servo fire
 

Had my SM L-39 out the other day, and just a static display, I started mine up and taxi'd it out to the tarmac to park it next to a full scale L-39. a few hours later I had to start it and bring it back. About 15 minutes later,

As I parked it in the pit area, I left the radio on, leaving the cool down sequence to finish, I walked a short distance away to watch the L-39 do some fly by's. I see over in the pit area a few guys around my L-39, then I see one of them running with a fire extingusher towards my jet. I get there, look for anything, pull all the batteries out, then I start digging.

What I found was a burnt out servo Hi-tec HS-5475HB. These were Flap servos....

Tonight i had a chance to really dig, not sure if the receiver went, servo went????? Both servos were locked up, no movement by hand, or by radio. I plugged two new servos in and it seemed just fine.

Anyone else have servos melt and burn up? curious as to why it happened........................


Mark

RE: servo fire
 

I had a 225 MG on a retract valve do the same it was just sitting there and it smoked up, and fryed my 9100 receiver. I have been flying with Hitec for years and no other trouble I think **** happens. Over the years I have seen all makes of servo's smoke up for various reasons.
Mav

RE: servo fire
 

Mark, I never had anything but bad luck with them. I got away from them about seven years ago, never looked back. I guess if your stranded in the woods and you need to make a fire and you dont have any matches you know what to use instead.

RE: servo fire
 

not sure why this number Hitec's were in there, I usually use the 5645 Hitec servos. but new ones will be back in the bird tomorrow night.


Mark

RE: servo fire
 

The fact that both servos were on the flaps and both burned up tells me they were binding....to have 2 servos both burn up at the same time "just because" is not gonna happen...I have seen that exact "melt" on the Hitec's once before....the guy had two of them on a rudder and they were fighting each other and smoked during taxi out....about 5 minutes worth...certainly no fault of the servo...it was 100% user error in his case.

RE: servo fire
 

Mark,

I just had an 8711 burn up. It was on the elev of my large Viper. I hadn't done a thing since the last flight. It moved freely with the system off while I was pushing the horz stab on. When I turned on the radio system, no movement of the elev. I pulled the stab out and touched the servo...really hot. I just counted my blessings...missed another bullet.

George

RE: servo fire
 

<div>I'm glad this happened on the ground!</div><div>
</div>How many volts do you guys run in your melting servos? I wonder if this is a factor. I agree that binding is likely a problem but I suspect that over voltage could be a factor as well.<div><div>
</div><div>Arnaud</div></div>

RE: servo fire
 

WATCH YOU BATTERY!
I had an 81 MG smoke a hole in its side and the power consumption of that event toasted my NiMh battery. I did not realize the battery had been damaged an it lead to the loss of a new glider[&o]

RE: servo fire
 

Binding can often be the problem on flaps. Depending on the stand (Harbor Frt) and the aircraft config, it is easy to run your flaps down and not know they are being restricted by the stand. On my elev. their was no restriction or binding. The voltage is reg through two JR regulators.

RE: servo fire
 

Totaly agree! There was binding against the end travel of the flaps.
.....it was 100% user error in this case.




.

RE: servo fire
 

Any piece of power electronics that allows itself to overheat and melt down is of poor design. This applies to all digital servos I have laid eyes on. People, we have amateurs designing our stuff....

RE: servo fire
 

I have done it twice while programing servo travel. They burn to a crisp with the all familiar electronic burnt smell. Agree binding is the culprit.

RE: servo fire
 

My flying buddy had the same thing happen to an HS 5945 servo . When we took the servo out it looked exactly like the photos posted. The inside of the servo bay also suffered burns.

RE: servo fire
 

Thanks. Now I feel a whole lot better.[&o]

RE: servo fire
 

I Had a 5485HB do the same thing and it was only used on a retract valve. Using 6.6 a123. It was during setup and was very slightly over traveled. My fault. But it was barely binding, never would have expected it. On the other hand I had a 7950TH burn up on me last month. I had replaced my rudder servo on a pull pull system with it. It started smoking within seconds and it was fresh out of the box. I sent that one to hitec and they told me the amplifier was bad in it....

RE: servo fire
 

Not necessarily, If you have a problem in the air would you rather have the servo stop working to protect its self, or to burn its self up trying as long as possible to maintain control of the attached surface.
Or if you wanted the electronics to be able to handle the power draw of an overload it would need to have huge heat sinks and your 2oz servo might end up double the size and weigh a half pound.
In the design process you always have to make compromises. You just need to decide your priorities.

RE: servo fire
 

225mgs are junk ive had 5 go out on me on light duty stuff like throttle and chokes sane with the 5425

RE: servo fire
 

I was just going to say that ;) That's why there is no circuit breaker or fuse in our models.

RE: servo fire
 

Agreed you want control, but digital servos have the ability to be intelligent (pending the designer) It will know that it cannot reach its final position at full power if it does not happen within a few seconds. It knows this from the feedback pot position! So it can back off enough to prevent stall and burnout. Pointless for it to zap full power when its obviously going nowhere, like on flaps in the OP's case. Could save a model instead of just burning out for no good reason altogether. Not much of a mental challenge now is it. Sort of like a rev limiter on a car.

RE: servo fire
 

I have had several micro and two or three standard servos alight as well. Not sure why. One micro was the result of too high a voltage battery, but the rest are unknown. Kind of annoying, especially if your model ends up smashed to bits as a result !

RE: servo fire
 

Mark, the first thing I would want to come to an understanding on, Is-How many flights on those servo's? At what point do I deploy flaps dowwind and how much torque is that servo induring? When they deploy at landing Pos, I would be hard pressed to think they were taking any more torque than a few seconds on a assy stand. I would say, Electronics is electronics. I have owned and operated some of the best Ham radios known to man. Cream of the crop and sooner or later you gonna see smoke. A main power supply transformer. A final. You replace it and key up again. What makes our losses so dramatic is seeing one of our beloved and expencive jets/aircrafts go in.

RE: servo fire
 

well, I stopped at my LHS, who is also a jet jock like us, and went over a few things. Now, these servos have been in the L-39 for almost 2 years. never a problem.
1) battery voltage. I use Electro Dynamics Battery backer system, even with the 2 - 6.0 volt batteries my voltage to the receiver is constant at 5.50, there abouts.....
2) I used an inline meter to check the servo and the draw on power, making sure I was not binding.

when I started my L-39 and moved it up to park it next to a full scale L-39, everything was fine. and hour or so later, they asked me to move mine so they can start theirs and do some low fly by's at this event IU was at.
when I started it, I noticed the right flap was not moving, but left one was ok. I then brought the L-39 back by our trucks. I left it on maybe 20 minutes, forgot it was on while I watched this L-39 fly.
late last night, I looked it over and seems only damage is to the servos and nothing else.
I was promised a ride as soon as I get my L-39 painted just theirs........ ok, I am off to by paint.....PPG?

Mark

RE: servo fire
 

Markthat wouldn't be Art Nolls black L-39 would it??? Ha. Ha.

RE: servo fire
 

I had this happen with 4-5 year old servos ,just took a crap on me one day.

RE: servo fire
 

NNo it is not, I bought this kit from Kerry Sterner and built it myself. also there is only 2 flights on the L-39, although built in the winter of 2009- 2010, just 2 flights on it last year and all went well. I have the same flap set up in another jet, I deploy the flaps a the same time as in all my jets, onlyy difference is the number on the servos, I picked up Hitec's 5645's today and tomorrow I will put them in the wings.