Asked — Edited
Resolved Resolved by Steve G!

Question With Jd Servo

Hi, I have recently purchased a JD Humanoid Robot and am having a pretty fun time using it. However, the servo, or joint in JD’s right upper leg does not go up past a 45 degree angle. I can’t see anything that might be blocking it or in it’s way and I’m not sure why else it wouldn’t go all the way up like the left leg. Because of this setback, JD can’t do many things including stand from a sitting position. I’m not sure what to do about this problem.


Upgrade to ARC Pro

Stay at the forefront of robot programming innovation with ARC Pro, ensuring your robot is always equipped with the latest advancements.


It looks like you have not taken any of the tutorials. Of all the revolution robots it is most important to take the tutorials on JD. Specifically on servo calibration, which I suspect is your issue here, but really you need to take all of them.

JD's tutorials start here: and the most important for your issue (if I am right about the cause) is



Actually, I did to all of the tutorials, I did the servo calibration and configuration correctly, but I still cannot even use the computer to make JD's leg move up past a 45 degree angle. I did all the tutorials correctly and I don't know why his leg is not functioning.



hi,did you save the callibration on the web page? is the batterie fully charged?

can you make a video of the problem?


The calibration is saved, and the battery is full.

I'm having trouble putting a video on but here is a picture.

User-inserted image

User-inserted image

The first image shows JD not being able to lift leg as high as the left. The left leg is shown in the second image.

United Kingdom


A couple of things you can check.

Ensure that there is enough "play" on the servo cables to stop any unnecessary strain on servo you're having issues with, as this will also prevents damage to the cable itself when the servos move to different positions.

Another thing you can do is to check if the servo is working as it should.

Open a new ARC project and connect your EZ-B to it.

Press "Project" on the menu then press "Servos" then click on either "Vertical servo" or "Horizontal servo" to add it to the project.

Click on the gear icon on the new servo control window, then select the port that the servo is attached to.

Then on the Click and drag your mouse on the "Min" and drag it down to 1, then on "Max" to 180. This will make the servo move to its minimum and maximum positions. If the servo moves the fill 180 degrees, then the servo is fine then we can look at what else could be the cause. You can test this further by saving the settings and click/drag the cursor over the main servo window.

As @nomad said, if you could post a short video, that migh be useful.


Just to make it clear for tinatina68, you don't save a calibration as this is a physical process of removing the bracket from the servo and realigning it (as you know) and it's a one time thing. I think what you meant was saving the servo profile, unless I'm missing what you mean.


hi steve g & tinatina68

i would redu the calibration.but did you do the fine tune? can you place a pic of that also.


@tinatina68 So it doesn't come up again if/when you ask additional questions, you should mark as complete when you finish a tutorial. It doesn't prevent you from reviewing it again if you need to, but it tells us that you have completed them so we get straight to answering your questions rather than telling you to go through the basics first.



upload your video first on youtube then here


It's possible that particular servo has been set to improper limits on it's travel. In the "Init" file for the standard initialization of a JD robot are a few script commands concerning setting the limits of travel of some of the servos. None of them include the upper leg servo you are having problems with, however, if there is some sort of min-max setting somewhere else in your project this could be the problem. It might look something like this:

# Right Upper Leg
SetServoMin(d16, 1)
SetServoMax(d16, 135)

Such settings would cause your problem.

I'm not saying this IS the problem, just that it's a possibility.

If the servo is binding somehow, there would probably be some buzzing involved, perhaps fairly loud.

Also, I see from your picture that it looks like the wire for the right foot is just a bit under the left foot.


steve g

i missed your last answer.yes i meant the servo profile.

United Kingdom


That's cool. I thought that was what you meant. No worries. ;)


I think the problem with JD's servo is in the hardware. Nothing has worked my problem is unresolved, I think I must buy a new servo.


One last question just to be sure. With JD turned off so that you can move the servos easily, can you move the leg all the way up, by hand, then?

United Kingdom

If the servo was like that when you got it, you can file a warrenty claim for a replacement. Use the Contact Us link, select warrenty, and leave a brief discription of the problem along with a reference to this thread.