Adding Tri-Mode Launch Switch to JR XP-8103
by Tom HoopesThis modification will allow three functions on the CROW (glider mode) switch (left, top, front side) found on the JR XP-8103 transmitter.The three functions include the standard landing mode, camber mode, and the addition of a spring-loaded launch mode that is useful for maximizing the launch of handlaunch gliders (HLG). The pilot holds the spring-loaded switch with the left index finger. Through the use of an uncommitted mixer, a precise amount of "UP" elevator can be introduced during the launch phase and removed at the appropriate time by simply releasing the switch. The switch will default in the landing mode when released but may be pushed rearward into the camber mode if such a setup is programmed in. The modification will not affect the standard functions of the radio for other setups with the exception of reversing the values from 1 to 0 and vice versa in the [Butterfly] menu.
You will need the following materials:
1. Two (2) 4.7K (4700 ohm) 1/4 watt resistors
2. 5" of light gauge insulated wire (#26 - #30)
3. Toggle switch (C&K part number 7207P3YZGE which is a DPDT (on-off-mom)). C&K Sales (800) 635-5936. They will refer you to a local distributor or Rep. Another source for the switch is Digi-Key (1-800-344-4539). They stock a C&K switch that is very close to the one called out above. Their part number is CKN1145-ND that crosses to C&K part number 7207P3YZQE. The switch includes the dress nut (tapered, threaded ring).
4. Soldering iron, solder, wire clippers, Phillips screw driver
5. Enclosed hand drawing of modification details.
PROCEED AT YOUR OWN RISK. IF YOU ARE NOT FAMILIAR WITH ELECTRONIC TERMS AND TECHNIQUES, THEN FIND SOMEONE WHO IS CAPABLE TO DO THE WORK FOR YOU. THE POTENTIAL DANGER IS DAMAGING THE RADIO AND VOIDING THE WARRANTY. YOU ARE ENTIRELY RESPONSIBLE FOR MAKING THE ENCLOSED MODIFICATIONS.
1. Unplug and remove the nicad battery.
2. Unplug and remove the RF module.
3. Remove the six (6) case screws.
4. Carefully separate the rear case half and its associated printed circuit board from the main circuit board by unplugging the 10 pin connector. Set the rear case to the side.
5. Remove the factory BUTTERYFLY switch (top, front, left paddle switch) from the transmitter. Carefully unsolder the green and black wires that attach to the switch.
6. Locate the "Dual Flap/Aileron Trim" (pot #7) knob and associated variable resistor (next to BUTTERFLY switch). There are three leads exiting the potentiometer. As you face the rear of the transmitter and the pot is located on your right, the far left lead on the pot should have a black wire soldered to it. Unsolder the black wire from the pot and solder a 4.7K (4700 ohm) 1/4 watt resistor in series with the black lead, then re-solder the other lead of the resistor to the left pin on the pot.
7. Solder a small length of light gauge wire (#26 - #30) to the junction of the black wire and the 4.7K resistor. The loose end will be soldered to the new switch later.
8. On the same pot (#7) the blue lead on the right connector pin must also be unsoldered and have a 4.7K (4700 ohm) resistor inserted in series.
9. A yellow wire should be soldered on the center pin of pot #7. Add another small length of light gauge wire (#26 - #30) to the junction of the yellow wire and the center pin of pot #7. The loose end will be soldered to the new switch later.
10. Thread the lock nut all the way down to the base of the switch. Insert the new switch into the transmitter housing making sure that the spring-loaded position is toward the front of the transmitter. Install the tapered bezel and tighten finger tight. Verify that the switch and the mounting hardware are correct, since they are hard to change or adjust once the final wiring is complete. If the mounting hardware is correct, make a small black dot on the rear of the switch housing (so that it is facing the rear of the transmitter) it will serve as a visual reference when soldering the new wires and re-inserting the switch. Remove the tapered bezel and remove the switch.
11. While facing the rear of the transmitter, hold the switch with the black dot facing you. Solder the green wire (removed from the stock switch in an earlier step) to the center lug on the right side of the switch. Solder the black wire (removed from the stock switch) to the front lug (closest to face of transmitter), right side of the switch.
12. Cut the two wire pigtails that were added in steps #7 & #9 to an appropriate length to reach the left connection lugs on the switch when it is in position.
13. Solder one of these wires (either one) to the center lug on the left side of the switch. Solder the other wire to the rear lug (closest to you) on the left side of the switch.
14. Inspect your work and make sure that there are no shorts or solder splashes.
15. Insert the switch into the mounting hole with the black dot facing you. Tighten the tapered bezel by using a small open-end box wrench or small crescent on the two flats located on either side of the bezel. Do not over-tighten.
16. Plug the 10 pin connector from the rear case printed circuit board into the main printed circuit board.
17. Carefully slide the two case halves together and verify that they are aligned and seated properly.
18. Insert and tight all six (6) case screws.
19. Re-insert the RF module.
20. Re-insert the nicad battery and its cover.
21. Turn on the radio and verify that everything is working as before.
22. Under the WING TYPE, set the Dual Flap to Active. This will display all of the pot statuses in the regular menu.
23. In the main menu, scroll down to the [D/FLAP T.] screen. Disable the pots (or at least pot #7).
24. Scroll to the next screen down [Butterfly] and verify that when the new BUTTERFLY switch is toggled from the center position to the rear lock position, the cursor arrow will move from 1 to 0. This is opposite of the action of the standard switch, so just remember that all settings under 1 on the Butterfly screen are landing mode and all settings under 0 on the Butterfly screen are camber mode. By reversing the landing and camber position, the pilot can have immediate access to landing mode once the preset launch switch is released. Without reversing the camber and landing switch direction, the pilot would have to release the preset launch mode switch then push it to the most rearward position, one more potential step that may be accidentally overlooked. Enabling the landing stick for proportional camber is available when the switch is in the most rearward position.
25. Let's enable a mixer to give some "UP" elevator when the new Butterfly switch is pulled forward in the spring-loaded launch mode. We'll use Mix3 for this example. Set the master to AUX2 and the slave to ELEV. Press the SELECT key so that the cursor arrow moves to the RATE: row. Verify that pot #7's knob is set just to the right of the center of pot ("0"). Pull the switch forward into the spring loaded launch mode and the small cursor arrow to the right of RATE: should move to the lower value position. Move to SW: and set to ON. Move back up to the lower value position and enter a number ~ +15. This number is the amount of "UP" elevator applied when in launch mode.
26. If you move up to the [SERVO] screen, you can see the elevator movement when activating launch mode switch.
27. You're done.
