servo 24/7 operation

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I’m using a Raspberry Pi, a PCA9685 controller, and a servo to control the air intake lever on my woodstove based on stove and room temperatures. My code adjusts the servo position every 2 minutes and there is no force from the stove lever on the servo except when it’s moving to a new position (and the servos were perfectly quiet when idle). The system runs 24/7 and is working great. Except that now two servos have burned out – the first lasted 6 weeks and the 2nd one only 4 (seems the internal electrics failed, all the gears are fine). Are servos designed to be “on” 24/7 for months at a time? If not, is there a way to turn the servo off via the PCA9685 controller to lengthen its lifespan?

  • Nothing to do with the Pi. There should be a better stackexchange site for the question. – joan 11 hours ago
  • 1
    The expected lifespan should be specified in the documentation. If they don’t last as long then (a) they’re crap or (b) you exceed the maximum ratings while using them. – Dmitry Grigoryev 6 hours ago
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    Common servos are built for radio controlled models and are not designed for 24/7. Expect to pay much more for better rated actuators. – NomadMaker 4 hours ago
  • Well, there are 101 tricks, Rpi or non Rpi, to make your servo last longer, or for ever: (1) Use metal geared servos, they worth your extra money, (2) Use not so crappy servos. let me know the web link of your servos, if they are the brand recommended by most Ri official tutorials, I am happy to give an evaluation basic on spec reading and do a stress test for you. (3) Your remark “no force from lever” is very likely WRONG. Show me a photo and I can estimate the force applied to your poor servo, and perhaps suggest how to reduce the loading on the servo, … Cheers. – tlfong01 3 hours ago   
  • You might like to read the following article, saying that the industrial grade servo’s MTBF is round 20k hours: So crappy toy motors is hard to say 🙂 Lifespan of a Servo Motor blog.repairzone.com/lifespan-of-a-servo-motor – tlfong01 1 hour ago   
  • As the expert says, lower servo speed lengths servo life span. So perhaps you thing you can try is the following: (1) Modify your Rpi python program to slow down the servo speed by moving servo in many small steps instead of one big steps. For example, if you want to move the servo from say 90 degrees to 180 degrees, you don’t specify the duty cycle for 180 degrees. Instead you say, 95, 100, … 180 degrees. – tlfong01 1 hour ago   
  • There is an Amtel 4 bit mcu inside the servo, adjusting the carbon film pot which is sort of feedback control. So if you move the carbon film pot contact slowly in small steps, the wear and tear, also fiction causing heat might be smaller. This way, even crappy hobbyist servos MIGHT last 3 times longer, … 🙂 – tlfong01 1 hour ago    
  • And one good thing of moving slowly in small steps, instead of one abrupt big step is that in the last steps before settling down, there is smaller overshoot/undershoot, sort of ringing which are indeed oscillations, causing unnecessary to and fro movements and therefore more wear and tear. – tlfong01 59 mins ago   
  • You can arrange you moving steps as trapizoidaly PID pattern: in the beginning bigger steps until you reach the plateau speed, then smaller and smaller steps when reaching the end. So you will see air intake level sort of “fading in, fading out” moving, making your crappy cheapy servos move like the CalTech rocket scientists designed space ship’s flaps, slowly and elegantly, and as I used to say, your neighbours will from now on respect you more than you deserve. Cheers. – tlfong01 59 mins ago   
  • One more thing, your poor servo is actually NOT moving continuously 24/7, but only one little movement every two minutes. In other word the servo’s duty cycle is only perhaps 5 seconds movement every 120 seconds, or 5/120 == 4%. In other words it is 96% idle. Otherwise your crappy servo would break in perhaps 24 hours. 🙂 – tlfong01 54 mins ago   
  • Yes, one more trick to prolong your life, I mean your servo’s life is the following: As you said, the stove air intake level needs “no force” or little torque, then you power the servo with a lower voltage: The spec for torque and speed is summarized below: (1) TowerPro MG995 Servo Spec servodatabase.com/servo/towerpro/mg995 Torque: 4.8V: 130.54 oz-in (9.40 kg-cm) 6.0V: 152.76 oz-in (11.00 kg-cm) Speed: 4.8V: 0.20 sec/60° 6.0V: 0.16 sec/60° – tlfong01 47 mins ago   
  • The servo spec of power supply is 4.8V to 6V. But usually hackers “over clock” to stretch/stress to limits of 7.5+V for higher torque and speed. In you case you neither need high torque nor high speed, so you can do the opposite, “under clock”, ie, decrease power supply to 4.5V or even lower. Now speed and torque are lowered which you never mind, but you should be happy to live longer! – tlfong01 just now   Edit   

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