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  1. #21
    Build cheap, crash cheap varg's Avatar
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    May 2017
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    Palm Beach County, FL
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    150
    Incredible.

    Built: Dyke Delta Mini, X-31 EDF, 56" Custom Sportster V2, FT Mini Mustang (big power!), A6M2 Zero (speed wing), KFm4 swappable flying wing, FT 3D, Cubly Stick, Baby Bugatti, Profile KFm4 FT 3D
    Bought: Durafly Excalibur

    Member of the cramming planes into a small car squad

  2. #22
    Toothpick glider kid foamtest's Avatar
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    Jul 2017
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    North East Ohio
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    215
    I'm definitely subscribing to this thread!
    There isn't anything a little packing tape and hot glue can't fix.

    Maker of toothpick glider and staple plane.

    Mystery link I bet you won't click it

  3. #23
    Pieliker96's Avatar
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    Jun 2016
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    Illinois
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    78
    3rd build log, covering the general construction of the wings and mid-fuse.


  4. #24
    Pieliker96's Avatar
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    Jun 2016
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    Illinois
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    78
    As I was planning out the wiring, I realized that I would have to have a way to transport over 5000W of power from the batteries to the ESCs. I plan to have one main wiring run that runs the length of the fuselage, and will be drawing a maximum of 320 amps at 16.8 volts through it. I have a spool of copper single-conductor 12 gauge wire that I intend to use, and I know that I will have to use multiple runs. The total distance from the batteries to the ESCs will be around 6 feet, although depending on final battery placement this number may decrease.

    Is there a generally accepted method to find the approximate cross-section or wire gauge that is needed for a specific current and voltage?

    Another thing I'm considering is the electrical interference with the lengths of wire that I'm dealing with. I've seen recommendations over on RCGroups to put some beefy capacitors right by the ESCs in order to stablilize the voltage, but I've also seen posts saying that this doesn't really matter.

    Thanks in advance, Pieliker96

  5. #25
    Jetman Mid7night's Avatar
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    Apr 2014
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    So Cal
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    1,070
    I'm close to the same stage on my build - setting up major wiring - and based on my experience from the C-17, I would HIGHLY recommend extending the SIGNAL wires from the ESCs to the EDFs, NOT the power wires from the batteries to the ESCs. The phase-signal wires are slightly smaller gauge, since there are 3 of them, so you can use 14 or even 16 gauge wire instead of 12 (depending on the length). Also, by extending the phase wires you don't have to mess with the power/capacitor issues on the battery side.

    I am still going to have a SHORT extension on the battery side of me ESCs, but I'm talking like 6-inches or less. And for that I will be using 10 or 12 gauge wire.

    For the C-17 I was running only four 50mm EDFs, for a total max possible current of 160A. Since that's not a crazy amount of current, I paralleled all the ESCs down to one XT90 battery connection, which plugged into my single 6000mAh 4S Graphene battery.

    For my XB-70, however; I plan on using one 5000mAh 4S for EACH 70mm EDF (each run thru an 85A ESC) - if each EDF pulls 70A, that's 420A! The power involved here is too great to bus down to a SINGLE battery connection. So each motor/ESC pair will get their own individual battery connection for power. The Rx controls will still be Y'ed down to one or two throttle inputs, but the power will be separate.

    I HIGHLY recommend you consider doing the same, for safety reasons, but I respect your build is your call.
    Champions are not those who never fail, but those who never quit. ~ Dr. Ed Cole

    Projects:

    XB-70 VALKYRIE - F-4 Phantom II - A-4 Skyhawk - Baby Bugatti
    F-5 Tiger II - C-17 Globemaster III - Folkerts SK3 Racer - ANGRY BEE!

  6. #26
    Pieliker96's Avatar
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    Jun 2016
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    Illinois
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    78
    Much thanks. I still don't know where the battery placement will end up being, so I'm running around 2 feet of battery extension and then 4 feet of motor leads. This will allow me to put the batteries inside the fuselage or the bomb bay for balancing purposes, as I still haven't quite figured out where the CG should end up.

  7. #27
    Pieliker96's Avatar
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    Jun 2016
    Location
    Illinois
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    78
    Parts have been coming in from my 5 orders to various websites last week. Everything is here now except my order from Hobbyking's China warehouse (my gear struts, nose retract unit, and some other stuff). I've just come to expect slow budget shipping from overseas at this point. I got back from boarding school to open the fan units today.

    Click image for larger version. 

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    The reverse fan housings and blades are in the back. I'll be replacing the stock housings with these for two of the fans to eliminate any problems caused by rotational torque, as well as helping handling during engine-out scenarios. I know that EDFs generally don't have that much notable p-factor as they take a long time to spool up from a standstill, but based on my experience with the 6-foot model, I'm not taking eny chances.

    Click image for larger version. 

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    I'll set up a thrust test stand tomorrow morning and get to work finding the optimal intake and exhaust geometry for static thrust. I'm not expecting these units to produce their advertised 1500g at full throttle, but we'll see.
    Last edited by Pieliker96; 01-13-2018 at 03:30 AM.

  8. #28
    Pieliker96's Avatar
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    Jun 2016
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    Illinois
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    78
    Just finished the first thrust test of one of the fans, and holy cow do they have some power! The batteries were at a total of 16.5 volts, meaning that the rotor was spinning at over 45,000 RPM. The tests stand still slid a little despite the twelve pounds of barbells and batteries holding it down. Total thrust produced was 1.6kg, 100g more than the manufacturer stated (although these batteries were close to fully charged). The exhaust jet attempted to rip one of my unfinished airframes off of its storage spot on the wall during a runup to quarter throttle. Assuming that thrust drops 10% with ducting (some of which can be taken back with thrust tube design), I'll have a thrust-to-weight of over 1.5 and should be able to cruise at quarter throttle. I could've easily gotten by with just two EDFs, although being able to pull something like this vertical and have it climb like a fighter jet (or rocket, for that matter) should be well worth the extra cost.

    Last edited by Pieliker96; 01-14-2018 at 08:08 PM.

  9. #29
    Ray K Ray K's Avatar
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    Oct 2017
    Location
    Houston, TX
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    80
    Quote Originally Posted by Pieliker96 View Post
    Another thing I'm considering is the electrical interference with the lengths of wire that I'm dealing with. I've seen recommendations over on RCGroups to put some beefy capacitors right by the ESCs in order to stablilize the voltage, but I've also seen posts saying that this doesn't really matter.Thanks in advance, Pieliker96
    If you're worried about EMI, I can tell you from my days as an MSEE with NASA that we handled interference by twisting the power wires together. Called them "twisted pairs", and they usually did a fair job of keeping EMI to a minimum. If you have a large enough ground plane, attaching the negative lead of larger capacitors to that ground, with the positive lead soldered to the positive power wire will drain power spikes and spurious signals to the ground. Caps should be on the order of 5 microfarads or so, each, with one for each power wire.

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