UDI-U818A MODIFICATIONS Part 2

3) UPGRADING BATTERIES
The original battery as supplied is a 500 mAh 3.7V Lipo. I upgraded to 600 mAh 3.7V Lipos. I bought them off of Amazon. 5X batteries plus  1X  5-way charger cable for about $20.00. 

5 - Way Charger Cable 

The new batteries fit in the same space as the old 500 mAh batteries. However, they are 600 mAh batteries. About 10-20% longer flight time. 

I bought them because flying for 5 minutes and then going home to charge the battery for an hour was not my idea of fun. I carry 20+ batteries. The new batteries are the correct size, but some of the 500 mAh ones that I had fit loose. 

I solved that by adding several turn of electricians black plastic tape of both ends. Snug fit now. This keeps the thinner batteries from rattling. The jacks on the ends of all the batteries are indexed to fit one way only. 

The index mark is a slot and ridge arrangement. I had a time figuring it out. So I painted a silver dot on each connectors side. Now I just line up the dots and pop the connectors together quickly.

The wires going into the connectors themselves are somewhat fragile. So I put a small tab of GEL superglue the two wires just as the enter the red plastic jack or socket to reinforce where the wires enter the jack.

Use Gel, only! Regular superglue is too thin and will wick its way in the metal part of the jack or plug. The I slipped a 5/8" long piece of heat shrink tubing ( 3/16" dia. ) on the battery plug and a slightly larger piece over the motherboard jack to reinforce plugs wires. 

I use a 5" hemostat to stretch all the tubing slightly, for an easy fit bu putting the nose of the hemostat into the tubing and pulling the handles apart. I inserted the battery plug into a jack and aligned everything and heat shrunk it all.

After heat shrinking with a cigarette lighter, I painted on the silver alignment dots. I used Testor's silver paint as it was handy and contrast well against the red of the connectors.

4) TRANSMITTER MOD

I added a 2.4 GHZ removable antenna. Bought it here:

2.4 GHZ Antenna on Amazon.com

I got the necessary SMA female RF coax connector also from Amazon.com. I bought 5x connectors for $2.48 plus - free S&H! Here's link:

SMA Connectors

The UDI transmitter uses a small piece of stranded wire (unshielded) as an stub antenna soldered directly to the transmitter board. It's exactly 31.25 mm ( a little over and inch) in length and is used as a "quarter-wave" antenna.

Antennas for 2.4GHZ  are cut to exact length to resonate at that frequency for maximum reception. If you add wire to the antenna or cut the antenna you could decrease the correct maximum distance of the receiver.

I found it necessary to use a piece of mini coax to connect the router's antenna plug to the connector. Then I soldered the center lead of the coax to the place were the original wire stub antenna was connected. 

One thing left to do. The coax has a shield. The shield is a braided wire wrapped on a teflon insulator surrounding the center lead which carries the signal to the antenna.

The antenna is about 5" long but only the tip is active. Again, 31.25 mm in length. I needed a ground for the coax, otherwise the antenna length would effectively be about 7 inches long. And reception/transmission would be terrible.

I soldered a small 8" piece ( the blue wire ) of stranded wire to the bottom of the coax's shielding being careful NOT to allow the shield to touch anything. 

I also soldered another wire (the black wire ) from the SMA jack. Then I soldered both ends of the blue and black wires to a ground point on the motherboard. See picture in Part 3.