Since I'm getting no bites in other threads on this subject, I'd thought I'd throw this question out there in it's own thread for the "experts" to chime in

I'm in the process of putting together a Flying Legends Hawker Hunter and I've noticed if I use small servo arms there is no way I can get proper control deflection without butchering the surrounding area in the stab or fin? What size are guys using for servo arms as appropriate to get good leverage and resolution from their servos? I mean measurements between the servo spline hole and the hole on the arm being used to drive the control surface? 1/2"? 1"? What's the gouge?

Thanks

Z

I use the smallest arm possible that gives me the necessary control surface deflection. I can't really give you an exact measurement b/c every install is different.. but i rarely go over a 1" arm

As short as possible that will still give you the required control surface throw.

I doubt any of my jets have servo arm lengths more than 3/4". If you need really long servo arms to get enough control surface throw it is quite possible that you could use shorter control horns at the surface, or that your control horns are mounted improperly (i.e. horn mounted too far behind the hing line).

The control horn ideally should be mounted so that the clevis hole(s) are on the same plane (inline) with the hinge line. It is best to have it supported between two of the hinges, and it should not be any longer than necessary to insure no movement if the pushrod was absolutely locked down. Then the servo arm should be as short as possible to achieve the required throw.

The longer your servo arm is any slop in the servo will be amplified at the control surface.
Using the shortest arm possible also allows you to us the full travel of the servo which will give you better resolution at the control surface than you would get if you used a longer arm and then had to adjust the control surface throw by cutting down the servo travel in the transmitter.

Thanks for the suggestions guys. In my limited experience, I've used the smallest servo arms (on jr servos) and the closest or second hole out. But in this application that won't work, but I think 3/4" would work.

Z

Z, I would try to give you pictures or measurements of my setup but I'm out on a trip series........
Suffice to say, I did my servo mounts so that the servo case lay just flush under the cover which gave the most clearance for the servo arm/pushrod clearance. I think 2nd hole out on a heavy duty JR arm. I did add some clearance to the servo covers by dremeling the slot farther back than stock.
-Mike

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If you search RCU there was a thread on proper linkage geometry , I forgot to book mark it[:@]

Anyhow one other thing to consider is the use of proper material, i.e. plastic vs. aluminum arms.
You may want to read the last couple of pages of this thread, starting at post 513.

http://www.rcuniverse.com/forum/m_10...page_22/tm.htm

Hi,

I use the SWB aluminium arms if I need to use ball links on the servo end. If I am using sullivan clevises at the servo end, I use the heavy duty nylon JR arms. Been jet flying since 1998....never a problem with that approach and the mechanical principles outlined by the other guys above.

Craig.

Yeah, I just stumbled upon that last night RCISFUN! That threw my whole going with hd arms out the window! [:@]
I'm hoping that was an isolated event in Dom's case?
Thanks guys

Z

If your going with Plastic arms, I never have had an issue with the JR HD arms..I have stayed away from the Dubro arms as the veterans in my club have told me they strip..After reading poor Doms thread, this just puts the nail in the coffin for me for ever using them..If you can fit in aluminum arms it's one of the best ways to go IMO..

That kind of seals it for me too with the Dubro HD ones... I've used SWB arms in the past in other applications 25% and 35% airplanes with much success, but they all come tapped for 4-40 ball link type connectors and I just wanna use the Sullivan gold n type? Besides, I'm using Futaba servos this go around, so the JR hd ones won't work![:@]

Z

Hi KFX450

Can you post the link for this thread. I have a jet with Dubro arms with arround 150 flights with no problems.

Regards

Nuno

Jamie,

This program was written by Oliver Nicolas (Ohlnico) and he has published it to the r/c community for free use.

I have found it excellent to figure out both simple and complex geometry.

With servos mounted inside the wing and the control arm and pushrod projecting outwards, it is difficult to get the right geometry. It is important to get as much servo throw as possible and not use too long an arm and then endpoints to get the correct throw. Your torque and resolution will be terrible.

I just recently looked at a guy's radio who was having problems with his set-up and found his EPA's set in the low 20's!!!

http://www.rcuniverse.com/forum/m_9257664/printable.htm

http://www.geohei.lu/olin/data/model...calculator.xls

PaulD

Thanks Paul...
I'll check it out


Z

Check out post 516..And you can read before it

http://www.rcuniverse.com/forum/m_10...21/key_/tm.htm

Im sure people have thousands of flights with them..I just stayed away from them, and this made it stick in my a head that much more..my personal preference..

Hi Guys,

Just another point to enhance the performance of your set up....

End point adjustment should be used sparingly to adjust symmetry of control throws. If you want to reduce your total servo throw you should do it by reducing your dual rates, not with the end point adjustment. If you do it with dual rates, you compress the resolution of the radio over a narrower range of movement, rather than cutting off travel at each end. By reducing your rates you will achieve your aim of reducing servo throw in a way that maximizes your resolution over your desired range of movement. This is why most gyro manufacturers advise you to set your travel (ATV) at 100% and reduce your servo throw with dual rate reduction.

Hope that helps.

Craig.