It’s time to build another 3″ quad! This time I will be using parts mostly from HGLRC – the first time I am checking out their products.
Here is my last 3″ build if you are interested.
Here are the parts I will be using in this build:
This is a 20x20mm stack, however the 4in1 ESC is still quite large in size due to the beefy MOSFET it uses (rated for 45A). The solder pads are well sized and easy to solder. The FC and ESC’s are designed to be used together, thus plug and play with a cable. Though the pins are also broken out to solder pads so you can use them with FC or ESC if you want. Very flexible.
The Specs are:
Forward F4 MINI FC
- CPU: STM32F405R6T6
- MPU: MPU6000-SPI
- Input Voltage: 2-6S
- Firmware: Betaflight OMNIBUSF4V6
- BEC Output: [email protected]
- Size: 25.0×25.0mm
Forward 45A 4in1 MINI ESC
- Firmware: BLHELI_32
- Input Voltage: 2-6S
- Constant Current: 45A(4S) or 35A (6S)
- Peak Current: 55A (5s)
- No BEC Output
- Size: 31.7×36.5mm
- Weight: 10.8g
The stack comes with the following accessories:
- 220uF 35V capacitor
- 14AWG XT60 pigtail
- A bag of o-ring (for soft mounting)
- Nylon standoffs and screws
This stack is small enough for micro builds like 3″, but since it’s rated for 45A on 4S, and supports up to 6S, you can use it on 5″ builds as well! It makes a good choice because of the light weight.
Great versatility when it comes to the specs, not so much when it comes to the accessories.
It makes sense that it comes with 14AWG XT60 pigtail because someone might use it on a 4S 5″ build, or even 6S! But then why does it only include a 35V 220uF capacitor, which is fine for a 4S 3″ build, but clearly too small for a 6S build?
It would be nice if they included an extra 16AWG XT30 pigtail for 3″ builds, and an extra 50V 1000uF capacitor for 4S and 6S 5″ builds.
The pin-out / wiring diagram is printed on a very small card, I wish it was done on a larger piece of paper because it’s very hard to read.
At first I wasn’t sure what the o-rings are for, there are so many of them! They are for soft mounting the FC like this. HGLRC recommends using 3 o-rings between the FC and 4in1 ESC, and another o-ring between the FC and nut.
For a 4S 3″ build, the FD-1408 3600KV motors from HGLRC are a good option. However the mounting screws that they come with are barely long enough for the HGLRC Arrow frame I am going to use. It would be nice if they are 1mm longer for more solid grip, or include screws of different length perhaps.
Naked bottom design, single-strand motor winding.
The magnets seem to be very strong, as the motor feels very “notchy” when spun by hand.
The Arrow 3″ hybrid frame from HGLRC is a slick design. Not the lightest though at 41g for a 3″ frame. But this is mostly for functionality and due to the thick carbon fibre sheet used.
The arms are replaceable and sandwiched by two 2mm carbon fibre plates. The arms are 4mm thick and the top plate is 2mm thick.
They make it really easy to work with by having nut inserts in the bottom plate.
Watch out for the arms, the front and back arms are meant to be different! I was so confused the first time I was assembling it. I really don’t understand the point of this, in my opinion it’s kind of unnecessarily complicated, why not just use the same arms?
Since there is no assembly manual, you just have to play with it a few times until you get it right. I don’t think there are right or wrong ways of doing it as long as you are happy.
If you have been in the hobby long enough, It kind of looks like a “dead-cat” config. An arm layout that was more popular back in 2013-14.
Also watch out for the slots in the bottom plate for inserting the camera side plates. I realized I have it the wrong way round, since I wanted to have the “wider” arms to be the front, so I have “less props” in the camera’s view. Again, not sure why they didn’t just make the bottom plate cut-out symmetric!
The frame kit comes with long M2 steel bolts for your 20x20mm FC stack (30mm long to be exact). These are long enough for holding 3 boards – 4in1 ESC, FC and VTX.
The blue standoffs are 25mm long, taking M2 screws as well, making the max stack height 25mm.
The arms should be mounted this way in order to get the battery strap through between the bottom plates.
First thing I did was soldering the receiver to the FC, and bind it to my radio. Because it’s an F4 FC, I have to connect the uninverted SmartPort from the R-XSR and to an UART on the FC.
I will be mounting the RX at the very bottom of the FC stack, right under the 4in1 ESC.
You are supposed to use nylon standoffs under the 4in1 ESC, but I am doing things slightly differently here. I am replacing them with some o-rings, and I will use the nylon standoffs between the FC and ESC.
Both the VTX and FC are powered off the 5V from the FC. Since it’s rated for 3A, it should be more than enough.
I will be mounting the VTX on top of the FC with some heavy duty double-sided foam tape. The antenna will be mounted directly on the VTX, and I will strap it to one of the standoffs for durability.
The finished quad weighs 155g without battery. The frame is actually big enough to run 3.5″ props if you wish.
It’s a roomy frame and the components I chose fit comfortably. I think VTX with 20x20mm mounting holes would work too, probably even cleaner as you can mount it on top of the FC.
I didn’t use their 3D printed antenna mount.
First of off, it’s not a good idea to cover your antenna with TPU mount as it “de-tunes” the antenna (changes its resonate frequency and affect its performance). The RX antenna mount is quite nice, but I didn’t use it and continued to use the good old zip-tie / heatshrink trick.
I like how the blue camera is matching the frame and the motors colours. I think HGLRC should replace those side camera plates with TPU mount. Not only it’s going to be easier to assemble, they can also reduce jello in the video.