Making servo linkages
Wing servo pushrods
I prefer to use the lengths of piano wire which have been threaded at one end to take a metal clevice. Cut these to length and at the control surface end either solder a threaded adapter to take a second clevice, create a z bend or use a ball and socket connector (my preferred choice)
Making a ball socket joint
Most model store sell the plastic ball and socket joints. However the balls are usually "bolt in place" and have nothing more than a hole to take a bolt. With the length of wire that was cut off from the pushrod, solder this into the hole on the ball. Be careful with the soldering to keep the ball "clean" from solder. Trim and file (or wet and dry) the wire protruding from the end of the ball, so that the socket can be fitted into place. Now cut the wire to length and epoxy or CAinto the control surface. Now you have a fitting clevice at the servo and a easy removable fixed connection at the control surface.
Make sure you choose the right pushrod for your application. Be careful of running conducting pushrods (including carbon rods) down the length of the fuselage particularly if you intend to run the Rx aerial down the fuz. This may cause interference problems or radio glitches. In the past, when I have used carbon pushrods, I have insulated the rods using tape ensuring that they are not rubbing against each other, and also run the aerial down the outside of the fuselage.
Make sure you choose the right pushrod for your application. Be careful of running conducting pushrods (including carbon rods) down the length of the fuselage particularly if you intend to run the Rx aerial down the fuz. This may cause interference problems or radio glitches. In the past, when I have used carbon pushrods, I have insulated the rods using tape ensuring that they are not rubbing against each other, and also run the aerial down the outside of the fuselage.
Fuselage pushrods
If you are building a HLG, it is possible to use a smaller pushrods. Planes where a lot of load will be exerted on the elevator linkage, such as an F3B model, slope racer, F3J or duration plane, a strong choice is a must
Music Wire
Music wire is nice and stiff, but must have a housing with no harsh curves to prevent binding. When installing, it is best to tack the housing at one end and then let the housing hang down the boom so it follows a naturally straight or slightly arched path. The only disadvantage with the music wire pushrods is that the diameter of the music wire must be smaller than the id of the housing (also to prevent binding) which builds-in an inherent amount of slop. Removing this slop is difficult since it is caused by the wire flexing in the "free space" within the housing. It is generally so little, that you may not want to worry about it.
If you want to minimize it, you can make the housing "porpoise" it's way down the fuselage. The arcs must be shallow and you must lightly tack and test the movement before securely bonding things in place. You must walk the edge of too tight and too loose.
If you want to minimize it, you can make the housing "porpoise" it's way down the fuselage. The arcs must be shallow and you must lightly tack and test the movement before securely bonding things in place. You must walk the edge of too tight and too loose.
Carbon Rods
For some models, like V-tails, a 5mm carbon tube that is "free floating" in the fuselage works very well. Generally one or two guides of an aluminium tube along the way (or a bulkhead with slightly oversized holes in it) will keep the pushrod from flexing and causing a "soft" linkage. To attach your clevises at either end, I have used hot glue to fix threaded piano wire links into the centre of the carbon rods. Then if you need to adjust the lengths all you need to do is get out the heat gun.
Making your linkages strong and slop free
Creating a linkage that's both free from slop and free from binding can be a challenge. Yet, the investment of time necessary to make a linkage perfect is worth it in terms of the handling and safety of your model.
Every R/C sailplane has linkages, some long and some short, they can all have slop in them which at times can adversely affect the precision of your centering or stick input or worse, can cause high speed flutter and possibly catastrophic failure.
Every R/C sailplane has linkages, some long and some short, they can all have slop in them which at times can adversely affect the precision of your centering or stick input or worse, can cause high speed flutter and possibly catastrophic failure.
Removing slop from threaded clevises and z-bends
A trick for taking slop out of clevises: seems crazy, but works perfectly. Put thick CA right where the clevis meets the horn, kick it, let it sit for a minute and then manually deflect the surface thereby breaking the glue joint free. What you end-up with is a perfectly solid bearing of CA that removes all the slop from your clevis.
The same trick can be used on metal threaded clevises. First, be sure the clevis is where it needs to be, then simply put a small drop of thick CA at the joint where the threads leave the clevis and kick it.
You can also use the lock nuts that come with the clevis to prevent the thread slop, but you need to periodically tighten them. If you rarely need to adjust the clevis or if it's out of reach, just CA it.
This method also works on Z-bends, but you have to be very careful that you don't over glue it.
Just a small drop right where the rod passes through the horn or servo arm (or both) does the trick. On all of these CA applications, you may need to repeat the process if the CA gets brittle and crumbles out of position.
Alternatively:
The method that has always worked for me, especially with metal clevises to plastic horns, is this: usually you will find that the clevis pin is just too big to go through the hole in a new plastic horn. So place the pin in the hole in the horn as best you can (it will be under tension), then simply touch your hot soldering iron onto the fixed end of the pin. The pin will get hot & melt its way through the horn. Take the iron off the pin as soon as it starts to move. 'Voila' slop free, a free moving link.
The same trick can be used on metal threaded clevises. First, be sure the clevis is where it needs to be, then simply put a small drop of thick CA at the joint where the threads leave the clevis and kick it.
You can also use the lock nuts that come with the clevis to prevent the thread slop, but you need to periodically tighten them. If you rarely need to adjust the clevis or if it's out of reach, just CA it.
This method also works on Z-bends, but you have to be very careful that you don't over glue it.
Just a small drop right where the rod passes through the horn or servo arm (or both) does the trick. On all of these CA applications, you may need to repeat the process if the CA gets brittle and crumbles out of position.
Alternatively:
The method that has always worked for me, especially with metal clevises to plastic horns, is this: usually you will find that the clevis pin is just too big to go through the hole in a new plastic horn. So place the pin in the hole in the horn as best you can (it will be under tension), then simply touch your hot soldering iron onto the fixed end of the pin. The pin will get hot & melt its way through the horn. Take the iron off the pin as soon as it starts to move. 'Voila' slop free, a free moving link.