SBerkheimer

A power Expander is not needed but will offer benifits if you decide to use it. First off it will supply your servos with a good solid power supply. A definite plus with 5955s. It will give you more than enough places to plug your servos without having to use Y connectors and any RF that the servo leads may pick up won't make it into the RX. If you are using the programmer things get that much easier. On my Comp ARF 260 I use 2 5955s per elevator half. All 4 servos plug into the Expander into the 4 elevator slots. Using the programmer all 4 servos were programmed on the bench. 2 of them were reversed and the centers were all set so that the arms were a perfect 90 degrees to the servo case. Then I set the maximum throw of each servo to 30 degrees each way. This will take a few tries on the programmer to get right as the programmer is a little funny to use. example here is that when you set the center the programmer will show that you are off to one side and when you set the end points the numbers being displayed by the programmer will not match from side to side. i think that is where most people run into issues with the programmer in that they think that the numbers should all match. I know it caused me lots of frustration until I watched the DOD video on using the programmer. While programming I kept track of the right and left throw numbers ( for example + 127 -138 ) then installed the servos. Now because this is not a perfect world there was a tad of servo fighting. What I did was take notes on how the outboard servo needed to be adjusted with the programmer to eliminate the bind. I adjusted the end points by reducing or adding to the end point numbers for that servo. It took a couple of hours total but the results are worth the effort. 100+ flights later, I have yet to have to adjust any of this setup.


As for Y connectors, Rcpilot does make the point that you need to install the Y at the RX and run 2 leads to the servos for less voltage/current drop and yes he is correct. However two things are still not ideal. One being that you are still running 2 high current servos through a single connector. It will work but you are not getting full potential out of your 100.00 servos. the second thing is that you are connecting the two servos together with the same signal lead. Not a good thing with digitals. you essentialy create a " feedback loop " that can mess with the input signals to the servo processor. take the case off of a good RX and you will see capacitors soldered between some of the servo connector pins. this is done to prevent this very thing. capacitors will only flow in one direction.
I know that someone will try to prove me wrong here but my experience building and testing 40-65 GHZ electronic test equipment supports these findings.


Shawn

JoeAirPort

My Feedback: (41)

Capacitors do allow ac currect flow in both directions. Diodes only allow current flow in one direction. Capacitors can be used to block DC current between amplifier stages. They provide filtering on DC power supplies. They are used in RC filters for AC signals (low pass, high pass). I believe the whole issue here is drawing too much current from a single rx output channel. As far as the lead lengths and the Y creating weird current loops, I know nothing about that.

PS: Edited to admit that I do not know all. Hopefully what I typed above is correct.

mglavin

My Feedback: (31)

Shawn

Why did you match the servos on the bench if you matched the linkage geometry prior to programming servos on the model this is not a prerequisite? When it’s all said and done you should have realized a major offset at neutral with regard to the servo arm being perpendicular or 90 degrees to the case. With a Comp-ARF the surfaces are hinged on the top side verses the center. It’s not plausible to have scalar/linear throw with the servo arm located as you note on a model with live skin hinges (you'll be lucky to see anyhing close with the hinge line offset to one side). Are your ATV percentages equal or close to same in either direction, probably not which affirms my assertion?

The ultimate goal is too realize equal servo angle/ATV percentages with equal surface throw. This generally equates to the surface moving in a smaller travel arc due to the linkage ratio in-play (mechanical advantage). In simple terms we shoot for 60 degrees servo angle either side of center which nets equal travel arcs and or surface throw either side of center. In many cases (linkage ratio is the variable) we might realize 60 degrees servo angle and 45 degrees surface throw, as long as the equal it’s all good.

mglavin

My Feedback: (31)

Option #2 is best...

Prior to programming the servos, setting up the TX or anything else physically match the linkage-surfaces to move in identical equal travel arcs… This will alleviate the frustration realized of miss-matched linkages/surfaces in the future.

Now program the servos to match the linkage/surface travel arcs and the TX. Everything in the TX should be zeroed out and all ATV percentages should be equal prior to starting… MAX ATV affords the best system resolution, I’d suggest setting the TX to MAX ATV less 5-10% this allows for anomalies realized with mixes-offsets and conditions.

There is simply NOTHING offered by any other manufacture that can parallel the programmables offered by Hitec. All other methodologies consume resolution and create offsets and induce non scalar response with regard to linear TX and surface throw.

JoeAirPort

My Feedback: (41)

Yeah I here the "set the servo arm to 90 degrees" statement all the time. Then there's "get the clevis rotation right on the hinge line". That works for very basic setups and will get you flying but will never yield pefect symmetry on the servo and surface (60/60 servo and 45/45 surface for example). To get that equal +/- servo throws with equal up/down surface throws, there's always an offset from my experience. The servo arm will never be 90 degrees to the servo....or parallel to the hinge line...etc. The servo arm tip is always 5 or so degrees back towards the hinge. And if you are not setting up each servo on a ganged servo setup to get these perfectly matched and up/down servo/surface throws with the respective "offset" centers, they will bind somewhere in the throw. RCU should have a video detailing this mechanical setup procedure, followed by the Hitec programming procedure. I have yet to see the mechnical part layed out step by step. DOD touches on it and cudos to them, but I had to do a lot of research to fill in the gaps. The DOD servo programming part is excellent.

SBerkheimer

Michael, I used 5955s on the elevators only so there is no hinge offset as would have been seen on the ailerons. I programmed the servos on the bench for several reasons. First was I had been instructed by someone much more knowledgeable of Hitecs than I to reset the servos. I don't know if this was absolutly needed or not but I assume it would not hurt. Because this is my IMAC airplane and will never see 3D rates i wanted to reduce the overall throw via programming servos and not the TX so I would not loose resolution and because I would be plugging all 4 servos into the elevator slots in the Power expander 2 of them would have to be reversed. The final reason is that it is near impossible to program the servos once buried in the stabs. Even though I was setting to 30 degrees each way while on the programmer the rotation is much greater and the arms would have contacted/damaged the outter skin. Some final adjustments were needed and to do them I had to remove the outboard servos, adjust their end points and then re-install them. The Newer Comp ARFs come with the control horns in place so if there is a small geometry offset you are pretty much stuck with it. Mine was very small as I just had to set the end points up or down just a couple of points to get them perfect.

Shawn

mglavin

My Feedback: (31)

I had forgot that the elevators were different than the wings on CompARF models...[&:] Are the servos mounted on their side with the rotational axis in the same plain as the elevators? In this case things are different than the atypical model with the servo axis 90 degrees to the surface axis. In fact it’s the best possible configuration and mitigates many problems of the latter setups...

Resetting the servos with the Programmer is the first thing I do every single time.

All that said why is it necessary to remove the servo(s) to program them while mounted in the stab? Why not use a throw meter and match the travel arcs-TX with the programmer and the servos installed?

SBerkheimer

The cutouts for the servo arms to protrude out the bottom of the stab were too small. While programming for the 60 degrees max rotation, the servos would actually travel far more while hooked up to the programmer. People who have used the programmer should know what I mean. I think that the instructions that come with the programmer are it's downfall.


Shawn

bzyguy01

I agree on the electrical portion of this reply but the air volume and pressure portion is incorrect! You WILL ablolutely lose some air volume(CFM) at the other end of a 200' Run of hose and the static pressure will be the same but as soon as you open the line to use air you will find the pressure drop drastically but stay steadilly lower than a 20' hose. I was an auto painter and I never ran over 50' of hose for this very reason.
Shayne