Unusual problem with Hitec HS-325 - RC Groups
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Feb 11, 2013, 11:41 AM
Registered User

Unusual problem with Hitec HS-325

Last weekend i had an unusual problem with the throttle servo of a calmato trainer plane. The servo was a new (out of the box) Hitec hs-325. During fourth flight ,when i gave full throttle to make a loop ,i realized that my engine had stoped responding to my commands. After making planty off cyrcles to burn up the fuel ,i landed the plane safely. Investigation showed that throttle servo was dead. It was not jammed like having stripped gears, just dead.
After returning home i opened up the servo. No stripped gears and no sign of fried electronic components. So i unsoldered the motor of the PCB and tried to power sypply it using a NIMH battery. No move. I supposed it was fried but my multitester showed opencircuit instead of shortcircuit ,which is the usual sign of a fried motor. I thought that brushes were worn out ,so i opened up the motor. What i found was that the brushes and the collector were in perfect contition ,so the problem could not be worn out brushes. I decided to use my multitester directly on the collector sectors to find out that the rotor windings had lost their connectivity. The winding terminals seemed to be well soldered on the collector sectors. No sigh of a broken wire but no sigh of connectivity as well.
Now ,the only thing i can suppose is that the winding wire either was cold-soldered on the collector terminals or it was soldered without removing the winding-wire insulation properly. So ,although that initially it was fine ,after a few flights the winding wire lost its connectivity with the collector sectors.
I use Hitec hs-325 servos for many of my planes and one of my nitro helis ,all of them having many hours of flying and i have never experienced any kind of problems. It is the first time i have an issue using hs-325 (fortunately the throttle). I was considering Hitec servos as very good servos but after that ,i am really concerned. I remind that it is not a classic problem of a fried motor or a fried motor drive. After investigation It is clear that there is a bad soldering issue.
The question is. Is it an isolated incidence or there is something wrong with quality control of newer batch of Hitec servo motors? Who knows?
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Feb 11, 2013, 12:22 PM
AMA 537620
ChillPhatCat's Avatar
I would not say there's anything wrong with the servos, it just sounds like you got a lemon there... One anecdotal tale doesn't spoil the bunch. I have a couple 325's and they work fine, and I've had a bunch of HS servos in general and never had one die from normal operation. Sometimes there are failures and you just can't predict, every plane has an expiration date.
Feb 11, 2013, 09:17 PM
Registered User
You should have sent the servo back I'd bet they'd have sent you a new one back to HiTec I mean
Feb 11, 2013, 10:49 PM
Closed Account
How much quality control are you expecting them to do on a 15.00 servo? Consider it lucky if they batch test 1 out of 100.
Feb 12, 2013, 03:19 AM
Registered User
@ jetmech05
We are talking about a 17 euros servo. It would be more costly sending it back to Hitec service than just buying a new one. Furthermore, as an electronic technician , i had the curiocity to find out by my shelf what exactly was the cause of the failure.
Given that such an issue into the motor could not be a result of misusing, i decided to crosscheck if it's a known issue or it's just a piece that "escaped the net" of Q.C.

I expect that they have better Q.C. than identical (on paper only) specifications cheap Chinese servos, offered in 1/3 of the price. And ,to be honest they have. As i have written before ,i have used hs-325 on many of my models for years without any kind of issues and only one of them proved to be a so called "lemon". On the other hand ,i had tried in the past some cheapo servos that gave me tons of "lemonade". .
Feb 12, 2013, 11:49 AM
AMA 537620
ChillPhatCat's Avatar
Originally Posted by exf3bguy
How much quality control are you expecting them to do on a 15.00 servo? Consider it lucky if they batch test 1 out of 100.
That's normal price for most standard servos, which doesn't point to bad QC. Also, you can't expect them to test every swervo either, 1/100 tested would be a pretty good rate... I doubt even $100 - $200 servos are tested any more frequently... In fact, I doubt they test more than 1/1000 for most servos.

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