How to make a 360 degree Continuous Rotation Servo Motor?



Okay, today we are going to take this regular servo and convert it into a continuous rotation servo. You may see a lot of videos like this on YouTube and a couple of them are really good and a couple of them are terrible. I also want to go over exactly what the differences and some of the styles and like explain why you're doing the things that you're doing because not every servo is the same and not every person has the same tools and depending on the tools that you have at hand you can actually approach this differently. So we're gonna try and make it a little bit more vague while also still being very specific on exactly how to do it.

Now one of the first things that I want to go over is that we are going to make this a continuous rotation servo — meaning that we will still be able to control the speed, and that we are still going to be able to control the rotation based off of a typical input. Now, I have seen a lot of people, they'll take this and they'll basically just turn it into a geared DC motor which is totally fine. But, that's not what we're doing here. If you want a gear DC motor you can follow a lot of these steps, but the difference is, is these wires you can just chop them and solder them directly onto the motor. But that's not what we're going to be doing. So with that, let's talk a little bit about the two steps that, well the two overarching steps that you need to do this.

First, in a servo there is a mechanical stop. Something that makes them so they can't go more than a certain amount of distance and we're gonna have to overcome that issue, and then also, the way these work is the way they know where they are is there's a potentiometer in here, and so as this moves, it changes the value of that potentiometer and there's a small circuit board in here that says, “oh the potentiometer is giving me this reading now so I know that I'm in this position”, and it gives it that feedback. So we are going to have to bypass that potentiometer and one of two ways, we'll show one way but we'll discuss another way and then also make sure that that potentiometer isn't causing any issues as we completely rotate.

So again servos are pretty cool because they are a feedback loop where it goes one point and it creates a voltage divider on that potentiometer and then the circuit says alright we're in in the right position then you send it another message and it says, “oh it's supposed to be over here”, and then it moves and tell it's in another spot and the potentiometer says, “okay now you're in the right position”. But when we're doing a continuous rotation, we basically want it so that the potentiometer is either completely out of the circuit or is giving bad information and that is where we have to trick it. So let's get right into it and start taking this apart and show the different steps.

So the first thing that we're gonna do is we are going to remove these screws on the back and so as you remove them, don't try and pull it off quite yet because we need to do one more thing before we pull everything apart. But as we also do this, you pull these screws out it pops the bottom off but it also allows us to take off the top.

Okay, so now that those are loose let's grab an X-Acto knife. This isn't actually completely necessary but even if it's not completely necessary, it's kind of nice to just cut this right here, cut this right there. For me it's twofold, one it makes it so this comes apart a little bit easier and then don't have to worry about other issues and then two, that's a quick way for me to know which of my servos I've converted and which ones I haven't, even though I guess you could just write on it a big C or something with a sharpie, or whatever.

All right! So now it is coming apart. So let us pull this bottom portion off. Okay, so let's look in there really quick.

So we've got the motor right here and this is what runs down here and turns the gears. But then, this is controlled by this little board right here and that board is what's talking to the potentiometer which is right behind it that is trying to say, “hey where am i right now and where do I need to be”. So what we're going to have to do is we're gonna have to make some modifications to that board to change the logic so that it is getting the same, it's getting one signal, even though there is actually another signal being produced from the potentiometer. So let's come back to that... let me get these out of the way.

So on this other side is where we see the different gears and here we need to worry about the physical aspects.

So this right here is where the motor is actually turning it and you can see it has a bunch of gears and it's going up, but it's also controlling, I don't know if you can really see it, a potentiometer right down here.

So as it turns, it's changing this signal right there and that is actually being turned by this top piece right here which I'm going to gently try and take off without breaking things. There we go. So you can see there is a, that flat piece right there that goes into this, so that as this turns, it turns the potentiometer.

So we're gonna have to make some modifications to this so that one, it doesn't actually turn the potentiometer, and two, to get rid of this little spot right here that up until this point is gonna jam into things and make it so you can't turn more than, a little bit more than 180 degrees.

Okay, so with that I have actually liked to take care of this first. So this is the physical thing. So if you're turning this into a DC geared motor or a continuous rotation servo you're going to need to do this or else it's going to be jammed onto that potentiometer and the internal limits of the potentiometer are going to stop it. So first, let's cut that piece off right there and then second let's use a drill to drill out the hole on the inside so that instead of connecting onto this firmly it can spin freely. So first things first, try and cut this piece of plastic without cutting my finger or my desk too severely. I have no idea where those pieces went. So it doesn't have to be perfect but if you get it nice and flat, there, now we know that that's not going to catch on anything and it's gonna rotate nice and smoothly. So that's the first thing.

Second thing is we want to drill this out. So I brought my cordless drill. I found it's easier to first drill through and get the spot that catches on the end and then also go back with a slightly bigger drill bit to and get it a little bit wider. So, alright, let's swap drill bits.

All right now we are done with our drill for the moment, actually entirely. So I have cleanliness issues. Okay, so that is it. Now you can see that it's completely flat right there and then we've made this hole just slightly bigger. So now it should be able to fit right back on here and spin freely on there once it is tied back up and we put that top back on.

So the way we are going to be faking out the potentiometer is we're going to just be bypassing it completely. But other people, other methods out there, are to basically use a special device which we don't have which is why we're not doing it that hooks up to your servo and centers it and then they will literally glue the servo in place at that point so that the servo can't twist. But even if you do that, you still need to do this top portion because this top portion needs to be able to spin freely.

So again in this case, at this point, if you are going to be still using the potentiometer and just locking it in place you'd probably want to take off all of these gears and glue that and also I may regret this but you may just want to take all of those off so they're not a problem as you're dealing with it but I'm going to put that back on and hope that I can deal with the other side without that falling off and causing any problems.

So now let's go back to this side which is more of the logic side so this is a bit of a challenge because you want to pull this board up without actually breaking any of the wires so you have to kind of find something tiny to cram in there that you not going to break so I'm hoping I'm not sacrificing these tweezers they haven't broken yet as I do this but you never know.

Alright and the reason it's being so tough right now is because it is physically connected to the potentiometer and I am physically bending some metal leads down there. Let's see if we can get a good shot of that in there. So as you can see, there's these three little spots right there and those are the three outputs from the potentiometer for me this to this and so I need to cut those because I don't want them and that's going to physically pull this out from here so I'm going to have a little bit better access to it and it's also going to be electrically disconnecting it so we are no longer going to be using this as the input and I forgot to grab a piece of tape but I usually after I do that I usually bend the leftover pins down and then cover it with a piece of tape so it doesn't accidentally touch things on the board.

If you have some really thin snippers or clippers or something that you can get down there, that's great. I don't and so I actually use these, I think they're called forceps or whatever I use these things all the time it's crazy and I'm definitely not using them what they're intended for in this case but I actually just reached down there kind of clip onto something and then twist and break that and it is a bit ugly and it works sometimes extremely well and other times not very well but it's a lot better than trying to get in there with something else to cut it. So I just grabbed them, just break it and then I check to see if I actually broke, it looks like one of them still attached, just keep doing this until it's actually apart and you're able to pull the circuit board out, careful not to go.

Okay now that it's a part you can see those three things that are broken and you can also probably see it down in there and those are the things that I want to bend over and cover up with a piece of tape make it so they don't electrically short out here.

Okay I think this is also a good point also - yeah I think this is also a good point in which to mention that if we were still using the potentiometer and if you had something that was able to center the servo and make it so the potentiometer is perfectly centered and then glue it in place we would not be breaking this connection. However, I happen to have a couple of 0603 resistors on hand that I can put them as a voltage resistor and even though these aren't precision resistors they're close enough. If you have precision resistors, so that's even better. If you have some through-hole, that will also work.

The only problem is it's pretty small because we're going to put one resistor here and another resistor here so that it is providing a perfect voltage divider across this so the center point will be exactly half the voltage between this spot and that spot and so that is what we are going to do next and I am going to break out my soldering kit.

Okay, so at this point we solder these two on there and they have to do it very carefully and hopefully you're better solderer than I am. I know that Sergey can do things that I can't do with my microscope and he can do them just with a so normal eyeballs. So that's super impressive. Hopefully you're impressive like he is and not half blind like I am.

So as we solder these in place make sure you aren't unintentionally shorting out with something else. There's that resistor at the bottom that looks like it got ripped off in the process that I'm gonna try and fix um so yeah just look for any damage that might have been done. There we go. That's beautiful!

So again the main point of this is to make sure that the input to the driver thinks that it's constantly in the middle and so when you send it a signal to say, “hey go to this direction”, it's going to keep on going and keep on going and keep on going until you tell it to stop because it's never gonna receive the signal that it's actually done. You also notice, as I've mentioned in other videos, I use my professional engineer stamp more as a weight when I'm soldering than I ever have to actually stamp plans. So that's kind of fun. The most expensive paperweight I've ever owned.

There are times like this when I’m soldering, I wish I were ambidextrous. Alright! It's not beautiful but they are connected.

So now we've got a 2.2 kiloohm resistor and series with another 2.2 kiloohm resistor and that's because I measured this and the potentiometer seemed to be go, seemed to go basically between zero and 4.4 kiloohm. So that’s my way of keeping it about the same but i think the most important thing is just making sure that they're the same so that you have a center voltage on the sensor. So that is all that you need to do on the soldering side. So you can turn off your soldering iron and then if you are blind like I am you can put your microscope back away.

So I went and grabbed my electrical tape that I had put back in the garage. I'm going to try and non spastically put this on. Of course it's gonna stick to my fingers when I don't want it to and not stick when I do want it to. But basically again the idea is to make it so that as I put this board back down it doesn't accidentally touch the terminals of the potentiometer and cause some problems, and if you've left the potentiometer in there and connected and just glued it in place then fantastic you don't need to worry about this.

Again the whole point of this is trying to trick this board into thinking that it is always in the center no matter what.

So with that, we are good to put this back together. We've put the board back into position. Now you look here, you see there's a little cut out there. So I'm going to make sure that I keep the cutout on the sides of the wires and then I'm gonna put this back together and I think the only issue with this is the first time I did this, I got this thing down tight and when you get it down really really tight you're pulling the top and the bottom together which you put a lot of pressure on the gears up at the top and so it actually didn't work and I kind of killed it. So don't do that. Tighten it, you want it to be snug but don't try and kill it or anything like that.

Okay and that's it! So now we have gotten rid of the physical things that we're stopping this from turning all the way around. We disconnected it from the potentiometer because we don't have anything to center that potentiometer. We had to cut it out of the circuit and instead put two resistors to create that voltage divider to replace the potentiometer and now it should be good to go.

So let me set up my Arduino to show this off. Black, brown, red to red, and orange is signal, which is, I just used the standard sweep program that comes with the Arduino and made some slight modifications to it because for some reason, when I do this, 70 is now my middle point instead of 90.

All right I'm going to put this on so you can actually see it rotate and then I also have it so that it speeds up in one direction, slows down, speeds up in another direction, and slows down, and that's one of the benefits of doing this versus the continuous like basically turning it into a geared DC motor is you don't need an h-bridge to change directions and you can very easily control the speed using your typical servo controls.

So with that let's plug in the control and see what happens. See, it’s getting good rotation there all the way around and so hopefully this helps you understand exactly why the different tutorials say what they're doing and then depending on what tools you have, you can do this with yours with minimal amount of fuss. That is my hope with this. So let me turn this off because as much as I enjoy that sound, it is kind of starting to grate.

So that's it! Hopefully that was clear. If you have any questions leave it in the comments below. If you liked it, give this a like, subscribe to our channel to learn more about electronics and all this stuff related to Electrical Engineering and we will catch you in the next video.

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