Capt Jim

My Feedback: (168)

The HS5975HB specs look great, and the other similar servos in this series are not discontinued...so whats up with this? Some sources still have inventory, and at a good price, but before I buy 'em, I want to know that they are OK, and not a problem item, and that gears etc will still be available.
Thanks very much for your response.

Rex Rutledge

My Feedback: (4)

I am curious about this myself! I purchased 4 of the 5975HB servos several months back. The aircraft that will be using these servos is nearing completion. Is there a problem with the servos?

The original post/question is from October and was never answered.

Thanks you in advance!

Rex

mglavin

My Feedback: (31)

The 5975's were replaced by the new 6900 series. More choices for speed and power and beefier gear trains. These new Karbonite gear trains have approximately 30% more mass.

The 5975 are not problematic. Some have had issue with gear train failure in extreme uses. These servos or more specifically the Karbonite gear trains are not designed for high load and shock environments.

lex2bits

My Feedback: (12)

The Karbonite gear trains are NOT designed for high load and shock?

Lex

mglavin

My Feedback: (31)

Correct. They exhibit excellent resiliecne to wear and tear, but have been known to fail when subjected to high dynamic loads and shock.

lex2bits

My Feedback: (12)

Can you define "high dynamic loads" for me?


Lex

jonlowe

My Feedback: (12)

Michael,
I'm confused by your statement that the new 6900 series geartrains have more mass than the 5975s. The new 6975 and the discontinued 5975 both use the same replacement gearset, 55005, according to your website. In fact, the both use the same case also. Is this a mistake on your website, or they, in fact, the same?

Jon Lowe

mglavin

My Feedback: (31)

I suppose I should digress somewhat BUT the concept is simple. "dynamic" as an adjective is defined as of or relating to energy or to objects in motion. Characterized by continuous change, activity, or progress: Marked by intensity and vigor; forceful, of or relating to variation of intensity. "Dynamic" as a noun: an interactive system or process, especially one involving competing or conflicting forces.

That said my reference is kind of a misnomer I suppose. I cannot provide any hard data or such. As I mentioned the servo was designed for small lightweight aircraft. A .40 size Funfly model with large control surfaces is not consistent with a small aircraft as the dynamic loads on these exaggerated surfaces are more than the gear train can withstand. The aforementioned conundrum together with the atypical poor or non existent mechanical advantage or linkage geometry associated with lots of travel and long servo arms is likely to be problematic for any mini servo IMO.

mglavin

My Feedback: (31)

Well, seems I was miss-informed. I will have to retract my previous statement about the taller Karbonite gear trains of the 6900 series servos, this is only true as compared to the 475 and 5475HB servos. Apparently someone jumped the gun with this information and later the idea was scuttled unbeknownst to me. I have mentioned this several time in the past to other's. [&:]

Thanks for bringing this to my attention, I was truly surprised when I attempted to verify my miss-information as I had discussed this many times with them previously.

lex2bits

My Feedback: (12)

Michael,

I apologize for not being more specific with my Q. Let's focus on the Karbonite servo in general terms.

I presume all servos are designed to stall before the gear train fails, or at least I would hope so.

Where does the word "high" fit in?

Is continuous or intermittent duty at the advertised max servo torque rating considered high? Or does "high" mean 125%, 150%, 200% of the torque rating?

The wear factor of Karbonite is highly desirable over that of MG's, but when does wear become secondary to strength?

For illustration purposes, let's say a manufacturer recommends 100 in/oz MG's for his 3D plane. Will a 100 in/oz Karbonite suffice?

Lex

Geistware

My Feedback: (16)

OK, let me put this in words and phrases I can understand.
If you are doing pattern or IMAC flying, then the servos are OK.
3D flying is a no - no

mglavin

My Feedback: (31)

I believe this typically not a problem. In as much as the gear trains seem to fail resisting flight loads. I to would expect any servo to live at its rated torque.

High loads are realized with over-sized control surfaces, poor or inadequate linkage setups, wings and surfaces that flex and induce flutter, speed, heavy models and specific maneuvers that are hard on air frames as well servos.

I don't have an absolute answer for you, however I believe this an incredibly viable question... Its my belief the gear train is subjected to loads outside there torque ratings intermittently for various reasons as mentioned above. When the gear train is subjected to this abuse it fails. Hitecs torque ratings from my tests and observations are conservative for the most part IMO. De-rating the servos maybe the answer. Additional research is needed here, I'll see what I can do.

I suggest it should not be a factor. The Karbonite gear trains may not work for everyone, there are simply to many variables that the users have control of that are outside the original R&D parameters. There are many modelers using the Karbonite stuff without issue and then there those that are having problems. I am aware of ganged installations on 33-40% models without issue. I am also aware of failures on 80" gas powered models on large aileron surfaces and such.

I think there are variables in this circumstance and its a tough call. That said I would probably not use the Karbonite's in this application. But as I mentioned the variables of the specific model and use might cause me to reconsider.

Sorry for not really answering your questions, I wish there was more concrete info available and we had answers for all circumstances. When you consider all the uses and abuses of these products its not uncommon to find many users with unsatisfactory results for whatever reason and then there all the happy users that far out weigh the problematic examples we often hear of.

lex2bits

My Feedback: (12)

Michael,
OK, I see your point, and thanks for responding in detail. [sm=cool.gif]

Geist,
Thank you for the absolute. [sm=cool.gif]

Lex

mglavin

My Feedback: (31)

I don't think I can answer this with absolutes... With small aircraft, maybe 72" or so, glow power and single servo surfaces yes. Gassers seem to impart shock loads into the airframe which cause the surfaces to buffet, this and the fact that the gas powered models are typically heavier and more demanding I'd approach these installations with much thought. As I mentioned there are many users with large IMAC models using the Karbonites ganged on ailerons and rudder with single servos on elevator halves without problems.

lex2bits

My Feedback: (12)

Well, we're just looking at possible alternatives as the gear wear in the 8411's has proven to be somewhat disappointing IMHO. Since the HB's don't seem to be ideal for IMAC or 3D gas planes, I guess we'll just have to try some MG's on the ailerons and see if the gears last any longer.

Thanks for the feedback.

Lex

XJet

You might want to change this text found here on the HitecRCD website (appears in a pop-up window whenever you click on the keyword "Karbonite":

"Hitec’s new KARBONITE composite gear train has eliminated lash and slop forever. They are less likely to strip under the shock and loads that would usually break standard gears"

As I've said, just very occasionally Hitec begs for problems by being a little "optimistic" about some aspects of a very few products in its promotional information :-) It's not the customer's fault if their expectations (based on such promotional information) are not met when the product breaks or fails to perform.

I would suggest that it's little snippets of disinformation like this and the resulting poor choices made by customers (rather than the quality of product itself) that are at the root of many servo failures.

hilleyja

My Feedback: (3)

Interesting insight here. Put me on your list of "not the customer's fault if their expectations are not met" Here is the requirements/recommendations straight out of my GP Christen Eagle II's instruction manual:

And, here is the specs from Hitec for the HS-5475 servos:

And, finally, here is my RC Universe thread with Hitec's responses to my complaint.

http://www.rcuniverse.com/forum/m_20...tm.htm#2064937

Now that you have all the supporting info! GP tells me I don't need high value/high torque servos. And, considering, the Eagle II uses (4) servos on the wings and (2) servos on the elevator, one would not expect too much need for high torgue anyway. Yet, I opted for what I thought was servos that exceeded the requirements. GP says servos with at least 51oz of torque. I installed servos with 76oz (5-cell, 6 volt RX battery) of torgue. I also went one step further and went digital. What happened? After the third flight I found EVERY single airlon servo had stripped gears. I didn't do any significant flying maneuvers and frankly was still learning how to handle this airplane. Hitec's position was I must have had flutter in my control surfaces. That might have been true for one airlon that had hinge failure. I subsequently replaced ALL of the gears in ALL of the wings servos and flew here a few more times. This time one of the servos came back with stripped gears. NOTE: This was after I replaced the CA hinges on ALL of the airlons and sealed the bottom hinge lines with transparent monocote -- where was the flutter this time? Well, this was certainly enough for me. My experience and Hitec's responses told me the Karbonite gears in the HS-5475 servos were not capable of supporting their torgue ratings and I was no longer going to subject my $2000.00 investment to them any longer. I pulled all of the HS-5475s from the wings and replaced them with HS-5645 metal-geared servos -- no problems todate. This winter I will also replace the elevator servos with HS-5625s. I'm still concerned that maybe I should replace the HS-5975 servo on the rudder, even though it is rated at over 100oz of torgue on 6 volts.

BTW, I found a home for the HS-5475s. I mounted them on a Hanger 9 Twist 3D. I hope they are sufficient for this light-weight 40-size airplane. The previous HS-322s did not give me any problems and I kinda hope the HS-5475 are at least as capable of this CHEAP standard servo.

XJet

I think the big problem here is that the market is demanding ever more powerful, smaller and lighter servos -- do you see the conflict?

Personally I think that some of Hitec's decisions in respect to drawing a compromise between power, weight, size and durability have been bad ones. It is simply *not* a good idea to design and build a servo that will self-destruct the moment it gets near its rated torque.

As I've said many times before -- I'd *much* rather have a servo that, when faced with excessive loads, simply stalled than one which stripped its gears.

A stalled servo will resume functioning once the excessive load is removed -- one with stripped gears will not.

There are some servos in the Hitec range that simply will not tollerate being stalled without suffering catastrophic failure of their geartrains -- that's bad, especially when you consider that to remedy this design flaw would only require the use of marginally stronger gears, adding very little extra weight/size to the overal product.

Of course Hitec are not alone in this -- the pressure to build smaller, lighter, more powerful and more durable servos applies to all manufacturers.

I would be a lot happier however, if I knew that *all* Hitec servos stood up to the stall-test and I'd be prepared to pay more for a servo that I knew would not strip out under its own power in the event that I'm flying an FM/PPM setup and get hit by a brief burst of interference that drives the servos to their stops -- or if I'm using a Hitec 555 receiver and forget to turn the transmitter on first (thus causing the servos to be driven to their stops).

I'm sure the last poster will have no problems with the 5475 servos on his 40-sized 3D bird - that's where I've been using mine and they work just great (albeit a little slow for agressive 3D stuff). I think the failure mode that he experienced was probably due to excessive shock loads from vibration and/or flutter.

Which brings me to an interesting observation -- back in the 1980s I used to use a lot of Futaba S20 mini-servos (0.75 oz from memory). These had metal gears that were robust beyond belief. In several years of *very* hard flying and crashing, mainly in 45-sized RC combat and sports ships, I never lost a tooth on those servos -- even though the mounting lugs tore off several of the servo-cases (once as a result of *severe* flutter) and I must have gone through dozens of servo-arms as a result of crash/impact damage..

They weren't hell of a fast or exceptionally high torque -- but they were small, light and unbreakable. I'd kill for a servo like that today.

lex2bits

My Feedback: (12)

This thread has become very enlightening. Thank you gentlemen!

hilleyja,
In the thread to which you directed us (Below), you mentioned an original thread. Is THAT thread still available?
XJet,
Yes, I see a definite conflict... AND I see that some of the AIRCRAFT manufacturers may be specifying inexpensive and inadequate servos just to make their plane appear to be more affordable. After all, they have a built in scapegoat... the servos! PLUS they are likely to sell an identical plane to replace the crashed one. The decision to purchase or replace an airplane in most cases may have largely been, and most probably was, based on emotion. I know when I am looking, a cool lookin' airplane that is purported to do what I want it to do has a great deal to do with my decision.

I think I said something akin in a previous post.


Now, with that said, let's consider a digital servo. Digital servos have tremendous holding power and do not back off when huge loads are imposed. It occurs to me that if all other things, i.e. horns, hinges and linkages, are also super strong, the weak link is the gear train. When the conditions for flutter are ideal, the loads imposed to suppress that flutter may be substantially beyond the gear's ability to withstand, and thus failure is imminent.

Also, it has become apparent to me, after reading everybody's input and my writing this, that we need to re-evaluate our methods of servo selection. In the meantime, maybe it's time to come up with a mechanical servo saver, akin to those in surface R/C, or an electronic servo saver that measures the current draw of the servo and backs it off when the rated load is exceeded...... just brainstorming.

Anyway.... thanks again.... my feeble mind is now overloaded.

Lex

XJet

Yes, I expect we're stuck between airframe vendors who are tempted to understate the servo requirements and servo manufacturers (not just Hitec) who are occasionally tempted to overstate the capabilities of their servos.

Combine those two and there's very real room for problems.

You make a good point -- but mechanical servo-savers are not a good idea -- they're more likely to result in control flutter because they have no damping.

A *much* better idea (and this is my suggestion to Hitec) is to introduce current (aka torque) limiting in the servo-amps of their digital servos.

This could be a parameter controlable by the Hitec servo programmer and allow users to set up a servo for either maximum torque or maximum reliability -- or some compromise between the two.

With a digital servo amp it's a relatively trival task to manage the torque produced by the servo motor and ensure that it's not going to exceed the strength of the gear-train. This would be a *major* selling feature from where I sit since it would allow *me* to make the choice as to whether my servos stalled or stripped when confronted with an unexpectedly high load.

All in favour say aye :-)

lex2bits

My Feedback: (12)

I should do so, but to date I've had no reason to pull the top and look at a modern servo gear train..... ideal design calls for three teeth engaged to some extent at all times. How it is that hilleyja's gears had only ONE tooth broken escapes me. IMHO there should be, at minimum, three damaged teeth.

So, if I catch your drift, you'd buy overkill servos and soften them up a bit.

To that I say.... Aye !

Lex [sm=thumbup.gif]