Making your own links in a snap
By Terry Dunn; email: [email protected]
As seen in the Winter 2015 issue of Park Pilot.
While I lived in Houston, I noticed that the metal pushrods on my models would often get rusty because of the constant high humidity. On some models, the rust was just a cosmetic eyesore. On others, it caused pushrods to bind in their sleeves or made metal clevises seize in place. I had one overlooked pushrod break due to rust.
To remedy this problem, I devised a way to outfit my park flyers with pushrods that would never rust. Although I now breathe the dry air in west Texas, this is still my preferred pushrod style.
These pushrods are nothing more than a nylon clevis or ball link glued to an appropriate length of carbon-fiber rod. The result is a simple, lightweight, and rigid pushrod. All you need are a few supplies and basic shop tools.
What You Will Need: The simplest, and my most-used, form of this pushrod employs nylon clevises that are meant to be threaded onto a 2-56 threaded pushrod. In the example shown in the photographs, I used Great Planes Nylon Clevises. I also used ElectriFly 1/16-inch diameter Carbon Fiber Rod. To attach the clevises to the rod, I used Zap medium CA glue and Zip Kicker accelerator (zapglue.com). You can also use the foam-safe versions of both.
All you need for simple, rust-proof park flyer pushrods are 1/16-inch diameter carbon-fiber rod and your favorite 2-56 clevises or ball links.
The Great Planes carbon-fiber rods are roughly 24 inches long, so you will need to cut them to the appropriate length. The best way I have found to do this is with Xuron Hard Wire Cutters (#2193; xuron.com). These cutters have a concave blade shape and sharp blades, which minimizes splintering when cutting the carbon fiber. They are well worth the small investment.
These wire cutters from Xuron are perfect for cutting small-diameter carbon-fiber and fiberglass rods without splintering.
What to Do: The first step is to clean one end of the rod with isopropyl or denatured alcohol and allow it to dry. Next, spray a shot of kicker on the end of the rod. Fill the barrel of a clevis with CA glue. Then, quickly slide the clevis onto the end of the rod and hold it steady until the CA cures. I like to give it a minute or so to really set and then I give the clevis a firm pull test.
Attach the glued clevis to either your servo horn or the control horn, whichever is least accessible. Connect a loose clevis to the more accessible horn. Make sure that your servo trims and subtrims are centered and that the control surface is firmly held in its neutral position.
After gluing a clevis to one end of the rod, center the servo and control surface to measure the length of rod you will need.
Position the pushrod above the loose clevis and mark where you will make your cut. For clevises that have a blind hole in the barrel, (the Great Planes clevises here have a through hole) make sure you know the location of the bottom of the hole.
Fill the barrel of the second clevis with medium CA.
Cut the rod to length using the Xuron cutters and clean the end with alcohol. Dry-fit the rod into the loose clevis, making sure to center the servo and the control surface. When you are satisfied that everything lines up adequately, remove the rod from the loose clevis. Fill the clevis barrel with CA. Slide the rod into the barrel again and center the servo and control surface. Spray the glue joint with kicker and allow it to cure. After a final pull test of both clevises, the pushrod is complete.
Variations: The standard clevises used in the previous example are ideal for setups where the pushrod aligns perfectly, or nearly so, with the control horn. There may be instances, however, where you need the pushrod to be a bit off-axis. In these cases, a ball link will work well. There are two basic types of ball links that can be used: the snap-on ball link and swivel ball link. Both types provide tight, no-slop connections at the cost of a little more friction than a standard clevis.
This swivel ball link works well in situations where you need zero slop or the pushrod must be off axis with the control horn.
Snap-on ball links use a ball stud on the horn side. They have little slop and offer a wide range of motion.
The snap-on-type ball link uses a studded metal ball on the control/servo horn. The ball is threaded into position and secured with a nut on the backside. A nylon female socket attaches to the pushrod. After the socket is pressed into place over the ball, it provides a wide range of unobstructed motion. The snap-on ball links shown in the photos are from Great Planes.
Swivel ball links have the ball embedded in the nylon rod end. A small bolt runs through a hole in the ball to secure the link to the control servo/horn. Many ball link sets, such as the Du-Bro swivel ball link set I used (part # 2135-Y; dubro.com), also include a tapered spacer to give the ball a greater range.
The process for building a pushrod with ball links is the same as with clevises. However, in the samples I used, there is a difference worth noting. In both cases, the rod was a tighter fit on the ball links than with the clevises. Instead of filling the barrel of these rod ends with medium CA glue, I first positioned them on the rod. I then wicked thin CA into the joint and allowed it to cure. Whatever rod ends you choose, use thin Zap CA for those that fit the rod snugly and medium Zap for those with a little slop.
If the rod end is a tight fit on the carbon fiber, it is a good idea to use thin CA when the rod is in place. Allow it to wick into the joint and use kicker if necessary.
I know that some of you will balk at creating pushrods with a fixed length. I was timid about that for a short while, but I soon embraced the simplicity of this approach. There is, however, an alternative for those who prefer to retain adjustability. You can glue a threaded brass coupler to one end (or both) of the pushrod. The clevis or ball link can then be threaded onto the coupler.
Insert the rod into the barrel of the second clevis and spray the glue joint with kicker. The pushrod is now complete, but be sure to pull-test it when the CA cures.
If you want to retain some adjustability in the length of the pushrod, glue a brass 2-56 coupler to one or both ends.
Because of the stiff nature of carbon-fiber rods, even long pushrods won’t require bracing. There are no absolutes, so use your best judgment. You may also want to try fiberglass rod. It is not quite as stiff as carbon fiber but is inexpensive. I usually purchase it from Goodwinds (goodwinds.com). Whenever I make a bulk purchase of various carbon-fiber bits for my foamie projects, I add a few 1/16-diameter rods of carbon fiber and fiberglass.
The simple pushrods described in this article are ideal for outfitting all types of park flyers, especially scratch-built projects. Whether you are looking to avoid rusty pushrods or just need a lightweight and rigid solution, this method could be what you’re looking for. Give it a try.
