It sounds like you're experiencing an issue with the internal mechanics of the EZ-Robot HD servo. When servos are powered off, they typically can be moved manually in both directions with some resistance due to the gearing. However, if you're only able to move the servo in one direction manually, it could indicate a potential issue with the internal gears or a physical obstruction.

Given that the servo operates normally when powered on and controlled through ARC, the electronics and motor of the servo seem to be functioning correctly. The issue appears to be mechanical rather than electrical.

Here are a few possibilities for what might be happening:

1. Internal Stop: Some servos have an internal physical stop to prevent over-rotation. If the servo was forced past its normal range of motion, it's possible that part of the gear train is now resting against this stop when unpowered.

2. Gear Damage: If the servo was forced beyond its limits or experienced a sudden impact, there could be damage to the gears, such as stripped teeth or misalignment. This might not prevent powered operation but could cause issues when trying to move the servo by hand.

3. Mechanical Binding: There could be a mechanical bind within the gear train that is overcome by the motor's torque when powered but is noticeable when trying to move the servo manually.

Since the servo is still functioning when powered, it may not be necessary to replace it immediately, especially if it's not exhibiting any issues during normal operation. However, if the servo is part of a critical system where reliability is paramount, or if you start noticing performance issues, it would be wise to consider replacing it to avoid future problems.

For more information on servos and troubleshooting, you can refer to the EZ-Robot HD servo product page and documentation: https://synthiam.com/Support/Hardware/EZ-Robot-HD-Servo

If you decide to replace the servo or require further assistance, you can find the EZ-Robot HD servo and other components on the EZ-Robot website: https://synthiam.com/Shop/Products/HD-Servo

Remember to handle the servo and your robot's joints carefully to avoid stressing the mechanical components, especially when the power is off.

hi dave

you still use the old HD servo ? i got new HDD that didn go less then 20 degree and not further then 150 degree . today it stops working complete . i also notest with the latest ARC servo script doesn work , at the first click of mouse button .

hi dave

found the problem . its a broken plastik tab . i took the plastiek out , still desame problem . i also notest the axel goes way further then normal .

jeremie is this warrenty ? this was a new one .

https://www.youtube.com/watch?v=YgnlyLHztf0&ab_channel=EDP

hi dave/jeremie

i notest somethin arkwart . am gessing this is done delibertly .  a tiny hole from 1 MM straight towarts the motor . dave do you have this too? also the circuitboard and rubber on the wire looks , not done properly .

@Nomad, Actually all the servos I'm using from EZ Robot are the new HDD. I really love them. I'm sure what ever is stopping this one HDD servo from manually moving it back to the left is my fault. It probably broke the physical stop inside the servo when I let the joint drop. I can't easily open it as it's embedded in a tight place in the robot arm. However I'm going to pull it out in a few weeks and replace it. I'll open it up and inspect it then.

I've never seen a hole in any of my servos like you show above. That's weird. From the pic the hole doesn't look drilled. It's got an odd shape. it's almost like the hole melted open.

hi dave

i wil open the servo compleet see whats inside . but if it melted what cause that ?

hey dave

it looks like its an contineus rotation servo with the wrong circuitboard or firmwire on it . it spins only in one direction . as soon the middle gear is connected it blocks .

@Nomad, I can't say if the servo is damaged. However I think it is not a continuous servo. From memory, I think the physical stop is inside the top cover that you have removed and set aside. Didn't you show a bit of plastic resting on the gear set in one of your other videos? I think this peace of plastic it that stop that broke off. Also there is a pot inside the servo housing and under the big gear you are turning with your fingers. The motor may be spinning until the pot is turned to a point in the one direction. I see that happening when you turn the gear with your fingers. So it may be that the circuit board is good. Now, you say the servo wont turn the other direction? Perhaps the pot is bad?

I don't know what caused the melted hole. However just a guess; maybe the motor overheated because of the plastic broken stop jammed in the gear set and caused the hole to melt in the servo housing next to the motor?

Time for a new servo unless you have parts from an old servo to replace these damaged ones.

hi dave

i dont have spare parts . but the top housing is broken . i wil not use this one anymore . i send the video to ez robot asking for a warrenty .cause this was a new one .  sofar no reactions , its winter and not many are present on ez robot . maybe i get a new one . for me its a learning proces . so contineus rotation have no pot ?

thanks for your responds

A continuous has no pot. You can modify a 180 servo into a continuous servo by removing the pot and cutting off the stop. There are a few ways to do this. Here's one way:

Hello @Nomad that hole in the servo is not normal, yeah it seems there is something wrong with that servo.

@Dave that does happen with a significant amount of servos, some do spin one way by hand but not the other direction. This is usually due to the way the gears mesh, the gears will turn freely as long as they don't bind internally.

Some servos will not bind in either direction when moved by hand, but some servos will bind in one direction or the other. This is likely because there is some play in the gears, the gears may twist slightly when you place some external twisting motion. Internally the gears mesh fine when the motor is driving them but when an external force is applied (which is not how they are designed) there is the possibility of binding.

I mean you could try and clean the gears as there could be a tiny bit of debris that's messing with the gear meshing, but I'm leaning toward this being an inherent outcome that happens.

You shouldn't need to replace this servo unless you require the ability to move it in both directions by hand.

*Edit I read Athena's response afterward, and I'm quite surprised that she (it) was on the right track.

@Jeremie, thanks for taking the time to explain this.

Just a reminder, the HD servos have been replaced by the HDD servos which are way better. You might want to consider upgrading to the most recent HDD servos. I have an adventure bot running off of two HD servos from 2014. I should upgrade it, but I have a Roli Chassis on the way. I also have a Six Hexapod running off of all HD servos. Again, I need to upgrade that soon. The good thing is that on the website there are options available for replacing all servos.