Concept

The idea behind this build was to create a 3" freestyle quad that uses one of the 'split' style HD/FPV cameras to practice freestyle with in areas where a normal 5" quad would be illegal or too noisy. I made this build about a year ago, but was never able to tune it to feel similar enough to my 5" setups to use it more than a few times. However, with the new regulations rolling out in the US, I thought it would be a good time to revisit. Because this is an older build, some of the parts are pretty hard to find, so I included a short section for alternative/upgraded components at the end.

Custom/Additional Components

I designed several custom parts for this build, and used a lot of non-stock hardware. However, stock hardware that comes with the frame and boards all work fine, and in fact may even save a couple of grams. I mainly made parts to try and slam down the frame as much as possible to bring the prop line close to the center of mass.

3D Printed Components:

• Spacers that go between stack boards
• Camera Canopy (replaces front plates and allows for shorter main standoffs) with RX tube slots
• VTX antenna mount
• Straps that hold down the receiver and VTX antenna U.FL connector, as well as relieve stress from the U.FL connector

Additional Hardware

• Longer M2 hardware for mounting stacks
• 20mm standoffs (slightly shorter than stock iH3 ones)
• RX antenna tubes

Build Notes

• The iH3 has enough vertical space to comfortably fit 2 stacks of 3 20x20 boards.
• Motor wires may need to be a little longer for the front motors since they have to run to the back stack.
• Capacitor nicely fits in between the back part of the frame in between the two rear standoffs.
• For Smartport telemetry, need to use SoftSerial on an unused FC pin (ie. PPM).
• Props just barely sneak into the HD footage when using stock carbon fiber mounting plates.
• Lumenier AXII heat shrunk to a zip tie keeps the antenna firm but unobstructed.
• The back of the top plate has some slots which are good for mounting RX antenna with zip ties.
• All up weight with 4s 520mah GNB battery is Just under 200g; with 650mah Tattu just over 200g.

Performance Notes

• FPV output has higher latency than a normal FPV camera, but this is to be expected of these types of cameras.
• 1404 motors with Gemfan 3035 3 blade T mount on 520mah battery gives about 3min flight times and is fairly quiet. There's a bit of a whine on punchouts and sharp turns but when cruising around it is pretty quiet. While flying in my local park, a mother with her kid stopped to watch me fly and they seemed totally comfortable.
• 1404 motors do drop off a little at higher throttle; there isn't quite as much top end thrust as a typical 5". Maybe increasing to 1408 would increase max speed/acceleration, but beefier motors that would likely require beefier batteries which would cause the mass to creep up, so that may have diminishing returns. Furthermore, 1408 motors tend to be very notchy (high cogging torque), which can be noisy and cause problems if not tuned carefully.
• I once got this stuck in a tree for about 15 minutes before getting it down and in that time the VTX had heated up the entire frame to be warm to the touch, but I guess everything still worked afterwards so maybe that's a testament to the products.
• I just upgraded to Betaflight 4.0.5 from 3.5.6, and am still in the process of tuning.

Alternatives/Upgrades

• Frame: iH3 v2 looks pretty good still, and has more camera protection. Acrobrat also seems nice, but is heavier.
• Camera: All newer version of the split-style cameras have a single board, so that can save a few grams (with the exception of a Tarsier).
• Motors: Any other 1404, 1306, 1304, or 1408 would probably work, but they would probably require different tunes (iFlight Xing 1404 look good).
• Props: With 13xx-1404 motors, use less aggressive props, ie. Gemfan 3035T, Windancer 3028
• FC/ESC: If you're ok with F4 and bl_heli_s, the Diatone Mamba stacks seem like good value