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Asked — Edited
Resolved Resolved by Steve G!

Controller Ar-1202Mg Servo With ARC


PLEASE describe to me exactly how to control an AR-1202MG servo using an EZ-B v4 wifi controller.

AS of now, when I plug in the servo to D0 and use the vertical servo control, the servo does not move and an LED quickly blinks. I can feel the servo and I know it is receiving power. Sometimes the EZ-B resets itself and I have to reconnect.


Please advise on what to do.


Dave Lawrence


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I was able to take the servos to a hobby shop. They checked out OK when connected to an RC car.

Power supply was at 8.2V before I dropped it to 6V. I have removed the wall adapter I was using and am now running the system solely on a 7.4V Lipo.

Right now I am using a 7.4V 2800 mAh Lipo battery connected to the EZ-B.

Voltage at PWR pin of D0 [middle red] : 7.9V

Voltage at voltage divider going to servo : 5.88V

I would prefer to not buy new servos for this project if at all possible.

Still no movement.

Save your project file you have been using for testing to this thread. I want to see the servo settings directly. I think we are missing something simple.

United Kingdom
Well after looking at you servo project, apart from an ARC version update that is needed, there's nothing immediately evident that is wrong as it is such a basic file.

I am almost out of ideas myself and there's only a couple more things I can add to what I have already suggested so far.

1. Maybe, just maybe you have managed to find a servo that is not compatable with the EZ-B/builder, although I do find this highly unlikely, I wouldn't count it out at this stage.

2. Maybe it could be something to do with the power devider you have in place. There is one thing you can try now you're using a 7.4v LiPo battery, leave the devider out of the equation and plug one of the servos directly in to the board. Yes there is a bit of a voltage variation, but I refer you to this thread from post #23 onwards explaining that this should be ok to do. If you are willing to try this then open up a scrip control and copy/paste the following script. This script asumed the servo is connected to port D0.



This will run through every servo speed option with the relevant pauses in between. It would be intresting to run this just to see if the servo moves of tries to move at any of these speeds.

So, apart from seeing I picture or, as Richard mentioned, a quick video of your set up, I'm not really able to help you much further as this is all I have to offer for now, as I am out of ideas too. Good luck.
I don't know a lot about voltage dividers but although yours is producing a voltage of 5.88 or so (which is good), are sure your servos are getting enough power (amps) through it?
I agree with Steve, try an initialization script, but there is nothing intrinsically wrong with the project (I was hoping for a simple mistake like incorrectly set min and max position settings). It works fine with my servos.

Only other thought would be to see if you could send one of your servos to @Jeremie for testing. He might be able to tell why it is not responding to the EZ-B.

I am tempted to buy one off of eBay... because this puzzle is really bugging me.... The servos should work....
I am wondering if maybe it is a bad EZ-B and not a servo problem at all.

I think we asked, but have you tried other ports on the EZ-B? One of my EZ-B's has a bad port.

Have you tried other devices on the EZ-B and do they work?

United Kingdom

Yes David did mention that he has used different ports, but to no avail.


2. I have tried both vertical and horizontal controls and have changed the min max settings on both the D0 and D1 ports.
3. I have modified an unused servo, for the 6 volts, and tried using it on D0-D5. Also with no movement.

I must admit this one is bugging me too (although probably not as much as its bugging David I'm sure). *confused*
@Alan... that could be... I have an ezb4 that I dropped a screw driver on and now 3 ports will not drive servos, but they will drive an led.... I wonder if David can get a hold of another brand of servo to test on his ezb?
Like @RR I am very curious about the voltage divider David mentioned he had. If it's resistor based it could be severely limiting the current being applied to the servo.
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That's what I was wondering myself when I mentioned it in post #32, and suggested to connect the servo directly to the EZ-B. I'm not familiar with voltage deviders myself, but it sounds like something similar to a regulator, and I know there can be regulator issues if using the wrong amp output with a servo (I.e, not enough power feeding the servo).
@Steve... I agree, scrap the divider plug the servos directly into the ezb... They should be able to handle the lipos 7.4v no problem....

Well I must say, that is probably the only thing I have not tried yet.

No voltage divider and running off LiPo only. I must say I am skeptical but I will try it anyway.

I still believe this is a problem with synching the pulses the D0 is supplying to the servo signal line.

I mean most manufacturers supply some kind of data sheet that details the wave forms needed to drive devices. I have not seen anything from these guys nor have I seen anything from ezrobot detailing the pulse widths and frequency. I would like to think that all manufacturers would hold themselves to a standard format making things easier.


Servo is now moving with only using the 7.4V Lipo battery and no voltage divider.

I was hoping to be able to run the EZ-B and servos using an AC-DC adapter while doing test/development for this project. That is why I was running everything initially at 8.2 Volts. Which as we can see is too much for our servos causing a reset on the EZ-B.

Also, we know that current limiting the servos via voltage divider on the red power line is not advisable for proper movement.

Also, we know that changing the code on the EZ-B hardware is not an option. Not that I would really want to if I didn't have to.

I am happy now with this purchase and I am sure there will be other issues that come up. We can handle that as need be.

Thank you all for helping me resolve this [now seemingly] trivial issue.


United Kingdom
That's great to hear David. Sometimes the simplest solutions can be overlooked.

In regards to bench testing, with the right mains power adapter supplying enough amps, I believe it is possible and some members of the community have done just this. Perhaps Someone who has done this could chime in and mention what adapter power specs they are using.

Anyway, I'm pleased your up and running.:)
Talk about an easy solution... Servos need power....;)

Minimum bench power supply should be 20Amps in my opinion... Power supplies differ from batteries... You have to buy a power supply with a high enough amp output to overcome the start up "inrush" of current required to get servos first moving.....
As Richard said, it wasn't the voltage of the power supply, but the amps. EZ-B can take way more than 8.2 volts (servos might not) but you need much higher than the rated amps when the servos start moving.

Glad you got it figured out David! And also wanted to echo a thanks to you gentlemen in the forum as well!