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[on:]

Hi everybody,

I am working on a Robotic gripper. to open en close the gripper a Tower pro SG90 micro Servo is used.
while i was testing the robotic gripper some strange things occurred. the servo sometimes starts sweeping (goes to 180 degrees than goes to 0 degrees and repeats this process) randomly.
at first i thought that is was a fault in my program. so i loaded "Servo knob" from the sketches included with the Arduino program. same thing happens.
hooked up an different servo (other brand) no problems whatsoever.

so my feeling says that the problem lays with the servo. i have multiple servo's and every one off them works as it should except for the 4 Tower pro's
so i started searching for information about the SG90. which lead me nowhere. only things i found where:

-Homepage off Tower Pro containing almost no information whatsoever: http://www.towerpro.com.tw/viewitem1.asp?sn=584&area=50&cat=159
-A guy that controls a SG90 with a ardumoto (pulse range 600mS to 2100mS): http://mechomaniac.com/ConnectingServosToTheArdumoto

does somebody know what the problem could be?

Robin

[Reply #1 on:]

does somebody know what the problem could be?

Does the servo get warm? As the other servos work as expected, the SG90 might be bad. The servo get warm? what you describe could be the result of the servo not being properly connected to the arduino/power supply ground.

[Reply #2 on:]

Sounds as though it might be power related, how is it hooked up? Unlikely to be a bad servo if there are four acting the same though - did you test them all?

[Reply #3 on:]

Hi Everybody,

Problem is solved! it was a power problem. when i use the 5V pin from the Arduino to power the servo than the servo starts sweeping. if i use a 12v power supply and a LM7805 the servo works fine.
could my on board voltage regulator cause the problem?

Robin

[Reply #4 on:]

could my on board voltage regulator cause the problem?

Servos should not be powered from the arduino. I don't understand how the other servos worked also being powered from the arduino, or were you powering them from an external power supply?

[Reply #5 on:]

Hi,

To save myself from typing I have added two relevant links to my signature. Read the first one and watch the second one.

If your project is going to be a big one, you will need a better regulator than the 7805, its good for an amp, you might need several amps as your project grows.

Duane B

[Reply #6 on:]

Note that the output of a 7805 regulator chip can be increased to ~5.7v using a small diode on the 7805 ground pin like below. Much improves servo performance.

[Reply #7 on:]

Hi everybody,

i am aware that is is not possible to power more than 1 servo from the Arduino. i have bought this power supply:
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16663
this will be powered by an 12V lead battery.

i thought that is was possible to power one servo from the Arduino because that is how the show it in the learning section under Servo library: Knob.

Robin