MSJ Assembly Details

  MSJ Instructions
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Micro Switch-Jack

Miniature Power Switch / Charging Jack for RC sailplanes

The Micro Switch-Jack is  designed for low current applications. Its maximum current rating is a conservative 1 ampere at 6vdc. This is a continuous carry load rating. It is more than sufficient for two small servos in our typical Hand Launched Gliders. The jack can handle the rough and tumble environment of the HLG with ease. Total jack weight: 1.3 grams! Enjoy!

 Parts List:

·           Jack with 0.016” washer, panel nut. Terminals marked with wiring codes in red ink
·           One plug with red anodized aluminum handle
·           12” x 1/8” red ribbon
·           1.125”L x 0.125”W 3M^® polyolefin heat shrink tubing
·           This 2 page instruction sheet
·           Schematic and assembly diagram sheet
·           (Optional) Connectors soldered and heat-shrinked to plug and jack

 Installation into fuselage:

The Micro Switch-Jack can be installed in any fuselage with a wall thickness up to 0.080”. If you are not concerned with flush mounting the jack, then just create a clean hole in the fuselage that is 3/16” diameter, and insert the threaded jack bushing though the hole, fastening it with the included panel nut and thin washer. A lock washer or Loctite^® can be used to secure the nut more permanently. Mine is tightened by pliars onto a glass fuse and has not come loose yet, and I crash regularly. Before drilling the hole, decide what side of the fuselage will be best for the installation of the Switch-Jack. I am right handed, and prefer the ribbon on the left side of the fuse, so I will see it if I’m launching with receiver power off.

 Flush mounting the Micro Switch-Jacks: An 11/64” diameter hole is drilled in a 1/16” plywood mounting plate. Cut or sand the mounting plate to size to fit your installation. Allow approx.   ¼” of plywood to remain all around the jack hole for gluing. Two #2 wood screws can be used to attach the wood mounting plate to a thin FG or wood fuselage. You may glue the mounting plate to the inside of the fuselage, screw it on, or both. Sand to shape the surface of the plate that will attach to the fuselage so it matches the curvature of the fuselage wall, if there is any. To prepare the inside of a fiberglass fuselage for gluing, J.P. suggested these steps: clean the area with alcohol several times to ensure a clean, chemical free surface. Then sand the surface so that there is no shine left. Clean once more with alcohol, then use Goop^® or 5 minute epoxy to attach the mounting plate to the FG fuselage. You may use epoxy, professional wood glue such as Titebond^®, or a good quality thin CA (ZAP^® or BalsaUSA^® CA) to attach the plate to a wooden fuselage.  Once the plate is installed, carefully drill or cut away material from the fuselage for the jack hole. A small, flat file is perfect for this. Twist the point against the fuse like a drill to start your hole, then enlarge the hole until it is just right (3/16”). Carefully screw the jack into the plate, keeping it perpendicular until the threads grab. The jack opening should be flush with the outer surface of the fuselage. Unscrew and remove the jack for electrical connections, etc. 

For final flush-mount installation, screw the nut onto the bushing of the jack, and screw the jack assembly with connected wiring harness into the wood with pliers against the jack bushing (metal band). Tighten the nut against the wood mounting plate. A drop of Loctite^®, if desired, will hold the nut in place permanently. Sometimes the bushing is pretty tight in the plywood, and the backing nut or loctite may not be necessary. 

In a thicker wooden fuselage up to 0.125” thick, install the jack directly into the fuselage itself. Carefully drill the required 11/64” hole in the fuselage by starting with a small bit like 1/16” and working your way up to 11/64” in small increments. Hold the fuselage securely and use a drill press at high speed if available. The twist file method (above) will also work here. Screw the jack into the wood to create threads in the wood. If fuselage is balsa, the threads can be hardened with CA if desired, but this is usually not necessary on 1/8” thick, hard balsa. The jack’s threaded bushing is 0.125” in length, so no backing nut is needed here. The outer lip of the plug hole on the jack MUST be flush to the outer surface of the fuselage. The base of the plug must make contact with this lip to ensure operation of the switch.

Electrical connections:

Solder your electrical leads directly to the jack’s terminals. While the Micro Switch-Jack is tough, it cannot withstand the continuous heat of a large soldering iron. Soldering specification is 485F for 5-7 seconds. A cheap Radio Shack 40 watt iron is 600F - way too hot. Use a PC board soldering iron (a small 15 watt electronics iron with a needle tip is perfect.) Only hold the tip to the terminal for 5 seconds at a time. If you fail to make a joint in that time, let the jack terminal cool before you try again. Use a clip-on heat sink above the terminals to further protect the jack. Use a good quality electronics solder with rosin core. 1/32” thickness is perfect for the MSJ but 1/16” thickness will work too. Note that the Micro Switch-Jack guarantee is void if the jack is heat damaged. The terminals on the jack are marked with red ink. ONE DOT is the battery and receiver negative terminal, TWO DOTS is the battery positive terminal, and THREE DOTS is the receiver positive terminal. Refer to the schematic diagrams for circuit details. Please call Hollyday Designs for assistance if you wish.

 We use 6” servo extensions for the jack’s wiring harnesses. Cut the extension 2” from the battery connector end (big connector) and leave 4” for the receiver connection. Remove the signal wire from the receiver end and cut it off of the battery connector. Before soldering, separate the positive and negative conductors of the battery wire and receiver wire about 1” from the ends. Strip ¼” of insulation off of the ends of the leads. Twist the battery and receiver negative conductors together. Twist the battery positive and receiver positive conductor strands separately. Pre-tin the copper leads. Trim the leads to 1/8” length. Pre-tin each terminal on the jack. Slip a 1/4” to 3/8” long piece of 1/8” diameter heat shrink tubing onto each lead. Hold the negative lead of the harness against the proper jack terminal (the middle terminal, with ONE DOT) and apply the soldering iron to heat up the terminal. The lead and terminal will swim in the molten solder and you will have a nice joint with minimal heat. Repeat for the two positive leads. When you are finished soldering, shrink the heat shrink tubing onto the three soldered terminals with a heat gun.

CAUTION!! Soldering irons and heat guns are extremely dangerous! They can destroy your parts and cause serious injury. Please be very careful with these tools. Ask an experienced modeler or a parent for help if you need it.

 We use a servo pigtail for the plug connection. Trim the pigtail to 2-3” length. Strip, twist and tin the leads, then trim to 1/8” length. A small piece of heat shrink will hold the conductors together if they separate completely when stripping. Use a needle tip on your iron and clean it well before starting. Make the positive connection to the charging plug first. Apply heat to the outside of the very small positive terminal “cup” and fill it to the rim with solder (1/32” solder wire is easier). Be NEAT and careful! Heat the cup again and insert the tinned positive lead into the molten solder. Connect the positive lead to the inside of the tall terminal using the same “pre-tinned lead” and “solder blob on the terminal” technique described previously for the jack terminals.

Final Steps

Tie the red ribbon around the tall lead of the plug, and use a micro drop of thin CA to lock it. Don’t skip the ribbon, you will regret it when you are looking through the grass for a $5 plug and those batteries are wasting away! Carefully crimp the two metal fingers around the ribbon and wires to provide strain relief.

Connect your charger to the plug. Insert the plug into the jack. Connect your Micro Switch-Jack to the receiver and battery and plug the servos in. Your charging light should come on indicating proper charging connections and polarity. Turn on your transmitter, then pull out the plug. Hopefully you won’t see any sparks fly or your street lights dim - Haha! Your servos should come alive and wiggle to tell you how happy they are with their new Micro Switch-Jack. If not, check your connections against the schematic for errors. Install the jack assembly into your plane, charge your batteries and GO FLY!

Other Notes

Dirt is the only achilles heel of the Micro Switch-Jack since it does not have wiped contacts like sliding switches do. Protect it from sawdust in the shop, and dirt on the field. The switching contacts are easily accessable at the rear of the jack. Clean periodically with contact cleaner sprayed onto a wooden toothpick. Protect the rear of the jack (inside the fuselage) from damage and debris. Don’t use tape to seal it in, the adhesive will get on the switch contacts and attract dirt. Just keep it dry and  clean.

Good Luck!