Hello,
I have a Tower Pro MG90S servo and when I take it to 180 degrees, it buzzes like it's under load. It does not behave like that at 0 degrees unless I try to force it to move to another angle.
Why is it buzzing at 180 degrees, is it broken?
Not all servos have a full 180 degrees of rotation. Many do not.
You can write a test to determine where the mechanical limits are.
Use servo.writeMicroseconds instead of servo.write
I like this better because it lets you use 1000-2000 as the base range. And many servos will support outside that range, from 600 to 2400.
So, try different values and see where you get the buzz that tells you you have reached the limit. Then only stay within those limits when you write.
Yoiu can set those limits when you use servo.attach(pin, min, max)
edit: I should say that if you want, you can set the min and max microseconds in the attach, then simply use servo.write. It uses map() to change the 0-180 degrees value you pass into a microseconds value.
I would say very few hobby servos have full 180 degree rotation in fact, 120 to 150 degrees is most common,
and different units will vary since these are not precision engineering components, but ultra-low-cost
manufactured components for toys, if you think about it!
The more expensive a servo, the more it is marketed as "robotics servo" rather than "RC servo", the more
likely it is to be accurate and repeatable (rather than cheap and cheerful). And more importantly the
more likely a proper datasheet exists.
alexandrutoki:
Why is it buzzing at 180 degrees, is it broken?
In simple terms it is not broken it is just stalled. Assuming you are using the Servo library, this basically means that when you write(180) to it you are asking it to travel further than it can go.
Try smaller and smaller values in the write() until it stops buzzing.
Steve
This is an old thread, but anyway...
My MG90S seems to work otherwise well, but if I do write(0), it goes to 0 degree and pushes over limit, slowly and vibrating. It obviously slips some gear meanwhile, because next write(180) turns it 180 degrees from the position where it twisted itself while performing the write(0) over limit. So if I use the range 1 - 180, I'll be fine.
Doing write(190) doesn't do the same thing. It seems to stop at the same point as write(180) and doesn't vibrate. So one has to kind of test each servo, just in case, and only use the values that make the servo behave ok.
Another good thing to test is measuring the angles, if precise angles are important. When I make my servo sweep from 1 to 180, it sweeps some 190 degrees.
It's easy to get confused by the Servo library and its "write(angle)" command. Except in a few odd circumstances the "angle" in that command has little to do with the actual angle that the servo travels. Write(0) and write(180) just mean go from one end to the other of servo travel. For many hobby servos that will be about 130-140 degrees, for some as low as 90, for others it may be 180 or as much as 240-270 degrees. If you happen to have a sail winch servo writing 0 to 180 may give 6 or 7 full rotations (2160-2520 degrees).
And as write(180) delivers the pulse length limit doing write(190) will hit that limit and send exactly the same signal.
Sometimes you really do have to look in the code of libraries to find out exactly what they're doing.
Steve
alexandrutoki:
Hello,I have a Tower Pro MG90S servo and when I take it to 180 degrees, it buzzes like it's under load. It does not behave like that at 0 degrees unless I try to force it to move to another angle.
Why is it buzzing at 180 degrees, is it broken?
It soon will be if you keep it at the endstop - it is pulling high current and heating up rapidly - its all
too easy to "cook" a servo by loading it this way for any length of time.
Find the true range of movement and make sure the code doesn't try to push it past the endstops, the
constrain() Arduino function is useful for this:
servo.write (constrain (angle, 10, 160)) ;// constrain the angle in the range 10..160