Converting a KO vantage Esprit II stick transmitter to 2.4 Ghz using the FrSky "hack" module.

Why convert?

The Spektrum 2.4 ghz system is by far the most popular amongst racers in the UK.
However, for those of us that choose a stick transmitter, the choice is limited, and the KO module upgrade is now becoming scarce, as well as expensive.
Recently, I became aware of a number of extremely low cost 2.4 ghz transmitters based around chinese chipsets.
I tried one, but found it to be functional, but very poor quality. understandably at the price.
There are also a number of "hack" modules. Small self contained RF modules which need to be fed a voltage, and a PPM signal from the transmitter.
These link into the transmitter electrics after all of the signal processing has taken place, so preserve, model memories, end points adjustments, and all of the other cool computerised stuff your transmitter can do.
The best transmitters to upgrade are those which already have a RF module design, either externally with a removable module, or internally, where the RF circuit board is seperate and recognisable. In these cases, it is relatively easy to identify the PPM signal output required to feed to the hack module.
With other, (cheaper), transmitters, such the enry level 27mhz AM kits, it can be far harder to find the required PPM signal output. An effort which will normally require an oscilloscope. Of all the hack modules available, I finally came down to two choices, both around the £10 price with receivers being about the same.
i.e. A complete upgrade to 2.4 Ghz for circa £20 (TWENTY) UK Pounds.

• Corona 2.4Ghz DIY Module Only (DSSS) CT8Z
• Frsky 2.4Ghz Conversion ( Hack ) Module V8HT

Of these two, I chose the Frsky, because...

• It has great reviews, some even suggesting better performance than Spektrum.
• The Corona system seems to have a problem with intermittent glitching.
• The Frsky system has excellent "reboot" times, to reaquire the signal if lost.
• It has a wider range of aceptable input voltages.
• It is more tolerant of a wider range of PPM signal voltages.
• It has built in protection on the signal line, (should you be silly enough to connect it to a +ve voltage rail by mistake.)
• It can deal with positive PPM encoding (Sanwa/JR), as well as negative PPM encoding, (Futaba/KO)

Fitting it into a KO stick transmitter

The KO Vantage Esprit is a transmitter which is designed as module based.
The Module slides in from the bottom, so does not lend itself to a straight replacement with the hack module, as there is nowhere to mount the aerial or the bind button.
However, being module based does give us an advantage in that the PPM, and voltage rails must be identifiable as the interface wires between module and transmitter main circuit board.
Here I must Pay tribute to the work done by Damien Gibbs, who published a home-brew spektrum upgrade for the KO some years ago, from which this information is drawn.
You can see in the picture where I have simply pushed the bare wires from the module into the socket, for testing.
It all worked first time, just with the wires pushed in, so it was time to figure out where to mount all the hardware.

The Antennae

I already have a hole in the top of the transmitter where the telescoping 40mhz aerial went.
Of course, the 2.4 Ghz antennae won't just fit in.
The aerial mount can be removed from the transmitter by undoing two locating screws.
From the inside, you can now carefully un a 10mm drill through, to widen the hole. This should provide just enough clearance to push the FrSky antennae through the hole far enough that it can fold down.
At this point, it should be an interference fit, (very tight), in the hole, and require no glue to hold it in place. If it is a bit loose, then using something like PTFE Plumbers tape will ensure that the antenae is replaceable when you break it. (Whereas gluing with hot glue or epoxy is a non reversible process.)

The LED

Once I had the back off of the transmitter, I removed the original aerial board, thinking I might replace the whole board with the hack module. This proved to be harder than the final solution, but it did allow access to the KO LED.
A slight tug, and it came free from it's hole. Measuring the LED on the module daughter board showed it to be the same diameter as the existing KO LED.
I placed it into the hole, and it stayed there.

The bind button

To get to the bind plug, I needed to drill a hole through from the front to allow a paper clip or similar to be inserted to operate the bind button.
Measuring the distance between the LED and the Bind button put the location of the hole as straight through the N in "Racing"
I started the hole with a lexan hole reamer, then drilled through with a 2mm drill.
Now the LED is just a push fit, so if you get too vigorous pushing on the bind button with your paper clip, you'll push the daughterboard away from the locating hole.
I considered glueing it in, but in the spirit of reversibility, I came up with another solution.
Note the two screws holding the trim ratchets in place. By carefully removing these screws, one at a time, it should be possible to fix something in place to hold the back of the daughter board steady.
I used a piece of lexan, with a pencil eraser glued to it with double sided tape.
The rubber eraser should be 6mm high, when stuck to the lexan.

The module

The module is so small it can be tucked up behind where you have placed the daughter board.
As I had an older type KO, with the voltmeter, I was able to locate it with a bit of double sided tape.

Finishing off

Now all that's left is to solder the wires to the pads, rather than just poke them into the socket.
This provides a better connection, and also allows the KO module case to be reinserted into the bottom of the transmitter to keep it looking profesional and tidy.
Remember to remove the circuit board from the plastic KO module case before reinserting, because even without a crystal or aerial, it may transmit interference on the 40Mhz band. Also, if left in, it will consume electricity, and reduce the amount of time your transmitter will run.
Here is a picture of the completed job, just before screwing the back on, the module in place, with the wires just gently bent out of the way. note that I have left the original LED in place. You may want to clip it off, or insulate the wires and tape it down to stop it moving about inside the case.

Receiver connections

The receiver connections can be confusing. The numbers marked on the case indicate the signal wire of the channel
In the picture below, the servo wire, Channel 1, is visible plugged into the top right 3 pins, with the yellow signal wire to the left.
The ESC wire Channel 2,is visible plugged in below the servo cable, Again with the signal wire to the left corresponding with the number on the case.
Other devices, battery and.or transponder, are plugged into channel 3 or 4 on the right of the receiver.
Note that the position of the signal wire is reversed for Channels 3 and 4, appearing on the rightmost pin.

Binding

Binding follows the same format as most other 2.4ghz systems.

1. Turn the transmitter on while holding down the bind button.
2. Ensure the red LED on the transmitter is flashing.
3. Power up the receiver while holding the bind button.
4. The Receiver LED flashes to indicate bind is successful.
5. Turn of Receiver.
6. Turn off Transmitter.
7. Switch on and use as normal.