Simplified Twin Control Harness (for The Kraken)

by craftydan | May 25, 2015 | (8) Posted in How To

I recently got a Kraken SBK -- man, that's a lot of foamboard -- and while watching the video, two thoughts occured to me:

  1. 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!
  2. 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?


  1. High current/voltage to the ESC
  2. Low current/voltage from the ESC's UBEC to the RX and Servos
  3. Signals from RX to all ESCs/servos 
If we divide the pods into "master"  (has the RX) and "slave" (doesn't have the RX) with each side having it's own battery power, #1 is covered -- the battery connects directly to it's ESC.  If we get the RX and servos to recieve power from the ESC closest to them, #2 is covered -- we'll need to buld something that shares these, so it' gets lumped into the harnes. Which leaves #3  . . . no way around it, for that we need to run wires.


How many wires you ask?  Three:


  1.  ESC signal
  2.  servo signal
  3.  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)



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.


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:





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!


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.



WhiskeyJack on June 21, 2015
Gee Dan, I don't about that. It seems to me that if you use 2 servo extensions, 1 from each ESC, remove the red pin from the slave, plug both into a "Y" harness and the harness into the throttle channel, would you not get the same thing? Just ask'in....WJ.
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craftydan on June 22, 2015
Close, but not quite.

First off you'd need to run two extensions, this allows you to run only one. On a twin, two instead of one this isn't much, but a third or 4th nacelle this would get . . . messy. This scales up.

Second, with a long servo run, particularly with thin wire, you risk the chance of brownout on the servo -- slim but still there. In this case the servo get's UBEC power directly from the nearest source.

In either case it does away with the large battery harness that's unnecessary, IMO.

It does run the complication of having trouble with fuselage servos on a twin -- they either need to be powered from a flight pack in the fuse or one of the nacelles will have to share power -- it will need two extensions to move power to the fuse.

It's not an end-all-be-all solution, but it's easy to build -- there's a lot of steps for clarity's sake, but it really isn't that hard or time consuming. In specific situations, like the kraken, it simplifies things . . .

. . . and it also acts as an intermediate step to a MUCH more complicated project, which will come later.
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grether2000 on June 24, 2015
Nice article.
I wanted to point out one disadvantage to this setup is the motors could have different voltage from the two batteries. This could be a bit of an issue with anything rudderless.
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craftydan on June 24, 2015
True, assuming you've gotten a significantly weaker or smaller pack on one nacelle, but you could easily run the throttle signals deferentially -- the diagram is already laid out to do that -- assign the mix to the rudder channel control (lookie there, it's not in use on a rudderless plane) then trim it out to taste . . . and as a side benefit you'd have yaw control from the differential thrust -- After all who *doesn't* want to put their wing in and out of controlled flat spins!

. . . or you could build asymmetrically and use the thrust differential to compensate. Not a very efficient way to go (and trim would be a headache) but it would look cool!
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planebouncer on June 25, 2015
Great idea, craftydan! :D I built an OV-10 with two ESCs and two LiPos and I cut a wire and spliced just to do the same thing you did. I just love it when there's a 'formal' way of doing things, not slap-together. It makes it so much easier to move things from a mangled plane to the next generation, also to adapt to another twin model. No fear of shorts or plugging errors. I don't tend to go for differential thrust, though
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Kurt0326 on June 28, 2015
Interesting. But this works if you have room for a battery in each pod. Or are you suggesting that the batteries be hung out in the open like the ft beginner series? I definitely see the potential, just worried about achieving proper cg on the rest of the ft twin aircraft with the batteries far forward of the cg. I suppose if you have fpv gear weighting the nose down it would work. Aw now look, I reasoned it out.
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craftydan on June 28, 2015
Also keep in mind that unlike a pusher versa, the motors on the Kraken are forward of the CG, helping the balance instead of fighting against it. They also have a sizable landing gear right next to it, so mounting to the bottom or side of the pod isn't unreasonable, if you wanted it on the outside.

Looking at the pictures on the Kraken build article/video, they mounted the single big pack right on the CG, which means you'd mount the separate battery packs on the back end of the power pod. that assumes, of course you're going to use the same size/weight motor, but sliding the pack a little farther aft wont' be the same problem as sliding it forward beyond the firewall.
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Simplified Twin Control Harness (for The Kraken)