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View Full Version : Bioloid AX-12 servo give up its torque



Roman Burdakov
12-29-2011, 08:55 AM
Hi, folks. Here is my problem. A new AX-12 servo from TR coupled with another one for arm joint (two of them should work in opposite directions in order to move arm) can't keep its goal state. I've tested both of the servos separately and one of them give up its torque. When I connect "bad" servo to the roboplus manager I see torque value as 0. Goal state is different from current state but servo wasn't even tried to change it. If I manually set torque to 1023 as all my other servos have, position will be changed but only for a second or two. Torque value will be dropped back to 0 and current state will become different from goal again (servo will relax it's position). At the same time I see red led blinking (on the servo). Torque is always set as enabled. Not sure what is going on but I have tested this many times and always have the same results that torque value is set to 0. I have no problem with another servo in the same joint. Any ideas? Thanks.

tician
01-02-2012, 10:59 PM
If you hook it up to RoboPlus Manager and select the problem servo, there should be an error byte named 'Alarm Shutdown' (address is 18 in decimal or 0x12 in hexadecimal). Using the values listed here (http://support.robotis.com/en/product/dynamixel/ax_series/dxl_ax_actuator.htm#Actuator_Address_12), you should be able to determine what is causing the failsafe shutdown. Is it failing only when assembled into the arm or does it always fail even when unconnected to any frames?

It sounds a bit like one of the dud servos we had in the lab. It might move for a moment if started by hand, but rapidly seized up and shut down due to a torque overload (pretty sure it was the motor, but scrapped it a while back).

lnxfergy
01-03-2012, 12:05 AM
A new AX-12 servo from TR coupled with another one for arm joint (two of them should work in opposite directions in order to move arm) ..... servo will relax it's position .... At the same time I see red led blinking (on the servo)

As tician said, you have either an overload or overheat issue -- if you have two servos fighting each other, one will inevitably overheat. You have to be very careful in this configuration -- or, play with the compliance slopes.

-Fergs

Roman Burdakov
01-03-2012, 10:19 AM
tician, I was rushing to put everything together so that I even didn't test new servos. I see your point, perhaps there is some discrepancy between positions of two servos. I will run new series of tests and let you know about my results.
Fergs, could you please provide more information about "playing with compliance slopes"? I've aligned both servos on the same base and I'm pretty sure that they have the same position values, may be +-1(but -+1 shouldn't be a problem, right?).
Thanks, for both of you.