The things that I have to do

Let's have a chat about thing highly related to this channel: what it is about, what I have to do, who am I and why you are and why I will try to be just honest. That the earth is flat and there are only two sexes. That this channel is not a free INAV support and affiliate link are the only way to get any kind of money back. That there will be no reviews of things sent by Banggood and I've seen some shit…

Betaflight and INAV in crisis – how money in RC hobby is distributed

Current money distribution in the RC hobby is at least not fair. All OpenSource flight controller projects (Betaflight, INAV, APM) and underfunded or not funded at all. Users expect features but developers are not getting any money for their work. Is it fair? Is it helping the hobby when the ones that provide so much are not compensated for their work? After all, all attempts to make any money on GPL OpenSource will fail. Crap…

How to make tape hinges

If you have a foamie or want to build your own airplane, this skill is a must: how to make tape hinges! In this example, we will make a tape hinge between to pieces of Depron foam board. But it can be any other kind of flat material: balsa, plywood, metal, plastic. The basic idea is always the same: two strips of adhesive tape on both sides

GoPro Hero 7 Black review (FPV edition) – many NOPEs and one YESSS!

To keep it nice and simple: GoPro Hero 7 Black is a great camera and HyperSmooth is just an amazing option. Really, HyperSmooth does the job on FPV quads in a way that I did not expect was possible without a real gimbal. But… like always, there are buts: GoPro Hero 7 Black is bloody expensive, heavy and not that tough as you might imagine. I hit a twig and LCD cracked… for a 400 EUR that was rather unexpected.

And finally example footage recorded with GoPro Hero 7 Black on this year's holiday in the mountains

FuriousFPV True-D X firmware update via Bluetooth from your smartphone

Today something that was supposed to be a very fast and nice experience but turned out to be quite stressful: how to update the firmware in FuriousFPV True-D X diversity module using Bluetooth and Android or iPhone app. It "almost" worked out of the box. Luckily True-D X was not bricked during the failed firmware upgrade!

How to choose motors for drones – especially 7-inch FPV quadcopters

One of the mistakes pilots makes when they build their first drone is they use too small motors. People think that if a motor works fine with 5-inch props, it will work with 7-inch props as well. After all, both have plenty of power and power is the key to everything.

How to choose motors for drone - 2207 motor with 5-inch propeller

It's not true. Power is only half on the story. Power is an effect of motor torque and rotation speed. The bigger torque and the bigger rotation speed, the power is bigger as well.

It's easy to guess that bigger propeller will be rotation slower than the bigger one. If the rotation speed is smaller and the motor has the same torque, the power might not grow after all. Also, the bigger propeller will have higher moment of inertia and will require more torque to change rotation speed, and generated thrust, as quickly as smaller ones.

How to choose motors for drone - 2507 motor with 7-inch propeller

This is why, when choosing a motor for a drone, you have to concentrate both on KV of a motor and a size. To be honest, the correct size is even more important than the correct KV.

How to choose the motor size

Drone motor manufacturers do not like to share torque data. I have no idea why. It would be so cool to be able to compare torque between motors of a different brand. Assuming, of course, they would be realistic. If we can not compare the torque of two motors, we can compare the next best thing: stator volume.

For our needs, we can just assume that bigger stator volume equals higher stall torque of a motor. Not very precise, but good enough. Luckily we can compute stator volume from the motor size. Two first digits are a stator diameter, two last digits are stator height. We can also skip Pi, since it’s a constant. And then:

V = (diameter / 2)^2 * h

Stator volume of different motor sizes

Motor size Stator diameter [mm] Stator height [mm] Stator volume [mm^3]
2204 22 4 484
2205 22 5 605
2207 22 8 847
2208 22 8 968
2306 23 6 793
2406 24 6 864
2506 25 6 937
2507 25 7 1093
2508 25 8 1250

Desired stator volume for propeller sizes:

Propeller diameter Min required stator volume [mm^3]
5-inch 600
6-inch 700
7-inch 900

To check is a motor will be good for a propeller size just check if stator volume is bigger than min. volume for a prop size. That's all. You can choose bigger volume but never lower. The lower volume will result in not enough torque and characteristical bobbing o pitch axis that is just impossible to tune out.

How to choose KV

In the case of motor KV, it's a similar case. Too high KV will result in an absolute lack of efficiency and overpowered drone (which is not desirable in most of the cases). Too low KV will result in an underpowered drone that will not be able to perform any fast maneuvers and feel very sluggish on the yaw axis.

The sweet spot/reference KV can be easily computed from this equation based on propeller diameter and supply voltage. Of course, more S will result in lower KV.

KV = Pc / S

  • KV – motor KV
  • Pc – propeller coefficient
  • S – number of LiPo cells

Pc for different prop sizes:

Propeller diameter Pc
5-inch 9600
6-inch 6400
7-inch 7600

Recommended motors:

How to setup INAV 2.2 on 7-inch quads – PID tuning

INAV 2.2 is with us and it brings a series of cool improvements that should make all owners of mini quads very happy. Those are:

  • Improved Airmode that is more suited for small and powerful drones
  • Iterm Relax that allows getting rid of bounceback at the end of flips and rolls
  • D-Boost allows having cold motors and a lot of Dgain when doing fast maneuvers. It's an equivalent of D_Min from Betaflight
  • Configurable gyro stage 1 filter type: PT1 or BiQuad
  • Faster D-term filtering
  • and a few other goodies
    In this video, I will show you how to set up INAV 2.2 for 7-inch quads to get the best flying experience possible.