malcolmm

I'm planning on buying some servos for a 1.60 3D plane - a Quique Somenzini Yak 54. Since I'm not made of money, I would like to buy servos that would also work in a 50cc size plane. This would be the largest plane I would plan on flying in the near future.

The new Hitec 6975 on ailerons and elevators, with a 6985 on the rudder would seem to be more than enough for a 1.60 sized plane. But would they be enough for something like the Extreme Flight Yak 54 87" (when it becomes available)? I guess the torque would be okay, but I am wondering about how the Karbonite gears would hold out. I would prefer to stay away from metal gears as I am concerned about the wear.

Any other suggestions on Hitec servos suitable for a 50cc 3D plane would be welcome, even metal gear ones. I am trying to get an idea of how much torque I would need. Extreme Flight list 90+ oz/in, but this seems pretty low, especially considering their 68" Yak has the same requirements.

Thanks for any info

Malcolm

JoeAirPort

My Feedback: (41)

I would strongly urge you to NOT use Karbonite on that size ARF. I don't care what anyone says, I crashed a 1/4 scale using the 635's and even though I did some things that might have helped them fail, I would never use anything but metal gear on a plane that size. Also I believe the gassers put more vibration on the servos than glow so that's another reason. So if money is an issue I'd use the 5645's. If you can spare another 20-30 per servo I'd suggest the 5945's. I ended up putting the 5645's on my 25% CAP after I got a new wing for it and it flies really nice with those servos, one per control surface. I have at least 75 flights and not a single problemo. A 1700 mah 6 volt battery gives you higher torque and speed and I usually fly all day on one charge.

Does Hitech recommend those servos you listed on a 1/4 scale 3D gasser? I'd be curious as they are very good at cautioning you if they don't recommend it for your plane.

mstroh3961

My Feedback: (4)

Tom from WildHare emphatically said not to use carbonite geared servos on his 50cc planes!

mglavin

My Feedback: (31)

Hitec does not recommend the Karbonite geared servos for large aircraft. Specifically single singe servo installations, ganged they have held their own. While these servos exhibit excellent wear characteristics they are suffering from dynamic and shock loads induced with gas powered aircraft.

The HS-5925, 5945's MP geared Digitals are well suited for this aircraft as are the new Titanium geared super servos HSR-5995TG and HS-5955TG.

hilleyja

My Feedback: (3)

Certainly stay away from the HS-5475s. In one flight I stripped gears in ALL 4 servos in my GP Christen Eagle II. It is running with a Fuji BT-50SA. I replaced them with HS-5645s (metal gear servos). I still have HS-5475s on the elevator but will change them out during the winter. I also have the HS-5975 on the rudder and am wondering whether I should change it out too. The problem appears to be that Karbonite gears, though strong compared to nylon and subject to less wear than metal, are brittle and break due to the inherent increase in vibration coming from a gas-ignition motor (IMHO). Hitec will not acknowlege that but they have indicated that you should not use their Karbonite servos on larger aircraft. It can't be because of torgue requirements because the HS-5975 has in excess of 110oz of torgue with a coreless motor. Even the HS-5475s are rated at about 71 ozs of torgue.

dirtybird

My Feedback: (5)

Static balancing the control surfaces will greatly reduce the stress on the servo gears.

JoeAirPort

My Feedback: (41)

And how is this done?

Geistware

My Feedback: (16)

You might want to read through this link.
http://www.rcuniverse.com/forum/fb.asp?m=2256224&key=
I found out a little too late.

dirtybird

My Feedback: (5)

Place a weight on the opposite side of the hinge that balances the weight of the control surface. On some TOC aircraft a simple arm is attached to the end of the control surface that extends ahead of the hinge and the weight attached at the end of the arm.
If you have an aerodynamic balance as seen on a lot of elevators simply load the front edge of the aerodynamic balancer.
BTW all full scale A/C have balanced control surfaces.

hilleyja

My Feedback: (3)

I must be real dense because this still does not make sense to me.

Place a weight on the opposite side of the hinge that balances the weight of the control surface ?????

dirtybird

My Feedback: (5)

How about this?
Place a weight on the opposite side of the hinge line from the control surface that balances the weight of the control surface.

hilleyja

My Feedback: (3)

i actually asked this question of one of our senior club members and finally came to the understanding.

Here is how I would describe the process:

1) After the control surface is hinged to the wing or stabilizer, and after the control horn is installed on the control surface, but before the pushrod is connected between the servo and control horn -- glue a small control rod section, bent at a 90 degree to the control surface with the threaded end extended past the hinge line facing the wing or the stabilizer. This rod can be either on top or below (would put it on bottom so it won't show from the top). Thread a small lead fishing weight onto the rod -- vary the weight until the control surface balances at a neutral position.

XJet

This control balancing can also reduce flutter -- which is a very good thing.

One of the (many) reasons that control surface flutter occurs is because of the way we hinge our surfaces.

In an ideal setup, the center of mass will be ahead of the hinge-line but when we opt to simply hinge our surfaces using CA or pinned hinges directly in line with the leading edge of that surface we have the center of mass *way* behind the hinge-line.

If you look carefully at most full-sized aircraft you'll see that some area of the control surface sits ahead of the hinge-line, usually for the entire span of that surface. This is most often done by recessing the hinges back into the leading edge of the control surface a little.

You can do this most easily with a model by using Robart point hinges -- but mass-balancing is another simple and relatlively effective option.

Mikerl

My Feedback: (1)

I would NOT use karbonite on ANY airplane, they will fail regardless of size, weight, power, etc. They failed on my Mustang causing a crash. Also a fellow club member used some hitec karbonite servos on a 10 to 12 ounce electric airplane and they failed, luckily on the ground. I sent an email to Hitec the same day my Mustang crashed, and to this day still have not responded. I have heard that Hitec states that the 635 servo is fine on 10 to 12 pound aircraft, but their packaging clearly states that these servos are intended for sport and high performance aircraft up to 1/4 scale. I guess this is why Futaba or JR products are the way to go. I have used a ton of Hitec servos in the past, but no more.

karolh

Karbonite geared servos in any shape of form are a no no for me, as I have be bitten by using them. As a matter of preference I now shy away from using Hitec units and use only Futaba. I'm playing it safe and staying with a brand that has not failed me yet.

Karol

rlmcnii

My Feedback: (3)

mglavin,
I have used 475HBs with great success on small (7 to ten pound) sport aircraft powered by .82 and .91 Saitos. I gather this is an appropriate use for those servos.
Recently I assembled, but have not flown, a Kange Waco powered by a ZDZ 40. It has four 5475 HBs installed on the ailerons and one on each side of the elevator. The plane has four ailerons which are not full-span. It weighs about 14 pounds. The 5475HBs were specified for those surfaces by Kange (I think the instructions were probably written several years ago). Is this set-up beyond the proper parameters for those servos??

Fighterpilot

My Feedback: (2)

After purchasing 8, HS635 Karbonite geared servos last year, I heard about the problem that they were having with them breaking gears on large scale aircraft. I personally called HiTek and was advised by them not to use any karbonite geared servos on anything larger than a 12 lb. aircraft. When I told them that I could hardly see a need for a 105 in/oz servo on a 12 pound airplane and that is not what their promotional literature had said, they simply repeated that the servos should not be used on anything larger than a 12 pound airplane. Seems like somebody in product research at Hi Tek really screwed the pooch. Anybody want to by some HS635 servos?

rlmcnii

My Feedback: (3)

Fighterpilot,
That information does not sound promising for my situation. One would think that the servos, any servo, would be designed so that the gear train would not fail under the force of the torque generated by the servo itself. Apparently, if what is being said here is true, the gears fail before the control surface is blown from it's deflection. That is, the gears will not withstand the holding force generated by the servo. In that case, any torque generated beyond the failure point of the gears is never usable.
Where's the beef?

hilleyja

My Feedback: (3)

I hate to be the one to blow your decision but those 5475s are NOT a good fit for that airplane, especially because of the ZDZ 40. I installed 4 of those on a Christen Eagle II, one for each of 4 airlons, and stripped every single one of them on the 1st flight. Figuring it was a fluke, I replaced the gears (they were all stripped on one tooth adjacent to center) and tried again. This time I only stripped two of them on the 1st subsequent flight. I replaced all airlons with 5645s and each elevator with 5625s. The rudder 5975 on the rudder was replaced with a 5945. The vibration alone from the Fuji 50 on the bird was the culprit and Hitec told me those servos are not compatible with 2-stroke gas engine airplanes -- they came up with the 12lb rule after getting my complaint. Hitec is usually very accomodating with repairs for their products but when it comes to supporting their servos to their documented specs they always seem to cop out. The six sets of replacement gears came out of MY POCKET.

rcairflr

My Feedback: (44)

You say you are not made of money, yet you are choosing a servo that costs $84 and it has been proven many times over that the Karbonite gears do not hold up to giant scale airplanes which could cause your whole investment (airplane engine and electronics) to dig a smoking hole in the dirt. For $5 dollars more you could buy Hitec HS-5955's, these servos could be used in any airplane up to 40% scale and would have a higher resale value if you ever choose to sell them. Also you could buy HS-5985's for $75 each. Your best bet is to stay with a good quality metal geared servo.\

XJet

I've been a long-time critic of Hitec's handling of the Karbonte fiasco (got myself in trouble for pointing out their change of recommendations and retraction of claims after gearsets began shattering on larger planes).

Karbonite was clearly the "brain child" of some marketing droid who read too many superman comics as a kid.

At its release, Hitec grossly overstated the benefits and strengths of Karbonite, claiming it offered near-metal gear strength but without the wear.

The fact that they designed and shipped hi-torque servos using Karbonite gearsets was clear indication that they figured it would hold up under the loads imposed by giant scale and other big birds.

Of course it doesn't.

Karbonite is like glass -- it's hard and strong as hell if you apply a steady force -- but introduce *any* significant shock (such as hangar-rash, flutter or even the weight of a large surface bouncing in response to engine vibration) and it shatters into lots of bits.

Once big planes started falling from the sky at an alarming rate (having been fitted with hi-torque karbonite-geared servos on Hitec's recommendation), the misleading claims were quietly pulled from Hitec's website and a whole new set of recommendations were rolled out -- including this 12-lb maximum and "not suitable for gasers".

So can someone please tell me what kind of plane (under 12lbs) needs a servo with 172oz/in of torque such as that which the HS6985HB purports to deliver?

I'm not a total critic of Karbonite, it is very hard-wearing and so long as you have well balanced control surfaces (no flutter), use relatively small/vibration-free engines and small control surfaces then it's quite a good option. To this end I have quite a few HS475HB servos that have provided excellent service.

However, I see absolutely *no* point in wasting good money on higher-torque servos that come with such a brittle gearset.

Hitec really blew this one and it has hurt their credibility. All they had to say was "oops, we goofed. If you bought a 635 (or other Karbonte) servo based on our original recommendations we'll swap it for a more suitable unit, now that we've discovered it ain't what we promised it would be."

Unfortunately however, I suspect that such an admission would open them up to potential law suits in the event that a plane using karbonite servos (installed under the original claims) suffered a failure and caused damage, injury or death.

Hitec: great servos, great service, lousy attitude to acknowledging product faults and issuing recalls.

exeter_acres

My Feedback: (2)

Guys....take a breath...


the original thread is over 2.5 YEARS old..........


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