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<250g FUFAA 4s 4" good motors?
#1
I have started ordering parts for a 4 inch build, suitable for a RunCam Split (ie. no props in view). I am just putting some finishing touches to my own design lightweight frame, (something a bit different with some unique elements). I am keeping it off the main forum so the unscrupulous don't nick it, but there is a thread in the VIP lounge that I will be updating soon...  

Basically I am attempting to create a 4s capable, sub 250g quad that can still capture HD footage, with the greatest possible thrust to weight ratio. Legislation here in SA is pretty lax, apart from not being able to fly FPV  beyond the LOS of a spotter, I can use a VTX up to 1000mW and fly anything up to 5kg as a hobbyist! Considering this, it's not the end of the world for me if the build does go over weight, but I would like to increase the options in the FUFAA class! 

I found this F4 FC with 28A 4-in-1 ESC, I was going to order from myRCmart.com but cheap 'priority line' shipping,  and cheapest place for my wife's Christmas present - ended up ordering from GearBest instead. 

Also ordered this VTX, I probably would have gone for the Matek VTX if GearBest stocked it. Maybe I should have just taken a bit more time to consider that I will be ordering other bits from elsewhere, (could probably save a gram or 2 on the VTX too) but I wanted to chuck as much in the priority line shipment as possible. Oh well  Rolleyes

I'm going to get an Eachine minicube FlySky RX and an FS-X6B RX too, probably going to go with the X6B on this build, but I might use the minicube RX for the buzzer. Just had confirmation that (contrary to the product info on BG) that the FS-X6B does have failsafe over iBUS, in addition to diversity antennas and telemetry, I could save a few grams here too, but if I can get the features and remain under the 250g mark...


Now this is where I want some help from you guys - 


What motors for a 4s 4"..?

I am stuck in a toss-up between the 1407 (3400kV) RCX motors from myRCmart, or the 1507 (3755kV) Garila motors from BG, they are basically the same price, at about $12 a piece but the garila's only come in a set of 5. 

Seems like the Garilas have some really good thrust stats with 4045 props on 3s, they can also run 5" on 3s, but there is no info on whether they would be ok to run 4" on 4s? (They can take 4s voltage running 3" though.) They do look very power hungry, 31A draw(!) for 706g on 3s with DAL PC 4045 Props (= 1.8g/W). They are 2 grams heavier than the RCX with shorter wires, 19g per piece with 100mm wires. 

Do you think that the motors will overheat running 4s, and will 35A burst rating of the ESC be OK?

The RCX motors are more efficient (2.13 g/W) drawing just under 20A for 689g thrust on 4s with GemFan 4045 props, 17g per piece with 150mm wires.

I did originally look at the 1707 RCX motors, but they seem to produce less thrust and get hotter than the 1407's running 4" on 4s.
Windless fields and smokeless builds
[-] The following 1 user Likes Tom BD Bad's post:
  • Oscar
#2
Just been looking at the brotherhobby returner range, there is a new 1507 that BG have just listed, EngineerX tests (only the 3600kv version) show upwards of 900g running 4" on 4s, that is pretty impressive for a motor that only weighs 15.5g. Waiting for test results from the 2800Kv version...

The Brotherhobby Returner R4 1806 2850kv show similar max thrust results, but weigh almost 5g more...

I had passed over brotherhobby motors because they are pretty expensive, but maybe my sis will get me a set for Christmas...
Windless fields and smokeless builds
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#3
Hi Tom, glad you are building a new machine Smile

Not sure if you are aware, the FC/ESC stack you have chosen has 20mm mounting hole spacing... the Split, and the VTX you ordered have 30mm spacing... so...

If you want to build it as light weight as possible, I think 1407 3500KV is a good option for 4S.
Take a look at this build log:
https://oscarliang.com/superlight-4r-mini-quad-frame/
Don't be a LOS'er, be an FPV'er :) -- Blog - Facebook - Instagram - Twitter - Google Plus
[-] The following 1 user Likes Oscar's post:
  • Tom BD Bad
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#4
Thanks Oscar, yeah I am aware, but with my frame design it's not going to cause any problems...
Windless fields and smokeless builds
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