I am building a quadruped robot from 10 MG996R servo motors. I am powering them with 12 Eneloop AA batteries, but I am starting to see that I might be lacking current. The servo spec says that each motor can draw up to 2.5 A of current when stalling. My servos are stalling when the robot is standing and support its own weight, and it is exactly during this time that one of my servos stopped working. Is it likely that it broke down because it lacked current, or will the servos continue to fail even if I provide ample amount of current to support the stall current?
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\$\begingroup\$ How are you driving them. 12AAs is 18V... You didn't leave that across the servo did you? They are not rated for that. Mind you the spec sheet for the servo really sucks. \$\endgroup\$– Trevor_GCommented Apr 3, 2017 at 21:12
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\$\begingroup\$ I arranged them in 2 sets of 6 AA batteries in series to achieve 1.2 V x 6 = 7.2 V, the maximum voltage rating for the motor. I am aware that this isn't the nicest servo motor model, but I am simply trying to make the robot walk, and I hope to know if providing sufficient current will prevent additional servo motors from failing like this. \$\endgroup\$– SkipherCommented Apr 3, 2017 at 21:15
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\$\begingroup\$ Keeping any motor at stall current for a long time is generally a bad idea. The spec shows no power rating so it is impossible to tell for sure. It may have overheated and fried. \$\endgroup\$– Trevor_GCommented Apr 3, 2017 at 21:21
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\$\begingroup\$ Even if I let the robot walk continuously, the servos will experience stall current for some time throughout the cycle as they have to push against the ground. What happens when a servo stalls but does not have enough current? Will they be less likely to fail if they have sufficient current and do not stay stalling the whole time? \$\endgroup\$– SkipherCommented Apr 3, 2017 at 21:25
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\$\begingroup\$ Do not confuse stall current with holding current. They are not the same. If the motor is prevented from turning with full power on ... that is stall current. It is a bad thing. If, by the nature of the operation the motors are frequently stalled, then you need to limit the motors starting current/ torque to a level the motor can handle without overheating internally. \$\endgroup\$– Trevor_GCommented Apr 3, 2017 at 21:28
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Most probably the motors are overloaded and the onboard electronics doesn't limit the current, therefore it overheats when holding such weight.
Now you have few options:
- increase gearing
- buy larger servo
- make a current limiting device, by using it your robot will not stand anymore
Replacing the battery pack won't help, the servos will continue to burn.
answered Apr 4, 2017 at 6:48