was at least 1000hz. So...how does that correspond?
like the shirt teacvher!!!
Thanks! My wife says it's true!
The whining of a digital servo is what makes people think you're fooling around with a toy :P
Thanks for the video.
You are welcome!
I'm working with Arduino to make mechanical eyes. The servos I use are extremely loud!
There's actually a lot of incorrect information in this video.
The explanation of how the PWM signal drives the servo is completely wrong. The explanation would be correct for a rotary motor, but the difference between a PWM motor drive and the servo input signal have been confused.
A PWM signal is used for motor control, and might be used for servomotors, but not in the way stated. The driving signal sent to the servo is a 50hz (generally) signal, though it can be as high as 160hz or sometimes more, with an on period of 1.0-2.0 miliseconds, and the rest low, meaning no more than 10% of the "duty cycle" will be active. (not "when it's going fast, there will be more than 50% duty cycle," as was said in the video.)
The active period will be 1.0-2.0 miliseconds, regardless of the overall signal rate, with 1.0ms being all the way in one direction, and 2.0ms being all the way in the other, and 1.5ms being right in the middle. This is true whether the servo is being driven at 50hz or 150hz.
Hi ClokworkGremlin, thank you for the comment and your interest in the video. Making the assumption that there was confusion has led you down the wrong path.
There was no confusion. Frequency, Period, On/Off Time and even Voltage measurements were taken with an oscilloscope and I know where the leads were placed on the servo.😉
OK smart guy.
Then how does it turn in reverse?
And did you notice, while you were looking through the oscilloscope, that the duty cycle never actually went above 10%, despite you claiming in this very video that it did?
I came here looking for information on how analog and digital servos are different, and I didn't get any useful information, so I went looking elsewhere. Turns out, as far as I can tell, basically all RC hobbyists have been passing around the same, incorrect information. PWM signals simply do not work the way you described them in this video. Wikipedia has a good article on the protocol used to control servomotors, and based on the way you've described the functionality in this video, the protocol would not work as described on Wikipedia.
And I know the protocol works, because I used it to write a servo controller not an hour before making that comment. And yes, I used an oscilloscope, too.
I'm spending quite a bit of time here trying to help you on a topic that you want to know more about. Saying things like "OK smart guy" and "I didn't get any useful information, so I went looking elsewhere" and "information is completely wrong" and others that I probably have missed doesn't make me eager to resolve the concern. On most channels I can only imagine these comments would get pushed to the bottom and never clarified or even realized. I truly do want to help. I am making the assumption that you have a deep understanding as to how these servos work and there may be some underlying confusion on RC terms or possibly something else that leads to the questions that you have just asked. I would hope that you are also making the same assumption for someone who is trying to help out.
In RC a servo is the entire unit. A servo motor is a component within the servo. In RC, digital vs analog (As advertised by RC servo manufactures) is on the circuit to the servo motor. (A brushed motor within the servo) The same input to an RC digital or analog servo is used - using the 3 input leads. It seems to me much of your confusion could be related to the terms and how these are used in RC. You continue to speak about the input to the servo and not the actual difference in RC that creates the advantages and disadvantages of digital vs analog.
I hope that above clears it up. If not:
The pulse width vs period (duty cycle) sent to the motor within the servo was measured well beyond 10% (and beyond 50%) depending on the torque applied to move the servo arm out of position. One could also refer to this as the percentage of modulation. This is exactly why an "RC analog" servo struggles to deliver sufficient holding torque under light loads requiring low duty cycles (long period on "RC analog" servos resulting in dead band) for proper control.
Practical examples within the video show me altering requirement from the brushed servo motor circuit. This is where I show a demonstration of changing the force exerted on the servo arm requiring the brushed servo motor circuit to respond. The control input never changed from my radio, however the brushed motor does require power in order to maintain the correct position.
Brushed motors turn in reverse by changing polarity to the motor. I know you know this.
Thank you for the discussion, I don't usually get the opportunity to discuss the inner workings in this much detail.
The explanation in this post is correct, but that's not what I got when watching the video initially, and that's not what I got out of the video when I went to re-watch.
I think the big source of confusion (mine and others') is that there are two signals being used here: a data signal, and a driving signal. The data signal is the one that comes in through the 3rd wire on the servo module, and which I assumed you were talking about throughout the video, and which I believe most explanations of servomotors talk about. This signal is nominally a 50Hz square wave with a 1.0-2.0ms active period and the rest low. A lot of people refer to this as a PWM, because it looks an awful lot like one (and you can actually use PWM drivers on most microcontrollers to run it), but that's not technically correct, as the active period will always be 1-2 miliseconds, regardless of the signal frequency.
Upon reviewing your post, I believe the *driving signal* is what you were explaining. This comes from the chip inside the servo module, and upon yet further research since my last comment yesterday, I believe you are correct in that a PWM is used. I didn't open up any of the (cheap, analog) servos I was testing, so I assumed they simply used an on/off driving signal to turn the motor at full speed towards the position indicated by the data signal.
I believe a great deal of my own confusion and frustration is because I came here looking for what kind of (data) signals are required to drive digital servos. Turns out they're compatable with the same signals used for analog servos, though what I've read also suggests that the chip in a digital servo also generally supports some programmable features such as acceleration control and damping (what I generally referred to as PID previously).
Basically, my understanding at this point is that the main difference between analog and digital servos is that analog servos are mostly "dumb" circuitry, which runs the motor forwards or backwards depending on the position indicated by the data signal, while digital servos are able to continue moving the motor to the last known position in between or even in the absence of input signals, suggesting a small amount(like 1-2 bytes, basically nothing) of onboard memory, which the analog servo controller doesn't appear to have.
I apologize for my initial misunderstanding, and appreciate the extra effort you've gone to.
Additional notes: I actually drove the servos I was testing yesterday (cheap 9g analog servos) with as high as 166hz signals, and I suspect I could go even higher, but given the turn rate appeared static, I suspect the controller chip ignores any signals which are less than 20ms apart. I was also able to "overextend" the range on my servos by going as low as 0.5ms and as high as 2.5ms, but that hit the physical endstops of the device, and I suspect isn't a good idea in a practical application.
Hi ClokworkGremlin, appreciate your reply.
I try and do my best by eliminating potential for confusion while talking about technical details. It's certainly not easy at this level. I thought I was clear when i was saying the servo processes the signal and sends pulses to the motor. (motor drive signal) I know in nearly every technical video I upload, there is room for misinterpretation or confusion. Sometimes I just misspeak and know it too after rewatching. I suppose that's where the comment section is super handy for any necessary clarification.
Interesting findings on the data signal. I would imagine if the servo can hit the end stops, it could be quite dangerous to the life of the servo if allowed to operate between that full input range. They will not be able to handle the stall current generated when unable to move to the requested position. I've blown out a few servos (one digital on a turbine powered jet) by accident this way.
What application are your servos going in?
My blue china servo keep locking up on my elevator. It’s crashed 6 times so I will buy a good servo to keep the elevator more reliable
Yes, replace that servo!
Thks but both use a PWM train inputs for control (one a ~50 & other at ~300 cycles per sec). So both are digital.
Soooooooooooooooooooooooooooooooooo ??What does the word 'analog' mean/refers-to in the name 'analog servo'??
12 minute video to find out of its normal for digital servos to whine, arrggg ! thanks though, good video.
Thanks Jon
Bro you are looking completely Like Jim Carrey
I wonder who named these servos the names they have , in general electronics we refer to something as analog if it doesnt have a resolution meaning theres no updatde frequency , infinite resolution. But for some reason rc stuff use these terms in such a wrong way. Same with the " current ratings " lol ridiculously high numbers , a simple google search against the current rating for copper thickness or even looking at the battery's disharge rate will show all those values as crap
Agree with the digital vs analog. As for current ratings on wire gauges, a Google search would simply just cause confusion and misunderstanding. Its not so simple. As for a batteries discharge rating, these suck and are crap. That's why I've moved in to battery testing.
Open for discussion? why not talk about the control signal (the combined input and feedback error) to the motor as being amplitude modulated in an analog servo and PWM in a digital servo? it makes understanding servo deadband so much easier.... the figures used to show the difference between analog and digital as a square wave with different frequencies I think conveys the wrong message....
Hi Makettle62, on the oscilloscope the analog servo was PWM controlled and not amplitude modulated. This is from the servo micro controller/chip to the electric motor. The servo's electric motor sees full voltage which is why square waves were drawn.
@@RCexplained I'm new to the RC world, the Analog vs Digital servo conversation caught my attention. Now I'm starting to figure out what's going on, and correct me if I'm wrong, but the motor in a true analog servo is driven by a linear device, normally an amplitude modulated pulse. While a digital servo motor is PWM driven. But, and this is where I'm getting confused, it appears that the linear portion of the motor drive has been replaced with PWM ( at a much slower rate) in todays analog servos. Am I understanding that correctly?
It's possible. I have not measured anything outside of today's RC analog servos.
explain with photos next time
The digital was connected i dont belive that it was a fare test
this video treats these things as black boxes, so you never learn what's truly going on that makes digital ones different. no, the higher PWM frequency isn't the crucial difference. analog ones could be made to accept 500 Hz PWM too. the difference is their internal operation.
This video does not talk about what frequency the servos "accept"
@RCexplained you were talking a about the frequency it accepts indirectly when you were talking about pulse being 50hz and 300hz lol.
Servo digital good TSM work analog no work TSM no good for Rc car