Servo melts after a few minutes

[control-k]

Hello,

First of all, i just became a member so tanx for having a open communety!

Now to my question.
I'm working on a RC project witch uses a servo in steering.
It is a JR type servo and a atmega32 to control it.

The atmega32 is powert by usb (trough a programmer)
To one of the ports i connected the orange wire of the servo (control)
The power from the servo commes from a 4xAA battery pack because the usb's current is limitted, the connection to the pack is direct.
Off course they share a common ground.

When i turned everything on it worked perfectly for a while but after some time (few minutes of testing) it stopped working.
On closer inspection i saw that the plastic packageing of the servo had melted around the motor....

Anybody seen this before?

tanx!

Control-K


ps: i'm using a HK-15339 analoge servo from hobyking.com

 

[albert22]

That servo is specified from 4.8v to 7.4v and you are running it at 6v. So it should be ok. Are you sure that the servo is not banging one of the limits? If you are commanding the servo to go to a position that is off limits in that case the motor will be stuck with the full voltage applied. Causing it to overheat.
Or you may be exceeding the torque or duty cycle that is capable of withstand.

 

[control-k]

Hello,

Tanx for the reply, i think you are right, it jams to the consturction that it is in when i move it from the center position and keeps trying to move more.
For some reason i only get the servo to rotate a multiple of 45 degrees, can this be correct? if i could turn it 25 or so it will be fine.

 

[BradtheRad]

Your control pulses need to be the right length. Between 1 and 2 milli-seconds is what my servos required (when I had an R/C plane).

It's a good idea to mark the servo arm's extremes of travel. After you do that, then do not let the arms go that far. It's the only way to be certain the internal motor is not overheating.

 

[albert22]

>>For some reason i only get the servo to rotate a multiple of 45 degrees, can this be correct? if i could turn it 25 or so it will be fine

The extreme positions for a RC servo are 1mSec and 2mSec (milliseconds) this should ensure that you are within limits. Anyway you may restrict that to keep it safe. The servo is capable of fine resolution, much less than 25 degrees. The problem is with the resolution that you are achieving with the pulse generation in the atmega. For example if your routine could generate 1 to 2mSecs in .01mSec increments then you will have 1/100 positions (around 1.8 degrees steps).
This can be done with a software loop, using timers or taking advantage of a pwm module which most uControllers include.
See here> **broken link removed**

 

[FvM]

The problem is with the resolution that you are achieving with the pulse generation in the atmega.

Utilizing ATmega hardware PWM or output compare, this isn't actually a problem.