coupar

dirtybird:

Yeah I didn’t believe it either (I also thought the smoke would rise first) but the thread poster was insistent. 1500mah battery drained in a couple of minutes....... It IS tuff to argue with a pile of Balsa.

But anyway, the main point was that lots of people advocate dual batteries with retracts. I’m not one of them ‘cause it hasn’t happened to me but there are guys who have had batteries drained by retracts. Even pulling a few amps constantly will drain the battery without you knowing. If someone has concerns, Leo’s fusing solution makes sense. Cheap, simple, light.

dirtybird

My Feedback: (5)

The trouble with a fuse is that you will have to set to the point that it will blow when the servo gets stalled. Then you run the risk that it will blow during normal operation. Our servos operate in the stalled condition most of the time. The amplifier adjusts the current to produce the required torque for the position its in except when its moving.
Its a better solution to use a separate battery for the retracts.

Spychalla Aircraft

My Feedback: (34)

John, Wow 6-7A stalled. Those are some pretty hefty servos compared to what I run. I don't have anything in my arsenal that will draw over 3A under any conditions.

Maybe your redundant line idea would be viable for someone who has a set-up critically dependent on each and every servo for survival of the plane. You will have to judge in relation to what failure modes you want to guard against. Since I started running dual receivers and fuses I actually don't care if I fail open or closed. I don't care if I lose a servo. It doesn't effect me. As I've said earlier, "Let them fry". How many other pilots can say that about their setup? Can you say it about your set-up?

I lost a servo to a failed linkage 3 weeks ago flying a Ziroli Stuka I recently purchased. It is fairly new and still going through the teething pains you see in the first 20 flights or so. Due to vibration the center screw fell out of the control horn on one aileron servo and the linkage fell right off. It was a metal gear servo and maybe I didn't tighten it good enough, but sure enough it fell off. I didn't notice it until I did an aileron roll in slow motion with full stick deflection. The airplane was still quite easy to control even with only one surface active. It builds my confidence that the loss of half the flight controls on any one critical function still leaves the pilot in a pretty good situation to save the plane. Leo

coupar

We'll have to disagree on that one. I've never felt dual batteries were necessary. Leo's approach seems like a good compromise. But each to his own. If it works for you, that's the best solution.

Spychalla Aircraft

My Feedback: (34)

I am really enjoying this topic and dialog. It must be my sadistic side. It demonstrates that even in the R/C hobby there is a general norm about what is acceptable and what is not. Everybody settles into a standard way of doing things. Yet when a challenge like fuses comes along that breaks from the norm it becomes controversial and threatening. Some accept the idea while others dismiss it or try to discredit the idea or its source. So it is with many new ideas and innovations. At the end of the day it is healthy because it will test the validity of the proposal and either kill it or give it strength. I am working hard to give this one legs. I think a lot of pilots will be fusing servos and it may lead to changes on the OEM equipment some day. Leo

coupar

Well said Leo.

JohnW

My Feedback: (6)

Leo, Futaba S9156s and JR 8711s... suck the current stalled, but they will also try to break your finger in the process. No, I cannot say that about my setups. But I have never experienced the failure mode you are protecting against nor have I ever seen it on other pilot's planes. I pretty much stick to high end JR/Futaba servos only in any plane I care about. Doesn't inherently mean I'm safe, but I've had very good results with the upper end offerings from those two companies. I'm with ya on the dual batteries and dual RXs in the right airframes. I don't really see anything wrong per se with fusing if done carefully. I think it is a valid procedure, I just questioned the need is all. On the fusing, I'd would stress that fuses should be properly sized such that they cannot ever blow when the servo is stalled with a freshly charged pack. This would mean peeps need to measure the current draw of thier servo with thier intended battery pack or a lab supply to determine thier stalled current. Differnet battery voltages due to 4c/5c/etc supplies will slighty change the stalled current. - Cheers

nagyizee

Well, I would liked to have some fuses on my servos ...
Yesterday I did a sort of dogfighting with an eagle ( no bird was harmed - we just played around in the air ) ... after a while my plane entered in a death spiral and didn't reacted on any of the controls, just plunged into the ground.
When I reached to the wreck I felt that electric burn smell - then I discovered that one of my aileron servos was carbonized, the wires melted where exiting from the servo.
Fortunately all my electronics survived, so I need an other body and a set of new servos.

Can a servo burn out so brutally to produce this kind of short circuit (it was directly linked to the aileron, worked without tension - checked before takeoff) ?
I am thinking also to an other theory: Could the wires touched each other where they are connected to the servo's PCB because of vibration? I opened a similar, good servo - the wires were glued to be rigid, so I don't see how it could happened.

What experience do you have about digital servos? Can they also burn out this way or microcontrollers can prevent this overheating?

dirtybird

My Feedback: (5)

I tested about 50 servos four years ago. The strongest I tested were the JR 8611A, the Hitec 5955, and the Futaba 9250. The 8611 was the strongest and drew 4A at max torque. If stalled and set to max torque it will burn out the motor in about 90 sec. It is its own fuse. The 5955 will last about 5 minutes at 3 amps and burn out the amplifier. The Futaba lasted about ten minutes and I quit trying. Its max amps was 2.5 amps

RCplanman

My Feedback: (16)

Hi,
Quesionhow can I have mandatory cutoff if I lose all power? I assume you mean if power is lost on one rec.? If every thing is hooked-up with a "y"coming out of the rec. 's and a short develops-wouldn't it go to both rec. 's?
[email protected]

Spychalla Aircraft

My Feedback: (34)

You need to buy engine cut-offs for your ignition systems. Don's Hobby Shop sells them. When you lose battery power the engine stops. You can turn off the power switches on my airplanes and the engine will kill.

I have not found a normally closed switch for magento engines so it is a little more difficult. I use an engine kill switch on one RX and the throttle servo kill on the other RX. It is a second best alternative for engine kill. I wish somebody made a normally closed switch versus the normally open that you can buy for magneto engines.

Don't use Y-harnesses to both RX's. This defeats the purpose of completely independent systems. This thread does not advocate the use of Y-harnesses.

Leo

carcraze

Hi all

I have thought about this when putting together my larger 40% models and thus far have not fused servos. I do generally run 2 RX's mind you I think on my new one I may go down to 1 with a smartfly. I always cross power my RX's so that in the event of 1 battery open failure I still have full control of the plane. If a single servo failure in a shorted condition or even a wiring short draws that type of amperage could it be guarded against by fusing the incoming power to each RX and/or the cross over cable (in my application) with a larger properly sized slow blow fuse, say 15 - 20 amp? This should be a little easier install with les fuses the down side being in the event of a servo failure shorted it would shut down an entire plane half mind you I think it should be fairly controlable in that state.

Thanks
Mat

Spychalla Aircraft

My Feedback: (34)

Mat,

I think you are seeing it clearly. You may want to go with a fast blow fuse considering that once you see a truly high amp load you know you have serious trouble. At that time it is in your best interest not to subject any of your electronic equipment to those loads for an extended amount of time.

I have an electronics friend that is after me to combine my dual batteries similar to what you are talking about. I struggle with doing that but have not been able to give him good logic as to why I am not willing. Something about having two completely separate flight control systems from start to finish gives me confidence. Yes, I can lose half of the controls, but I will always have half. So that is good.

As you consider combining your batteries into one common supply keep in mind that fusing between them will still protect you from a direct short in one of the packs. Fusing only from a common buss to each RX will not. So you have some choices. I once had a flight pack short out in the plane due to wires wearing through due to vibration. Found it during charging on the ground. Smoke was pouring out the bottom of the plane! I am glad it didn't happen in the air!

Before you buy the SmartFly or any power distribution panel I would encourage you to call Don at Don's Hobbies and have a chat. See them at: http://www.donshobbyshop.com/ He has been at this a long time and has some very good commentary on these things. His large hobby shop does not carry them for a reason.

Leo

tkilwein

Pulling 30 amps thru the servo wires (22-20 gauge) would smoke the wires, not to mention most power systems.
I agree with Johnw, I have seen up to 4-6 amps with servos stalled. The new 8711's the highest in stalled mode I have checked.

carcraze

Thanks Leo I will give him a call and listen to what he has to say.


Mat

radfordc

My Feedback: (14)

I met Leo this weekend in Minn and we talked about the need for fused protection in servos. I agreed that it was probably a good idea, but had never had a servo short closed in all my years of flying. On the very next flight one retract servo shorted and burned up. Lucky for me the short cleared before the Rx was toasted and I was able to land OK.