servo failure
 

I just had the unfortunate experience of losing my giant scale Taylorcraft, which I flew off water to servo failure. It was her maiden flight so the loss was really devistating. Uopn take off all was fairly normal accepept for the tendancy for the plane to be banking fairly hard to the left. All my control surfaces were properly set to there respective nutral points. I would expect a certain amount of trimming necessary with the first flight. After the second curciut in a banking turn she suddenly continued to roll until it reached a point where it went inverted and dove straight into the water from aprox 175FT. No amount of input, elevater or aileron made any difference, it just slowly spiraled in contacting the water with a sickening crack. No amount of trim seemed to work to control the insistant banking. Apon retrieval the fuse was totaly wrecked so repair wasn't an option. So I did what anyone who crashed a plane would do and brought the wreck home to see if I could possibly find out what caused the malfunction. Looking at my cable connections I found nothing wrong, everything was tight and intact. Then I found that the elevator servo had stripped! I also found that one of the alerion servo had also partially stripped. The servos in question were Futaba 3010 with a torque value, at 6v of 90 oz. It's possible that the stripping may have been caused by impact but I have my doubts on this. When I built the plane the hobby store said that these servos should be adequate for what I would need them for. I only like flying scale so acrobatics and no high G forces should have made for a long life for these particular servos. Loosing two servoes at the same time is unbelievable. I am planning on building another giant scale, a Balsa USA Piper Cub. My problem is now what servoes to use, I certainly don't want a repeat of a crash. I was looking at the Hitec 645MS that would deliver 133 oz of torque at 6v. I'm wondering if replacing the nylon gears for metal gears is the way to go only they are very expensive. I need to do the right thing here, any suggestions would be greatly appreciated.

I would think the Hitec 645MS would be a good choice. What I learned with my Giant Scale Super Sporster was that once you're in the game, don't scrimp. Trying to go cheap will only bite you in the @$$. I have those 645's in my Giant Super Sporster running a 6 volt system, and it runs fine. Know what I mean? So think big and strong, you have to.

Servo City has one of the best websites and their servo charts are one of the best resources. I will buy from them just because they have pretty good prices and and I love how I can research between different servos. https://www.servocity.com/servos/hitec-servos#large

It's been my experience that working at a hobby shop does not guarantee any expertise in the hobby. They make recommendations based on what they have in stock. I would challenge the person that told you to use completely unacceptable servos and press for compensation for your loss.

You make a valid point. There are more factors to consider. I stand by my claim that many hobby shop employees make recommendations with zero or little experience to back it up with. A much wiser course would be to reference the assembly manual or seek and experienced mentor.

Gears in two servos stripped on takeoff? Not likely. More likely you got some bad servos in the first place. But it could also have been something completely different like a loose connection to your elevator servo. I even had a situation one time where a low battery voltage caused one aileron servo to go nuts when I moved the rudder. Just one aileron servo, everything else worked fine until the battery dropped even more. But stripping two servos on first takeoff? I don't think so.

Have you considered and examined your battery pack?

All sorts of strange things happen when a pack is near or at it's critical low voltage. A single servos or several can suddenly go to maximum throw and stay there as if locked. You can wiggle the transmitter sticks all you want and nothing will happen. Then just a suddenly, everything can appear to be normal, followed very soon after by a repeat. Bye bye plane.

You must check the battery right after the crash with a voltmeter which puts a load on the battery. These are called ESV - the kind you get from your RC supplier. You do it right away so that the battery does not have any time to recover from its current voltage.

As for your Futaba servos, we don't know what condition they were in when you started. From my experience, I can say that the output shaft is prone to becoming wobbly very soon once put into use. There is plenty of slop in the movement of the gear train as well. A much better alternative is the 3050 which is basicly the same servo with an upgraded output shaft and gears. They don't immediately develop slop.

I have a set of the 3010 servos (as well as the 3050). They were installed in a clipped wing Senior Telemaster. OK for that plane. However, given what I found, I'd not use them in any high demand or critical condition.

And a question - how big and heavy was your Taylorcraft? A 3 foot wingspan model is giant in some people's and mini in some others' minds.

In any case, it would be a good idea to establish what happened before you start blaming someone else for the incident and demanding compensation. Pilot error may be one of many contributing factors. Did you use rudder to help correct the uncommanded bank? Did you cut the throttle to help minimize crash damage? Did you follow the plane manufacturer's recommendations for radio equipment? Lots of things to examine.

The 3010 should have been enough torque to fly your Taylorcraft. And I doubt they failed on takeoff. The servos have plastic gears and probably stripped upon impact. Big scale control surfaces have a lot of inertia when hitting something solid and that force can easily strip plastic gears. Since you made 2 laps and then a slow roll to the water would indicate to me a battery failure. And you said "the trim" couldn't correct the roll. You did apply aileron for correction?? And don't count out that something got wet and quit working.

Just wondering how many times you plan on posting this?

First thread from the 18th

First flight!
Banking hard left!

Sounds like a warped wing to me. OR, maybe even you had one or both your ailerons reversed. Though one should be noticed during pre-flight.

Quote: "Uopn take off all was fairly normal accepept for the tendancy for the plane to be banking fairly hard to the left. ............................. After the second curciut..."

I see a great potential for Pilot/Builder Error in this scenario. A "tendency to bank fairly hard to the left" is anything but "fairly normal". So you take off and experience problems right away. So instead of returning to base to check things out, you keep flying (second circuit) until the problem manifests itself into disaster. Not knowing your experience or anything but I'd say this entire project was beyond your current abilities. Both in building and flying. And I think you're doing what everyone has done at some point and lay the blame on equipment rather than admit that you may have screwed up. The fact that you relied on the hobby shop for servo selection tells me you were in new territory as far as building experience goes. And while I too would consider what the local hobby shop had to say, I would also seek the advice of others. And I have 50 years of experience in this stuff.

Banking hard left? Let me guess, for your two circuits you flew a left hand pattern? That would be like turning into a dead engine on a twin.
For future reference in such a situation:
You noticed the hard bank right away.
You should have set up to return to base then.
First choice would be to land straight ahead if the size of the lake allowed. If not...
Make a 180 turn to the right and if wind allowed, making a straight in landing opposite the departure.
If the wind wasn't cooperating, make a single downwind leg followed by a second 180 to the right and line up for a water landing.
At no time should you have turned into the hard bank. I suspect that is what led to the final spin in.

Major problem with all this is having enough control authority at slow speed to keep the wing level on approach and landing. It's possible the plane was doomed the moment it left the water.

There is a reason I only use either Savox or Power HD.

I use the Futaba S-3010 servo in all of my giant scale airplanes. The latest of which is a 43 pound 80cc powered Cessna 206. My only stripped 3010 servo happened when a friend lost his balance and kicked the rudder, never any issues inflight. Did you use the correct servo horns? Trouble shooting a similar problem a you describe on friends new 1/4 Super Cub revealed he had the wrong servo horn on his aileron servos and they were slipping n flight.