That looks pretty cozy. You could add in the motor model (step file is in github) and assume a prop mount. Might give you a better measurement.
Thereās 190mm space between back plate & props, so you could probably double up the packsā¦
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This raises an interesting question- Assuming that two packs are only 140mm tall, and that they are not too heavy when stacked, I wonder if we can arrange the electronics so that a second pack could be added for some flights? I do this for my FPV planes and lipos by just putting them in parallel. I donāt know if the BMSs fight with each other with these packs, however.
One pack is about $1200, so this gets expensive, except when you consider that a Carbon Scout is about $9k plus all the maintenance, drama with airlines and fuel, and noise. Iām not saying Iād turn down a Carbon Scout if I could afford one, but it does put things into perspective.
@tombusey thanks for checking whether this fits, or not. However I am thinking to place the battery rather lower, between the legs. In either case this is probably going to be a trial and error process, and see what works best, when the whole setup is on my back.
Hereās the battery with the first layer of nickel strips:
and a closer look
The serial connections will definitely need a second and third layer of nickel strips welded on top, to support the high current flow, I also still need to add the BMS and the cables to connect the whole thing to the openppg.
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Nice work! Which cells did you wind up selecting?
see above, first post, for a parts list. (itās the LG 18650 HG2)
Really pretty work!
This was a helpful series for me to watch. He suggests keeping weight higher and as close to the body as possible. But I agree that eventually you just have to try different positions once you have the motors and harness in place. Our setup is different in that our motors are much lighter and we donāt have a fuel tank that is lower.
Has anyone thought of a batery pack they may be jettisoned in the event of a thermal runaway or fire?
I thought the general consensus was that it was not required.
Cheers
quick update:
I received the missing nickel strip, that I still needed, also the 8AWG Silicone wire. Still waiting for the RC Pro Plus bullet connectors.
Iāll be coming to the States for the duration of one week, I hope to be able to continue my build by the time I come back to Germany.
Also waiting for @Pdwhite to starting to accept orders again for batch 3, as I havenāt ordered the openppg kit yet.
Thanks @tombusey for the hint with keeping the weight higher. Logically you are right. and yes, the video series from Miroslav/Scout is indeed awesome for some background information.
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Can this battery be made in two 13S8P configurations? With all of the discussions around the failures of the Batch2-included switch, it seems like a good idea to split the current into two switches, each of which would support two motors. If these were diagonal from each other, and spinning in opposite directions, this would provide some redundancy in the event of a prop or esc failure (which IMHO are far more likely than a motor failure). In the event of an ESC failure, you could just turn off one circuit and land using the other. The amount of current going through any one set of wires is also half. Presumably one set of motors wouldnāt have torque or other spin issues.
Maybe a downside is the need for two BMS? There is also the need to link the grounds (maybe not a problem?), and there is additional complexity in monitoring both packs.
2 BMS is a bit of a PITA - as would be 2x the switches and 2x the current monitoring, etc.
What would be ideal (not sure we can find the parts however) would be going to a higher voltage configuration - like 24S. Weād halve the current everywhere, which would open up a ton more options.
Now, we start getting into HV potential concerns, and the safety associated with thatā¦ but I think our issue might be finding the parts, and of course the motors would need to be re-wound to an ~90kV configuration (assuming the insulation could handle the voltage)
24s stuff out there - dont know if stuff available for our needs:
Charger is less important than ESC IMHO
Goblin 700 KSE running APD-ESC @ 24S
https://www.youtube.com/watch?v=xURebVJf8og
CHARGERY BMS and Charger for up to 24S LiPo, LiFe and LTO battery
https://www.youtube.com/watch?v=d-ZKr9Cd4co
Cheers
Iāve seen such thingsā¦ havenāt found readily available, reasonable priced sources for any of them, however. They mostly seem to be the subject of obscure YouTube videos 
Alien sportII does 4 to 24s
https://alienpowersystem.com/shop/esc/alien-sport-ii-450a-4-24s-esc-hv/
Correct, but each of those weighs nearly 2 pounds and costs like $400US. So thatās a no-go for our configuration.
Yes ā forgot this is a 4 motor unit ā¦ as Homer would say, doooooo!
I am jumping back and forth from eppg
@etienne , I am happy to say that I got in on batch 3. I hope that you got in also.
Do you have any updates on your battery build? I have ordered a spot welder like yours and have begun collecting the other parts too. Malectrics appears to have designed a good welderā¦one of the best that I have seen on the web. I believe that your 13S15P 18650 pack is a great choice for a battery, and I do plan to follow your progress.
Thank you very much for your postings.
Bill
@1066 I have just ordered my batch3 kit two hours ago, next week is paragliding in the alps (one week of holidays) and after that I will resume my battery build!
Will continue to post pics
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@etienne , thanks for the update! Iām very glad you got your order in too. I look forward to the project. Have a great holiday!