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Author Topic: SG90 Servo Difficulties  (Read 1763 times)
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Well I'm afraid you have a broken servo... There is probably something wrong with the pot or the wiring from the pot to the little controller board in the servo.
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There is probably something wrong with the pot or the wiring from the pot to the little controller board in the servo.
How could I determine if there's an issue with the controller board itself? I've detached and reattached the pot to the board, and I know it's a good connection. Also, the pot is working well.
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The simplest test is almost certainly to buy another cheap servo and DON'T TAMPER WITH IT! If that works as expected it's a fair bet that the first servo is broken.

...R
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The simplest test is almost certainly to buy another cheap servo and DON'T TAMPER WITH IT! If that works as expected it's a fair bet that the first servo is broken.
Let's go with the assumption that this servo is broken, because my other servo works fine. Is there anything I can do to fix it, or determine exactly where the issue is?
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Let's go with the assumption that this servo is broken, because my other servo works fine. Is there anything I can do to fix it, or determine exactly where the issue is?

If your servo is spinning around like a continuous rotation, then two possible things may have happened. First most hobby servos have some type of travel stop to limit the rotation of the servo horn shaft. Your servo appears to not have one. Second, the servo pot must be attached to the servo horn shaft so that the pot rotates with the servo horn shaft. It appears the pot in your servo is either detached from the servo horn, or the pot has been damaged in some way. Below is a typical servo pix.

« Last Edit: June 05, 2013, 06:04:42 pm by zoomkat » Logged

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Your servo appears to not have one.
Mine had one - it's one of the things that stop the servo from rotating past the 180 point. I removed it before starting this thread, hoping that the stop was the cause of my problem.

It appears the pot in your servo is either detached from the servo horn, or the pot has been damaged in some way.
I have attached pictures of one horn to show that the pot rotates with it, the movement is smooth and clean. I have also measured the resistance of the pot, and it seems fine (approx. 3.35kohm).

If I take off the metal "V", there will be no stop for the pot, and it should be able to rotate freely. How will this help the pot from locating different positions throughout its rotation?


* 0.jpg (622.56 KB, 890x1000 - viewed 12 times.)

* 180.jpg (638.05 KB, 916x1000 - viewed 16 times.)
« Last Edit: June 05, 2013, 09:09:38 pm by bloogoo » Logged

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If I take off the metal "V", there will be no stop for the pot, and it should be able to rotate freely. How will this help the pot from locating different positions throughout its rotation?

In a normal servo, the pot shaft rotates ~180 deg with the output gear. In a servo modified for continuous rotation (like the one modified in the picture I posted), the pot shaft does not rotate with the output gear. You can test your pot by sending your servo a 90 deg position command from the serial monitor, then slowly rotate the pot from 0 deg to 180 deg. The motor should change rotation direction as the pot cross the 90 deg position.
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You can test your pot by sending your servo a 90 deg position command from the serial monitor, then slowly rotate the pot from 0 deg to 180 deg. The motor should change rotation direction as the pot cross the 90 deg position.
I tried this, and it didn't work. I did, however, rebuild the potentiometer and checked its resistance once more. This time, it was measured as 5.2kohm. When I rebuilt the servo and I ran the sweep program, it worked perfectly.
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