3Inch Build Time

Well its that time again…

Time to get a new build under way.

The plan…

  1. I’m going to build a light weight, medium range, 3inch.
  2. I’m aiming to get the AUW (All Up Weight) under 250 grams, with good flight times.
  3. I’m looking for a medium range cruiser more than a freestyle build (even though it will probably freestyle just fine).

Getting the AUW under 250 grams shouldn’t be too difficult if I choose my parts carefully and try to avoid 3D printed parts, as they add more weight than you think.

The Parts:
Frame: iFlight iH3 V2 Dual Split Mini 3 inch FPV Frame
FC Stack: Mamba F4M F25 Flight Stack MK2 (20×20) (F4 FC, 20A ESC)
Motors:iFlight Xing 1408 Motor 3600Kv
FPV Camera: RunCam Split 3 Micro
VTX: TBS Unify Pro32 Nano 5G8 VTX
Antenna: Lumenier Micro AXII UFL 5.8GHz Antenna (LHCP / RHCP)
Rx: Crossfire Nano
Lipo: Tattu 650mAh 14.8V 75C 4S1P Lipo Battery Pack
Lipo: TheFPV 850mAh 3S 80C 11.1V Micro Battery XT30
Props: DAL Cyclone T 3056 C Propellers

This is just my own build, its priced at roughly £260 and should weight somewhere around 210g AUW.
As long as it comes under 250g then I’m happy.
But lighter the better… less weight = longer flight times.

You could build this for cheaper and lighter by changing out a couple of parts.

I’ll be posting part pictures with why I picked them, build pictures and notes.

Please feel free to comment, make suggests (its too late the change the parts, I have most of them now).

Lets see how this build goes…

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The Frame : iFlight iH3 V2 Dual Split Mini 3 inch FPV Frame

Why this frame… it weighs in at 42.5g when I could have gotten something lighter, remember lighter is better with these smaller builds.
So why did I pick this frame…
Two reasons…

  1. Twin 20x20mm mounting, which is good for me as I want a FC Stack and RunCam Split 3 Stack.
  2. Its a dead cat style frame, so the props will not be in the FPV/HD view.

FC Stack : Mamba F4M F25 Flight Stack MK2 (20×20) (F4 FC, 20A ESC)

This stack is tiny 20x20mm and has a 4in1 ESC as part of the stack.
(not looking forward to the soldering)

Its an F4 with 2 full UARTS broken out.
Now I need 3 UARTS:frowning:
So the plan is…
UART 3 - Crossfire
UART 6 - RunCam Split 3 Micro
Use Ch4 on the Crossfire for smart audio. :slight_smile:

Now the ESC is rated for 20A, I’ve checked how my much motors and prop combo will pull on 4S and I should be fine :crossed_fingers:
More on that later…

Motors :iFlight Xing 1408 Motor 3600Kv

Not only do these motors have a good track record but they just look great.
Now I went for the 3600kv versions cause I don’t need the top end speed that 4100kv motors will give me and they should be a bit easier on the lipo.
BUT as I look at the numbers again, I can’t help to think did I get something wrong?

1408 3600kv Spec on my props…

1408 4100kv

On paper the 4100kv look to have slightly lower amp draw, better efficiency and are nearly 1g lighter.

Did I miss something here?

FPV Camera : RunCam Split 3 Micro

Not arrived yet


I picked the split 3, not only cause its the latest version from RunCam, but it should also mount nicely at the front of the frame and offer 1080@60fps or 1080@30fps and only weighs 13.5 grams, lighter than a GoPro or any other HD Camera.

Now I have a Caddx turtle v1 here that I can use, but I want to give the new Split 3 a go and see what the footage looks like, plus its lighter than my caddx.

I’m going to use the UART connection back to the FC stack to control the recording and settings of the camera, I’ve done this on another build and it works well.

VTX : TBS Unify Pro32 Nano 5G8 VTX

Now I said I wanted to do medium range cruising and I need something that is light weight.

at 15x13mm and only 1g and it goes upto 400mW…

Do I need any more reasons?

Antenna : Lumenier Micro AXII UFL 5.8GHz Antenna (LHCP / RHCP)

Not arrived yet


Lumenier make really good antenna’s and this thing is small and only weighs 1.4g (short version) and 1.6g (std version)

I’ll have to find a good way of mounting it, away from the carbon to get a good strong signal, cause carbon and the lipo will block RF.

Rx : Crossfire Nano

Not Arrived yet


Now again this thing is really small (11x18mm) and really light (0.5g) and will give and extra UART for smart audio, confidence in the range that I’m flying.

Now do I go with

TBS Crossfire Immortal T Antenna V2

TBS Crossfire Micro Receiver Antenna

The immortal T is heavier (3.4g) but easier to mount and stronger
The Micro Receiver Antenna is lighter but after I find/make a mounting solution it could end up being heaver.

Lipo : Tattu 650mAh 14.8V 75C 4S1P Lipo Battery Pack
Lipo : TheFPV 850mAh 3S 80C 11.1V Micro Battery XT30
'Lipo : Tattu 850mAh 11.1V 75C 3S1P Lipo Battery Pack

With lipos its all about weight, power, flight time.
So I’m be trying a couple of different sizes to see which one works best for me.

Bigger lipos with a higher mAh capacity may fly longer but with the added weight compared to a smaller capacity lipo may have a short flight time.

So this will be mostly trial and error.

Tattu 850mAh 14.8V 75C 4S1P Lipo Battery Pack = 109grams
Tattu 850mAh 11.1V 75C 3S1P Lipo Battery Pack = 85grams
TheFPV 850mAh 3S 80C 11.1V Micro Battery XT30 = 78grams

Props : DAL Cyclone T 3056 C Propellers

These are the same pitch used in the motor spec sheet above.

I thought these would give a good starting point to try first, I’m sure I’ll try different props at some point to see how they feel and effect flight performance.

So i did some “dry fitting” ( screwing parts onto the frame, to get a feel for size and location )

and damn this thing is a lot smaller than I was expecting…

Motors are fitted with only 2 screws and the FC stack is fitted.
The RunCam Split 3 board is going to sit really close to the FC Stack and the ESC to FC wires may even get in the way.

There isn’t going to be a lot of room left for the VTX and Rx its a good job there are tiny.

I’ve ordered the rest of the missing parts and they should be here before the weekend :slight_smile:
So look forward to more pictures, more information and the finished build.

Something I have done is made XT30 to XT60 adaptors. Yes you can buy these, but why, just make some.

Simple to make… solder POS to POS, NEG to NEG no need for wires.
BUT check and double check you have it the right way round and for shorts.
you really don’t want to short a lipo.

added some heat shrink to give them a clean look.

TOP TIP… a heat gun wont leave loose black marks

arh post day… my favourite day…

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Thats some nice and neat XT60>XT30 adaptors :slight_smile:

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So the build has been finished… :slight_smile:

So what did i find during the build? cause all builds are different.

  • Its a tight build.
  • The FC to ESC stack cable gets in the way.
  • Mounting the VTX and Rx it wasn’t easy to find a good place.
  • VTX gets really HOT (even at 25mW). I used double sided tape at first but when it heats up it just lets go.
  • Mounting the VTX on top of the FC isn’t a good idea… I get temp warnings from the FC of 90 Degrees. ( but this is when its on the bench and not in the air ).
  • I’ve used electrical tape on to the bottom of the top plate, the top plate should help and act like a heat sink ( a little )

Now for some pictures… AUW is at the end of the post :wink:

The pads are really close together, use a good soldering iron and take your time.

Crossfire is fitted…
The antenna is mounted at the front under the camera cage.
I’m using Ch4 from the Crossfire nano for smart audio from the VTX

Really happy to how this has turned out so far :slight_smile:

VTX is fitted now and connected.
But as I said before, it gets REALLY HOT and upsets the FC.

In the end I just spun the VTX over and taped it to the top plate.

Also notice the FC to ESC cable is twisted… thats cause the cable port on the ESC touches the RunCam board when its the other way round… I get about 1mm of clearance this way round.

Finished build…

AUW weights

With the 3S 850mAh Tattu

With the 3S 850mAh TheFPV Micro Battery

With the 4S 450mAh Tattu

So all in all… this project works so far… even with the heavest lipo its still under 250g which was the point of this build…

Next up the maiden and flight footage :slight_smile:

RAW flight video with 3S 850mAh and 4S 450mAh

Running BF4.1.0-RC1 on default PIDs and filters
A little wobble but more than flyable at this stage.
Next up community PIDs and Filters.