The custom frame I ordered for this build finally shipped! Can't wait to start building this thing.

The actual flight test might be delayed by all of the snow we just got, but at least I'll have plenty of time to figure out the sub 250g part

Ohh so exciting
I think this build will be +250...
PROVE ME WRONG !!

Progress! The frame arrived from Armattan in between snowstorms, along with some random hardware. Assembled with titanium screws (M2x8mm) and nylon standoffs (20mm), it weighs 18.9g. (Budgeted: 20g)
   

I initially started building it with aluminum screws, but the head of one of the screws SHEARED OFF just threading it through the carbon fiber. I don't know if they were really crappy aluminum screws or just because they're so tiny (M2), but I decided to use titanium or steel for the rest of the build after this. 

I mounted up the SunnySky R1104-5500 motors with some M2x5mm steel screws. The motors come with 4mm and 7mm screws, but with the 2.5mm baseplate the 4mm were too short and the 6mm looked like they were almost hitting the windings. 

Frame + motors weigh 45.4g. I assume this will go down slightly when I trim the wires. (Frame + motor budget: 46g). 
   

I picked out two FC options for this build, the Flywoo Goku F745 16x16 2-4S Stack/Combo (F745 FC / 20A ESC) or the Flywoo Goku HD 745 EVO 2-6S 20x20 AIO. The 16x16 stack was advertised as weighing 4.8g, and the 20x20 AIO 8.5g. Actual weights (with mounting gummies) are a bit higher. The 16x16 stack is 7.2g, and the 20x20 AIO is 9.2g. 

Flywoo Goku F745 16x16 2-4S Stack/Combo (F745 FC / 20A ESC) - 7.2g
   

Flywoo Goku HD 745 EVO 2-6S 20x20 AIO - 9.2g
   

Next I need to figure out how I'm going to mount the VTX. I really want to try to make the Air Unit work, but if I'm over on weight I can swap in a naked Vista to save ~11g. My plan right now is to come up with a way to secure the Air Unit to the top plate. I think I'll try to mount it inverted, so the hotter CPU is on top, and I'll try to thermally couple it to the top plate with a thin silicone pad. This also lowers the MMCX connectors for the antennas, so they can be directly connected and stick up like rabbit ears on either side of the battery. Whatever mounting solution I come up with will need to securely hold the antennas as well, and hopefully prevent them from ripping out of the AU in the event of a crash. 

I thought the frame had 16x16 mounting holes, but it only has 20x20 and 25.5x25.5. So I'll need to use an adapter to mount the 16x16 stack, which will add a little weight and take away from the 2g difference with the AIO. It does give me the possibility of mounting the stack either front or rear, however, which could leave enough room for the AU on the baseplate.

   

I'm waiting on a few TPU parts to mock things up, and I also ordered the Armattan Tadpole aluminum camera mounts per iFly4Rotors's suggestion. I'm interested to see how the weight of the aluminum mounts compare to the nylon standoffs + TPU camera mounts, and if the difference is minor the additional camera protection will certainly be worth it!

nice unibody frame

i would drill the 16x16mount, shouldnt decrease the durability. probably i would drill the holes 45degrees different to the actual holes.

Got the Armattan Tadpole front camera mounts in. They're a little heavier than using standoffs and TPU camera mounts, but I think the extra gram or so is worth it. They look much nicer as well!

   

I noticed in post 78 you mention needing a mounting system that securely holds the antennas of the AU.  Have you seen how the Flywoo Mr. Croc handles the AU antennas?  (See attached)  I wonder if this concept might work for your build?

They are made of TPU and mount on a frame standoff.  So if you could make something similar but that bend upward you could then simply zip-tie the AU to the top frame plate and these antenna "holders" might do the job very well.  I'm just not sure how much weight they would add, but might be worth exploring.

(13-Feb-2021, 05:41 AM)Skavage Wrote: I noticed in post 78 you mention needing a mounting system that securely holds the antennas of the AU.  Have you seen how the Flywoo Mr. Croc handles the AU antennas?  (See attached)  I wonder if this concept might work for your build?

They are made of TPU and mount on a frame standoff.  So if you could make something similar but that bend upward you could then simply zip-tie the AU to the top frame plate and these antenna "holders" might do the job very well.  I'm just not sure how much weight they would add, but might be worth exploring.

Thank you! I hadn't seen this before, but I think this will be the way to go. I'll probably have to design something myself to keep weight to a minimum, and I may be able to incorporate a mount for the top plate as well. 

Please keep the ideas coming!

(13-Feb-2021, 05:17 AM)V-22 Wrote: Got the Armattan Tadpole front camera mounts in. They're a little heavier than using standoffs and TPU camera mounts, but I think the extra gram or so is worth it. They look much nicer as well!

Hi V-22,

I got a new scales because the one I had been using only measured to even grams.

This set of Armattan Tadpole Cam Braces weighs in at an even 3 grams.
My standard camera mount {above deck} consists of aluminum columns and TPU cam mounts. I was surprised to see that this setup weighs 2.1 grams which is about a gram lighter than the Tadpole Cam Braces, however, no protection for the camera.
Plus, I think the Tadpole Cam Braces look cool; a little more "polished".


See picture HERE

Thanks iFly! That's interesting your Tadpole mounts are a little lighter, I may need to borrow your scale for my final weigh in

(15-Feb-2021, 04:44 PM)V-22 Wrote: Thanks iFly! That's interesting your Tadpole mounts are a little lighter, I may need to borrow your scale for my final weigh in

I have several additional sets of the Tadpole mounts which I will weigh. My guess is that they don't all weigh the same...maybe there is .1 or .2 tolerance...or...maybe it just doesn't matter to them. On the one had it is worth the extra gram for good looking camera protection...on the other hand, I might still use the columns and TPU mounts for an extremely light build. For me, both are actually pretty good options; just different. 

Found a few more new motors that could be interesting for lightweight 3"-4" builds:

New iFlight Xing2's 1404 in 3800Kv and 4600Kv versions:
https://www.racedayquads.com/collections...icro-motor
https://www.racedayquads.com/collections...icro-motor

And for 1-2S builds:
NBD Flow 1202 in 8420Kv and 11420Kv versions:
https://www.getfpv.com/newbeedrone-flow-...mount.html

Happymodel EX1202.5 in 6400Kv and 8000Kv versions:
https://www.getfpv.com/happymodel-ex1202...motor.html

Hi V-22,

I will add them to my Parts Guide.

I might have to check out the iFlight Xing2's 1404 motors.

I have a set of GEPRC 1202 6000Kv motors in the Tiny-Black-85 whoop build. They seem to be very good motors.

My Phantom-3A was running Flywoo Robo RB 1202.5 5500Kv motors; fly nice, but cracked the frame when I hit a light pole; disassembled it and used the frame as base for the Phantom-4X build. Since I really like the Flywoo Robo RB 1202.5 5500Kv motors and I have read a lot about Happymodel having low quality or quality control, I probably won't buy those motors.

Thanks for the information. 

Still trying to work out how the FC/ESC stack and Air Unit will be mounted, and I've been stressing over the weight. I assumed the 3S 18650 pack would be 150g, meaning the dry weight of the frame needs to be <100g. 

After trying several mounting configurations I just didn't think this would be possible and I would be over by a few grams. Then I came to the realization that the 3x18650 cells themselves only weigh 139.9g, and it would be possible to make up the difference in weight by just using shorter wires and less electrical tape when assembling the pack   

It's still going to be close, but now I'm confident it's possible!

Hi V-22,

Did you include about 4 grams for an XT30 pigtail? 

At about 46.6 grams per cell that would be...   139.9 + 4 = 143.9 grams +/- {depending on the wire}.
Presumably, you will solder the individual cells together; I figure a few grams for this as well. 
Plus tape or something to hold them together. 
I will be curious to see what your fully assembled 3s 18650 pack weighs 

Also, don't forget to factor in the weight of the battery straps.  

Yes, XT30, balance lead, and nickel strips to wire the batteries together are about 4g (keeping wires as short as possible). Battery straps are included in the dry weight of the build (see table in the first post). I was coming in at about 102-103g dry, so if I can keep the pack under 146g I should be good! It's probably a good idea to do that first so I know exactly what my hard limit for dry weight is though.