I recently got a Kraken SBK -- man, that's a lot of foamboard -- and while watching the video, two thoughts occured to me:
- Why are they using one BIG battery instead of two medium sized batteries? I've got tons of 3S 2200's. Who doesn't?!? It's a nearly universal 3S battery size!
- That power and servo harness is a lot of wire with a lot of fishing!
I thought about it for a while and there's NO good reason not to run each wing half on it's own and bridge the gap with only the servo extensions . . . then I realized just how simple it can be!
What if you could run the connection between the power pods with only a single cable run?!?
Wiring always comes down to routing what you need to where you need it . . . so what do we need?
- High current/voltage to the ESC
- Low current/voltage from the ESC's UBEC to the RX and Servos
- Signals from RX to all ESCs/servos
How many wires you ask? Three:
- ESC signal
- servo signal
- ground refernce
GREAT! There are three wires in every servo extension, so al we have to do is build that harness in the dotted-box that will share power to the servo and route the signals to the other side . . . but out of what?
We'll build one out of two 1x3 right angle header pins, solder on a servo pig-tail, mold a strain relief. We'll then run the servo extension with a break in the middle so we can assemble it in the wing halves as we build then connect as we finish the wing.
Parts you'll need:
- electronics for the slave side
- two servo extensions (one for each wing half)
- a servo pigtail with a male connector (I harvested this one from a dead servo)
- a right angle pin headder row (at least 6 pins to make 2x 3 pin right angle headers)
- Genral build materials (tape, solder, DTFB scraps, hot glue, heat shrink tube)
BUILD THE HARNESS:
Lots of steps but they're all simple and easy . . . except for the waiting. Waiting is never easy.
Take the esc and servo wire and tape them together with the ground wire of both on one side:
From the right angle headder pins, cut two sets of 3 right angle pins:
On one 1x3 header, trim the bend off an end pin, and on the other 1x3 header, trim the bend off a middle pin to get these:
Insert the one missing the middle in one side, faceing away from the other plug:
Insert the other one next to it with the pins facing the same direction, then press down until both are sitting flush with each other (the tape will give a little to allow the connectors to twist):
Clamp and tin the pins. The pins touching will now be solderd together:
Strip/Twist/Tin the servo pigtail, then solder the ground wire on the pigtail (darkest wire) to the pair of end pins soldered together:
Solder the middle wire to the lone uncut end pin:
Solder the last wire to the lone cut end pin. Middle pins are solderd together, but NOT solderd to the pigtail.
Soldered connector (removed from the servo and ESC):
Good! So we've got a harness that shares power between the ESC and servo (#2), and passes the signal down the line to the RX in the Master pod (#3) . . . but that's a lot of exposed and unprotected wire. Let's build a molded strain relief to seal it all up and give the wres some strength.
MOLD A STRAIN RELIEF:
Place a strip of Packing tape over two scrap layers of DTFB (two becasue the pins are longer than one layer)
Press Pins through the tape into the DTFB
Pins protected and back ready for "moulded plug"
Lift the wires and inject a glob of hot glue under them, into the pins:
bend the wires back into the glue:
put a glob of glue over and around the pins:
Make sure everything is coverd with excess:
NOW GO WAIT.
Take 5 . . . or 10. Go watch a FT episode.
It takes a while for a glob this size to set and you want it hard before you proceed.
Now that that's over with, trim away the excess from the three non-wire sides
And peal the excess glue away (you'll probably cut the tape and the paper will peal away from the foam. This is perfectly fine)
Clean connector still stuck in the foam:
Peal it away from the foam (again you'll probably end up pealing the paper away. Again, that's fine)
trim the excess that's easy to get and you've got the completed connector :)
Plug it in, being sure to match the ground wires on the servo/ESC plugs with the ground wire on your harness.
All set! now for the rest of the harness!
PUT IT ALL TOGETHER:
As you build the wing, go ahead and run a servo extension from the power-pod hole inside the spar as you install it, down to the middle edge of the wing half. When you join the halves, connect the pigtail to the first extension and connect the two extensions together, ensuring polarity matches:
You'll be left with a male end on the master side,and a female end on the slave side. plug the pigtale end of the harness into the slave side, and on the master side, use a knife to remove the middle pin from the male plug:
cut a piece of shrink tube to cover the middle pin:
To ensure the pin is coeverd flush to the end, position the heat shrink then shrink only the very end (slide the heat shrink into place if you have to)
Then shrink the whole tube, starting from the end
Since the red wire is now a signal, plug it into the RX on the signal row at the right channel -- check the other end to see if that pin is the servo or motor to know which channel it goes in. Plug the other connector into the correct channel, and the ground connection for the two will be automatically made.
All set! That's the simplified harness, letting you run only a single wire from one side to the other and power each side with it's own smaller batery.
The beauty of this is, this harness will improve many multiengine planes. Cruiser? Guine? B-17? As long as each pod has it's own power battery, you'll only need one servo wire from each pod have full control of a motor and servo sitting at that pod.