Hi Torque 120 degree servos overheating and burning out

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kittykat
 
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Hi Torque 120 degree servos overheating and burning out

Post by kittykat »

Hi there.

I am using the Adafruit 16-Channel 12-bit PWM/Servo Driver to power 7 Hi-Torque servos. The servos are getting a bit hot, and one seemed to have burned out. I have a 470uF capacitor soldered on the driver. I'm using the 5V, 10A switching power supply recommended on the servo driver product page. After thoroughly searching on the forum and other sites, I am thinking it's due to my SERVOMIN and SERVOMAX settings. I have them at 160 for min, and 590 for max. (I know default min and max are 150 and 600).

Should SERVOMIN and SERVOMAX be different values for these servos since the Hi-Torque ones are 120 degree? If so, what do you recommend for min and max?

If SERVOMIN and SERVOMAX are not the problem here, should I be adding a higher capacitor value (1000uF instead of 470uF)? 6 motors seems to behave ok, but adding a 7th made it misbehave (twitchy and noisy), which was the one that burned out.

Also, is there any big danger in having a servo overheat and burn out, in terms of fire hazard?

Your answers are much appreciated! Thank you!

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adafruit_support_bill
 
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Re: Hi Torque 120 degree servos overheating and burning out

Post by adafruit_support_bill »

Should SERVOMIN and SERVOMAX be different values for these servos since the Hi-Torque ones are 120 degree?
That depends: Are the servos hitting the hard stops? This is one cause of overheating. Another cause is overloading the servo. What kind of load are these servos moving?
what do you recommend for min and max?
This varies from servo to servo - even the same model from the same manufacturer. The recommended procedure for calibrating servos is here: http://learn.adafruit.com/16-channel-pw ... it-library
Also, is there any big danger in having a servo overheat and burn out, in terms of fire hazard?
I have never seen actual flames from one, but I suppose it is possible. You probably want to get them working normally before installing them anywhere where they could be a source of combustion.

kittykat
 
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Joined: Wed Dec 11, 2013 1:11 am

Re: Hi Torque 120 degree servos overheating and burning out

Post by kittykat »

Thanks!

I'll double check again to make sure the limits are not hitting a hard stop. They are indeed pulling a load with some resistance. I'll try my best to alleviate that. Hopefully that was all that causing the overheating and burnout.

So, the default SERVOMIN and SERVOMAX are not entirely different values for a 120 degree motor as opposed to a 180 degree? I just wanted to make sure it was the same approach and that there was no major error there.

Do you suggest increasing the capacitor value from 470uF to 1000uF for the 7 servos? Or is that not related to the overheating?

Thanks again!

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adafruit_support_bill
 
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Re: Hi Torque 120 degree servos overheating and burning out

Post by adafruit_support_bill »

So, the default SERVOMIN and SERVOMAX are not entirely different values for a 120 degree motor as opposed to a 180 degree?
No. They are still nominally looking for a pulse of 1-2mS every 20 mS or so. But, being analog devices, there is variation in response from sample to sample. So you have to test each one to find the real limits.
Do you suggest increasing the capacitor value from 470uF to 1000uF for the 7 servos? Or is that not related to the overheating?
It probably has nothing to do with the overheating, but it won't hurt to have the extra capacitance to smooth out the power surges with 7 high-torque servos going at once.

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