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View Full Version : Safe temperature limit on AX-12/RX-24?



Pi Robot
05-06-2011, 10:02 PM
I have a pair of 6-jointed arms with 2 RX-24s at each shoulder and 4 AX-12s for the other joints. I've burned out at least two AX-12s over the past year by running a servo too long under load. What do you guys set your temperature limit on these things to prevent burnout? I'd like to set it low enough that the Overheating protection kicks in before it gets damaged, but not so low that the arms are always shutting down.

Thanks!
patrick

lnxfergy
05-06-2011, 10:09 PM
I have a pair of 6-jointed arms with 2 RX-24s at each shoulder and 4 AX-12s for the other joints. I've burned out at least two AX-12s over the past year by running a servo too long under load. What do you guys set your temperature limit on these things to prevent burnout? I'd like to set it low enough that the Overheating protection kicks in before it gets damaged, but not so low that the arms are always shutting down.

Thanks!
patrick

I've set my limits at 60 degrees typically (the default is 80), and I've never killed a servo (I have stripped out gears by turning torque overload detection off -- almost instantly). This is especially a good idea for the bigger RX servos.

If you're connected with the ArbotiX-ROS drivers, you can fire up the "robot_monitor" node (same package name) and see the diagnostics data streaming out of the ArbotiX. This will flag any temp over 50C as a "VERY HOT" in the monitor. Similarly, you could easily monitor the diagnostics_agg topic that robot_monitor subscribes to and have Pi declare "I'm overworked, come back later" and relax the servos when they get hot.

-Fergs

Pi Robot
05-06-2011, 10:26 PM
Thanks Fergs,

This is exactly what I needed to know. I'll definitely check out the robot_monitor package as that was going to be my next question. (It's like you're readin' my mind, man!)

--patrick

Pi Robot
05-06-2011, 10:43 PM
Hey Fergs,

I'll read up on the diagnostic packages tomorrow, but I noticed that the ArbotiX driver.py script is publishing the data to /diagnostics while the robot_monitor node subscribes to /diagnostics_agg so I am not seeing any data in the GUI. Is there a simple way to connect up the two topics.

--patrick

Pi Robot
05-06-2011, 10:49 PM
Ah, I just found the runtime_monitor package (versus the robot_monitor package) that looks at the /diagnostics topic directly so I now I see the data. Very cool.

--p

Peter_heim
05-07-2011, 07:06 AM
Hi
Over the past 6 weeks I have rebuilt Robbie's arm about 4 time chasing various problems relating to over load's and over temps I run the servos at 12 volts any servo under load has a temp above 40 C at start up and then goes to 62 C within 5 mins this is for a arm of 5 servos and brackets no extensions. Doubling the servos has not helped making a useful arm the extra weight in the servos and extensions results in the same overheats and overloads. It would be interesting to know what is the largest size arm that can be made with AX12 servos (for testing) and what kind of servo combination would be required for useful work ie get a can (of beer) out of the fridge. And I think having the program setup to get the item and put in down and returning to rest position will help a lot. if you can offer any advise on programming that would be great I have managed to move the arm to a xyz location but the problem is it very hit and miss how can I work out the the valid locations for a arm of a given size?


Regards Peter

lnxfergy
05-07-2011, 08:31 AM
Ah, I just found the runtime_monitor package (versus the robot_monitor package) that looks at the /diagnostics topic directly so I now I see the data. Very cool.

--p

Patrick,
You need a diagnostics_aggregator, there is a sample yaml/launch file in arbotix_python.

-Fergs

Pi Robot
05-07-2011, 09:05 AM
Over the past 6 weeks I have rebuilt Robbie's arm about 4 time chasing various problems relating to over load's and over temps I run the servos at 12 volts any servo under load has a temp above 40 C at start up and then goes to 62 C within 5 mins this is for a arm of 5 servos and brackets no extensions. Doubling the servos has not helped making a useful arm the extra weight in the servos and extensions results in the same overheats and overloads.Hey Peter,

That does sound odd. I'm running all my servos at 12 V using an SMPS2Dynamixel adapter. As we speak, I have Pi Robot's arms on with just the AX-12 servos activated. (I have two RX-24s in each shoulder but they are currently off). So the load is near 0 on all of them and they start out at about 27 degrees and then rise to no more than about 30 degrees. I then rotated the two forearm servos 90 degrees so that they were lifting the weight of one servo, a bracket and the "hand" plate which is a total load of 64 and the temperature on these two servos climbed to 44 degrees over 5 minutes and stabilized. Finally, I hung a weight off the tip of one of the hands and the load on the forearm servo when up to 160, but the temperature only went up to 49 degrees and has stayed there for 10 minutes.

--patrick

Pi Robot
05-07-2011, 09:08 AM
Patrick,
You need a diagnostics_aggregator, there is a sample yaml/launch file in arbotix_python.

-Fergs

Thanks Fergs--will check it out.

--p

Pi Robot
05-16-2011, 07:29 PM
If you're connected with the ArbotiX-ROS drivers, you can fire up the "robot_monitor" node (same package name) and see the diagnostics data streaming out of the ArbotiX. This will flag any temp over 50C as a "VERY HOT" in the monitor. Similarly, you could easily monitor the diagnostics_agg topic that robot_monitor subscribes to and have Pi declare "I'm overworked, come back later" and relax the servos when they get hot.
-Fergs

Fergs,

I just noticed that the "VERY HOT" threshold in driver.py is 40C, not 50C as you mention above. Since I don't know what's considered hot for these servos, should the threshold be changed to 50C in driver.py or is 40C already very hot?

--patrick

lnxfergy
05-16-2011, 08:36 PM
Fergs,

I just noticed that the "VERY HOT" threshold in driver.py is 40C, not 50C as you mention above. Since I don't know what's considered hot for these servos, should the threshold be changed to 50C in driver.py or is 40C already very hot?

--patrick

Whoops -- 50C was the intended level, but I was having trouble getting servos up to that level to test that it actually works and accidentally checked in the "40C" version... with a 60C cutoff, 50C is a decent warning before shutdown.

-Fergs

Pi Robot
05-16-2011, 09:26 PM
Glad to hear it! My head tilt servo (supporting a Kinect) hits about 42 degrees after a few seconds of tilting back or forward. So now I won't worry as much. :)

--p