Erratic servo tripping voltage regulator

Hi,

I am using one of these servos: https://hobbyking.com/en_us/hobbykingtm-waterproof-analog-servo-3-2kg-0-17sec-40g.html?countrycode=GB&gclid=EAIaIQobChMI49nT2_bE3AIV6L3tCh2vgARTEAQYASABEgJqdfD_BwE&gclsrc=aw.ds&___store=en_us

I have adapted it for underwater use by covering board in liquid tape, packing it with marine grease, and placing o-ring on output shaft. I know the simple answer to my question is water has got in, but I was wondering if anyone had any other ideas.

Ok the servo is externally powered by one of these, set to 5.2v: https://www.ebay.co.uk/itm/5x-MP2307-Mini-DC-DC-Buck-Converter-Step-Down-Module-like-LM2596-UK-SELLER-FAST/182050240664?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2648

The code for servo is:

for (pos = 1; pos <= 180; pos += 1) {
    myservo.write(pos);              
    delay(50);                       
  }

Everything worked underwater for a few days, but then it started moving erratically and overshooting its end stops.

The only way I could get it to move to its positions was to use servo.write(180) or servo.write(1) and give it a delay of 30 seconds to allow it to eventually get there. The loop didn't work.

I put voltmeter on output of regulator and found that when it started going erratic the voltage was dropping and rising quickly. I'm guessing the regulator is tripping out and then recovering. Would this mean short circuit in servo? Is there anything is software that could cause this? Or has it just got water in it?

Cheers

If the software was working then it would keep working and it would not change. You seem to have a hardware problem, possibly a problem with the power supply but more likely a problem with the servo.

A good thing to do would be to measure the current, but if you cannot do this then troubleshooting would include trying a different servo and trying a different power supply.

It’s was water

I think we all knew that. :roll_eyes:

Sorry to hear about the water but THANK YOU for telling us. We don't usually get to hear the end of these.

By the way, I have been successful sometimes at resurrecting "wrecked" electronics by flushing with distilled (or de-ionized) water, and then drying in the sun for several days. (I used to live in Tucson, Arizona, USA, and the sun and the dryness there really helped in these situations.)

The distilled water is not guaranteed to work but may cost less than a new servo.

Moisture barriers almost always fail when pressurized water (ie underwater) is involved. Try a pressurized, sealed case.

Hi,
What are you doing with the servo in the water?

Tom.... :slight_smile:

Marine grease? No idea it that's even an electrical insulator with all the additives it has...
Potting compound is the way to get hermietically sealed electronics. Anything requiring
air spaces must be sealed mechanically to prevent ingress as pressure changes.

If its salt water you have a real challenge BTW as many plastics allow salt and moisture
to leach through, for instance ordinary electric wires will corrode inside their insulation in
a marine environment. Your O-ring seal needs precision machining and ultra-smooth surfaces
to work reliably under pressure I suspect (hydraulic components are never cheap!)

MarkT:
Marine grease? No idea it that's even an electrical insulator with all the additives it has...
Potting compound is the way to get hermietically sealed electronics. Anything requiring
air spaces must be sealed mechanically to prevent ingress as pressure changes.

If its salt water you have a real challenge BTW as many plastics allow salt and moisture
to leach through, for instance ordinary electric wires will corrode inside their insulation in
a marine environment. Your O-ring seal needs precision machining and ultra-smooth surfaces
to work reliably under pressure I suspect (hydraulic components are never cheap!)

You cannot run an o-ring dry on a turning shaft. There is o-ring grease. Buy a tube. Really stingy stuff!

Paul

Paul_KD7HB:
You cannot run an o-ring dry on a turning shaft. There is o-ring grease. Buy a tube. Really stingy stuff!

Stingy or sticky?