Toy Stirling engine = best toy ever and best Christmas gift?

How is it until Christmas? 2 months and something. Pretty close. And like every year there will be problem: what to buy someone who has everything? Tough one, right? Sweater? Socks? Toy Stirling engine? I vote for Stirling engine for sure. There is only one precondition: recipient has to like mechanics πŸ™‚

I’ve tested the cheapest toy Stirling engine from china you can get. For less that $20 you get a functional engine model that, surprise, surprise, works. Amazing, right? Here is my video review of it:

Oh, by the way, for me, this is the best toy ever!

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And the most popular flight controller for INAV is… (August 2017 edition)

More than 2 months after previous “What it the most popular flight controller for INAV“, welcome to second edition.

I mportant, this is not the number of boards flashed with INAV, but rather number of times a board was connected to Configurator!

This counts TARGET software name, not retail name. For example, all clones of Naze32 will be counted as Naze32

Data was taken in August 2017, multiple connections during single user session are stored as single entry.

  1. SP Racing F3 – 25% of all boards, lost 4 percent points
  2. Omnibus F4 Pro (aka v2 aka SD) – 15% of all boards, gained 5 percent points
  3. Naze32 rev. 5 and 6 – 13% of all boards, lost 6 percent points
  4. Omnibus F3 – 12%, lost 1 percent point
  5. Naze32 older than rev. 5 – 7%, gained 2 percent points
  6. Omnibus F4 v1 – 4%, gained 1 pp.
  7. Omnibus F4 v3 and v4 – 3%, first time in TOP 10
  8. SP Racing F3 EVO – 3%, lost 2 pp.
  9. CC3D – 3%, lost 1 pp.
  10. AnyFC F7 – 1%, first time in TOP 10

Other targets have 14% in total.

This data also says something about CPU generations distribution:

  1. STM32 F1 – 27%
  2. STM32 F3 – 47%
  3. STM32 F4 – 25%
  4. STM32 F7 – 1%

What changed comparing to June?

  1. First F7 board appeared in TOP 10!
  2. F1 and F3 targets are loosing market share, while F4 and F7 are more and more popular
  3. Naze32 is no longer second most popular board
  4. OpenPilot Revolution and Airbot F4 (more less the same) are out of the TOP 10
  5. Boards with integrated OSD are more and more popular. They already have 47% of market share

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RunCam Split very late pseudo review: it’s not good

Yes, I know it’s few months too late. And it’s not really a review but rather, since I was never able to use it or I describe my friends experience with RunCam Split.

I own RunCam Split. I own it for like 2 months now, and it’s still in a box. Never connected, never really used. And in the meantime, I’ve build 2 mini quads are rebuild third. Why is that? Is there something wrong with RunCam Split that I’m not using it anywhere? And not planning to? Let’s be quick about it:

RunCam Split camera module and PCB

Continue reading “RunCam Split very late pseudo review: it’s not good” »

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Testing 868MHz LoRa range, part 3: round trip

After determining that range of 868MHz LoRa wireless modules E45-TTL-100 have, at least, quite impressive range (5,7km and I was out of line-of-sight to test further) I’ve decided to test something else.

In the beginning I was planning to use those radio modules for telemetry only, but then another thought crossed my mind: why not to build DIY TBS Crossfire for the poor? After all, TBS Crossfire also uses 868MHz LoRa (SX1272 vs SX1276), so it should be possible to build DIY radio link for medium range (up to 5km) for RC planes, right?

First of all, I will need to know how fast data can be transferred and how much delay can I expect in real life. So I’ve modified Arduino code and E45-TTL-100 configuration:

  • UART speed bumped from 9600bps to 57600bps
  • air speed bumped from 2400bps to 19200bps
  • output power lowered from 100mW to 50mW (17dBm)
  • transmitter sends 5 bytes of data (current microseconds and prefix)
  • relay receives packet and resends it to transmitter
  • current received number is deducted from current microseconds and round trip time is showed on OLED display

LoRa E45-TTL-100 round trip test

Results:

  • Round trip time is 82ms on average and it does not changes with distance
  • at lower output power (50mW vs 100mW) reception at 2.8km is worse. 100% of packets are received only then antenna alignment is not worse than 45 degrees
  • with slightly bigger payload size (up to 7 bytes) it should be possible to archive at least 20Hz update rate

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Quick note on SEMTECH SX1276 100mW output mode

Few facts about SEMTECH SX1276 LoRa modem and 20dBm (100mW) mode:

  1. +20dBm (100mW) is possible only on PA_BOOST pin
  2. Pins RFO_LF and RFO_HF allows only up to +17dBm (50mW)
  3. Maximum allowed duty cycle while using +20dBm mode is 1%
  4. Maximum allowed VSWR while using +20dBm mode is 3:1

The biggest problem with +20dBm on PA_BOOST is allowed 1% duty cycle. On the other hand, +17dBm mode (50mW) does not have such a limitation and maximum range should be only 1.42 times shorter than in 100mW mode.

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Hands on: Tiny Frsky 8CH Receiver from Banggood

I have a nasty habit of buying things and then forgetting about them. Something like that happened to Tiny Frsky 8CH Receiver (Wolfbox F802 software compatible) from Banggood I’ve purchased last year. For some time I used it in JJPro P175 quadcopter, but then it landed in a box and I forgot about until last week.

Tiny FrSky 8CH DIY Receiver Pinout

So, let’s do overdue “hands on” on Tiny Frsky 8CH Receiver from Banggood… Continue reading “Hands on: Tiny Frsky 8CH Receiver from Banggood” »

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Testing 868MHz LoRa range, part 2: open space

It was a good weekend. At least for me and CDEbyte E45-TTL-100 868MHz LoRa serial wireless modules based on SX1276. Why? Since weather was nice and looks like those modules are way better than datasheet specifies. Specs states: 3km in open space. And I’ve proven almost twice that much range! Last Friday I’ve placed one E45-TTL-100 with stock antenna on my balcony, took second with me and went for a car ride.

E45-TTL-100 LoRa 868MHz range test results

Area around my home is full of small hills and copses, so most of the time something was blocking the line between transmitter and receiver. But every time I was high enough, I was getting clear signal without any packets lost. At the furthest point of my trip I was 5.7km from the transmitter, inside a car and a copse was between me and TX module. That means no line-of-sight and as a result I’m pretty, pretty sure E45-TTL-100 should be able to work on much higher range that that. I only have to find a good place to test it.

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Betaflight 3.2 Dynamic Filtering Explained

With upcoming Betaflight 3.2, we will be given a new, outstanding, new feature: dynamic filtering. An belive me, it was worth waiting for Betaflight 3.2 only to get it. I do not care much about other changes that happened with version 3.2 but dynamic filtering it the thing! In this post I will explain, in simple words, what is dynamic filtering and how to enable it.

The problem of noise

Gyro has a nasty tendency to pick up a lot of noise. Vibrations. After all, there are a lot of things that can vibrate (motors, propellers) and resonate (frame). Without a good way to filter all that noise out, our racers would not fly as good as they fly now. And you would be replacing motors and ESCs even more often. I you want to know more about gyro noise sources and filtering, please watch my Gyroscope and filtering series on YouTube.

Continue reading “Betaflight 3.2 Dynamic Filtering Explained” »

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Testing 868MHz LoRa range, part 1: urban area

With a (more less) free evening I decided to finally start testing range of 868MHz LoRa E45-TTL-100 radio modules I described only yesterday. Instead of building new testing rig, I only upgraded testing setup I used to test range of FS1000A and XY-MK-5V 433MHz radio modules. Few hours later I came up with this:

LoRa range testing equipment

  • E45-TTL-100 at 9600bps, transparent serial mode
  • Stock (crappy) antannas
  • Logic driven by Arduino Pro Mini
  • Transmitter send 1 byte counter
  • Receiver counts packets and check if all subsequent packets arrived and then displays results on OLED screen
  • Powered from 2S LiPo batteries

I’ve left transmitter on a desk and went for a walk. Even before leaving the building radio signal had to cross around 1 meter of bricks. Then travel through another building and only then go into the direction when I walked.

LoRa range in urban area with E45-TTL-100

I must say: I was impressed. I still am. At 511 meters transmission was clear only when I was not blocking it with my body. Or standing near to metal fence. So I can safely assume: 500m is maximum range in densly populated urban area. On stock antennas and 100mW output power. Next week I will try stronger, dipole antennas.

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Understanding Dterm: how Dterm really works

I will be very honest: until very recently I did not really understood how PID controller’s Dterm really works. Yes, something with dampening, something with “looking into future”, bla bla bla. But the reason for not understanding was because I was overthinking it. There is no “magic” only simple mathematics and few basic concepts which I will now explain.

Setpoint

Setpoint is the value which we request from our system. In case of multirotors, PID setpoint will be a rotation speed around axis given in degrees per second [dps]. Setpoint 0 means we do not want to rotate (keep current attitude) and setpoint 200 means we want to rotate at 200dps

Measurement

Measurement the value that represents actual state of the system measured by some kind of sensor. In our case, it will be the gyroscope and rotation-around-axis speed measured in degrees per second

Error

Error the difference between Setpoint and Measurement computed as Error = SetpointMeasurement. In our case, when Error is above 0, that means drone is rotating too slow and should speed up. If Error is below 0, drone is rotating too fast and should slow down

Understanding Dterm - setpoint measurement and error Continue reading “Understanding Dterm: how Dterm really works” »

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