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HS225 and 225MG servos

1536 Views 14 Replies 10 Participants Last post by  xjet
After a really bad run with some HS225MG servos I bought recently I decided to do some investigation into what's wrong with these things.

Turns out that the second gear (the one driven directly from the motor) is a *very* weak link.

This gear is just 0.8mm thick (that's just 0.03 inches!).

The motor in these servos has sufficient torque to simply grind away the teeth on this flimsy nylong gear if too much load is encountered.

And, if you think you're getting a more rugged and stronger servo by purchasing the metal-geared version -- you're wasting your money (about $7 per servo).

Both versions will strip this second cog *long* before any of the others are even lightly stressed, even if they're nylon ones.

According to Hitec, the 225MG is rated at 66.5 ounce-inches of torque (4.8Kg-cm) so today I thought I'd see whether this was actually the case.

I connected a 4Kg weight to an HS225MG such that it was exactly 1cm from the center of the servo-arm.

I then plugged everything in and *slowly* moved the sticks on the transmitter so that the weight was lifted from the bench, through 120 degrees of the servo travel (over about 3 seconds), and back again.

On the third repitition the servo arm began to jerk and slipped back slightly while the motor was heard to spin.

On inspection, that nylon gear had stripped -- and this was with a load of just 4Kg-cm - just 83% of the rated torque for this servo.

Hitec have built a lemon with these servos -- the engine is far too powerful for the geartrain -- and using the metal-geared version won't make one bit of different because that weak-link nylon cog is common to both.

Mike from Hitec says that they're planning to offer a metal/plastic replacement gear for these servos but unfortunately it won't make a scrap of difference because the part that they're making out of metal (the small center-cog on this gear) isn't the one that fails -- so they'll still strip the guts out of the thin nylon outer cog.

Quite some time ago I asked (either here or on RCU before they pissed us off) whether the HS225 servos were a good idea for a 40-sized profile. I can now say with some authority that they're not.

If you're using them with success then you're bloody lucky!

I've had one fail while simply being exercised on the bench and two others while serving as throttle servos on my Katana P. One of the failures just about produced a rather nasty accident too!

If you value your model then I'd suggest that the HS225 isn't a good idea.


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I'll also throw in that the motors don't last very long in the 225 series either.

I've gone through 3 HS225 servo motors in a flying season....on the same servo (throttle).

I won't use the 225's anymore either.
I'll double...even triple what latch said. The motors are trash when it comes to longevity. I love the size of the 225's but I'll never trust the motors again. Tooooooo many of them have malfunctioned in my profiles. Aside from the 225's, I've never dogged any servo and had no reason to, but the 225's are risky business in your profiles.

Plus the centering is the worst you'll ever see. No more Craptec servos for me either.
I must have been lucky with the ones I had. Bought 4 225MGs for the aileron servos on a DP Ultimate, then moved them to my OMP Edge and flew it for a year with no problems. Sold the plane to another guy and he's still flying it. But, I'm probably not as harsh on them as a lot of guys are, and I don't get to fly nearly as much, either. It would be nice if somebody made one in that size and torque to compete with it, though.
Ive had pretty good luck in my edge with the 225's as well. Ive never had one just strip or fail for no reason though. If you bang your control surface into the ground yes they will strip, you have to treat them a little better than a full size servo, you dont get the small size and weight for nothing, but alas it would be nice if hitec quit putting plastic gears in there metal gear servos. The inner gear is the only one Ive ever stripped. maybe if we bitch enough they will get the point. The question is what else is out there. Who else makes a 1 ounce servo with comparable torque and speed for 30 bucks or less
I've purchased only two of these servos. They first went into the tail of my Sledge, which had oversized surfaces, and did not fail there. Their second assignment is in the current Super Sledge, controling ailerons. I always run 5 cells, so the torque is at max.

Maybe I got two of the good ones, but the seem to be holding up. My first Sledge had a few hundred flights, and three fuselage breaking crashes, and no failures. The SS is at perhaps 20 flights and still good function.

I will agree that centering on many of the lower priced Hitecs is a joke. I'v had 55s, 81s, 81MGs, 85MGs, and 225MGs. All seemed to center ramdomly. If I ever get to where I think I'm getting better than these servos, I'll switch to 100% JR. As for now, I'm still the weak link in my flying, so I'm OK with the Hitecs.

Everyone knock on wood for those of us still using the cheapos! :wink:
This really sucks :x , I just finish building my burrito wing got the servo mounts set up just right, the wing sheeted and looking good to me now the servos I set up in the wing are crap? yes I installed these really bad 225's.
So now I get to go buy more servos, and tear up my center section of my wing. :x
These servos came out of my Webra .50 powered FFHots, they have been in service for maybe a 120 flights (and one nasty crash!).

If that is not bad enough I have a .40 size Extra, with a .72 Satio on the nose, that has 4 new 225 MG's in it that I have to replace and modify all my mounts also :x

I can only conclude;
A. I have been lucky not to have a servo failure.
B. They are about to fail because of the time on them.
C. There is a wide variation in Quality on these and I have some good ones?
This makes my day,
Well maybe it will worth it if I can save a plane :?
I had put brand new 225MG's in a my Spiderman Sledge (RIP) and on the maiden flight one aileron servo locked up in a full down position. :shock: As of today I am still not sure how I was able to get it down without damage. I did of course changed them out later for some good JR digis.
I then put the other 225's in a Lanier stick and one of the elevator servos froze up too. :roll: Glad it happened during the radio setup. Exchanged it for another and still have those in the stick. They have been holding up, and I am not going to change them out since I will sell the Stick shortly anyway (if anybody needs one let me know).
Have had very bad centering experiences before hand with these type of servos on my Sudokhoi.
I've had more words with Mike from Hitec and it seems that although they're not prepared to admit it, they are aware that these servos have major problems -- hence the plans that were already underway to offer a replacement part metal, part plastic gear (which wont actually address the problem at all).

Even if they used a slightly different motor or current-regulated the amp so they were derated down to 45oz-in they would then be a fine little servo -- but apparently, even given the potential for some very nasty accidents produced by these servo failures, they're still quite happy to flog them to unsuspecting modellers.

I'd hate to think what would have happened if I'd been flying a 1/3-scale ship when the HS225 on throttle decided to strip its cogs and stop working at the exact moment I blipped the throttle and turned in towards the flight-line and other fliers (shudder). A 40-sized profile ship whacking into your shins will just leave a bruise and even a 12x4 prop spinning at 6K RPMs isn't going to do much damage -- but an 80cc gas engine with a carbon-fiber sythe doing the same could cause some *real* damage.

If Hitec continue to knowingly sell a servo that doesn't meet its rated specifications then there must be some liability there.

Clearly, and as I suspected, lots of people have had bad experiences with these servos -- yet some seem to have had none. However, the former category appears to outnumber the latter quite significantly.

When *any* servo has a catastrophic failure rate of over 50% then there's something very, very wrong with it.

It's also worth pointing out that Hitec's HS5245 Digital Mini servo (rated at 76oz-in) is just a 225 with a digital amp. There's already been identical failures of these at our club -- and they're almost a $50 servo.

Ultimately, Hitec's response to my measurements and observations are a big fat "so what?"

They claim they've been selling these things for several years so why should they stop now?

It's even more of a disgrace that they sell these things for $7 more with a metal gearset when they know full-well that this tiny nylon gear will already fail long before any of the others -- even in the nylon geared version. It's a straight rip-off.

Right now I'm working on a webpage with video that shows how over-rated their torque and transit-time ratings are. If Hitec won't act responsibly I'll put the information in the public domain so potential purchasers can make their own informed decisions.

In my case, where I've spent $80 on these servos, relying on the printed specifications when making my selection, they're not prepared to do anything other than have me send them in so they can change the damaged gear -- something I've already done myself twice at a cost of $4 per gearset. Their solution is no solution at all.

Hell, if Ford or GM kept selling vehicles with a badly designed component that could fail at any time and produce an accident they'd have their asses sued off.

So much for Hitec's much vaunted customer support and willingness to stand behind their products eh?

I would suggest, in light of the evidence I've produced here, that if anyone loses a bird to a stuffed 225 servo, they claim back all their expenses from Hitec who have knowingly sold a product that doesn't perform as claimed and which they well-know is of faulty design.
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My last fling with 225's was when I JUST finished doing a demo (profile plane of course) for a Cub Scout Troop and an aileron servo quit on the ground. So, get this, I decided to let others fly and use mine as a static demo on the ground.....and the FIRST time I demo'd it, the OTHER aileron servo quit! Two 225's quit within 30 mins of each other and I wasn't repetetively working the shit out of them like some might think.
I was told by Hitec that one had a burned pot and the other had a bad motor. Free replacement of both servos so no out of pocket expense, but I can't trust them.

Had another 225 quit at a probro in boliver mo. Had another quit at the field just using it as a throttle servo. I could go on with more examples, but my point is, none of my other servos continually quit, just the 225's.

I've had tons of servos over the years and currently have at least 90 working servos in different planes. The 225's are the only ones that keep malfunctioning. Dangerous servos IMO.

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Here's an interesting footnote to the Hitec 225 saga...

I was discussing the matter in a thread in the Hitec support forum on RCU and after I published my own findings proving that the specs proffered for this servo were grossly exagerated, Mike M locked the thread.

In a private message to Mike I questioned as to whether Hitec might be exposing themselves to law suits if the failure of one of these servos caused damage or injury -- in wake of the fact that I'd shown their torque claims to be totally bogus.

Continuing to sell a product you know to be faulty surely exposes you to all sorts of legal remedies should the failure of that product produce an accident.

Well what do you know -- the whole thread appears to have been deleted -- but Hitec continue to flog the 225 servo, advertising it with bogus torque ratings that will encourage people to use them in applications for which they are decidedly unsuitable.

Hitec make some good servos (even though I know some will disagree with that statement) but I think they're taking the wrong approach to this problem by simply trying to erase all evidence that the 225 has been exposed as a dangerous lemon.

I sure hope a 225 doesn't cause any kind of accident that might see Hitec have the snot sued out of them by some disgruntled or bereaved party -- I'd kind of like to be sure that their better products remained available for the forseeable future.
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i just wish they would fix then already, how about a karbonite version :?:
good work guys, ive been sortof lucky with my 225's but i dont have much time on them either.
I dont want to go against what everyone is saying but I have three airplane sets of these along with two spares and havent had one fail yet. I have stripped three though two trying to move them when they were off and not connected probally shouldnt have done it but I do it with my other servos with no problem, and the other when i went to step over a plane in the trailer and kicked the aileron i kind of expected that one. I have yet to have another problem though and they are in alot of planes so I would have suspected a problem to show up if it was going to. There is also some complaining about plastic gears in metal gear servos well I hate to tell you but even companies like JR do this. I had a 8411MG strip when i had aileron flutter (which crashed the plane) and it was on the elevator and I had plastic geared ones one the Ailerons. So please dont think that Hitec is cheap having plastic in metal servos. Also I have yet to have problems with my 81s or 55s not centering and I have them in a few electric planes. I am not trying to cause problems I just want to give my opinion. I also want to take this time to thank and congratulate the PRO BROS for there great site, i havent spent much time here but I will in the future.
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I think the biggest problem with the 225s (and something that explains why some people have had no problems) is that they are one of the few servos that will strip its gears before it will stall the motor.

Personally, if I've got a choice between a servo that will stall and one that will strip its gears, I'll go for the former every time.

A servo that is stalled briefly (for whatever reason) will continue to work when the load on it is reduced. Imagine a servo of "marginal" power being used on elevators in a large 3D ship and doing a wall at speed -- it may very briefly encounter loads close to its rated torque. If the servo stalls then all you end up with is a slightly less tight manouver because once the load is reduced the servo will continue to work as normal.

However, if that servo strips its guts then you probably end up with a bird burried in the dirt because once those gears go you no longer have (reliable) elevator control.

A *well designed* servo will have a geartrain that can handle the full power of the motor without stripping -- just like a well designed automobile will have a transmission that will handle full-throttle without flying into a million pieces.

The HS225 suffers from a transmission (gearset) that is just too weak for the power of the motor and if you try to stall this servo you *will* bust a gear. In fact, if you come even close (within 83% in my tests) of trying to use the rated torque -- you will bust a gear.

That's kind of like designing a car that will blow a transmission if you try to use more than 83% of the gas pedal's full travel.

I'm thinking that those who have had no problems are just lucky in that their flying style or particular aircraft is imposing only very liight loads on these servos. If however, they decide to push the limits a little harder one day -- well disaster could be just around the corner :)

However, it should also be pointed out that one of my 225MGs stripped its guts while simply being exercised on the bench and it seems that I'm not the only one to have encountered this situation as this thread on RCU would indicate.

I had *exactly* the same experience -- maybe my first one was assembled wrong or maybe someone sneezed in its general direction and stripped that gear while it was on the assembly line :)
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