Build a 5/6ch pistol Tx for $120
 

I've started a new thread for the actual build, following on from my thread here:http://www.rccrawler.com/forum/electronics/190457-6ch-pistol-tx-cheap-alternative.html

I was hoping to get this build done for under $100. You may be able to hit this target if you get lucky on eBay, but $120 should be possible without too much trouble.

The aim is to build a pistol Tx using the electronics from a cheap 2.4GHz airplane stick Tx and the case from a cheap 27MHz AM pistol Tx, plus a handful of resistors, potentiometers and switches. There's also a small transistor and diode circuit that makes the low-voltage warning LED work properly, but this is optional.

The pistol case used was found by another forum member (thanks, Carlos"thumbsup") and it's the perfect size for the job. You could use any pistol Tx you like, as we only need the case, battery box, trigger and wheel, plus the power switch and charging jack if they can be re-used.

I'll be building a 5ch Tx. 2 channels are used for steering, with a rotary switch to select front only, 4ws, crab 4ws and rear only, all using the steering wheel.
I'll also fit two 3-position switches. I'll be using them for diff locks, but they could be used for a dig and a winch.

The basic build can be adapted for any combination of switches and channels to suit your needs.
There's very little styrene work involved in this build, and the wiring is pretty straightforward


The 6ch Tx I'm using is a low-cost computer 2.4GHz unit, sold under the brand names "Turborix", HobbyKing" and "FlySky". It has 3 programmable mixes. It's available direct from the Far East for around $30 plus postage.
Because it's a basic Tx, it doesn't have a display. You have to connect it to a PC to program it. The lack of a display isn't a problem, and it makes the build a lot cheaper and easier! It comes with software, PC link cable, Rx and bind plug.

The pistol Tx is branded "HSP". Again, it's from the Far East, at around $20 shipped. I found both Txs on eBay.

For some reason I've lost the pictures of the Txs before I started work on them, but here's a pic of the Turborix in a partially-dismantled state:
http://i572.photobucket.com/albums/s...9/IMGP1316.jpg

There are a couple of mods you can do to the PCB (see post 2). If you decide to fit these mods, do them and make sure that they work before you strip the Tx.



First job is to strip the 6ch Tx, after you've tested it to make sure everything works. We need the main PCB, RF module and antenna, and the pots and control knobs.

Main PCB:
http://i572.photobucket.com/albums/s...9/IMGP1344.jpg
RF module and antenna:
http://i572.photobucket.com/albums/s...9/IMGP1343.jpg

Be very careful when removing the RF module, as the coaxial cable is delicate. I cut a slot in the case to get the cable out:
http://i572.photobucket.com/albums/s...9/IMGP1349.jpg


Make a note of what all the cables connect to, as some aren't labelled. All the cables (except the antenna cable) can be snipped off from the switches and pots.

OPTIONAL MODIFICATIONS:

The Turborix Tx runs on 8x AA cells, but it can be modified to use just 4x AA cells. In 8-cell standard form, there are 2 voltage regulators which drop the voltage down to 5v. If these regulators are bypassed, the Tx works perfectly well on 4 cells.

You just need to add 2 wires, one to bypass each regulator:
http://i572.photobucket.com/albums/s...9/IMGP1346.jpg
http://i572.photobucket.com/albums/s...9/IMGP1347.jpg

If you decide to modify the PCB to work with 4 cells, don't forget to modify the battery box! If you connect 8 cells, you'll let the magic smoke out.

The loose wire in the second picture is used to connect the low-voltage warning LED. This needs another modification, as it's designed to work with the original 12v power supply. There are 2 ways of doing this mod. The first works 100%, but involves making a simple transistor and zener diode circuit:
http://i572.photobucket.com/albums/s...999/BatMon.jpg
This circuit was designed and drawn by "mis-b" on RC Groups. Link to original:http://www.rcgroups.com/forums/showt...967207&page=66

EDIT: In some installations, it may be necessary to increase the value of the 10K resistor below the zener diode to 15K, as there might not be enough adjustment available to make the LED change colour at the correct voltage.

When made up, the circuit looks like this:
http://i572.photobucket.com/albums/s...9/IMGP1329.jpg
The parts cost about $2.


The other option is to add a single red LED. This alters the switching point of the tri-colour warning LED. If you use this method, the LED goes from green to orange after a few minutes, then stays orange for hours before switching to red:
http://i572.photobucket.com/albums/s...999/T6_LED.jpg
Note that the LED doesn't have to show, it's just soldered to the PCB.


I'll be fitting the transistor circuit.

You also need to remove a few parts from the PCB - the warning LED, the trim pots and the charge socket.

The LED will be fitted to the front of the case. I added a servo plug to make fitting easier, and a spacer made from 3mm styrene, hot-glued to the LED:
http://i572.photobucket.com/albums/s...9/IMGP1342.jpg

I soldered a matching plug onto the PCB with a short length of servo cable.

That completes the PCB mods

MODIFYING THE PISTOL Tx CASE

Strip everything from the pistol Tx. The only parts we need are the case, the throttle and steering assemblies, the power input board with switch and the battery box.
Unsolder the wires from the pots and put the main PCB in your spares box.

Since I'm going to run the Tx on 4 cells, there's some free space in the battery box. I'm fitting the PC interface PCB and the trim pots in here.

Remove the unused contact strips from the battery box and move the black wire. Cut a hole in the box to allow the PC connector PCB to sit flush with the "bottom" of the box. Glue the PCB in place, using CA to tack it, then epoxy to fix securely:
http://i572.photobucket.com/albums/s...9/IMGP1332.jpg
http://i572.photobucket.com/albums/s...9/IMGP1331.jpg

Modify the power input PCB.
Remove the trim switches, the yellow LED and the 4-pin socket.
Cut out the middle of the PCB to clear the toggle switches that we'll fit later:
http://i572.photobucket.com/albums/s...9/IMGP1362.jpg
http://i572.photobucket.com/albums/s...9/IMGP1361.jpg

I also fitted the power cable from the Turborix to the switch terminal (red wire) and the ground track (black wire).
The wires from the battery box will get soldered on later - red to middle switch terminal, black to the ground track.

The 2 remaining LEDs aren't used, but they will fill the holes in the case.

I'm going to fit 2 toggle switches, so the rectangular holes that were used for the trim switches need opening out with a round file:
http://i572.photobucket.com/albums/s...9/IMGP1334.jpg
http://i572.photobucket.com/albums/s...9/IMGP1336.jpg

The middle LED hole needs enlarging to fit the tri-colour warning LED from the Turborix (5mm).
There was a silver aluminium trim covering this panel. I removed it carefully, as it will be re-fitted later:
http://i572.photobucket.com/albums/s...9/IMGP1360.jpg
I've left it soaking in acetone to strip off the laquer and printing.

On the other side of the wheel, cut off the crystal housing and lips round the trim pot holes on the inside of the case:
http://i572.photobucket.com/albums/s...9/IMGP1333.jpg

I'm going to fit the rotary switch where the crystal went, and the 2 VR pots and knobs from the Turborix to where the trim pots were fitted.

Enlarge the crystal hole with a round file to fit the switch, and fit a styrene disk into each trimpot hole to fit the VR pots:
http://i572.photobucket.com/albums/s...9/IMGP1333.jpg
http://i572.photobucket.com/albums/s...9/IMGP1335.jpg

this is a cool tutorial, but the dx5 is only 99.99. is the goal to have it all in a pistol grip?

Yes - all in a pistol grip. The DX5 doesn't have programmable mixing, so it can't do full 4ws from a single control.

The Turborix main PCB almost fits - it just needs one corner trimming.
The board can be fitted with one screw through an existing hole, and another needs a slot filing in the edge of the board:
http://i572.photobucket.com/albums/s...9/IMGP1351.jpg
http://i572.photobucket.com/albums/s...9/IMGP1350.jpg
It's the top left corner that needs trimming slightly. I just snipped off the edge of the PCB with sidecutters.


To make the PCB more secure, I fitted an extra post. It's made from styrene rod:
http://i572.photobucket.com/albums/s...9/IMGP1352.jpg
A small screw goes through an existing hole on the PCB into the rod.

Now the delicate part - fitting the antenna. On some models, the antenna unscrews from the base, mine didn't. The base almost fits the moulding on top of the pistol case.
http://i572.photobucket.com/albums/s...9/IMGP1354.jpg
I trimmed the bottom "ring" moulded on the front case:
http://i572.photobucket.com/albums/s...9/IMGP1353.jpg
And I cut off the top 2 rings on the rear case:
http://i572.photobucket.com/albums/s...9/IMGP1356.jpg

The antenna base is now glued onto the front case, ensuring that it's square. I used medium CA. Ensure that no glue gets near the coaxial cable, as it moves when the antenna is rotated:
http://i572.photobucket.com/albums/s...9/IMGP1355.jpg

To support the antenna more firmly, I fitted a piece of styrene rod and a couple of scraps of sheet to brace it:
http://i572.photobucket.com/albums/s...9/IMGP1357.jpg
A small screw through the antenna into the rod holds it firmly.
The rear case should slip into place. If it doesn't, trim the top of the moulding where it goes under the antenna base.

The RF PCB needs to be secured. I used another piece of styrene rod and a piece of styrene tube to brace it:
http://i572.photobucket.com/albums/s...9/IMGP1358.jpg
http://i572.photobucket.com/albums/s...9/IMGP1359.jpg


This is as far as I've got with the build, so it might be a few days until I post the next phase - fitting the controls.

Hi Steve, that's a cool work"thumbsup"

I'm waiting for more!!!!:mrgreen:

Steve, you know it is possible, he just have to make a "multisteering switch" like a have PMed you.:mrgreen:

Carlos
But will it work with a wire missing:-P

Do you still have an unmodified HSP Tx? If you do, could you post a picture here - I had camera problems, so I can't post a picture.

:mrgreen:Yes:mrgreen: I corrected the "how to" thread and added the pic I forgot post:oops:

Now I havent, but this week I'm receiving a couple more. Then I'll take a picture and send it to you.

I'm building a new one for me, also whith 4cell mod, "multisteering switch"(w/o mixes), reverse switch, and I thought locate the PC connector the same way......:mrgreen:

Excellent - took me a while to figure out where the missing wire had to go.

Now I would like to know how you will reverse the rear servo when you are controlling both channels with one potentiometer?
When I know that it works, I'll help you with the translation.

"thumbsup"Give me some days to prepare a video to show you how it works. I'll post it in your first thread.

Thanks Steve.

fantastic thread! I will never do this but great thread!

One more thing I've done. The "bind" pushbutton will fit through a hole drilled in the rear case. Measure to the centre of the button from the edges of the front case. Mark these measurements on the rear case and drill a small hole (2mm). Stick a piece of masking tape onto the button, then hold the rear case in position. Mark through the hole onto the tape with a fine-tipped felt pen.

despite my best efforts, I was a couple of millimetres out with my measurements - the pen mark was off-centre on the pushbutton.. Drilling a small hole allows you to correct the error with a small round file, bringing the hole to the right position:
http://i572.photobucket.com/albums/s...9/IMGP1337.jpg

FINISHING THE PCB MODIFICATIONS

I cut down the warning LED PCB that I made earlier:
http://i572.photobucket.com/albums/s...9/IMGP1363.jpg
http://i572.photobucket.com/albums/s...9/IMGP1365.jpg

The schematic for this PCB is earlier in the thread. Simple to make. The components cost less than $2. I found all the components on eBay.
You need:
2x 10K trim pots
2x 10K 1/4 watt resistors
1x 2K2 1/4 watt resistor
1x BC557 transistor
1x 4.7v zener diode
A piece of strip board. mine is 9 strips x 12 holes.

There are 2 track cuts on the back of the board.

I'm going to fit this PCB directly onto the main PCB:
http://i572.photobucket.com/albums/s...9/IMGP1367.jpg

There's a wire jumper in the way, so I put a couple of pieces of electrical tape over the jumper.

The PCB is just stuck on with 2 strips of servo tape and some hot glue:
http://i572.photobucket.com/albums/s...9/IMGP1368.jpg

The wires are tacked to the PCB with hot glue, then routed round to the back of the PCB.

The wires are connected to the back side of the PCB. There's also a link that shorts out the place where the power switch used to be (just to the right of the power connector), and the 2 links that were added earlier to short out the voltage regulators for the "4-cell mod":
http://i572.photobucket.com/albums/s...9/IMGP1369.jpg
http://i572.photobucket.com/albums/s...9/IMGP1371.jpg
The points where the blue wires solder on are quite small, so you can't really use normal stranded wire. I used some wire stripped from cat5 cable, the stuff that's used for wiring the structured cabling in computer networks. It's single strand and easy to work with. The join in the blue wires is where the stranded cable from the LED PCB meets the single strand wire.

That's all the modifications done, except for fitting the switches, pots and resistors.

Switch knob arrived today, so I've started putting it together.
http://i572.photobucket.com/albums/s...9/IMGP1373.jpg
http://i572.photobucket.com/albums/s...9/IMGP1378.jpg
http://i572.photobucket.com/albums/s...9/IMGP1381.jpg

With help from forum member "meao" (thanks again, Carlos), I've figured out how to get all 6 channels working, by moving the rear steering servo from ch4 to ch6. This saves a "physical" channel - channels 5 and 6 need a mix to make them work.
This means that we can have all the 4ws options from one rotary switch, plus up to 3 channels for 2-position, 3-position or proportional (pot) control.

I think that I'll be replacing one of the unused pots above the rotary switch with a 3-position toggle switch for a dig.
The other 2 toggle switches will be 2-position for my Creeper's diff locks.

I had a set of schematics drawn up, but the change to the rotary steering switch means I'll have to do them again. I hope to start the wiring soon - more info will follow when I get a couple of free hours.

Great Job Steve!"thumbsup"
In my next build I'll use the same schematic as you in my 2.2.:mrgreen: Just a couple of differences, all my "free channels"(3+4+5) will be dually actued(pot+toggle switch), cause I'll use it also for the scaler. And, maybe, I won't use "the pair of resistors". I'll put a pot to have another channel working in the scaler(cause I dont need 4ws). I still have to test the "new multisteering switch" you have designed.

On Monday I'll go to the Post Office, the HSP TXs are there waiting for me....
I'll PM you the pics on monday.

Cheers

Carlos

What will you use the ch3,4 & 5 pots for?

In the 2.2 for nothing, but in the scaler for "remote switched leds", 2 speed gear box, dig or front disconection system(Rwd), winch. Also to actuate the "limpiaparabrisas"(I dont know the word:oops:). "Limpiaparabrisas" are that couple of rubber arms that clean the front glass.
Depending on the car I use I would need a pot or a switch, so I build it with all the options. And you can also use the pot as Trim when you are working with toggle switches.

Cheers.

Limpiaparabrisas = windscreen wipers.

Using the pot as a trim makes sense.