The pull pull rudder system I have is putting so much stress on the aluminum support bracket that it's causing binding on the servo. Someone told me about a ball bearing that is enclosed in some kinda bracket I can screw to the support. Anyone know what I'm talking about?

I think you need a bell crank. Try SWB, but other people have them too. I wish he had pic's of them on his site. I found a pic on his site that shows a 3 servo system that shows the bell crank. It's the bigger of the 4 arms. Hope this helps. Also why is there so much tension on the cables that it does this? Is it at center or at the ends? All over?

http://www.swbmfg.com/

Here's another from Airwild hobbies.

http://www.airwildhobbies.com/MoreIn...&level=2&id=24

http://www.airwildhobbies.com/MoreIn...&level=2&id=32

If you provide some numbers on the double servo arm and cotrol arm sizes as well as pivot offets at the control arm as compared to the hinge line we maybe able to find your problem.

Is the binding a problem at neutral and full deflection or? A bearing supported tiller arm or bellcrank won't fix a binding problem IMO.

What plane, what servos?

I only ask because this must be a 40% because there is no reason to run more than one servo on a 35% or smaller plane with the 8611's, 5995's and 5955's out today. I would of hoped you would of figured out this stuff before buying a plane this big, but we would be more than willing to help out just in case.

If you do the math, a single 5995 at 7.4V is just a little less than three 8411's combined!

420oz compared to 465oz

A single Sekio is a sure bet for 40% planes also btw and removes the need for complicated trays.

1800oz of torque!

Darrinc,

I see you recommending the 5955 at 7.4 V all over the forums. For the record, neither HITEC nor Troy Built Models, nor anybody else, recommends running the 5955 at 7.4V in aircraft applications. They are only recommended at 7.4V for robot applications (that's actually the 5995, but they are basically the same servo) where stresses are far less and a burned out servo does not result in catastrophic failure. Also, a fresh LiPo is burning that servo at 8.4V... it gets pretty warm at anything over 6V.

Anyways, it's hard to tell what he's talking about, but it looks like he only has a single servo with poor geometry.

Wanted to clarify... don't blame HITEC when you start smoking motors.

Hey all,
I am actually building a Bob Holman B-17. 120" wingspan, 90" fuse. I'm using one Futaba heavy duty servo (w/ metal gears) It's binding only with the wires at tension. I disconnect the servo arm, and it swings pretty freely. When it's hooked up and I run it full left and right, it doesn't return to nuetral and the servo is humming. I think I need to support the bottom of the shaft that I put the control arm on. I figure using some kind of ball bearing device would take the tension off the shaft and make movement alot smoother. Kinda like the difference between metal on wood vs. metal on metal. Thanks for all the help.

Dan

Whew... from your description your cables may just be too tight?... it really is hard to tell.

So, here's the basics af pull pull:

If your cables are a straight shot to the rudder:
1) The servo arm width must equal the rudder control horn width
2) The rudder control horn pivot point should be over the rudder hinge line if possible... behind it if not possible.
3) If the rudder control horn pivot point is over the hinge line, then the servo arm should be straight. If not, it should have an offset to the rear equal to the distance of the control horn's offset behind the hinge line.

If your cables are crossed:
You will need extra offset... if they are crossed write back and I will tell you how to figure out the right amount.

As an option, look at www. swbmfg.com. Give him a call, he will help. He will tell you what dimensions to measure and set you up with something that works. In a plane that size, you mught want a tiller bar (ball bearing thingy), but there are lots of guys running 35% planes with a servo connected directly to the rudder, and I'm pretty sure a 35% Extra's rudder is bigger than a 120" B-17's.

You can also call Jerry at www. nelsonhobby.com. He's pretty good as well.

Good luck.

One season running 5995's at 7.4V, and everything is doing just fine. Six years with running a system that way, everything is running fine. A friends is working just fine too.

I doubt if my friend and I are just lucky.

Do the people saying this won't work sell regulators by chance? I doubt if the want to get into their profit.

pic's needed.

Last I heard, Hitec doesn't sell regs. They do lay out what they are willing to certify their equipment for, and I can't help but believe that this would affect the warranty of the gear. Maybe you sell airplanes and motors and want us to burn some in???

Since we are attacking credibility... no offense, but I don't know you from Adam... for all I know you are a 14 year old convict. I do personally know several Hitec sponsored Unlimited Class pilots who stand by the 6.0V limit, and I trust Gene at TBM.

If it does work for you, great. I'll wait 'till the company endorses it through a larger sample size than one season of flights on your plane. I'm not going to experiment with mine. I won't try nitrous in my car just because some Cali yahoo thinks he gets that extra couple horses on the 45mph roads. Maybe I'm a prude?

I think you are right about the torque of either of these servos being enough but i also think you might want to consider gear size in a standard size servo so maybe two of the 8611 5995 or 5955 servos is a bad idea in a 35% aircraft so he might have put some thought in it before he bought it

Marine,
Please read this:
http://members.cox.net/bdfelice/Ackerman/ackerman.htm
A lot of folks do it wrong.
Putting the control horn takeoffs ON the hinge line is not what you want.
Hope this helps!
Good luck!
JLK

Gene is my hero, btw. Hi Gene if your watching! We will be in Washington State in a few weeks for our next UAV deployment! But i believe you already know that. Sorry, maybe when we are home next time.

I feel bad that you will not do a experiment in the garage to find out real answers instead of "listening" to what ever anyone else has to say. Typical though.

I have been running a lot of servo's at this voltage for a while, I find it funny you want to pick on the one that was technically made for that voltage. (and we ran a similar servo at a higher voltage (12V) when I was in the robot business)

How many servos and rx's have you tried at this voltage? Did they fail?

Humm, I'm try to make you not spend money on crap btw!!!!

Everyone must be rich, since they can buy all of these powerboxes and regulators and such. I was poor and had to figure out how to afford bigger planes by experimenting with my old equipment.

But that is what i do for a living, figuring things out!

Hey, I just adjunct teach eletrical engineering classes, build missle defence systems, space ships and fly UAV's in combat

Not bragging because I taught myself everything in my garage by experimenting. I have crashed more planes and screwed up more composite parts and fried more electronics than the whole state of Texas will ever see. (I picked a big state)

So when I find something that workes, I like to share so others will not go through the same pains. Take it for what its worth to you.

Don't be the sheep!

McMaster Carr and Aircraft Spruces could not "endores" what we where doing with their products when we build Space Ship One, BTW.

We really will need pictures (lots of) to help with the problem of the system though.

Darrinc,

Would you please get together with Gene and figure out what voltage that the 5955 can be run on and still be covered by warranty. Maybe get Gene to change the info on his website if he suddenly decides that the tests he did in his garage (that I talked to him about a couple weeks ago) were all bogus. As for extra stuff... I found the cheapest and simplest way to set up a nice LiIon system is to use Fromeco SuperReliaRegs... this way I do not need a switch, it is actually integrated into the regulator chip... open circuit = on. This way there are no mechanical switches to fail (failsafe on, no moving parts, uses a pin to short the two poles on the chip to turn the reg off), and it costs just slightly more than buying 2 quality switches.

If you want to compare notes about our lives I will do it off line... not a place for me to brag, especially since we work for the same people.

Sorry you burned up all your gear.

Then you must be rich and can buy what you want. Us poor people experiment in our garage and then in the air and find what works then pass the info to others free of charge.

Warrenty does not mean much to a poor person, shipping back and forth is usually out of our budget.

Hey... I didn't know you needed an offset arm to counter a control horn that was offset from the hinges! I have a question for you guys then... In my setup on an extra 260, when the rudder is thrown to either side, I get slack in the opposite cable. When the rudder is in a neutral position, both are taught. Is this my problem, maybe it's the horn / arm not equal??? This plane is grounded till spring, so there's no worry about crashing... It flies well now, but that slack worries me.

Thanks a million,

MPB

That is normal. Sam Malone makes some very nice offset arms btw.

Nice cop-out answer... honestly, it makes no sense. It sounds like you burned a lot of stuff experimenting... alot of stuff for a poor guy. A poor guy with a 2.6m comp arf yak. You could have bought an airframe that's $80 less and had regs, so don't give me this poor boy load of crap. I'm not going to waste my time on you any more. Good luck with your cheap toys.

Shag555,

It's normally not a big problem if there is slack when the rudder is deflected as long as the cables are tight when centered. The rudder is loaded when deflected, and flutter normally only happens around nuetral. I believe the only issue comes when doing a tail slide... if the rudder has max throw, and the "pushing cable" is loose, when doing a tail slide the force on the rudder can reverse and the rudder can slap over and hit the elevator.

The following is only a point of interest for those that care about aerodynamics.

There is a phenomenon that can occur in the C-130, but I don't know if it can occur in IMAC planes. It's called a "fin stall", or "rudder lock". Basically, the rudder is so efficient, that at certain lower airspeeds and large rudder deflections, the sideslip angle can exceed the rudder deflection. The result is that the relative wind switches to hitting the opposite side of the rudder and tries to lock it to full deflection (in the full scale it takes a lot of pedal force and maybe a power reduction to get the rudder "unlocked"... assuming you have altitude since it usually results in the inside wing stalling and a large loss of airspeed). Servos have plenty of power to center the rudder again, but if you have a lot of slack in the cables, when this "fin stall" occurs it would push the rudder against the slack cable and slacken the tight cable. This would cause a sudden increase in rudder deflection and a bump in the yaw axis. There should be no danger of an oscillation since, once the "fin stall" occurs, the sideslip angle will increase further and tighten the rudder lock.

The only reason I bring this up is that I have seen planes (such as mine) that can fly across the field in knife edge at fairly high AOAs with minimal rudder deflection. Luckily with our IMAC planes we have centerline thrust which help keep the pressure on the correct side of the rudder. If a "fin stall" were to occur, it should only be at very low or idle throttle settings, probably in level upright or inverted flight. You would see a sudden increase (or bump) on yaw. As soon as you center the stick it would go away. Much more dangerous in full scale.

Thanks! That puts me at ease!

MPB

Yep, I have spent a ton of money burning up standard servo's and cheap rx's. You probably do not want to know how long a these will last at 12V.

So far only a month.

But I guess everyone knows that already.

I am trying to find you Sam's email, he is very knowlegable about these types of projects.

Hey, isn't he the bartender on Cheers? I think you mean Sam Monteleone http://www.wideopenwest.com/~surelink/

He is good, but usually very slow. Try Scott at SWB. He is very knowledgeable, has top notch products and usually ships same day http://www.swbmfg.com/

Of course, if you are as poor as Darrinc, you could make one out of scrap aluminum or carbon fiber like I did. fortunately for me, I can afford to buy the other stuff, but needed a custom offset to keep the tension the same throughout the throw and did not want to wait for a custom one to be made. (I know, I know, I am an idiot because I use regulators and 2 Rx's, but I like the pretty blue color and needed something to waste my money on)

With that much offset at the servo may I see a photo of how much you have at the rudder?
Thanks!
JLK