general question about servo motor

Hello, I am trying to make some experience with basic robots. I'm using servo motors (SG90 and MG90), just to make some simple project and mod something found around.
With servo motors I have a doubt. I have got two MG90. Both of them work correctly if driven using arduino. One of them, when disconnected, could be manually moved (carefully) in its 180° range. The other one not, is 100% locked, cannot be moved manually in any direction. I disassembly both of them and I did not note any difference. I repeat, when driven both work correctly, but one of them cannot be moved manually in any position, and that's a problem when I have to assembly some project.
What's behaviour is correct? is there a way to make the one locked moving "statically" ? Thanks :slight_smile:

Never power servos or motors from the Arduino -- it will be damaged or destroyed. Use a separate power supply and connect the grounds. A 4xAA battery pack should work well for up to 2 servos.

cla68:
What's behaviour is correct? is there a way to make the one locked moving "statically" ? Thanks :slight_smile:

I assume neither of the servos is powered while you are trying to move them by hand.

Short of pushing harder and risking breaking the "locked" servo I have no idea what you can do.

However moving it manually won't make any difference to the Arduino. It will still go to the same place with Servo.write(90).

...R

Turning servos by hand is a very bad idea. More servo gears have been stripped by doing that than in normal use, particularly if the servo is powered.

If you want to move servos without the Arduino you could always get yourself a servo tester (though they basically do just what the Knob example sketch does).

Steve

Thanks. So, what I have well understood is: do not try to move servo motors in manual way! otherwise gears could be definitely damaged. Ok, clear :slight_smile:
I do not understand the reason why 4xSG90 plus 1xMG90 servos could be rotated manually but another MG90 not...maybe is a matter of tolerances among each gear or some other reason which I do not understand.
One question, why should I not use arduino to supply servo? It’s a typical layout which I found around. The servo gets supply from 5V pin. Its ground is connected to same GND of arduino. I use a potentiometer and a capacitor....same layout found on Arduino basics...what’s wrong?

why should I not use arduino to supply servo? It’s a typical layout which I found around.

Yes, you can find plenty of bad advice on the web.

The voltage regulator on the Arduino is not intended for motor or servos, and will overheat and shut down. Motors and servos also inject severe electrical noise into the wiring and cause the Arduino and sensors to restart or malfunction.

Always use a separate power supply for motors and servos.

cla68:
I do not understand the reason why 4xSG90 plus 1xMG90 servos could be rotated manually but another MG90 not...maybe is a matter of tolerances among each gear or some other reason which I do not understand.

Friction is not well-behaved - there will be enough variation in the friction to tip the balance between
turnable and stuck, for a massed produced cheap reduction gear system. A very small amount of friction
is multiplied up by the gear ratio to a very large value if you attempt to back-drive.

If you need to be able to manually adjust when powered down, some sort of mechanical means should
be employed which doesn't involve rotating the servo shaft.

+1 to what @jremington said about always using a separate power supply for servos.
95% of all problems discussed here with regards to servos have been helping new users get away from the misconception that it is OK to use the arduino 5V for higher current demand applications like servos.