Momentary Lapse of Sanity (3" 2S)

By Burning North on Jul 19, 2017

28  1,658  8

Update - 23 July 2017: I ran a few more bench tests with a clamp meter on the battery lead. On the upside, the Wave 4x18A can handle the Spintechs at full throttle (around 19A per motor) without breaking a sweat. However, the motor bells got a bit too warm for my liking on the Gemfan 3025s, so I tried again with the rebranded DYS 2435 props that PiroFlip RC sells for the Torrent 110. The motors were much happier with these props, so I'll probably use them for everyday flying and save the Gemfans for special occasions. :P


After my first brushless build went so smoothly, I decided to challenge myself by trying my hand at a 2S micro racer. I'm not generally a fan of frame designs that mount the flight controller on structural standoffs, so that eliminated a lot of popular options right off the bat. I settled on the Tomoquads XBL2 for its Micro Swift mount and 4mm brick house of a baseplate.

Spintech's new 1106 8000kv motors are absolute beasts, but notoriously amp-hungry even on 2.5" props. I hadn't considered using them for a 3" build, but changed my mind after I saw a few people reporting decent efficiency and sub-20A current draws with Gemfan 3025s.

I knew it would still take a substantial 4in1 ESC to feed this motor/prop combo, and I wasn't encouraged by reports of shaky quality control on most of the 20x20 boards rated above 12A. I ended up taking a chance on some just-released boards from Airbot: the Omnibus F4 Nano V3 and the badass-looking Wave 4x18A.

Because they're new and still sparsely documented, I've included shots of the boards along with the FC schematic. The FC runs Betaflight 3.1.7 on the OMNIBUSF4SD target, and the ESC runs a 16.4-based firmware that BLHeliSuite didn't recognize, so I didn't risk updating it. The boards connect with a single 8-pin cable that carries motor signals and lipo output, but no current sensing.

The Wave 4x18A is only rated for 2-3S, and Airbot was adamant about the need for an external capacitor. Thankfully, the board has lipo pads on both sides, so the XT30 pigtail went on the bottom, and a Rubycon ZLH 25V/330µF cap went on top. The solder joint on the pigtail was quite close to the frame, so I placed some electrical tape over the carbon for peace of mind.

Because all four edges of the board are used for motor output, the solder pads are generous and a breeze to solder. I would love if this became the new standard for 4in1 micro ESCs.

Soldering everything else to the flight controller was mostly straightforward. I attached the XM+ receiver using the pins that came with it, but I ended up having to add a small jumper to connect the output to a different RX pad (F4 boards can only receive an SBUS signal through a port that has a built-in inverter, which on this board is UART6).

The hardest part of this build was organizing the ass end of the frame. The capacitor, buzzer, and VTX all had to be routed out the back and secured as far from the props as possible, which took a lot of patience and a cat's cradle of zipties. The rearmost standoff is squeezing the hell out of the XT30 pigtail, but at least it should provide a bit of strain relief in a crash.

Without a current sensor, it's difficult to tell whether this ESC can actually handle these motors in practice, but bench and hover tests went perfectly smoothly. Once my new goggles with DVR arrive, I'll take it out and maiden it.

I do like how this one turned out, but I don't know if I want to build any more micros for a while. The tolerances are so tight that it's frustrating to even think about opening this thing up to make repairs, and I'm not crazy about having to secure so many components to the outside of the frame.

I bet it's gonna heckin' rip though!

Photos

Part List

Frame

XBL2 Race Frame Kit V1.1 Xtreme Edition *Preorder *Free Sleeve and DVR mount
Tomoquads.miiduu.com
See Site

Flight Controller

OMNIBUS F4 Nano v3 with LC filter (9 builds)
Store.myairbot.com
$35.99

ESCs

Wave 4in1 ESC 4x18A 2020 HC
Store.myairbot.com
$39.99

Motors

4 x 1106ST 8000kV Brushless Motor (10 builds)
Spintechmotors.com
$30.00

Propellers

RotorX RX 3025 T-style Props (2CW & 2CCW) (5 builds)
Airbladeuav.com
$2.99

FPV Camera

RunCam Micro Swift (11 builds)
Shop.runcam.com
$29.99

FPV Transmitter

Eachine VTX03 Super Mini 5.8G 72CH 0/25mW/50mw/200mW Switchable FPV Transmitter (425 builds)
Airbladeuav.com
$14.99

Receiver

FrSky XM+ SBUS Mini ReceiverDefault Title (1242 builds)
Airbladeuav.com
$12.99

Batteries

AirBlade Premium 500mAh 2S 7.4V 65C XT30
Airbladeuav.com
$10.99

Misc Parts

2.4" x 3.5 x 4 PC (2CW-2CCW) Green (2 builds)
Pirofliprc.com
$1.58

Misc Parts

Rubycon (2 builds)
Digikey.com
$0.42
Show stores (7)

Discussion

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Ryechz   Sep 22, 2017  

Could you post your BetaFlight settings? I have a nearly identical build, buy an using a spectrum receiver. I'm having some issues. Was wondering what your so was. Maybe a diff output would do? Thanks!

Burning North   Sep 23, 2017 

This build is actually running stock everything on BF 3.1.7. The motors still get far too hot for my liking and it definitely needs tuning, but this quad is grounded until I can find time to replace a motor whose windings I damaged while trying out new soft mounts.

I don't know what issues you're having, but if you've got hot motors, I'd love to know the solution, because I haven't touched the PIDs or filters on this one yet!

the Skonk   Jul 23, 2017  

nice man hows the performance on the spintechs, i built my micro with room for 2.5" props. i had to design my own frame though

Burning North   Jul 23, 2017 

The Spintechs are awesome! As long as you have ESCs that can handle the current, they've got thrust to spare. Just be careful not to overprop them, because they can get really hot really fast.

And make sure to pair them with a high-discharge battery -- I'm using 500mAh 65C lipos and even they get pretty warm.

the Skonk   Jul 23, 2017 
1

have you seen this?

Burning North   Jul 24, 2017 

I hadn't seen it actually, thanks for that! Interesting that he got pretty much the same amp draw on the DYS 2435 and the GF 3025, but with such a huge thrust difference.

Now that I know I don't have to worry about the ESCs, my only concern is motor temperature, so I'll compare them next time I fly (probably next weekend at this rate).

FannyPack_FPV   Jul 19, 2017  

Amazing build, and walkthrough. Great job man.

Burning North   Jul 19, 2017 

Thanks! Hope it was helpful. :)

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