Nemos Twig Introduction
A quadcopter frame reviewed by UAVFutures recently caught my eye. It is an extremely compact and lightweight frame called from the Twig. It is produced and sold by an online quadcopter shop running out of Australia for the extremely reasonable price of $50AUD.
The Twig drew me in because it looks to be the absolute lightest frame design that is technically possible while still running 5″ props and full-sized motors. Every non-essential millimeter of carbon has been shaved off of the frame. I have been working on the concept of an racing miniquad that incorporates modifications which clean up the aerodynamic profile so that it operates more like an airplane in forward flight than a helicopter. I think with it’s already slim form and cheap cost, the Twig is the perfect platform for experimentation with this concept. But that’s a story for a future article – first I have to build this thing.
Before we dive in, I want to put forth a warning. If you are getting into the hobby – for the love of god do not buy or build this quadcopter. This quadcopter is designed to be light and nothing else. It is going to break in horrible ways every time you have a “moderate” crash. It has been shown that light weight doesn’t even make your average FPV racer faster due to the limitations of FPV camera angles. Get an Alien, an Armattan, a Flynoceros – anything else! Check out our frame guide. This frame is truly just a “fun” frame for experimentation of the bleeding edge of what’s possible with light weight. Also, if you’re looking to learn how to build a miniquad – you’re in the wrong place! Check out our detailed guide for that here.
Here are the parts I am using for this build:
Frame – Nemos Twig Quadcopter
Motors – E-max RS2205S 2600kV
ESC – RacerStar 30A 4-in-1
Flight Controller – OmniBus F4 / Betaflight F4
FPV Camera – Foxeer HS1177
VTX – ImmersionRC Tramp
RX – LemonRX Diversity RX
With such a compact build, the parts you can use are pretty restricted. Integrated components is the key. If you want an OSD or a PDB – it better be integrated into the flight controller. This is also the first quadcopter I have built that requires the use of a 4-in-1 ESC. The the 4-in-1 version of our current favorite ESC line, the RacerStar’s was the natural pick for this reason.
Similarly, the Omnibus F4 / BetaFlight F4 is the easy pick for flight controller. It includes a built in OSD and some of the functionality of a PDB. It supports every feature of BetaFlight you could wish for and sports an F4 processor to boot. I ordered this FC before they came out with the “pro” model which has a built in current sensor – if I could do it again I definitely would have ordered that model.
In my opinion, the EMax RS2205S is the best 5″ miniquad motor on the market today. It is narrowly beat out on thrust figures by a small number of motors, but the margin is extremely small. On the other hand, it is $5+ cheaper than any of those other motors. I have a lot of experience with E Max motors and like them. They also have a ton of support state-side so it is never an issue to find replacement parts when needed. I chose 2600kV because I expect this quadcopter to go fast. 2300kV motors will give you better punchouts and performance at low speed – but they simply start losing steam at full tilt.
I’ve been meaning to try out the ImmersionRC Tramp VTX for awhile now and this quadcopter is my chance. I have long thought that ImmersionRC has put out the most well-engineered electronic components in the hobby and I’m sure this VTX will not disappoint for that reason. I’m particularly interested in experimenting with it’s integration with Betaflight OSD. Hopefully there’ll be an article on that in the near future.
Unsurprisingly, the package the Twig came in was not very big. Fine by me – shipping costs were a pittance as a result. One “cool” thing about this product is the guys at Nemos ship 6 arms with each kit. I guess the assumption is you are going to breaking arms. Sounds fun!
With the quadcopter unpackaged, I set to work removing the EMax motors from their plastic boxes. This was a novelty the first time I bought EMax motors, but it’s gotten pretty stale lately. I have quite a pile of these plastic boxes and hardware at this point. I’d love a frustration-free packaging option for these things.
Lower Frame Assembly
The first step of the build is assembling the lower frame. This goes together pretty easily. Each arm is held in place by one long screw. The screw threads through a locknut glued into a 3d printed baseplate that comes with the kit. The arms are held together by screw tension and by the square fit of their ends.
When assembling the arms, make sure that they all line up properly. The arms are not symmetrical so you want two sets of arms lined up together.
In this build I am using a 4-in-1 ESC so installation consists of planting the ESC on the screws that are doing double duty securing the arms in place.
Plastic spacers are provided with the kit to provide clearance between the bottom of the ESC board and the bottom plate. This is where I encountered one problem, though. Without modification, the edges of plastic spacers were snugging up against FETs on the 4-in-1 ESC rather than having the spacers fully seat against the holes on the ESC. For this reason I needed to use a hot knife to cut the inside edges off of the spacers so that the ESC could sit flush. This wasn’t a hard modification – just one you want to be cognizant of. There’s not a lot of room on this thing!
I’m pretty disappointed by RacerStars choice in battery leads with the 4-in-1 ESC. This ESC purports to support a combined burst current of 140A through 18 gauge wire. I would have appreciated some thicker battery cables.
Next up I installed the motors. I found a certain amount of irony here in that the EMax RS2205S come from the factory with relatively short (~1.5″) motor wires. On any other quad, this’d be great! Less wastage as I normally clip the wires all the way up to the bell.
In the case of using a 4-in-1 ESC, however – I needed the motor wires to be about 2.5″ long. So, for the first time since I’ve started building miniquads, I had to extend all 12 motor wires. Luckily, I had some old wires from other builds laying around.
When splicing wires like this, you want to twist the strands of the wires together before soldering. This adds strength that just isn’t there if you solder the wires together while sitting side-by-side.
I toyed with the idea of soft-mounting the motors for the build but ultimately decided not to. Since each motor is only secured with 2 screws, it simply seemed to risky. Instead, I added a little extra elbow grease when seating the screws and made sure to use threadlocker on each one.
I found soldering the motor wires to the ESC much easier after securing the wires to the arms with zip ties. This located the wires really well and resulted in a really clean and secure wire configuration. Even without zip ties, these wires aren’t going anywhere.
Flight Controller Installation
With the power system installed, the flight controller is next up on the chopping block. The Omnibus is powered directly from the battery so the first thing to do is to is to build up a pigtail to provide power to the flight controller. The pigtail is soldered directly to the battery leads and was made from the red and black wires from a servo extension cable. I keep hundreds of these things lying around my build area for just this type of thing.
Next up, the pigtail was soldered into the VBat and GND pins of the flight controller.
I was extremely pleased to find that the omnibus comes with a 5 pin connector that exactly matches the connector and harness that comes with the RacerStar 30A 4-in-1 ESC. This makes the process of connecting all 4 ESCs and the Flight Controller a non-issue. Simply plug that 5-pin connector into each board and you are good to go.
With the FC powered and the ESCs wired, I added another set of plastic spacers to the 4 screws and seated the flight controller down onto the frame. Once again, the flight controller did not sit flush with the spacers and the spacers needed to be trimmed with a hot knife.
FPV System Installation
Moving on to the FPV system, we’ve got to keep things very compact to fit inside of the small area between the standoffs in the Twig. To do this, I’m opting to mount my VTX directly to the back of my HS1177 FPV camera using double-sided tape. I then run the power wires from the camera connector directly into the 5V output from the VTX. Nice and clean.
Since the Omnibus F4 includes the fantastic Betaflight OSD built into the flight controller, I’ve got to wire the FPV system to the flight controller. I talk about this in more detail in my Omnibus review, but here’s the gist of it:
VTX power and video signal to one connector, camera video signal to the other. All hard soldered. Then power the “RAM” power which goes to the VTX by making a solder bridge in the lower left hand corner of the flight controller. Finally, a little hot snot applied all over the board to protect against shorts and secure the wires.
FPV Camera Installation
With the FPV system wired up, it’s time to get it secured to the frame. All of the Twig builds I could find online secure their cameras to the top plate of the quad using the metallic bracket that comes with the HS1177. That’s a problem for me because I’m reusing this camera from another build and have long since tossed that bracket.
Thankfully, Vesp has a 3D printer so I designed some plastic brackets which slide over the standoffs. The camera then screws directly to these brackets, giving me a nice, secure mount with plenty of tilt capability.
I’ve shared these plastic brackets on Thingiverse for those that are interested. You can find them here. They require a little bit of finishing work with a drill set, but it’s nothing too complicated.
That completes the functional part of the build. From this point on, it’s just wrapping various things up.
Top Plate & Antenna Runners
The top plate needs to be added onto the standoffs. Because the holes on my camera mount weren’t perfectly centered, I needed to bend the standoffs a bit to get the screws to seat properly. I might come back and fix this later.
I also added RX antenna guides in the form of zip ties. These guides could be integrated into the camera mounting struts and I think I might do that in a future revision. For now, I just used heat shrink to attach them to the standoffs.
The VTX antenna SMA connector needs to be pushed through the to plate and screwed down. No biggie there.
Finally, I stuck the RX on to the top plate using double-sided tape and used heat shrink to adhere the RX antennae to the zip tie guides.
The video transmitter is just stuck to the back of the FPV camera with several layers of double sided tape. In this configuration, if the tape fails, the VTX is going to fall through the prop disc.
To secure the VTX better I used a zip tie around the rear standoffs that presses the VTX into the double sided tape.
Well – kinda. I still need to secure the motor wires a little better.
10.8oz = 306g
1300 Infinity Race Spec Graphene LiPo = 160g
Total = 466g
Static Thrust: 1400g+ / Motor (Measured with DAL 5×4.5×3 props)
Total = 5600+g
Thrust:weight ratio = 12:1
This might not be as ridiculous as the 6″ XBR 220 builds – but it is a damn sight more aerodynamically sleek. Especially after I get done with it. I better get used to flying at 60 degree camera angles…