Construction Manual
Radio Install
I use all JR 281 digital servos so that is what you will see here. They are not the smallest servos out there so anything else should only be easier! Lots of batteries will work but I make up a pack from 289 mah, NiMH batteries that are the same size as the old 110 mah nicads. I make it up in a T configuration so that it will go as far foreward as possible. XP-4’s are designed to balance with the chosen gear with little or no extra weight. This, of course, depends on your build. Add an extra 10 grams to the tail and you will add 2 or 3 times that much to the nose to compensate. Pretty soon a glider that was designed to weigh 10-10.5 oz’s or so becomes 12 oz’s. Pictured below are the battery configuration and a finished radio instilation with the pictured battery, 2 JR 281 servos and a HiTec Electron 6 still in the case. If you carefully place and center the servos you will be able to easily remove either the receiver or battery.
As you can see from the picture to achieve this the servos are pretty much centered in the fuse and kept tight together. I also remove the mounting lugs from the servos to be able to gain that space. Place one of the servos in the fuse and it will become apparent that the end with the control horn needs to be raised for clearance. This is accomplished by glueing two small blocks, off center in the bottom of the fuse. One advantage of this is it allows the front servo wire to be routed underneath the servos to keep it out of the way.
You can start with either servo but, I like to start with the front one so the wire can be routed underneath both back the center of the fuse. NOTE: For a right hand thrower the right pushrod will be the rudder and for a Left hand thrower the left pushrod will be the rudder. It doesn’t matter which is front or which is rear. Place the servo into position and mark the pushrod housing so that just enough of it is removed to allow for servo arm travel and trim housing. Prepare the end of the carbon rod by attaching a small Z bend. A piece of roughly .030 or .035 wire is excellent for the Z bend. NOTE: A straight pin is a good source for this small wire. I like to sand the portion of the wire that will attach to the carbon rod and the rod to insure good adhesion. I like to wrap the joint with kevlar thread or even heavy sewing thread and wick on some this CA. This can also be done with heat shrink tubing but I have had one come apart with heat shrink and have never had a failure when they are wrapped. I also like to drill my own hole in the servo horn with a piece of the wire that has been snipped off to insure a snug, slop free fit. Place the servo into position and center to insure enough of the pushrod housing has been removed to allow travel. Mark the position. Lift servo and put on some goop where the bottom of the case will contact the fuse and where it rests on the spacer. Place it into position and make sure you are satisfied. You can lock the servo into place with a few drops of thick CA so that you can keep working while the goop sets. Repeat with the rear servo (servo arm to the opposite side of the fuse) You should now have something that looks like the left picture below.
As you can see from the right picture above the receiver will now go in right behind the servos with the plugs easily accessable. The battery will slide in the front and is held in place on my planes with a small EPP block between it and the front servo to keep it from shifting.
The pushrods are now VERY close to the sides of the fuse. Put a drop of goop between the fuse sides and the pushrod near the end of the housing on each side to secure.