ABCs of Ball Links

Oct 17, 2013 1 Comment by

Improvements in RC helicopter design and performance have resulted in the almost universal use of the ball link in all modern helicopter control systems. Most major manufacturers make their own ball links to their specifications, with their name, logo or other such mark on the body of the link. Although these links are slightly different, they still have the same basic design features and require the same good techniques for proper use.

The survival of your helicopter depends on ball links. Properly fitting links result in a better flying model.

This Revolution control rod setup tool makes it easy to fabricate pushrods of equal length.

To start the link on the pushrod wire, chamfer the hole slightly with a hobby knife.

Save your fingers with a clevis tool to ease the installation of the ball links. This one is from Heli-Max.

Ball link sizing tools, such as this one from Mavrikk, help you get the perfect fit to the ball.

In general, the lettering or markings on the link face away from the ball. Check your instructions to be sure.

You can size the link by carefully squeezing the link while it’s on the ball. Do not use excessive force or you can break the link.

Improvements in RC helicopter design and performance have resulted in the almost universal use of the ball link in all modern helicopter control systems. Most major manufacturers make their own ball links to their specifications, with their name, logo or other such mark on the body of the link. Although these links are slightly different, they still have the same basic design features and require the same good techniques for proper use.

THE PARTS
The Ball Link. Sometimes called just a ìlink,î it’s often made of plastic or composite material and it’s designed to screw onto a metal rod at one end and connect to the control ball on the other. Two ball links, attached to each end of a metal rod, make up a pushrod.

The Pushrods. Connecting the servo arm to the helicopter, pushrods transfer both the motion and power of the servo to the flight control system. Some helicopters use a single pushrod for control, while others use two pushrods connected to opposite sides of the servo arm to obtain both push and pull control as the servo arm or wheel rotates. Although a push-pull control system does balance the loads to each side of the servo output shaft, the biggest advantage of this design is the added control redundancy if one pushrod fails.

Pushrods are designed to handle the loads placed on a specific control system. Small, light pushrods are used on the small electric helicopters, while larger, heavy-duty pushrods are used on large nitro and gas helicopters. But no matter what the size, they all look the same and have two ball links connected by a metal rod. A standard helicopter kit will have a variety of metal rods, with sufficient ball links to make the needed pushrods.

MAKING A CONNECTION
Making pushrods certainly isn’t rocket science, but as with most things there are always some techniques that make the job a little easier and result in a better connection.

  •  If the ball link is a tight fit on the metal rod, it can be difficult to get started. However, you can enlarge the end of the ball link by rotating the point of a sharp X-Acto knife in the hole.
  •  A ball link driver is a handy tool that slips over the end of the link and allows the link to be turned as if you’re using a screwdriver. I get a ball link started on each end of the control rod, and then hold one link with a pair of pliers and screw the remaining link on with the driver. Because of the increasing drag of both links on the rod, they will be screwed in place at the same time.
  •  The instructions will provide the required length of the pushrod, measured either from the end of the links or from the ball centers. Whatever method you use, make sure that each link is screwed on the rod the same distance. You can tell this by the amount of threads showing on the rod.

INSTALLATION TIPS
Although installing a pushrod may seem to be straightforward, these techniques will help you make a solid connection and avoid potential pitfalls.

Orientation. Although ball links come in all shapes and sizes, almost all are designed to snap on the ball in one direction. The instructions should tell you how to determine what side of the link faces the ball, but if there aren’t any instructions, I have found that any type of lettering or marking should face the outside of the ball. And this is logical, as the proper orientation of the link can be seen during preflight, maintenance, etc.

Tools. You can snap the links on and off the ball by hand, but several ball link tools on the market make this job easier. I use HeliProz Mavrikk Ball Link Pliers, which are designed to both install and remove the link from the ball. They have a long, curved tip that easily reaches almost any ball.

Reduce drag. As each link is snapped onto its respective ball, move the link around and check for excessive drag between the link and the ball. This drag could be caused by a tight design fit or just a slight deformation of the link as it cools from the manufacturing process. Whatever the cause, this drag will take power from the servo and also produce a twitchy control of the helicopter as the link breaks free and moves to a different position on the ball. There are three basic techniques I use to reduce or eliminate this ball link drag:

  1. The quickest and easiest technique is to squeeze the sides of the link with pliers while it’s on the ball. This slightly deforms the link and reduces any internal stress to the material, providing a smoother fit to the ball.
  2. Use a ball-sizing tool to remove some of the material inside the hole. I use the Mavrikk Pro Ball Link Sizing Tool. This tool is adjustable, so you can only remove a slight amount of the link before refitting to the ball. Remember, it’s always better to remove a small amount of material than to remove too much and ruin the ball link.
  3. The final technique is to rub a little petroleum jelly on the ball and link. This will act as a lubricant, and after a flight or two the link will wear into the ball for a perfect fit.

PRO TIPS & TRICKS
The people at HeliProz help their customers with all parts of the helicopter, including ball links, on a daily basis. I talked to Todd at HeliProz and asked if he had anything to add. He said that some of his customers are using thread-lock on the rod ends, but this appears to be eating into the link and eventually weakens it. You don’t need thread-lock (I’ve never seen a ball link unscrew from the rod). Another point T
odd made was that the ball could wear out before the link, and if this happens, both the ball and the link should be replaced. HeliProz also offers a socket-head ball with stud that uses a hex driver for installation and has a shoulder to provide a little clearance between the link and the servo arm or bell crank. If the balls do not have a shoulder, you can make one by placing an extra nut between the ball and the bellcrank, etc.

MAINTENANCE AND REPAIR

Ball link pliers are available from a variety of sources. This should be one of the modeler’s first specialty tool purchases.

Balls and ball links will wear out over time and must be replaced during regular helicopter maintenance. I keep a good supply of spare links on hand (my favorites are from Miniature Aircraft and Rocket City). Miniature Aircraft links are extremely durable and slop-free, and the Rocket City links can be installed on either side. This is a real plus when you need to make very fine adjustments. Because ball links are used in very high-stress areas, they can be easily damaged during a crash. Not only is a good visual inspection needed, but also push and pull on the link to make sure it’s well attached to the ball. Replace the ball and link if there is any doubt. Good maintenance habits like these will pay big dividends in a slop-free helicopter for many years.

Helicopters

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One Response to “ABCs of Ball Links”

  1. Jeff Armbruster says:

    How do you disconnect the link without bending the push rod. Is there a tool that can help?

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