This one (no longer in stock but maybe you can find the equivalent) https://www.amazon.com/gp/product/B07R4SDSP8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Is what I have been using, crank it up to 450 degrees and it works great.
Since I’ve essentially logged the construction of my X4 here and I’ve applied to register it I’m thinking this is a public version of a maintenance log for my aircraft. Therefore I will log the maintenance. Back in May the magic smoke came out of the electronics. Voltage regulator quit regulating. I’ve received new parts from Paul and Zach. Took a while but they did solid support sending out all updated parts: dc-dc converter is a beefier unit,
the new hub includes overvoltage protection,
the new controller board has the updated batch 5/6 programming including altitude above field and outside air temp. I did have to remove the buzzer and pot (the part you push to go up) from the old controller board and solder it onto the new board. Used a much smaller soldering iron for that. Sorry I didn’t get a pic. Too excited.
Here’s the new dc-dc, and hub installed.
The new controller is set for right hand whereas the original was left. Haven’t decided to reset it for left hand or reroute the cable to right hand. I seem to be ambidextrous for throttles. Flew it Wed with the readout upside down in my left hand.
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Looking good!
You can change the screen orientation by plugging in you throttle via USB and visiting Redirecting to https://config.openppg.com/configurators/x4/ in Chrome.
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Done! Man that was easy. Selected the 6S battery limits and metric temp & alt while I was there. Spent a few seconds looking for the “apply” or “save” button then noticed it was changing the settings in real time like flipping switches. Very nice!
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Registered!
C-ILXQ
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Break in the flying season. 
Pulled out all my velcro battery straps and started working on a new idea. I want room for eight. I want to keep all the wires short. I think they’ll fit if they’re stacked four across and two deep. Made a shelf.
I’m using the 15/16" holes just below centre to take the weight. They’re spaced really nice. These plastic tubes are for proof of concept. I’ll use aluminum of maybe CF.
They support the shelf which will be an aluminum or CF channel. Not sure if I want to tape the batteries together into a single brick. It’s a lot of weight to handle.
Batteries clear the motor arms and props nicely. I have a piece of white foam in the gap to show it.
The motor arm swing bolts are in perfect position to anchor straps holding the “brick” against the frame. Just velcro for checking the concept, will switch to some hold down straps.
It seems to be pretty solid. I’ve put it on. The higher cg is ok. With four more batteries on a bottom shelf it’ll be lower again.
Upper battery mount created. I made a couple of aluminum tubes from 1" tube stock. These are miles down to fit through the holes but I left one end too big. They fit through from front but don’t push through.
Flew it with the four across the top batteries and everything was fine. I noted the vibration may be slightly higher. Perhaps due to the weight of the batteries connected solidly to the frame through the mounting tubes or perhaps something else (props are fine), or perhaps I was just paying more attention to it.
I’m going to tape the set together with strapping tape into a single brick with the shelf included. This will reduce setup time and steps at the field and will be safer I think.
Next it to figure out how to hang a lower tray for four more.
Speaking of four more I need to get them shipped to Canada and there’s no solution for my address on the order form so waiting to hear from OpenPPG with an option there.
Battery mount refinements
The battery straps coming through the motor arm mounts were getting pinched when the unit was folded. Since my X4 is folded when stored and transported this would have eventually cut the straps. I rerouted them over the arm mounts
Left side - Pinching!
Right side - routed safely
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Net hooks
I also have changed the net cord hooking. I originally was simply hooking them together behind the leg hinge. It worked but this is better.
I knotted the cord as needed to get things pulling tight. The loops are made from knotted paracord coming through extra slots in the frame. I shaved the CF to round the edges where the cord rides on them.
Updated pic of the batteries mounted and plugged in.
I decided to tape them into a single brick and to the aluminium shelf. I’ve used double faced tape between the packs and between the packs and the shelf. Then fibreglass reinforced tape to hold the assembly together.
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Part of the reason for the battery mount redo is to get another set of four Bonkas on there. To that end I needed a way to connect them. Rather than a pair of “Y” plugs I decided to add another pair of main power leads to each side.
On the rack and opened up for the new cables.
I’ve connected the negatives. The positives are waiting for ring connectors to bolt then to the switches.
I also opened up the holes to make room for four wires and grommet … On each side.
This is a lot of battery. My wife is skeptical of me running with all this on my back.
They’re currently
being discharged. Weather was good yesterday but I left the net and hoop at home so spent the afternoon kiting my new APCO Hybrid. Now it’s snowing and don’t expect to have flyable weather for at least a week.
Also just wanted to note here that I noticed a 3m bolt missing on the bottom of the leg assembly. 
Replaced it then checked the torque on all the bolts. The bolts on the motor arms were all tight. The bolts on the leg assembly all moved about 1/8 turn to tighten. Of course I’ve pulled the back plate of so those will all be re-tightened. I’ve also noticed a trace of surface rust on all the hex head bolts.
Back plate reinstalled and some grommet cut in to protect the wires where they come through. Through firewall plug mounts would be ideal but this works too. Since each pair of cables are connected at the other end it doesn’t matter which two are used when I fly with two pair of Bonkas.
Two sets of plugs on each side. Total, for sets of plugs.
All eight. Two bricks of four. Four pairs.
Sixteen cables. A lot of wire!
I strapped in and stood up. It’s heavy! Once I got up I found I could walk around and maneuver it ok. Don’t think I’ll be doing any nill wind launches with eight batteries.
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Very nice! Quite a bit of heft, eh? 
Yup. But it feels pretty solid. My only real concern is the total weight of the batteries - 20kgs worth - is entirely supported on those two 1" holes in each of the frame body plates and my aluminum tubes. I’m not planning on doing any acro with this but I do wonder how many G it would take.
Maybe doing some jump squats with it will improve the landing gear strength as well as test the battery mount strength.
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Not sure if I’m doing the right calculation. Maybe an engineer on the site can help. I looked up some tables for strength of aluminum tube. It varies a lot depending on the alloy of course and I’m not sure what I have.
- The weakest, 99% Al tube, has a yield strength of 5000psi ( sorry I’m working on Imperial units here).
- My tubing is 15/16 outside diameter and 1/16 thickness which is a bit more than 0.37 square inches total.
- 5000X0.37 is 1850lbs per tube. Two tubes is 3700lbs total.
Seems like enough.
I’m thinking the carbon fibre will start crushing before the tubing is even deformed.
I’m in the process of wiring my new batch 6 X4. Would you consider 3D printing a spark arrestor knob assembly for me? I’d be happy to pay in advance for your time and costs.
Dorian Olson—seawindpilot
One concern with dual battery mounts is that straps are secure when only using one. First time I attempted to launch with both packs (all 8) mounted - no success, fickle breezes. So I decided to dismount the top pack to make the launch easier. Left the strap for the top set loos and of course it caught a prop. Of the four blades between the two top propellers the blade that was already chipped took the hit. It cracked.
Fortunately I’ve repaired it. I’ve also ordered 2 more props. Could only find the DFDL branded ones on aliexpress.
First landing damage. 
. Came in after a really cold 20 minutes of cruising. The chill must’ve affected my brain. I was thinking the approach seemed fast but didn’t therefore reach the obvious conclusion that the slight wind had switched around. Fast downwind and damp early evening grass caused a slip. Basically I butt landed and caught the left side of the cage on the turf. Something went crack. Turned out to be the left leg-tube connector sheared.
I also cracked both inner leg plates. They seem still solid enough and the outer plates are fine. The right one is the worst. These parts are not loaded in flight.
On the left leg a couple of the standoffs and a half dozen M3 screws bent.
One flight later I’ve discovered the right side leg-tube connected is also broken. I’ve epoxied it as well.
That is rough! Sorry buddy.
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