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Jan 18, 2011, 09:04 PM
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Install Internal Push Rod Sleeves

At the request of a DLG pilot asking how to install internal push rod sleeves in a Blaster 3 he is about to build I have compiled pictures from a Blaster 3 I am in the process of finishing along with several pictures from a Blaster 2 build a few months earlier. Both planes are built with the push rods located in the boom. These techniques can be massaged for a number of different DLGs and larger gliders.

I had to re-stage some of the Blaster 3 pictures where the magnets were involved because I hadn't really planned on doing a build thread on this procedure. You can see that some other work has been done that normally would not have been if I took pictures of the actual event. I found that some of the Blaster 2 pictures I had taken earlier detailed what I was missing from this current project.

Rather than take over the Blaster 3 build thread with this I decided to do one dedicated to just this procedure, which may make it easier to find in a search if there is future interest in seeing how this technique is accomplished.

It is probably way more detailed than necessary for many builders but I just never know what the level of a builder may be and I hate to leave someone with questions that could have been easily answered.

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Jan 18, 2011, 09:42 PM
Registered User
The first steps for preparing to run internal push rod sleeves on your this case a Blaster 3 you need to figure out exactly the servos will be placed that will control these push rods. You also need to know where the elevator and rudder horns will be positioned.

I drilled the exit holes for the Blaster 3 push rods about 1.5 from the servo horns. On the Blaster 2 the push rods simply exit into the pod and drilling is not required. The rudder and elevator holes are located about 2.25 from the control horns of each. You want the end of the sleeve to be far enough from the hole in the control horn so that whatever fixture you attach to the carbon fiber push rod to connect to the control horn has enough room to travel back and forth without hitting the end of the push rod sleeve. Also, it is very important to keep the bends in the push rod sleeves shallow as possible so you can easily move the push rod back and forth in its sleeve. A footnote here is that the carbon fiber push rods supplied are more slippery than wire push rods and negotiate bends easier than metal. So, another reason to use the ones supplied is they are not only lighter but smoother as well.

Now mark the spots for the rudder and elevator push rod exits for the servos. It is a good idea to hold the ballast stick alongside the cap of the boom where the servos reside and mark a line just under the thickest part of the stick with a very fine tip sharpie marker. This marks the space the ballast stick needs to pass through on its way to its resting space. When you will drill the two holes making sure both are below this line your sleeves should be out of the way for the ballast stick to pass. Stagger these openings fore and aft on the boom if possible so that you don't structurally weaken it. You want the holes to be low in the boom so the push rod sleeves can be glued inside close to the floor of the boom. This will allow the Ballast stick to slide in on top of the sleeves when you are done. It is a desirable to drill one hole just a bit higher than the other so one sleeve will lay over the other where they bend toward the tail from opposite sides of the boom.
Jan 18, 2011, 10:06 PM
Registered User
When you have marked the carbon fiber fuselage for the two exit holes for the push rod sleeves and the the elevator mount, wrap masking tape on each side of the areas to be lightly scuffed with 120-150 grit sandpaper. This helps with the bond. Now tape over where the hole is to be drill with masking tape (to keep the bit from slipping). Make a 1/32 pilot hole for each of the two sleeves. Then find the drill bit that best matches the diameter of the sleeve and enlarge the holes.

Use a very narrow rat tail file with a tip that can fit into the hole without making the hole a bigger diameter. You can either do this by chuck this file into a variable speed, low power drill. Slowly push the rat tail file while it is spinning in and out of the hole at a very shallow angle to the boom. This will elongate the hole. The push rod sleeve will not kink but rather have a desirable gentle bend where it passes through the hole. You want to end up with a 3/8 long hole followed by a short trough behind the hole. Remove all tape and clean the areas with Acetone. You will also need to clean the inside of the boom with acetone to glue in the push rod sleeve. For this I use two short pieces of Q-tips taped onto a wire rod or wooden dowel that fits inside the boom. Soak the Q-tips with acetone and pass through both ends of the boom several times.
Jan 18, 2011, 10:18 PM
Registered User
Lightly sand the push rod sleeves so the CA glue will hold them in place. On other DLG builds I have found Sullivan's small diameter yellow sleeves to be my favorite. For one thing they are just about a gram less each per sleeve, more importantly I believe they provide a much better CA bond. Having said that, I decided in my 'dry tests' the yellow Sullivan sleeves to be a little too stiff to make the turn in the belly of the Blaster 3 boom up by the servos. This is a pretty tight radius and you don't want any binding in the push rod travel. The black sleeves provided are softer and more flexible.

When the holes are drilled and prepped slip a .032 music wire from your LHS in either hole at the tail end of the boom. Hold a rare earth magnet over the other the hole you want the wire to exit from for the proper servo. When the wire gets close to the hole the magnet will pull it out just enough that you can continue pushing or grab it with needle nose pliers to take it out of the hole an inch or two. Now go back to the tail and slip a push rod sleeve over the wire and work it through the fuselage and out the hole in front. Do the same thing with the other hole. You will end up with one sleeve crossing over the other inside the fuselage at the pod end of the glider near the servos. Peer into the nose opening for the ballast stick and you should be able to see where they cross.
Jan 18, 2011, 10:53 PM
Registered User
Take the stack of three large (5/8 magnets) and put them under where the sleeves cross. Look through the ballast stick hole and you can see the sleeves, with the wire still in them, pull down toward the bottom of the boom as you move the magnets around. Slide the ballast stick into the hole you were looking through and see if it slides easily all the way into its position in the fuselage.

Assuming that it does you can add several of the next smaller size magnets (7/16) from the back of the black pod housing straight along the bottom of the boom as pictured. When doing this slide the magnets just a bit from side to side to make sure they are pull the sleeves inside the boom toward the center of the bottom.

Ad a magnet every 3.5 or so. I happen to have both 7/16 and 1/4 magnets. I would suggest all 7/16 if you have to buy them anyway because they are more powerful. $15-$20 will buy all the rare earth magnets you need at Ace Hardware. The elevator boom should have a gentle sweep up to its exit hole and so should the rudder. You can see in the pictures the magnets begin to wrap along the side of the fuselage for the rudder sleeve to make a smooth gentle sweep out the opposite side of the fuselage. All this can be seen looking in the rudder slot at the back of the boom.

It is important that the two sleeves are side by side going down the boom until they separate to go out different holes. You want to use a minimal amount of Thin CA to secure these sleeves. If they are nestled together one application of Thin CA will adhere both sleeves. Use caution, excessive CA can build a significant amount of weight to the tail.

I like to first replace one wire at a time with the carbon fiber rod to see it it moves freely in the sleeve without binding. When satisfied with the travel on one I trade back for the music wire and then try the other. This will sometimes disrupt the magnets but they are easy enough to replace.
Jan 18, 2011, 10:58 PM
Registered User
With the magnets in their proper place and just before you glue in the sleeves test fit your ballast stick one last time. Assuming all is well. Use a CA eye dropper applicator made for Thin CA and apply just a small amount on all the sleeves where they pass through the fuselage. A tip to prevent a chance of accidentally getting CA at the opening of the sleeve is to dip a toothpick in some Chap Stick and spread around the wire and where it exits the sleeve. At this point I take a tooth pick and dip the end into medium Thick CA and run just a little along the seem where the sleeve comes out the fuselage hole. Now hit with a bit of CA Kicker. Sealing this joint will prevent thin CA to escape through the exit holes and goober up your fuselage in the next step. It is always a good idea to have CA remover handy or Acetone at the very least in case you end up with CA where you don't want it.

Do this step with the back of the fuselage hanging over a wastebasket. Make one last inspection in the hole at the front of the fuselage. Check your magnets. Then hold the fuselage at a very slight angle down with the back over the wastebasket and squeeze off about 3-4 drops of Thin CA from the front hole onto the inside bottom of the boom. Slowly Tip the tail end of the boom down at a steep angle over the wastebasket so the CA has chance to run along the sleeves on the way toward the back.

Hold the boom vertically over the wastebasket until all the excess CA dribbles out the back end of the fuselage. After a minute or so squirt a few spray-fulls of Kicker into the hole at the front. Let that dribble out the back end of the fuselage. Let it set up for 10 minutes or longer before removing the magnets. One thing I like to do but is not critical is dip a Q-tip into Acetone and stick it into the rudder hole right after the last drops of Kicker come out. This helps keep that area clean so the rudder fits properly in the slot.
Jan 18, 2011, 11:18 PM
Registered User
Slip in the carbon fiber push rods and test travel. They should be fine. Now you can wrap Carbon Tow, Kevlar Thread, Black or colored button thread, thin fiberglass cloth, etc. around the exterior of the push rod sleeve exits and then soak with a thinned solution of Epoxy. Wipe off all excess Epoxy with a paper towel. I slightly dampen one with denatured alcohol to wipe off as much as possible. You want to keep the weight down. I usually do this twice.

One other hint is when you secure connectors on the ends of the carbon fiber push rods it is a good idea to put a thin wrap of thread or tow or across the carbon rod and connector then glue with Epoxy or CA. I had one come loose on my DLG rudder, which gave me a real thrill on the launch...all ended well but now I make sure they are anchored together.

That is pretty much it. The first time you do it just take some time to think the steps through. I promise once you have tried this you will find it goes much quicker the 2nd, 3rd, 4th, 5th...time.


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