MCR-RCU

My Feedback: (2)

Oops! Looks like I broke one of my own "rules". I just took a photo of my aileron setup on my H9 1/4 Cap and it only has the standard nylon arms that came with the JR 4721 servos. I do have H9 Aluminum arms on the rudder and elevator servos with Sulivan ball links at the servo ends and metal quicklinks at the control surface end.

One word of caution: Be careful of using ball links on nylon control arms. The combination of the Dubro HD arms and B&B Ball links was part of the problem with the Sukhoi. The ball link moves the line of force above the arm causing the arm to twist. Quicklinks keep the force in-line with the center of the arm. If you use ball links, I would highly recommend aluminum arms.

I also noticed that I don't have the pushrod all the way to the top of the Sulivan 1-1/8" horn, but one hole from the top. 4-40 pushrod and metal 4-40 quicklinks with lock nuts.

I have a BME 2.7 Gas engine in this plane and it has many, many flights on it without any problems.

splais

My Feedback: (25)

This has been one of the more inlightening threads in awhile. But I have read a couple of things that I'm not clear on yet. Question: To reduce the forces on the servo I want as short a servo arm as possible on a longer control horn, correct? This is superior to either equal distance control horn and servo arm or a long servo arm and short control horn. Thanks.

DGrant

My Feedback: (4)

You want longer everything...the servo needs to move to take advantage of torque.

Think of it this way.....your servo arm with control surface centered is at 90degrees from the angle of wire. This is actually the weakest postition in the link. As it should be...there's little force with control surface at center. The force is just off center, where your deflection comes in. If the servohorn/pushrod doesn't travel far enough to lessen the angle of the linkage, your servo/linkage remains near that weakest point.

In other words, if you could take that whole linkage from servo to control surface and straighten it out...that would be the strongest you could achieve, since you can't, you need to get at least let it move off of the center area to take advantage of the torque of servo/linkage. It's the ANGLES of the linkage at center that are the problem, not the travel.

If you take this, and amplify it with turbulence over surface, and little movement of linkage, your keeping your linkage at near that 90degrees I mentioned above....not good.

Use the SUPER DUTY horns as I mentioned, or any of the larger ones that others have mentioned, and get that wire AWAY from the centers!

I really hope I explained this so it could be understood. I have a good pic in my head, and it would be easy to show in person. Let us know though.

MCR-RCU

My Feedback: (2)

I have to disagree with DGrant here. You want the shortest servo arm and the tallest control horn that will give you the throw you need. The longer the arm on the servo, the more force is being put on the servo. I do agree that you should use the full traval available in the servo.

Try this. Take a pencil and hold it between your thumb and finger. This would be the pivot point on the servo. Now, push out on the end of the pencil. It doesn't take much to move it, does it. Now push on the pencil half way between the end and your finger. You will notice that it takes a lot more to push it. The closer you get to your fingers, the harder you must push to move it. The same thing is happening with a servo.

On the surface end it is the same. If you have a aileron that is 3" wide behind the hinge and are only 1" above the hinge where your link connects, for every ounce of pressure put on the trailing edge of the aileron, 3 ounces of pressure is put on the control rod. It works just like a prybar.

The larger the plane and it's surfaces, the more critical this all becomes.

Marty

DGrant

My Feedback: (4)

Well, I see the analogy here, and can't say I agree or disagree, it definately has application.
Try this though....if you take a straight wire between your fingers, push it on both ends, you get little if any flex/bow. Now, take that same wire, put a 90degree bend in it, about an inch from one end, you get more flex, alot more, hence my point about the angles being the weakest link.
Knowing a straighter line is generally stronger then one with an angle in it, when the servo rotates, and pushes/pulls the pushrod, it needs to straighten the linkage out more as travel increases. You can't straighten that linkage out, if your not using servo travel, if your servo only travels 30degress, that 90degree angle only goes to 60degrees. I just don't see how a wire/linkage with a 60degree bend can withstand the forces that are exerted.
I can see though that a shorter arm would not matter here, except for fact it would not give enough throw to the surface control horn, at which point one would need to move the pivot at control horn closer to surface to get the throw.
That to me is not the answer though. I would figure the way to get that linkage to the straightest points, as the throw of the surface reaches the point I'm looking for.
I'm still learning(everyday), and do appreciate input, and being questioned, I respect this...so what do you all think about this thought?
As I stated before, I'm running this type set-up in a CG Sukhoi,running a Moki 180, with no prob, and 605's are the order of the day on ailerons/elevator. Even tonight I was tossing this plane around the sky, it just keeps on going though, with no prob, I do know I'm fortunate, but also believe it has something to do with how I set it up. This is good stuff though.

ooo..ooooohhhh...just had another thought,,,
Splais, how long are your pushrods? I'm running less then 12" or so, as my servos are mounted near the control surfaces.

MCR-RCU

My Feedback: (2)

I understand what you are saying about the linkage being stronger in a straight line, try to use a bent pushrod and see what happens. But that isn't what we are talking about here. If I were setting up a mechanical retract then I would definitely want the servo arm pointing at the retract when the gear is down so the load is no longer trying to rotate the servo arm.

An aileron usually doesn't require as much throw as the elevator or rudder. And the only time you would see max throw is in some type of violent maneuver. Flutter problems rarely ever happen at max throw. Most of the time they happen in straight and level flight. All I am saying is to stay in as close to the servo as possible. Yes, if you need more travel, move out on the servo arm, not down on the control horn. Just don't move out any more than you absolutely need to.

Usually, the longer the servo arm the more likely you are to have to turn the travel adjustment down using the Tx. The closer you are to using the load limits of the servo, the more critical this becomes. On most planes 120 size and smaller, this is probably not much of an issue.

Marty

splais

My Feedback: (25)

It sounds an aweful lot to me like you are both saying the same thing in a different way. and my pushrods are very short, like about 4". I have maybe 16" pushrods on my elevator servos with 605 and no problem with them, thats the strange part. I have maybe four flights on the digital 5625's with no problem so far. but I'm ordering the Dubro balllinks today. And I definitely know they need metal servo arms because of the twisting forces on the arms when using balllinks.

Westbender

My Feedback: (1)

Shorter servo arms and longer control horns give the servo help in terms of leverage. It's an age old principle that will always hold true. The closer the load is to the pivot point of the "driving" lever, the easier it is to move the load. The drawback is that you get less travel on the control surface. That means the more leverage you apply (closer on the servo and further out on horn), the easier it is for the servo to push it AND the less the control will travel. It's just like gear ratios. I would maximize the leverage and increase the end-point adjustments on the radio. If you're not getting the travel you want after that, then little by little move out on the servo and in on the horn. But know that you're putting more stress on the servo when you do this.

Think of a 10-speed bike. Smaller sprocket on the front and larger sprocket in the back means it's a lot easier to pedal, but the rear wheel won't turn as far as higher gear ratios. It's exactly the same principle with our control linkages. The servo is the pedal (or driving) "sprocket" and the control horn is the rear wheel (or driven) "sprocket".

DGrant

My Feedback: (4)

In the case of a bicycle, when your talking about the servo being the front drive, on a bike you put longer cranks on it for more leverage, shorter cranks for more speed. If your point about the bike sprocket is accurate, wouldn't you want that longer crank(read horn) on the servo for more leverage? I do know bicycles, and yes, you definately go to longer crank for climbing and leverage.
I'm in this thing to learn, and this is some good stuff here, so don't hold back, this is a good debate, and I can see all your points, and I really think there apps for all this stuff. I'm not even close to saying I'm right or wrong here, I just want to know why my set-up works well, and Splais is having trouble.
Mostly why Splais is having trouble, I didn't mean to take his thread, oh well.. :stupid:

Where are you Splais??

MCR-RCU

My Feedback: (2)

On a bicycle, you go with longer cranks to INCREASE the amount of torque applied to the drive sprocket. On an airplane, you want to REDUCE the amount of torque transmitted back from the control surface to the servo. By moving the pushrod closer to the servo center pivot, as much as possible, you can keep that force to a minimum. One needs to remember that were not only looking at the torque required to move a surface, but also the amount of torque that is required to hold it there when that surface pushes back.

As far as to why your setup works on your plane and Splais setup failed, I can only guess without seeing them. I believe you indicated your setup was on a CG Sukhoi and Splais was a H9 ¼ Cap. The CG Sukhoi is smaller than the ¼ Scale Cap and I believe it has a much narrower aileron. Obviously your setup on your plane is well within the limits of your servos. On the H9 Cap, that limit was exceeded. As planes get bigger and surfaces get larger, this all become very critical. Could Splais have used the same servos and altered his linkage and been successful, maybe. I’m not familiar with the Hitech servos so I don’t know what they are rated for. I do believe his decision to change servos to the digital ones was a wise decision.

There are many advantages to using the mechanical advantage to you benefit. Not only can you significantly reduce the amount of stress put on a servo during flight, but also reduce to risk of stripping a servo by bumping the surface (hanger rash) while handling the plane on the ground. Many a servo gear has been stripped by a seemingly innocent bump. Plus, the effect of any slop that might be in your linkage can also be reduced or minimized with the proper use of linkage geometry.

Westbender

My Feedback: (1)

DGrant,

Let me elaborate a little more on my analogy using a bike and I'll try to tie it in with what MCR is saying.

The pedal crank length on a bike are analogous to the gear-train ratio inside a servo. The bike rider (the one that pedals) is analogous to the motor in a servo. Since the output power of the motor and the gear ratio in servo are both fixed, the only thing we can do to help our servos deal with control surface loads is to utilize leverage between the servo output shaft and the control surface.

(One point to note here is that you CAN change the output power of a servo motor by going to a 6V pack. However, given the same leverage ratio and load on the linkages, it would mean even more pressure on the servo gear-train)

Let's assume the pedal crank length is FIXED (same as not being able to change the gear-train ratio in a servo). Now we can talk about the gear ratio between the driving and driven sprockets and the effect that has on the force required against the pedal cranks. If you make the drive sprocket smaller and the driven sprocket bigger, it's easier to pedal the bike. It doesn't take as much force against the pedal cranks to move the load. That translates to less force required through the servo gear-train from the motor to move the "driving" servo arm. However, the rotation of the driven sprocket/control horn is not as far relative to the rotation of the driving sprocket/servo arm. This is the key point here! You're trading control travel for power by altering gear ratio/leverage.

Here's a scenario for you: The cranks on your bike are made of plastic. You're sitting still at the bottom of hill ready to start up the hill. If you try to climb the hill in "high" gear, chances are you'll snap off your pedal cranks. However, in "low" gear, there's a lot less pressure required against the cranks to get up the hill. It's less likely you'll snap off the cranks, but it'll take more revolutions of the driving sprocket to get there. Remember, the pedal cranks are analogous to the gear-train in a servo! Snapping them off means stripping the gears in the servo!

In Summary:
The diameter of the sprockets on a bike represents the distance our linkage rods are from the pivot points of the servo arm and control horn. The pedal crank length on a bike represents the gear-train inside the servo, which is FIXED. The attachment points on servo arms and control horns move in arcs, same as pulleys, gears and sprockets, So gear ratio and the associated leverage will always apply because of that.

I hope that clarifies things. Sure is an interesting conversation.

splais

My Feedback: (25)

Well I'm not real happy with Hitec right now. It has been two weeks since I emailed them and they have not bother to provide even the common courtesy of a perfunctory response.

zero244

My Feedback: (1)

I just ordered a couple of Hitec mini servo's for small glider. Ive never used Hitec servo's before........Ive always used Futaba and never had a failure.
Based on some posts at this forum Im glad I only ordered two. Going cheap on radio equiptment is asking for disaster to strike. From now on I will only buy futaba servo's. I may send these two hitec servos back and get futaba. No amount of savings is worth the hours and money you invest in a model. Not to mention someone could get seriously hurt.

With the centering problems you guys are having with the 605 servos........I dont know how you can accept that, especially if your flying a 20 plus pound plane around.

I had no idea Hitec was having quality problems with some of there servo's.

I think you guys should re-think this out............you save money at the grocery store not the hobby store.

splais

My Feedback: (25)

I finally got an anwser from Hitec after two weeks. I sent them a rather complete email outlining the problem and providing a link to this thread. "It would be about $40 to convert them to metal gears." was the curt one line response that I received. No comments, no were sorry for the problem, nothing. I sent them back for warrenty replacement.

This kind of response indicates to me that this company is probably having more problems then people think. I still have their digitals in two planes and have not had a problem to date. But I believe Hitec over hypes the 600 series standard (nonmetal) servos. These servos probably should be restricted to .40-.60 series planes. I personnally will not use them any more. A price that is about 65 percent of the competition is inticing; but I guess the old rule that you get what you pay for still stands. And I think this thread has run its course.

Dazzler

My Feedback: (6)

I flew my H9 Cap, all weekend with the 605BB's on all surfaces except throttle(3003), and rudder(645MG), the plane performed flawlessly, no constant trimming at all. I think these servo's are getting beat up on this site for nothing. This is the 2nd 1/4 scale plane I've put them in and havent had one problem. I worked the Cap out very well this weekend, and no problems. The servo's were excellent, and would recommend them to anybody needing a high torque servo for 1/4 scale planes.

BTW, the Cap is one beautiful flying plane, I really like this plane and would not risk putting servo's in them that I felt didnt work.Bottomline, 605BB's are a great servo. Just dont put extra long servo horns on them, you will have some centering problems,as you will with any non digital servo. If you wanna go with long servo horns use digital servo's. My thoughts, Daz...

Radman

I totaly agree with mcr and westbenders tips on control setups.

Another thing to consider is the holding power at neutral. This is where the digitals shine. I have the sig cap with a brison 2.4 in it. I also have the 605 mg servoes in it. The centering on these servoes is not the greatest when you are doing the setups but to tell the truth i am not a good enough pilot to tell the difference when the A/C is flying.

On my R/C America Cap with a zdz-60 in it i run the 5645 digitals with a metal servo horn that comes with the servo. For the control surfaces i use the mk tear drop shaped control horns. (large) They have the dubro hd plastic links. Ball links on the servo horn and 6-32 push rods connecting everything.

My servoes are set up to give the max rotation at my desired max control surface angle. I do not fly 3-d so i don't need 45-60 degrees of surface deflection. I find the plane flys much smoother and have never had a flutter problem.

Run the best servo you can afford, Use metal horns on the servoes, 4-40 min pushrod size, hd control horns, and max servo rotation for your surface deflection. This, I.M.O is a bullit proof setup and will actually make your plane fly smoother.

embpic1

I have the H9 1/4 cap 232 powered with the Moki 1.80 (Great engine!). I am new to the larger planes and decided to use futaba 3004 standard servos for everything except the rudder which used a Hitec 645MG. I also used two servos for the elevators and a 6V rx pack. I flew it about 30 times doing mostly 3D maneuvers etc. I knew I was kind of pushing it but it flew well and the servos never had a problem. After some guys at the field finally talked me into getting some higher torque servos, I bought 4 Hitec 605BB servos with the nylon gears. I was able to get more throw from the elevator and ailerons and am pleased with the results(I had set the control throws pretty low so as not to beat up the 3004s). I have about 10 flights with the 605's and have had no problems. I will keep a close eye on them however after reading these posts.

shess65-RCU

My Feedback: (7)

Just came across this thread and wanted to add my 2 penny's worth. I had the same problem the the 605 servos. I stripped 3 on the flaps of an ultra stick 40 size. All 3 were the small gear. I did not know this gear was plastic in the metal gear set and ordered metal gears for 7 servos. Ended up costing me a bunch for the servos buying the gears seperately. I have a thread on the hitec support formum where I went around with them for weeks but they never would admit any problem or offer to replace the gears. Luckily I have not had any more strips since the metal gears went in even the the problem gear is still plastic.

Steve

embpic1

Well here is an update.

I have flown my H9 Cap 232 200+ times now with the Hitec 605's with nylon gears. The only metal gear servo I had was the 645 on the rudder. The metal gears wore out extremely fast. The rudder became very sloppy. I replaced the 645MG with a 605 Nylon gear. This airplane flys very well with these servos. I do lots of 3d flying and these servos have held up the the task very well.

dirtybird

My Feedback: (5)

If you are using the ball links, one way of defeating the servo arm twist problem is to use the disk output arm that comes with all Futaba servos. ( It won't work on other brand servos)

Dazzler

My Feedback: (6)

My 605's are also working great. I have them on a GP Giles 1/4, and the H9 Cap, both fly great. Daz...

rmorhan

My Feedback: (17)

i have 6 605bbs in my 1/3 lanier xtra 300s , 3w 80 & have had no problems yet( only a dozen flights ) i used these as they had more torque than the plans called for. is it worth changing over to metal gears if the weakest gear is still plastic?? my i/4 scale h9 cap st2300 had standard airtronics 94102s all around & i flew the crap out of it 3 seasons no problems. further my planes get more abuse going from inside my house to the field than in the air !! i,ve lost count of the dings on the extra,s control surfaces ( BIG PLANE !) including the crater on the rt elevator where my dremel hit after a 2' drop , toasted the dremel switch but the servo is good as new !! (hitec 605 - 1 , dremel -0 ) now i know i,m not lucky ( dremel costs more than servo) so why are my servos holding up. just wondering how many of these stripped servos suffered hangar damage at some point before the failure ? by the way i did manage to strip every servo in the cap ( AFTER I SPUN IT IN AT 50 MPH!!)

RysiuM

My Feedback: (1)

I see you guys are using HS-605 all over the 1/4 scale planes. I was wondering if I can use them on my Hangar 9 Edge 540 on ailerons. I never had a problem with 605 except the centering (like every non digital servo).

Now I was amused reading the comments regarding what is better: loner or shorter servo arm. The golden rule I use is: The longer is better. Here are the reasons:
1. Use long servo arm, so when servo goes +/- 140% the pushrod will not bind by shaft. If I use standard DuBro clevis on standard (white arm) then on 140% the pushrod will bind by the servo shaft.
2. Use long horn on the control surface to achieve proper movement when servo is moving +/- 140%. Always set linkage so desired maximum surface deflection needs 140% servo movement. All servos have some slack: on the shaft bearing, on the gear, on the resolution, on the center holding limits, on the linkage. Ball bearing eliminates shaft slack, digital servos have small holding limits, good hardware eliminates linkage slack, but there always be some. Now the longer horn, the less free movement is transfered to the surface.
I always calculate length of the horns so I get desired deflection in 140% servo movement. Then I will get every ounce of torque I paid for.

Finally returning to the main subject. I might suspect, that this stripped gear is the result of micro flutter. As I pointed above, surface will always have some slack which may cause a flutter. In your plane this might be the problem. Aileron is vibrating with the same frequency, as entire mechanical circuit (starting from the first servo gear ending at the aileron horn). Then the weakest point will give up, in you case this small plastic gear. To fix it try to change the resonance frequency of the entire circuit:
1. use other type of servo (different gears)
2. change the length of both horns
3. Use other type of pushrod (heavier or lighter).

I bet, your servo was killed by resonance.

RysiuM

RJConnet

Could be that RysiuM is right. I had about 15 flights on my GP G202 1/4 scale and wanted to try the APC 17-6 prop on it. I balanced and installed the prop, tied the plane down and started it up. This is the first prop I had tried on the plane which allowed the Webra 1.20 to turn over 9000 RPM. I found that at about 9100 RPM the right aileron developed a sympathetic resonance that turned it into a blur. It was vibrating at least 1/4 inch either side of neutral. Needless to say I quickly shut it down for I am sure the servo gears would have failed. I checked the prop again for balance and found it OK, the problem was in the cheap aluminum spinner I was using. I balanced the spinner and the problem was cured.

You might put a smaller prop on your plane that would allow the engine to spin up on the ground to the RPM it reaches when unloaded in the air, then check your ailerons for excessive vibration. I wouldn't call this flutter it is sympathetic resonance.
Good-luck, sure hope you find your problem.

john316

I think RysiuM is on to something here also. I am running 605's on a Great Planes Giles 202 with Saito 180 power and the APC 17x6 prop with no problems thus far. At certain rpms though, the engine/rpm/airfame will come into resonance and the ailerons will go absolutely nuts! The entire airframe is experiencing resonance but the effect is magnified at the ailerons. Also I noticed the wheel pants will come into resonance as well at the same rpm. Increasing or decreasing rpm will stop the resonance. I am not an engineer, but I am an airframe and powerplant mechanic on full size aircraft as well as an aircraft inspector (IA). Full size propeller driven aircraft will often have a yellow cautionary range on the tachometer. This is a critical vibratory range where the engine/propeller combination will come into resonance and ultimately result in a crankshaft failure. It seems to me that operation in this range on a model aircraft could be causing some of the problems that we are attributing to flutter. The gears are actually fatiguing over time from what is in effect a low amplitude, high frequency flutter mode induced by propeller/engine/airframe resonance. Just my thoughts on what is an intriguing puzzle.