Your first 7-inch FPV drone

I love 7-inch FPV drones and during the last year, they were my most used FPV gear. For freestyle, cinematic, cruising and long-range. I currently own 3 7-inch FPV drones and 4th one in the assembly process.
I think of myself as a 7-inch expert. I’ve wasted enough money and equipment to know what works and what does not work well with 7-inch propellers.

TBS Source One 7-inch FPV drone

If you are thinking about building your own 7-inch FPV drone, here are some tips that might save you a lot of time and a lot of money on wrongly chosen equipment.

The Frame

Of course, the frame is the most important part of a build. No matter if you will be building a freestyle or long-range rig, there is one thing that you have to know: Horizontally scaling 5-inch frame by making arms longer is a no-go. Longer arms require more stiffness and they also have to be thicker! The sweet spot is 6mm thick good quality carbon fiber. 5mm thick might work too but forget about 4mm or thinner arms. They will be too flexible and the whole quad will be in a state of a constant wobble!

Alfa Monster 7-inch FPV Frame

If you are looking for 7-inch frame recommendations, here are my choices: Team BlackSheep Source One with 7-inch arms, Alfa Monster and AlfaRC Fighter.

Propellers

Kind of obvious, right? The choice of good 7-inch propellers is not that big as one might imagine. Sure, you can buy some “inventions from 4 years ago for cheap” but believe me, they are not worth it. There are 3 types of modern 7-inch propellers that I find worth looking at in late 2019:

  • DAL T7056C – good for freestyle and thanks to aggressive pitch they are very dynamic. Can be used no longer flight, but this is not where they really shine.
  • HQProp Durable 7x4x3 V1S – a more aggressive version of 7×3.5×3 that in my opinion works much better than original. Slightly more pitch only helps during steady flight. They are rather for cruising than for freestyle.
  • GemFan FLASH 7042 – kind of good propeller, but don’t get me wrong, you should try 7042 only if DAL or HQProp are too heavy for your motors. So if you have 2207 or 2306 you might try FLASH. If you have bigger motors, just go with DAL or HQProp.

Motors

Brotherhobby Avenger V2 2507

Probably the most often made mistake by the “7-inch virgins” are too small motors. Beginners think that putting the same motors that work great with 5-inch propellers on a 7-inch frame is a good idea. OK, maybe sometimes they lower the KV. This will not work. I know. I tried that by myself and only wasted some money and a lot of time and nerves.

What you need are big motors. In a size of 2506-2507. 2208 might work as well and 2508 is rather the max size that makes sense.

On the KV size, the rule of thumb is that on 4S you should aim at 1500-1500KV and on 6S at 1200KV. Those values give a nice compromise between efficiency and raw power. Of course, this is only a rule of thumb and when needed you might choose higher KV. For example, my 7-inch freestyle drone uses 1700KV on 4S motors.

My recommendation is rather simple: for now, there is only one motor that comes is wide enough KV range and it’s called BrotherHobby Avenger v2 2507.

Everything else

For the rest of the equipment, you can choose whatever you want. Any equipment will work and you do not have to match it to the propeller size. My choices are:

FrSky R9M vs R9M2019 teardown

I do not why, but FrSky does not want to keep things simple. Not only it’s migrating from ACCST to ACCESS, it also makes a mess with FrSky R9M system by releasing new hardware that looks like old hardware, has a very similar name and can run ACCESS but only on some radios, not on the other. The nightmare…. Today let’s compare the FrSky R9M transmitter module I own for last (almost) 2 years with a brand new FrSky R9M2019

3D Printed Impeller Fan aka Centrifugal Blower

I have a 3D printer and some CAD skills, as well as basic engineer training. I never studied fluid dynamics, but I also never studied running a website or how to be a father, but here I am.
Anyhow, I want to put an impeller fan (yes, not a turbo) on an airplane and use it as a propulsion system. After a few days with CAD software, I came up with a small 3D printed impeller fan that hopefully will be strong enough to make airplanes fly…
The centrifugal fan is power from a “standard” drone brushless motor and a standard RC ESC. It sounds terrific!

What happened to INAV horizon drift?

INAV suffers from horizon drift since day one. It’s not that Betaflight does not suffer from it (both Betaflight and INAV originate from the same parent: Cleanflight). In Betaflight it just does not matter at all. In INAV it’s a real-life problem tho.

So far, we somehow managed to mitigate horizon drift on airplanes but it’s not really fixing the problem. It’s there and it’s irritating as hell.

Last month I published a post that describes my intent to use the external board as a secondary IMU for INAV. It is “of the shelf” Bosch BNO055. Today I finally put it into a test and to be honest, the results are very optimistic!

More about INAV horizon drift:

Matek VTX-1G3, VRX-1G3 and ANT-Y1200 ready for testing

The upcoming 1.2GHz FPV system from Matek called 1G3, where VTX-1G3 is the transmitter and VRX-1G3 is the transmitter and ANT-Y1200 is the antenna, are ready for some flights!

Matek VRX-1G3 connected to Fat Shark HDO FPV goggles

So far I have a couple of remarks:

  1. VRX-1G3 fits nicely inside a standard Far Shark receiver bay and you can use the standard bay cover too. SMA connector is in the correct place! The standard cover blocks access to the button that is used to change channels. You can not change channels from the goggles menu.2. ANT-Y1200 has a nice stiff coax cable and you can position it however you want
  2. ANT-Y1200 is much bigger than antennas used for 5.8GHz FPV and it’s much harder to find a good place to position it on a model.4. VTX-1G3 is luckily small enough to fit in many places and does not overheat. Even when powered from 4S it stays relative cold (50C) at 28dBm of output power. I got the word it’s because of much more efficient energy conversion that is possible with 1.2GHz band

Matek VTX-1G3 and ANT-Y1200 on a Flybot Flux

The best flight controllers for INAV – 2019 Q4 edition

Believe it or not, but choosing the right flight controller for your next airplane or a drone build is quite important. Yes, I know that some of you might say that hardware does not matter and your kwad will fly as good with the latest F7 flight controller as it would fly with Naze32. It is, not true. It would fly with Naze32, but do not even try to compare modern flight controllers with more advanced filtering, inputs, outputs, and peripherals.

Best flight controllers for airplanes

Matek F722-WING

Matek F722-WING

Matek F722-WING is the second generation of a big WING flight controllers started by a famous F405-WING. Comparing to the original, F722-WING offers more input/output options, including dedicated airspeed port, switchable camera inputs and switchable power supply for FPV installation.

FuriousFPV F35

FuriousFPV F35 is a well know and proven airplane flight controller brought to by by the FuriousFPV. Based on STM32F4 MCU provides plenty input/output options in a relatively small form-factor. Can be bought with matching GPS, Bluetooth and Airspeed modules. F35 utilizes plug & play idea, since most ports are broken out as JST-GH connectors.

Matek F411-WING SE

Matek F411-WING SE

When small size is required, F411-WING SE comes into play. Super small and lightweight but offers enought serial ports and outputs to satisfy most lighweight builds. Vertcal USB port makes it easily accessibke when installed inside alsmost any foam airplane.

Best flight controllers for drones

Kakute F7

Holybro Kakute F7

Holybro Kakute F7 managed to do what others failed. It fits powerful STM32F745, OSD, SD Card and enough serial ports for everyone in a form factor only slightly bigger than standard 36x36mm. The unique feature of the whole Kakute series is a gyroscope installed on a separate board connected with the main board with a thin ribbon cable and sponge. It helps to keep gyro noise under control. Made to use together with 4-in-1 ESCs.

Matek F722-SE

Matek F722-SE

Matek F722-SE is probably the best STM32F7 flight controller for drones on the market. Integrated OSD, power distribution board, output for 6 motors or 4 motors and 2 servos, integrated camera switcher and "power on a switch" function. INAV, Cleanflight, and Betaflight supported. Enough Serial ports of everything you need, including ESC telemetry.

Matek VTX 1G3 Long Range Video Transmitter Power Test

New long-range 1.2GHz video transmitter and receiver from Matek are hot topics of the last few weeks. They seem to be a very interesting proposition for all long-range flyers that are not happy with more popular 5.8GHz FPV systems.

Matek 1G3 VTX and VRX with antennas

Last week I’ve connected Matek VTX-1G3 to an RF power meter and this is what came out of this.

Bottom line: this looks like a very decent 1.2GHz FPV system and Matek VTX-1G3 and VRX-1G3 might be what long-range community really needed!

Ohm’s Law for beginners

Yes, Ohm's Law for beginners, not for dummies. I do not want to offend anyone and if you are interested in things like Ohm's Law, you are clearly not a dummy.

In this video, we will talk briefly about what Ohm's Law is and how it influences everything connected with electricity. That it describes the relationship between voltage and current. That when you increase the voltage, you increase the current as well. And that voltage and current combined together give you power! And that doubling the volatge, you increase the power 4 times!

Matek F765-WING specification and images

Matek makes probably the most advanced hobby level flight controllers that run Open Source like Ardupilot or INAV. The Matek F765-WING is currently best-of-the-best. Here are some images and full specification:

Matek F765-WING Flight Controller

  • Dimensions: 54 x 36 x 13 mm
  • Weight: 26g
  • Input voltage:
    • 3S-6S LiPo
    • Integrated TVS diode
  • ESC outputs: 2
  • Servo outputs: 10 PWM outputs with DSHOT support
  • 6 ADC inputs
  • 7 hardware serial ports. UART1, UART2, UART3, UART4, UART6, UART7, UART8
  • 1 Software Serial option
  • Processor: STM32F765 at 216MHz
  • Dual Gyro: MPU6000 and ICM20602
  • Barometer: BMP280
  • Built-in OSD based on AT7456E
  • SD Card slot with Blackbox capability
  • External buses: 2xI2C, SPI4
  • Dual camera input
  • Switchable output (PINIO)
  • 123A current sensor
  • Airspeed sensor support: Analog on Air pad and Digital
  • BECs:
    • 5V, 2A constant, 3A burst
    • 9/12V, 2A constant, 3A burst, voltage user selectable
    • 5/6/7.2V, 8A constant, 10A burst, voltage user selectable
    • 3.3V, 200mA

Matek F765-WING Flight Controller

Matek F765-WING Flight Controller

Matek F765-WING Flight Controller

Matek F765-WING Flight Controller