Screwy servo?

These small servos can easilly be stripped by moving them by hand such as moving the control surface with power off or by turning the receiver on before the transmitter and the servo goes to the end and jams.. Good Luck Gene

Sounds exactly like the symptoms I had a few weeks ago when I stripped the gears on two Futaba S3004s (aileron servos) on my Ultra Stick 120. Taught me the importance of doing a full control surface check prior to taxiing out. It's also making me think twice about servos with plastic gears.

Take the servo apart and I'll bet you'll find gears with missing teeth. Seems unusual though for it to happen to a rudder servo given how little it's used in a flight.

Were the other two failures of Hitec servos similar in circumstance/symptoms?

Jim

In response to Jim. The other two servos just simply quit. They were both Hitec HS-55 mini servos in a glider. There were hardly any load on them as they were used to actuate an on-off throttle switch. I have only two that I kept, the HS-81 and HS-55. Think Hitec would want to know what might have gone wrong with their servos?

Wan

Thats odd. I fly almost nothing BUT HS55's and I haven't had a single problem with any of them. Must have about 20 by now (gasp, THAT many!!!?)

Hitec wants you to continue buying their products. To that end, they will either repair or replace servos that die under mysterious circumstances for FREE, if you send them in. However, stripped gears don't count, because they're usually the result of a crash or abuse.

The gearset in the HS81 is particularly fragile, because the servo is so small for the torque it puts out. Playing with the servo by twisting its arm back and forth, or playing with the control surface to make the servo move manually is a BAD thing, and it'll generally weaken the servo's gear train.

I'd guess teh elevator, but its marginal.

People who have copuled steerable tail wheesl or skids, will need a strong rudder servo tho.

Which one would YOU prefer to fail in flight tho :-)

The flight load may be slightly higher on the elevator, but it is the ground load that strips servos.

If you fly your tail-dragger over grass, the blades of grass trying to straighten your rudder on landing will cause the HS-81 to strip the pinion driving the output arm. I've seen slow-motion videos of very soft landings showing the rudder being whipped from side to side by blades of grass.

-Fritz

That's why many people prefer to use some sort of spring to connect the rudder to the tailwheel, ala Sullivan tailwheels.

You can make a spring-loaded tailwheel yourself, Wan. Just firmly mount the tailwheel pivot onto the fuselage, and have the tiller arm tied to the rudder with a spring or rubber-band. Tail-whell brackets are made by Du-Bro, CG, Sig and several other plastic parts molders.

This only solves one problem, though, the other is that the rudder is actually whipped by the grass. You need a tail-whell that puts the rudder high enough off the grass until your plane has bled off its speed.

-Fritz

You might try another trick several of our members use on the smaller sized tail draggers. Instead of a hard, solid connection between the rudder and tail wheel, separate the steering rod and connect with a short length of fuel line. It absorbs most of the hard shocks, and doesn't reduce ground taxiing control enough to even notice.

Olin McDaniel, AMA 30932, W4PFZ

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I have used the smallest Sullivan tail wheel mount (1/16" wire) on a 4.25 lb airplane. Worked great.

Reduce the gap to about 1/2 inch and you should be in business. I have put a tail wheel arm into fuel tubing and screwed it to the bottom of the rudder and had it work.

Olin,

Thanks for the tip to reduce the gap to about 1/2". I did just that but had to find fuel tubing tight enough. I still had to bend the push rod into somewhat a "V" bend on both ends of the push rod, and added an outer plastic tube to prevent the "push" part of the control from flexing too much.

I had to experiment a bit to find how long the outer tubing should be. Now it works like a charm, just enough give on push and pull and the rudder stays true.

I'm going to fly this afternoon. :-)

I'll let everyone how it goes after the flights.

Wan

Olin,

Thanks for the tip to reduce the gap to about 1/2". I did just that but had to find fuel tubing tight enough. I still had to bend the push rod into somewhat a "V" bend on both ends of the push rod, and added an outer plastic tube to prevent the "push" part of the control from flexing too much.

I had to experiment a bit to find how long the outer tubing should be. Now it works like a charm, just enough give on push and pull and the rudder stays true.

I'm going to fly this afternoon. :-)

I'll let everyone how it goes after the flights.

Wan

Olin,

Thanks for the tip to reduce the gap to about 1/2". I did just that but had to find fuel tubing tight enough. I still had to bend the push rod into somewhat a "V" bend on both ends of the push rod, and added an outer plastic tube to prevent the "push" part of the control from flexing too much.

I had to experiment a bit to find how long the outer tubing should be. Now it works like a charm, just enough give on push and pull and the rudder stays true.

I'm going to fly this afternoon. :-)

I'll let everyone how it goes after the flights.

Wan