Hitec HS-81 Servo
 

I just bought two of these for a 2 meter sailplane. They are rated at 36 oz of torque. These are micro servos.
Im hearing problems with the 605.....do these problems carry over to other servos.
These micro servos were only 18.00 dollars each. Should I return them and get a better quality servo.???

Also should I consider not using Hitec servos at all.???

I would rather not lose a plane because of a cheap servo. There are already enough reasons to crash a plane other than using equiptment that is not good enough quality.

Thanks

Hitec HS-81 Servo
 

If you think 36 oz. in. is OK for your application, then the 81s will be OK. Just be careful with it. Every time I've crashed a model with 81s in it, at least one or two seem to get stripped, so avoid bumping control surfaces when landing, etc.

Small servos tend not to be as robust as standard servos, even with similar torque ratings. I guess it's due to the small teeth on the necessarily small gears.

Hitec HS-81 Servo
 

I also have stripped out the gears on a HS81 by just bumping the control surface of my 2 meter glider. I substituted the HS81 for some HS85BB's, a little beefier servo.

Hitec servos are still the best radio value going. The truth be known, the JR & Futaba die hards would be floored to learn who makes their servos.

Vince

Hitec HS-81 Servo
 

81s are great with metal gears. If you don't go metal then you better be carrying around a few packs of back up plastic gears ($6).

go w/ the HS-85s... maybe.
 

The answer here really depends on the type of sailplane.

If the bird in question is a 2M R-E floater the HS-81s will be fine. The gears do not tolerate shocks well, so use a little care while handling. As for flight loads... if you are flying it fast enough to flutter the control surfaces you've probably torn the wing off already :)

I'd advise against using them on ailerons. I had a set in the wings of my Sparrow sloper - I had gears strip several times after landing (softly!) in long grass. Forgot to raise the flaperons before touchdown. :rolleyes: After a season of use the servos had developed quite a bit of slop due the case wearing. (The HS81s don't have ball bearings or bushings - the top servo case is the only thing supporting the output shaft.) I swapped hem out for HS85s and haven't had any problems since.

Hitec micro servo's
 

Let me tell you what I did with (to?) some of the Predecessors to the HS 81's, namely the HS 80's.

I bought a pair of HS 80's micro servo's and installed them to directly drive the "largish" barn-door ailerons in the wing of a Cosmo King 40 SR sport ship. No big deal? Well, I didn't power it with a 40 size engine - I bolted an MVVS .61 screamer up front, and let her rip.

I didn't hold back. I rung that poor 'plane out many times over. Absolutely caned it. That the wing never folded was a testament to it's sound construction, and fibreglassing of the joint.

Many people said those little servo's wouldn't take it. But I wanted minimal weight in the outer parts of the wing, and I used them. Guess what. The ONLY time I stripped the gears in those tiny servo's (and I did that a few times) was when I was loading the wing in to my car, and I accidentally bumped the aileron.

The tiny output gear would give way to save the servo. It NEVER happened in flight.

The hitec micro servo's get the thumbs up as far as I am concerned.

fiery

Hitec HS-81 Servo
 

zero244

My suggestion is that don't go for what you are doubtful and can risk you plane. Replace HS-81 with some other good servos. I never trusted the specs listed by the manufacturer, specially Hitec.

Hitec HS-81 Servo
 

I can't add much except to back up what's been said already. These are tough little servos and they work well in my GP Spirit (2Meter). I have used this ship to learn how to fly and have done the lawn dart routine more than once. I have stripped gears twice, they are inexpensive and easy to replace. I'm now using a red servo saver on the rudder servo, since that's the one that's been striping, and so far so good.

Hitec HS-81 Servo
 

Here's a tip for all of you guys that have stripped servo gears due to bumping the ailerons when handling. On my planes - large and small - when I am done flying, I take a small piece of cardboard (about the size of a pack of matches), fold it around the joint between the aileron and the solid portion of the wing - then secure it with a black spring paper clip. The two wire handles on the clip then fold flush with the wing, and "viola" - no more stripped gears.

servo's & stripped gears from loading wings into car!
 

Nice one Jim!

Thanks

fiery

Hitec HS-81 Servo
 

I stripped my HS-81s crashing my FMA Razor during my learning curve. ;)
Put in the metal gears and they rule. When I need more, I always order them with MG. (servocity.com)

Good Luck,
Rich<>

Good stuff
 

These servos are a favorite far and wide for glider flying. I have a full house 2M glider with an -81MG on each surface (6 total). This plane probably cruises for thermals faster than a 2 channel floater would ever go. It's more unusual to see someone in my glider club who doesn't use Hitec. If you are worried about control power, don't. The only worry would be stripping a nylon gear thru some non-flying impact.

I would say always use MG's on wing servos because of the potential for landing damage. Full flaps down landing on rough (or not so rough) ground puts alot of stress on the gears.

On your's, you have to think about whether you can protect the surfaces from bumps & bruises enough to survive with the nylon gears. Bracing the surfaces for transport - like Jim - is a very good idea. I once crashed a 40-size plane by taking off with an elevator servo I had stripped while loading it in the car. That was a regular size servo though.

I have some 605's and have seen their problems. I have not seen anything similar on any other model of Hitec servo. Just got in one of the 5125 digitals - man is that cute. I'm surprised at how tiny it is. Thinner than a -81 even - but a little bit bigger from the side.

HS85's for my 2M
 

I bought 4 of these 81's on sale at a contest and I just can't get the courage to put them in any plane yet with all the stripped gears happening at my club. HS85's drive most my gliders including open class ships and they are only $5 more. Call me chicken, but I wouldn't use them in anything larger than a Gentle Lady or a Speed 400 plane (non-foamy due to impact probs.) Metal gears would help my courage, I'm sure.
Jack

RE: Hitec HS-81 Servo
 

Hey there everyone! I realize that this thread has been dead nearly as long as King Tut, but I have a question here. I'm currently building a Gentle Foamy from Mountain Toys (www.mtntoys.com) and I need to use the HS-81 servos I already have. I'm concerned about the flexing of the foam in a crash causing the pushrods to push on the servos and strip the gears. I want to use a servo saver on each servo, but the guys at the local Hobby Town said that they'd never heard of them being used on the HS-81, but they might be able to help me if I gave them a part number. I saw in this thread where someone mentioned using them on HS-81s, so I hope someone can help me here. Thanks in advance!

RE: Hitec HS-81 Servo
 

Dubro has a genaric servo saver set that is typically used on throttles. Don,t have the number but it is in the Dubro catalog.

John

RE: Hitec HS-81 Servo
 

Just spend a couple bucks more and get the MG's. They'll take the abuse.

RE: Hitec HS-81 Servo
 

Thanks guys! Someone on another forum gave me a part # for Kimbrough, but I'll check into both of these options, too. I'm really limited on budget and I mean REALLY limited! Johng, are you saying I can get a new set of metal gears for my nylon geared servos, or do you mean that I should get metal geared HS-81s brand new?
Thanks again!

RE: Hitec HS-81 Servo
 

Either way. I would get them as-bought if I didn't have them already. I did have a couple of Hitec 225's that were going into a giant scale glider so I bought the MG kits and did the upgrade myself. Not much to it. I think the gear kits are available at a good price from Servocity.com

RE: Hitec HS-81 Servo
 

Johng, thanks for the advice! I didn't know that there was actually a conversion kit. I missed your post while I was at work. I went down to the local Hobby People on my way home and found that the Kimbrough #131 fit perfectly, so I'm going to try them first. If I experience any problems, I'll go ahead and spend the extra for the metal gear conversion kit.

RE: Hitec HS-81 Servo
 

It's not a special conversion kit. It's just a replacement gear set. The plastic comes out & the metal goes in. Make sure you do it on a clean table. Might be usefull to have 2 servos open at a time so you can look at one while putting the other one back together, for reference.

RE: Hitec HS-81 Servo
 

Johng, thanks again for the info! I figured this one out last night at about 2:00 AM while I was looking to see how much a set of replacement gears would cost. I found out that the crash that did in my Spirit's wing also stripped the gears in the rudder and elevater servos. I'm sending all three of my servos in to Hitec for service for an unrelated issue, but I'm going to keep the metal gears in mind as I might want to go that route rather than the savers once I get them back from the service dept. Have fun!

RE: Hitec HS-81 Servo
 

I am using a Hitec HS-81 as a kill switch on my H9 Sukhoi. I was moving the arm back and forth a few days ago when it felt like it stripped. The servo stopped making the usual noise that it makes when you move it without power. I turned everything back on and exersiced the servo with the transmitter and now it works fine. I pushed on it and it was fine. I turn it off and move it back and forth again and the same thing happens, but everytime I turn it on it works fine. Can somebody tell me what is happening? Thank you.

RE: Hitec HS-81 Servo
 

Sounds like you should open it up and see if any gear teeth are damaged. You also need to be carefull about back driving the servo. They weren't meant for it, so some - like this tiny one- won't like it. When you have it open, check that the gear axle hasn't hollowed out it's mount in the case. There might be some play in the axle that lets the gears uncouple.

RE: Hitec HS-81 Servo
 

I use a bunch of HS-81's in my combat planes. Most are the MG variety, but I have some plastic gear ones. I also have a couple sets of metal gears around, so if I strip a servo, it gets converted to metal, since obviously that application needed it. :)

I've also had a couple of HS-81's develop bad pots. That makes the servo jitter or "center" in the wrong spot for a moment. Very strange until you've seen it. Those I sent back to Hitec, and they fixed them right up.

RE: Hitec HS-81 Servo
 

I will try that. What would make the servo start working again after power is applied? Why is backdriving bad for a servo?