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View Full Version : [Question(s)] ax-18 abrupt stop makes grinding noise



lookitsash
09-27-2012, 09:58 AM
I have an ax-12 servo connected to a gear and track (so when the servo spins, it moves my mechanism horizontally along the track). The problem I have is that when I move at full speed from position A to B (in joint mode), the servo makes a loud grinding sound. Does anyone have an ideas as to what is causing this issue? I don't want to damage the servo. I suspect its from the inertial shock of stopping abruptly from full speed. Maybe playing with the compliance margin and slope will help, but I'm not too sure how changing the default values will help.

Upgrayd
09-27-2012, 11:56 AM
the servo makes a loud grinding sound

It sounds like the gear train in the servo has already been damaged.

tician
09-27-2012, 01:18 PM
I realize there is a degree of futility in arguing about the description of sounds over text communications, but a sharp and distinct clicking sound (following a regular beat as the horn is rotated) indicates broken teeth, a lower constant groaning/grinding sound indicates the servo struggling against excessive loading, and a low 'jittery' groaning indicates the servo is rapidly changing motor direction trying to maintain position against a load. A little bit of increased resistance following a regular 'beat' as the horn rotates (but no clicking) indicates damaged/deformed teeth or other internal damage from overloading.

As for the servo parameters, see here (http://support.robotis.com/en/product/dynamixel/ax_series/dxl_ax_actuator.htm) for an in-depth description of all the registers and see here (http://forums.trossenrobotics.com/showthread.php?5501-Generating-a-sine-wave-angular-velocity-motion-with-AX-12&p=51887#post51887) for the technical details of how they work in servo mode (or at least the best explanation I can muster).

If you are planning to use the AX-12 in wheel mode, beware as there is not very accurate speed control. Also, any attempt to switch back to servo mode while the horn is outside of the valid range of the potentiometer (~300 degrees) will lead to unpredictable movement.

lookitsash
09-27-2012, 01:39 PM
thank you for that explanation of the different noises. I don think think I have any broken gears. The servo (when powered off) rotates fine without making any noises. Even when powered on and rotating at full speed, it sounds perfectly healthy. Its just when its connected to my machinery and moves really fasts and stops abruptly does it make that grinding/clicking noise. I think it sounds more like what you said with "servo is rapidly changing motor direction trying to maintain position against a load" I read up a lot more on the compliance slope and will experiment with that to see if it helps. I can also try moving to by destination and slower and slower speeds to avoid the shock of an immediate stop.