Conference vmszoo::rc

    I prefer the solid pushrods because I can get maximum deflection
    at the control surface.  This is not to say that flex-rods never
    do, and that I never use them, because sometimes you have to so
    as to get around fuel tanks etc...  I also make my own pushrods
    from dowels and metal rods that I get at my hobby shop.  
    
    Everyone has there own technique and preferance, but experience
    is your best bet.  Try different ones and see how they react and
    from there you can decide which is better for the plane that you
    are building.
    
    
    Ken
    

    
    
       I USE BOTH PUSH RODS.THE WIRE PUSH RODS I USE FOR THROTTLE AND
    FRONT WHEEL TURNING AND THE PLASTIC TUBE RODS I USE FOR ELEVATOR
    AND RUDDER CONTROL.I REALLY DON'T SEE MUCH OF A DIFFERENCE IN THE
    DIFFERENT MATERIEL THEY USE.JUST WERE YOU USE THEM.
    
    
                                        KEEP'EM FLYING
                                        JERRY

I vote for wire cables inside plastic.  Of course, I've only built small
gliders lately...  I have trouble with wood pushrods, they seem to always 
require modifying the kit.  I know, if I scratch built...

Monte

    One absolute rule: NEVER use a rod that is threaded at both ends.
    Vibrations can cause the rod to turn, which won't change its length
    (it's unwinding from one end and winding into the other) until it
    comes out of the one end. Then...
    
    I've heard that the "Goldenrod" is quite sensitive to heat, so you
    have to constantly readjust your trim. Never used it myself, having
    been warned off.
    
    I like the flexible braided cable for the nose wheel and throttle.
    I used the steel wire inside a plastic tube on my last plane and
    it seems to work fine. If you make a pushrod out of balsa sticks,
    be sure to use hard balsa, or run a line of Hot-Stuff CA along it
    to stiffen it.
    
    How about hearing from some more of you experts out there who
    have built a lot of planes (I've only built 2 1/2 so far). Any more
    words of wisdom?
    
    Dave

    I use multiple methods depending on the plane.
    
    For throttle and nose gear stearing I use a solid rod if possible.
    Threaded end with a clevis and a "Z" bend at the other end.
    
    If I can't use a solid rod I use the braided cable inside of a
    plastic tube.
                        
    On a sport ship I'll use a steel rod inside of a plastic tube for
    rudder and elevator.
    
    On a pattern ship I use a cable pull/pull system for rudder. It's
    the most positive set up I've found.
    
    For elevator I use either a fiberglass rod with steel ends or a
    3/8" balsa stick with 1/4" .007" carbon fiber laminated to all
    four sides. This then had steel rods attached to both ends.
    
    I never use plastic in plastic. To much variation.
    
    						Tom

    
    I have used wood, plastic in plastic shroud, and cable in plastic
    shroud.  I prefer cable.  In my last two planes I used 1/16" cable
    for elevator & rudder, 1/32" for throttle.  For tight fits like
    getting the throttle pushrod around the fuel tank you can't beat
    it.  Only problem is that you can't just Z-bend the servo end because
    it's braided cable.  I like those set-screw type servo connectors
    for their adjustability while building.  When finished building I
    CA the set screw and put a bead of solder on the cable on both sides
    of the servo connector, in case the screw comes loose.  I also check
    the screws periodically.  Another option is to solder a solid wire
    Z-bend piece to the cable.  Make sure you don't leave long lengths
    of the shroud not secured to the fuse.  You need the shroud secured
    to provide strength and stiffness. Also, minimize the length of cable
    outside of the shroud (at both ends) and secure the shroud to the
    fuse as close to the ends as possible (so the cable has no room to
    bend).  This will give you a very strong and stiff pushrod.
    	I have used this on a small Super Sportster .20 model and a
    fairly large Sig Citabria with no weight or screw looseneng problems.
    I have not had any flutter or trim change problems with it either.
    I don't have weight comparison data with, say, balsa pushrods.  That
    might be interesting to see.
    	I don't like the plastic pushrods because of the aformentioned
    temperature drift problems.  I've seen planes that need to be retrimmed
    several times after sitting in the sun or in a hot car.  Apparently
    some plastic pushrods are better than others, but i've decided not
    to bother with them.  Getting a plane trimmed right can be a lot of
    work.
    
    Bill

    
    		A recent experience may also help you to make up your
    	own mind.
    		I have a PT20 trainer and was having a problem keeping
    	the nose wheel trimmed because of the bend that the building
    	instructions had you put in a solid wire in order to get it
    	where it had to go. Lets try a picture;     
                                             ________________
                                            /                \
                                           /                  -----
                                          /                  ___|_______
                                         /                   |         |
                                        /                    |  SERVO  |
                                       /                     |         |
                                      /                      |         | 
         bottom of fuse  ------------/----------------------------------
                                    /
                     ======________/
                      CLEVIS TO ATTACH TO NOSE WHEEL
    
    		The bends where not quite that steep however the flex
    	in the middle due to hard landings kept me quite busy retrimming
    	the steering. I thought I would get smart and replace the whole
    	thing with goldenrod. Well taking my plane out on several occasions
    	since I have found that as a result of a ten degree temp shift
    	from one day to another I have to turn my clevis three turns
    	to compensate. The moral is that although the golden rod
    	instilation was simple I still have the same problem but for
   	a slightly different reason. Next try will be with a good 
    	rigid metal cable.
    
    
    					Michael Gallant
    

    
    	Engage brain before typing.
    
    	Last reply should have said at the end "flexible metal cable."
    
    				oops Mike
    

Can you mount the servo upside down?

    
    		Never thought of it. Just a plan follower at heart.
    	I was and still am a beginner and didn't have anyone around
    	to give me words of wisdom. Thanx mayber I'll learn to be
    	a bit more flexible now.
    
    					Mike
    

    re .8.. I have the same plane (PT20). I found the same tendency.
    
    My solution is much simpler: I push on the wir at the top & pull
    on the bottom to put the nose wheel back into alignment.
    
    md

    re golden-rod: I wnet flying last sunny:hot & muggy. I have golden-rods
    for elavator & rudder. Instrcuctor mummbled something them being
    sensitive to heat & cold. (he have to retrim every time). I was
    disapointed. I would expect mfger to think about these possible things
    before bringing stuff to market. 
    
    I used wire rod for throttle after trying 1/16" braided cable. The
    cable collapsed on itself when card barrel jam due to incorrect
    idle needle adjustement.
    
    From now one, plastics rods are out unless the expansion factor
    is very well controlled. I plan to use either braided wire (big)
    or some variation from Tom T. list.
    
    md 

I've been wanting to try the braided cable, but I always thought
that you needed two lengths to make it work.  Guess that if you
anchor it as described a couple of replys ago, it works just
fine.  Can someone describe how to handle the stuff, and how to
make the end connections?  How do you cut it; I know that the
cable used in bicycles is a stinker to work with.  What size
cable would be used for a .20 size model?  What would be the
maximum allowable distance that you'd let the cable end dangle
out of the sheath?

    You can also just tin the cable with solder were you want to cut
    it, then make the cut with a large pair of diagonal cutters.
    
    Wayne
    

    
    I think I read a few replies ago that some people use the braided
    cable for elevator and rudder applications. I cannot argee with
    this application. The only time I have seen this work is when the
    outside plastic sheathing was glued 100% of it's length to a fuse
    side. If not done in this manor your asking for flexing and that
    then leads to problems. I use the cable (and see no problems) on
    throttle and nose gear steering.
    The only other way I use cables is in a pull/pull system on rudder.
    I only use this on my pattern ships because it's the most positive
    system going.
    Someone asked about cutting cable. I use a very tuff shape set of
    cutting dikes. I have also used a dremel saw with an abrasive wheel.
    Someone else said that you can't put "Z" bends in cable. Thanks
    for telling me I guess I'll stop doing what I've been doing for
    the past two years.
    It's easy simple make sure that you have about 1-2 inches of excess
    cable past where the "z" bend is needed. Bend the "Z" bend using
    "Z" bend pliers and then cut off the excess. It works great on 1/16
    inch cable. I then tin the cable between the "Z" bend and the
    outside support tubing. A threaded solder link on the other end
    and your all set.
    
    
    						Tom

    The reason I don't like Z-bends in braided cable is that I found
    it difficult to make it smooth and this can result in wear of the
    hole in the servo horn.  As the hole widens the control backlash
    increases.  But I'm not one to argue with an expert like yourself.
    
    	Regarding wire cable for elevator/rudder, I'll have to agree
    that solid wire is better for this application.  Just in time to
    change my plans for the next plane.
    
    Bill

    I'm trying something a little different in pushrods so will
    detail what being done and then in the near future report on
    how it works.
    
    
    To begin most pattern birds use a split elevator. By this is
    ment that there is mo connection between the two elevator halves
    except for the pushrod. In most applications a "Y" pushrod is used.
    Understand that slop in a pushrod, any slop is now appreciated.
    So in an effort to eliminate the slop and inprove the "Y" 
    pushrod I'm trying somethin new.
    
    
    Ops, got to go report latter.
    
    Tom

    
    
    	OK,
    
    	To continue where I left off...
    
    	What I'm doing starts as a Dave brown pushrod. A hardwood dowl
    2 inches long is glued into the end. Then a slot is cut into the
    end of the pushrod to accept a 180 degree bellcrank. This bellcrank
    is made from a piece of carbon fiber laminate from Bob Voilet
    app.1/16 inch thick. The assemply of the bellcrank and the pushrod
    is dry fitted together and a 1/16" hole is drilled to accept a screw.
    One pont to note is that the bellcrank is sized so that the two
    ends protrude outside the fuse. Next a piece of plywood is drilled
    to accept the O.D. of the fiberglass rod and sized to fit inside
    of the fuse directly beofre the exit slots in the rear of the fuse.
    The dry assembly is taken apart and the bellcrank is slipped into
    the fuse through the exit slots. The pushrod is inserted into the
    fuse from the radio compartment and mated to the bellcrank. The
    elevator servo is installed and the length of the fiberglass
    rod is marked. The rod is then removed and cut/finished per the
    rod assembly direction supplied. Now comes the final assembly.
    CA is applied to the Slot in the pushrod end that is to accept the
    bellcrank. The rod is inserted into the fuse and mated with the
    bellcrank. Then a small screw in inserted from a hole in the bottom
    of the fuse. The plywood piece is slid over the fiberglass rod and
    the pushrod connected to the servo. Stand the fuse up with the engine
    pointing towards the ceiling and allow the ply to slide down into
    the fuse. Align the bellcrank so that it is in the middle of the
    exit slots and then from the radio compartment drip CA into the
    fuse to affix the plywood plate to the inside of the fuse. Allow
    to dry. Install a helicopter ball/balllink assembly on both ends
    of the 180 degree bellcrank. Fabricate short pushrods that fit from
    the bellcrank to the elevators.
    
    This assemble gets the elevator rod running down the middle of the
    fuse and hopefully will eliminate all slop. We'll see if we are
    successful.
    
    Tom

Tom - please draw a picture - I can't figure it out.
We all know how good you are with those VT100 pictures:-)

Bye          --+--
Kay R. Fisher  |
---------------O---------------
================================================================================

    Old note, but correct topic...
    
    I've got a cable-in-tube driving the rudder on my Sagitta 900 that
    seems to have a lot of friction, especially where the cable bends
    slightly. I've considered going to a smaller cable (the one Airtronics
    provided looks like it could pull cars out of ditches), but a smaller
    cable would be kind of sloppy inside the large tube.
    
    Would a lubricant help? What kind should I try?
    

    Try powdered graphite if you can get it down into the area in question.
    Removing the cable and applying the graphite to it is the least
    messy method.
    
    Another reason for pull-pull cables.
    
    Terry

>               <<< Note 198.22 by CIM::LOREN "I <heart> OOPS" >>>
...
>    I've got a cable-in-tube driving the rudder on my Sagitta 900 that
>    seems to have a lot of friction, especially where the cable bends
>    slightly. I've considered going to a smaller cable (the one Airtronics

Not the answer your looking for but consider this.  If the rudder still turns
OK and doesn't really load down your servo it might be a feature.

For instance Walt Rady (an older fellow who has been flying gliders
in contest for years from N.H.) says one of the reason he likes the
Airtronics 102's servos is because of all the hysteresis slop they
have.  He claims that you can initiate a turn and since the servo will
not fully return to zero when you let go of the stick it will make
a nice thermal turn and spiral up with his hands off the sticks.

Sounds awful to me but I must admit my Chuperosa behaves in a similar
manor (although my rudder is not tight or sloppy and I have a Futaba 133
on it) and I'm getting to kinda like it myself.

Try thinking like the VMS group.  
"It's not a bug - it's an undocumented feature!"

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################

    Thanks, the graphite helped. The rudder servo still chatters a bit at
    idle, but it's better than it was.

Well, this is about the best place for this so I'll put it in here. Last night
while checking out my Alcyone for a session today (wow, someone who preflights 
the night before in the shop where repairs can be made 8^) I found that I 
needed to better attach my elevator cable tube.

I've been having elevator compensation problems with crow and decided to check 
it out last night. I found that I have about a 1/16" of hysteresis in the 
control surface (at the point I mark and check to) depending on whether I 
center from up or down. Since the tailboom of the Alcyone is open crossbraced 
structure and I covered it with transparent yellow, I noticed that my cable 
sheath had come loose and was flexing quite a bit. I've always used sawdust and 
CYA glue to embed the cable tube at several points and it came loose through my
rigorous landing attempts. 8^)

I came up with what I thought was a neat method to tie them down. I cut out the 
covering on one side so I'd have access but that didn't really allow me to get
a good attachment to the fuselage floor so I cut some 1/2" wide strips of 6oz 
fiberglass cloth and looped them around the tube and pulled it to the side. 
I then wicked CYA glue onto the cloth which drank it right up and stuck well to 
the structure. Neat as can be and no more sheath flex. This cut my centering 
problem in half which makes it acceptable. The rest of the problem is the cable 
flexing in the tube.