Hi guys, im working on pen plotter, using Arduino nano on CNC shield as a controller.
I use SG90 9g (plastic gear) and MG90 9g (metal gear) servo for pen lifting. Both types keep to break after few hours of working. There is no sound from servo when it is broken. Servo get warm during operations, but not hot.
I power servo from external source set to 5.7V.
Servo rotates 90 degrees, depending on printing type there are more or less operations, but in general:
the torque isn't big, there is very small weight to lift and a weak rubber for pressing pen down
typically there are up to 2 operations per second (rather less)
I add delay of 0.2 sec after each operation command to give servo time to execute fully (to avoid moving pen when it could still touch or not yet touch the paper)
Can anybody tell me whether I do something wrong to cause the damages or these servos are just so bad quality? If it is about the quality, can you suggest a reliable one within reasonable $ range?
That's impossible to say on the information you have given. We would need a wiring diagram at least. In principle if you are powering the servo with 5.7V it should not fail.
As for a quality servo, it depends on where you are, as shipping can be a significant cost.
Wiring is simple - servos red cable goes to +5.7 of external source, brown goes to ground common to whole system (power source, arduino, CNC shield) and yellow is the signal connected to arduino D11 pin
Beyond the other excellent comments so far, I have to ask - are you running 0-90 or 90-180, or have you set up to run 45-135? I've a couple of servos I suspect died because I was hammering limit-to-limit; setting up to stay away from end points might improve lifetime. Or Not. Lifetime on a $2 servo might be short regardless.
I have $2 aliexpress SG90 clone running almost "non stop" 12h /day for two years now.
Either your voltage is too high (measure) or you might have problem with your mechanical setup.
@bobcousins power source is 12V power adapter going through regulated step down converter. It was set to 5.7V and multimeter showed that value at the end of the wire (100cm) where it was just about to connect to servo.
@jim-p I provided worst case scenario. In fact it is much less. ChatGPT says these servo should last 100k-500k cycles (cycle=0-180-0) so I would say my servos were breaking much faster
@camsysca servo is 0-180 degrees, but it only operates in 0-90 range
@ahsrabrifat I have now lowered voltage to 5V and will make some endurance tests. But I'm a bit confused, since internet says these servo are fine for 4.8-6V.
@Railroader I didn't do it yet, but for sure it is not about gear damage (there is no sound from motor, also to reomve that possibility I tried with metal gear).
To be honest it's hard for me to say, don't know how to compare 1,6kg/cm to my setup. I reduced the max torque by replacing standard servo arm with a round knob, so that per degree rotated the pen lift the same amount of milimeters, and the whole lift is just about 5mm.
Pen is forced down with a rubber that is quite weak.
Your experience with those servos is not uncommon. Many others on the forum have complained of them being dead on arrival, rotating continuously or lasting just a few hours. However, we only here about the failures and not the successes but seems to be the luck of the draw with those servos.
For hobby purposes, I've only used Futaba and Hitec servos.
@jim-p other topic was about unstable work of servo and it has been fixed by using external power source for servo. This topic is about servo breaking after some time of stable work
@kmin just confirmed, servo moves -45 - 45 degrees, so in totally safe zone. I know that saying "weak" about the rubber doesnt say much:) Once current servo breaks I will do the no rubber test. But for now it seems that lowering voltage to 5V makes servo much happier (but I have no statistics to prove it, since it didn't break yet)