noname-RCU

Hi,

I have a Doghouse Extreme with a Saito 100. I am using brand new Hitec 225BB (not MG version) servos all around (except throttle) and on my plane's 3rd flight, the elevator servo gears stripped out of nothing. I *wasn't* doing any high "G" maneuvers nor was I pushing the plane to its limits (actually, the plane was mostly flying right above stall speed).

All of my servos are brand new and I find no reasonable explanation why would the gears strip under these circumstances (again, given the fact that the plane was flying right above stall speed and that the elev throw was *very* limited).

Can anyone tell me what a reasonable explanation for this may have been ? Is there any chance the servo gears might have had a manufacturing defect ?

(This is the first time I use Hitec servos so I don't know if this is a common issue or not. According to the 255BB specs, it should be better than a standard Futaba S3004)

BTW, the plane crashed

NCC-1701

I don't believe it's a quality issue. While the HS-225 has better specs (speed and torque) than the S-3004, it is physically smaller. This means the gear teeth are smaller than those found in a standard sized servo. The teerh can't take the loads imposed by the elevator on a model that sized.

If you go with metal gears, you'll be fine.


Rob

LuvBipes

My Feedback: (4)

Interesting, you don't mention if you're using a single or dual elevator setup. FWIW, I have a 9 lbs Laser 200 that I fly IMAC and pattern with that has dual nylon gear Hitec 225's in the tail for elevator. After about 50 flights there hav been no probs.

That being said, the maximum elevator deflection on high rates is about 15 degrees as the plane is not setup for 3D.

DeadSticker

My Feedback: (18)

I had that problem too. One of my 225bb's stripped in normal flying on my pitts. Wasen't pretty................See thread

http://www.rcuniverse.com/showthread...hreadid=347853]

noname-RCU

Hi!

My elevator setup is only 1 255.

I guess I'll have to go the MG way

I'm just like most guys using these servos in a "normal" plane to save weight. So ... if these servos aren't strong enough and according to most threads the MG are, why should one go the 255MG route when they can go the 85MG way ?

The 85's have impressive specs also, but in terms of weight savings one will take the jackpot !!!

Does anyone have comments on using 85MG on a 46 - 60 sized plane ?

Puppet Man

The DogHouse is a high performance 3D plane. Don't use anything but high performance servos or you are inviting trouble. HS-85's are even smaller than the Hitec 225 product and metal gears won't help in this case.

Nobody should use HS-85s in a .60 size plane.

bgi

My Feedback: (7)

My 225 experience (brief)

A good RC pilot working at a LHS recommend HS225BB's for my 1/4-scale Lanier Edge elevator tail installation because of the torque, speed, and weight. So I bought 2. Then I read about the stripping gears here. Then I upgraded them to metal gears. Fortunately I kept reading about the 225's here. No way will I fly that plane with the 225's in the tail.

The servos may appear to be more robust with metal gears, but!:

1) The gear which normally strips (this is hearsay from this forum) is the very small nyon gear directly geared to the motor. This one is still nylon in the MG servos. So IMHO there's no good reason to go MG on these servos AT ALL.

2) With the metal gears, they are VERY NOISY!!

3) Centering is the worst I have seen. When I setup the edge for 3D rates, the resolution is about 1/8" elevator travel. MG's may contribute to this. It seemed much worse after I installed the metal gears. There is negligible slop.

There's no way they have the advertized torque. I can deflect the elevators, then hold the servo horn with my hand while re-centering the stick - no problem holding the horn. It's not pushing very hard at all. Sometimes when I release the horn, it doesn't center until I blip the stick again. Scary! Nowhere near an airworthy setup.

These servos are no longer in my Edge. Heck, I'm not so sure I even want to put them in my .40 sized fun-flys. The 425's have more real torque (measured by my hand) and will be much more durable. I'm not sure what to do with these 2 servos I have about $70 in (including the 2 MG kits). Suggestions?

Gotta work out another elevator solution for the Edge now.

Rant mode on:

I can't believe Hitec sells the 225's with the advertized specs. This leads people to use them in applications they're TOTALLY inappropriate for. I believe the torque rating may be measured while the servo is moving. Once it gets going, it's strong. But they have very low start-up torque. No 225's for me. I think they're just dangerous unless they're installed in a .20 size or smaller plane.

Rant mode off:

Some people tried to tell me the 225's were not appropriate for medium to large planes. I didn't listen. I said to myself, "Heck - look at the specs!" Fortunately I learned before I lost a large plane due to misuse.

PS: I love the other Hitec products I have (645MG, 5625MG, 425BB, receivers, etc.)

my $0.02

HarryC

My Feedback: (1)

A friend very kindly gave me a model, but it has Hitec 225MGs installed on the wings. The model had never flown, the servos were brand new. One of the 225MGs had to be replaced before the model had ever flown because it shredded the teeth off the one plastic gear that Hitec claims is unbreakable. It broke the gear just by operating the radio normally while setting up travels rates etc., with no load being placed upon it.

Harry

LuvBipes

My Feedback: (4)

Harry, I think the geartrain Hitec advertizes as "unbreakable" is on their new line of high-end servos - NOT the lowly 225 series.

I'm no defender of Hitec (I actually prefer Futaba coreless when I can afford them), but let's make sure we have our facts strait.

noname-RCU

Hi!

Well, after checking the gears of my 225 servo, I was astonished by the findings !

No, the gears didn't strip !!! .... one of the thick gears broke in half (transversal break)!!!! ... There is no way any reasonable load could have done that (specially considering its a BB servo) so what I'll do is take some pictures of it and send it to Hitec (I'll also post them here).

HarryC

My Feedback: (1)

Oh well, maybe it is breakable. And it certainly did, all by itself.

Harry

zippo

I'm the one responsible for the 225 in Harry's new aircraft. I have quite a few 225's and its the first time I have had or seen a problem. I've got the servo back and it looks as if the the nylon first stage gear stripped because of (1) bad alignment with the motor or (2) possibly some plastic 'flashing' on the case base molding getting in the way. This was a brand new servo .. so possibly a manufacturing fault. IMHO - just one of those things.

I'm also the idiot who put two HS-81's on the tail (YS-53 powered Hirrobo Stream 50K) - so I guess at least one person has done it. The tail fluttered, the servo gears stripped and the rear fuz shattered under the tail mount. I guess the carbon tube pushrods stopped it breaking off - Give Harry his due he landed it back on the strip with no further damage! If you press him, he might give some more details (as I know he was repairing it last night).

Soar Head

My Feedback: (5)

I have used over 10 HS-225 and 225MG's, over the last 3 years, so I have some considerable experience with them.

Sounds like some of you guys are using these servos beyond what they are designed for. You cannot just go by the torque/speed specs.

Smaller servos have smaller (thinner) gears. They can, and do, generate the spec'ed torque ratings.

But, the thinner gears in mini and micro servos (any brand) are much less able to take sudden shock loads. These shock loads can be imposed by flutter, high speed, or dragging the flaps when landing a competition glider.

If you're flying a 1/4 scale plane, then by all means, by 1/4 scale servos. Even if the micro servo has specs enough to move and hold the surface.

Take apart any micro or sub-micro servo and look how thin the gears are. Then do the same for any 1/4 scale servo.

Do you see any difference?

bgi

My Feedback: (7)

Soar Head,

That's so true. I should have pointed out that I couldn't find any GOOD recommendations from stores or Hitec which would explain this.

From Hitec:

"The HS-225BB is deal for applications that call for a small lightweight, high speed, high torque servo." (The typo is Hitec's - I'm guessing they meant to say this servo is "ideal" not "deal")

That's a really good description of what I want in the tail of my 1/4-scale Edge. Physics and current technology may preclude meeting those requirements with a sufficiently robust servo.

Hitec isn't the only guilty party. I've found no servo manufacturer that will publish "robustness" or "shock tolerance" ratings. This important quality should be published right alongside the torque/speed/weight/current specs. Otherwise, how do we know without going to the school of experience?

daven

My Feedback: (1)

I have owned at least 100 Hitec 225 (Nylon geared) servos. This servo is very commonly used for Quickee 500 and even Q40 racing planes. Of all the servos I have had, these have been some of the most reliable I have ever owned. I have never had a gear break or a servo fail without midairing or crashing the plane. I have seen a few fail on others planes, but an extremely small percentage compared to the amount of racers using them.

For racing (speeds close to 190 mph) they seem to work quite well. However, most of our surfaces rarely move more than 3/16". It seems the troubles occur on large surfaces, with large servo travel.

jelaird

My Feedback: (1)

I love these little servos and use them when I can for gliders, small .25-.40 sized planes and throttle on larger 1/4 scale planes. But there is one thing I can tell you not to do. Plugging one of these into a small HS-555 receiver is asking for damage to the gear train and your control surfaces/hinges. The 555 has something wrong that when switched on, servos of any kind jump like crazy for an instant thereafter. I was checking out my airborne system before installing into a .25 sized racer with limited aileron throw. It's a good thing I did, with the servos jumping to almost 40% throw from neutral, I would have ripped the ailerons off my plane. I've repeated the phenomena with another 555 right out of the box. Another brand receiver fixed the problem.

noname-RCU

Until now, I had never seen stripped gears like these:

noname-RCU

Another pic

George E.

My Feedback: (16)

I opened up one of my new 225 MG's and it has NO nylon gears in the drivetrain. There was one nylon (white) gear but it just connected the drivetrain to the pot. From motor to output was solid metal on mine.

Unless they are painting the nylons to look metallic.

Please clarify.

George

bgi

My Feedback: (7)

I bought two MG upgrade kits. They both came with a nylon gear which is the first gear in the train from the motor. Can't say what comes with the MG factory units, but folks here tend to speak of the same arrangement.

Swazzi2000

My Feedback: (4)

I also have two HS-225BB that I am using to control separate elevators on my Aeroworks Edge 540T. Upon installing it, I put one of the servos in the channel 7 slot thinking I can use that channel to mix the two but what it did I wasn't expecting. The power was on and I put it in the slot. Quickly the servo went to one side and tried to keep going, then I heard a crack. Unfortunately that stripped it. Now I have to wait for my LHS to get them in stock.
The Edge I am using is a .60/.90 size plane and I am powering it with an o.s. 1.08. I need small servos and the space is already cut out to fit the 225's so Im going to keep them and see what happens.

Any Suggestions would be greatly appreciated.

Thanks
mike

cloudniner

My Feedback: (87)

I have losted two 225's while on the ailerons of a YS 53 powered Pizzaz. They both travel not too bad in one direction but stall in the other????

Not sure what to do with them. These are both MG type.

Swazzi2000

My Feedback: (4)

Cloudniner,

The 225MG's also have a nylon gear inside. Its the first gear that the motor powers. So metal gear really isn't better in much ways.

Mike

JWN

My Feedback: (42)

I have yet to find any metal gear servo that doesn't have a single nylon gear somewhere in the system.

225's are small servos for small aircraft. If someone puts them in an application larger than they were designed for, they are asking for trouble. Regardless of the torque specs, the gears are small and no where near as strong as a comparable torque servo with larger gears.

John

JWN

My Feedback: (42)

In support of my last post. This is a direct quote from the General Servo Information sheet included with all Hitec servos. Note the BOLD text.

"The Appropriate Servo for Your Application"
4. Even though micro servos like the HS-81 may offer 38 oz/in of torque, they are not appropriate for larger powered aircraft use due to the flight loads placed on the control surfaces during flight. The geartrain can fail under excessive flight loads. Smaller servos have thinner gears that are inherently more fragile than those of "standard" sized servos.

John