Multi function electronic control - RC Groups
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Sep 03, 2009, 03:27 PM
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Build Log

Multi function electronic control

This is a build log for a multi function, electronic, control system for control line (U control) models.
I will take you through the building and setting up of the system and give step by step instructions to enable anyone who can solder a wire to build a 6 function proportional control system.

The Concept.

Basically the system is based around an R/C transmitter and receiver. The difference here is that we don’t use the RF (radio frequency) section of the R/C. Instead we send signals directly from the TX encoder section, mounted in a control line handle, via insulated control line wires to an RX decoder in the model. After that it’s the same as R/C, Servos, battery, switch etc.

In an R/C model with 6 channels you will have

With a control line model the elevators are taken care of by the bellcrank and we don't need aileron or rudder so with a 6 channel system you can have throttle and 5 additional functions. flaps, gear, bomb drop, lights, whatever takes your fancy and 5 of the six are proportional control, not just switches.

So what Tx and Rx?

I have been working on this system for some time now and have tried many makes and models of Tx and Rx. Some work , some don’t. The Tx that works is the Futaba challenger 5 or 6 channel Tx and the Rx that works is the old style Sanwa 6 channel Rx .

As both these are now considered old fashioned and ‘not computer’ they are readily available and cheap to buy Typically 10 – 15 GBP for a Tx and 5GBP for an Rx.

If you want to try and convert an old set you have kicking about go ahead but this build log is for those particular items as I know they work. As I am taking the pictures of this build I am building ‘live’ so at the end of the build we will have a working system.

Ok so you found an old Challenger and you’re looking for the Sanwa Rx. A word of warning. The one you want is the OLD style in the black case as in the pic NOT the blue cased version, this won’t work.
Ok so you found an old style Sanwa Rx NOW we are ready. First thing to do is to paint the case with red and white paint as shown. This is because the Sanwa servo leads, battery leads are the OPPOSITE polarity to JR, Futaba, Hitec etc that is the red wire is towards the outside of the Rx case not in the middle. You can, of course use Sanwa (old style) servos etc but if you want to use Futaba etc you MUST swap the red and black wires in ALL plugs for servos and battery.

In the next Post we’ll start on the Rx
Last edited by Ospreyman; Sep 04, 2009 at 01:31 AM.
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Sep 03, 2009, 03:39 PM
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Ok, First start by taking the circuit board out of its case, cut off the antenna wire and open out the hole in thse case it passed through to take 2 wires.

You will need a futaba shielded plug ( the bit with the pins in) with about 3" of lead, bare the ends of the red and black wires by about 3mm and tin with solder, the white wire can be peeled back to the plug and cut off.

Now, with a fine soldering iron bit carefully solder the black and red wires onto the back of the circuit board at the locations shown. The black wire solders to the neg rail at the plug block and the red wire solders to the point on the board where the signal enters the decoder. I know where this point is so don't worry. If you solder the wires as shown the thing will work. When I made these connections I tested the Rx with a handle/Tx that I have already built.

Now run the wires out through the enlarged hole in the end of the case and re assemble the RX. Now that wasn't so bad was it? ( the picture can be zoomed to ensure you hit the right spots with the wires)
Last edited by Ospreyman; Sep 03, 2009 at 04:23 PM.
Sep 03, 2009, 03:40 PM
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Now we need to address the handle/TX.

Start by removing all the screws at the back of thre Tx case and remove the back (See pic)Now remove all the screws holding the main board to the case and lift it forward. Simply unplug the 'daughter' board from the main and discard.

Now the interesting bit. Start removing all the pots, switches etc from the case. this won't take long. First carefully cut all the cable ties so you can see the wood for the trees. don't cut any wires at this stage. Just undo the screws that hold the throttle, aileron, rudder and elevator trims to the case , leave the pots attached to the trim wheels as these form the operating wheels for the handle/Tx .The other pots atached to the sticks can be removed from the gymbals completely.

When you have released all the pots etc from the case identify the power lead, this will be an orange, red and black wire twisted together and soldered to a fitting near the 'daughter' board plug, cut these wires as long as possible , this will allow you to remove the loom from the case. Now strip out the orange as it won't be used.

Now temporarily solder a 9v (pp3) type battery connector to the red and black power wires and protect with heatshrink. Because the Tx wont be supplying RF it will run happily for MONTHS on a PP3 battery .

Take a futaba PLUG lead with about 5" of wire, bare and tin the last 1/8" of the red and black wires and cut off the white. Now solder the black wire to the point on the back of the circuit board as shown in the picture. On the other side of the board the black battery wire is connected. Now study the photo and solder the red wire to the point shown, this is where the signal is extracted from the board before the RF section. The plug will eventually exit the casing and be attached to your control lines.

Ok take a well earned break and we'll continue separating the worms.
Last edited by Ospreyman; Oct 29, 2009 at 04:02 AM.
Sep 03, 2009, 04:40 PM
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Identify the trim pot with white and blue wire attached to the outside two lugs. There are a pot, rate swith and rate trimmer attached to this trim pot. Separate them as in the picture just leaving the blue and white attached to the trim pot .Locate the twisted brown and green pair attached to that set. unravel the green from the brown and then twist the brown with the white and blue.cut off the green. Now solder the brown wire to the centre lug on the trim pot. This is now one of the six channels prepared.
Sep 03, 2009, 05:00 PM
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It's so much easier to catch up with you through the Internet.

I am reading this thread with great interest. I was particularly keen to get throttle control. My current electric control liner uses a JMP timer for the motor run which of course has to be preset before launch. With your setup here I would have more controllable functions than I know what to do with. The more the merrier I guess.
Sep 03, 2009, 05:12 PM
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Now locate the trim,pot etc group that are connected to the main board by a yellow/green twisted pair and a purple/red twisted pair tease them away from the rest of the wiring to make it easier to work on. Leave the yellow/ green twisted pair attatched to the outer lugs on the trim pot but remove the other yellow and green leading to the other pot. Remove the purple from the centre lug of the trim pot .

Un-ravel the red/purple twisted pair and cut off the purple. Now twist the red with the yellow/green pair and solder the red to the centre lug on the trim pot, between the yellow and green. Hey presto, Thats channel 2 done
Sep 03, 2009, 05:20 PM
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Hi Eric,
Glad you like the thread. perhaps you could tell me if it makes sense to you. The trouble is I've made so many of these things that I can do it in my sleep. The thing is I know what I'm doing but am I putting it across Ok. I am trying to proof read as I go to see if there are any errors. As you can see from the time of posts I am doing this 'live' and it really doesn't take that long. The trouble with timers is that they are just that- full throttle for a set time. With a proportional throttle the possibilities are really opened up.

Sep 03, 2009, 05:56 PM
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On to channel 3 now.

Identify the group that has a red and brown twisted pair terminating at the outer lugs on the trim pot. The red and black leading to a small pot can be disconnected from the trim pot lugs. The white wire leading from the board to the centre lug on the trim pot can be removed but make sure you leave the green that it is twisted with alone, this goes to the retract switch. Identify the yellow wire that is twisted with the red and black to the small pot, this one comes from the back of the board. Cut the yellow about 5" long and twist with the red/brown twisted pair. Now solder the yellow to the centre lug on the trim pot. You must be getting used to this by now.
Sep 03, 2009, 06:20 PM
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Nearly there Guys Channel 4

Locate the final trim pot,. This one has a grey/purple twisted pair and orange/grey twisted pair. Remove the purple and grey leading from the trim pot to the small pot, leaving a purple and grey leading from the trim pot to the board. Disconnect the grey from the centre lug of the trim pot, un-ravel from the orange, cut the grey and twist the orange with the purple and grey to the trim pot . Solder the grey to the centre lug.

Just to tidy things up locate the retract switch ( orange/grey twisted pair and a single green) unsolder the green from the switch,twist it with the others and resolder, thats neater eh?

The other pot is for the flaps/whatever and the knob will be put back on later
Ok, so now you should have something resembling the last picture. As I mentioned before I have being doing this LIVE and have tested each channel before starting the next, so I know it works. In the next post we will connect everything up and test the system but now, I gotta sleep
Sep 03, 2009, 06:42 PM
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Here are a few models I am currently flying with electronic control

HP Heyford nats winner 2007 and 2008
bomb drop
ventral turret

VQ models harvard

HP Harrow
84" span
Last edited by Ospreyman; Sep 04, 2009 at 01:32 AM.
Sep 03, 2009, 07:01 PM
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WildManWillie's Avatar

would using the lines as an antenna and then the reciver picking it up be better than insulating the lines?

Sep 04, 2009, 01:28 AM
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Dont think so wildman. the whole point here is to get away from the radio side. no crystal , no interfernce no transmitter control later in the log i'll be making up a set of lines, really easy.
Sep 04, 2009, 04:32 AM
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v22chap's Avatar
this is great stuff ,,,destroy a perfectly good rc radio and still have control ,,, my type of stuff
Sep 04, 2009, 09:08 AM
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Thanks for the comment V22chap The great thing is that even if a Tx or Rx does not work for radio its probably the rf section thats kaput and we discard that anyway
Last edited by Ospreyman; Sep 04, 2009 at 09:28 AM.
Sep 04, 2009, 10:07 AM
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Testing Time!!!!!

To test the system and to find out which trim pot works which channel we will need to connect the Tx to the Rx. When we come to use the system this connection between the two will be done by using insulated control lines, more of this later.

If you used two servo extension leads to get the plugs for the Tx and Rx, rake down the bin ( trash can)and find the other ends, the sockets. with these soldered together we will have a short link which will do the same job as the control lines on the field.

WARNING before you go any further make sure that all futaba servo leads and battery leads re and black wires are reversed. If you don't reverse them on the servos you will fry the servos and if you don't reverse them on the battery you will fry the RX Not maybe, WILL.

To reverse the leads on futaba or jr etc carefully lift the locking tab on the socket and ease out the wire with socket on the end, then replace them in the opposite position be careful with battery leads not to let them touch.

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