HC-12 433MHz wireless serial communication module configuration

Description

HC-12 are cheap 433MHz wireless serial port communication modules with a range up to 1800m in open space. Each costs about $5 when bought from China, and 2 of them can create wireless UART link that can be used, for example, to transfer telemetry data from UAV. Or drive IoT device. Or connect sensors. Or whatever else one can think of.

HC-12 433MHz wireless serial communication module

It is based on SI4463 RF chip, has build in microcontroller, can be configured using AT commands and allows to use external antenna. Working frequency is divided into 100 channels starting from 433,4MHz up to 473,0MHz with 400kHz channel separation. Maximum output power is 100mW (20dBm) and receiver sensitivity differs from -117dBm to -100dBm, depending on transmission speed. It accepts 3,2V-5,5V power supply and can be used with 3.3V and 5V UART voltage devices (3.3V safe). Continue reading “HC-12 433MHz wireless serial communication module configuration” »

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FPV frequency fetured image

Setting up iNav on 250 class racer

Although iNav (iNavFlight) with advanced GPS and navigation support is best suited for larger, GPS equipped drones, there is absolutely no reason not to use it on something smaller like 250 racer. Why? Well, why not? Basic flight mechanics is the same like in Cleanflight or Betaflight. FP-PID is brand new PID controller, not very popular and not very well documented, but in many ways superior to LuxFloat. The way it handles D term is just outstanding. It can be pushed very, very high without introducing noise.

OK, it has a drawback. High computational requirements and floating point logic causes users of STM32F1 based flight controllers like Naze32 or CC3D can forget about looptime 1000us. 1400us is all those boards can do. On the other hand, looptime 1000us (or even 500) is quite new thing introduced and made popular only about half year ago. And people were racing before that somehow… So, 2000 is not that bad after all. Good thing SMT32F3 board are strong enough not to have to worry about this issue. So, let’s go! Continue reading “Setting up iNav on 250 class racer” »

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Three flying weekends with Turnigy Graphene batteries

It is still too early to decide if new Turnigy Graphene are worth the money, but after 3 flying weekends with them I do have some thoughts about them already.

Turnigy Graphene LiPo Battery

  1. They discharge differently than Turnigy Nano-Tech I'm using in parallel. Discharge curve seems to be flatter
  2. Voltage drop on high load is much smaller comparing to Nano-Tech. Also, they do not regain voltage when disconnected. I usually try to fly until voltage goes below 3.5V per cell. More less 4:30 up to 5 minutes of flight with my regular style. Before charge Nano-tech's voltage usually goes up to 3.7V. With Graphene, it's different story. Before charge voltage per cell is around 3.65V. Maybe it's only half volt, but does tell something about discharge curve and general battery performance
  3. Althought they behave different than Nano-techs, they both accept more less the same charge during load
  4. My Graphenes are new, while Nano-techs not, but Graphenes seems to balance faster. Looks like cells are a better match. I still would have to confirm this
  5. They are indeed quite heavy, but I did not noticed lower flight times or worse performance

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iNav: Waypoint Mission

This video was taken few weeks ago during my tests of Waypoint Mission implemented in iNav.

Hardware setup:

  • Transporter Q7.6 600mm quadcopter frame
  • SPRacingF3 Acro with BMP085 external barometer
  • Beitian BN-880 (ublox Neo-M8M)
  • 10×4.5" APC props
  • EMAX GT2218/08 1100KV motors
  • 5000mAh 3S battery

Software setup:

  • iNav pre 1.1
  • Default navigation PIDs
  • Slightly tuned FP-PID, quite close to default values
  • GPS nav model: HIGH_G set gps_nav_model=HIGH_G
  • Velocity calculation done by GPS module set inav_use_gps_velned=ON

Mission plan:

  1. Take off in Angle model
  2. Follow 3 waypoints on total distance of about 300m, constant altitude of 10m
  3. At last waypoint goto Position Hold mode
  4. Manually engage Return To Home mode
  5. Automatic RTH and land

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Improving cheap radio range

Radio range of my first drone, UDI 829A was pretty pathetic. OK, it was (still is, I only have to finally replace motors) pretty indestructible, quite stable and reasonably priced. But effective radio range as quite short. More less 50 meters. Above that limit strange things started to happen. The reason was pretty simple. Just take a look at this picture.

Antenna too short

Can you see the transmitter antenna? Yeap, that it this short cable. Not only it does not go into “antenna cover” of the receiver, it is also horizontally polarized and when receiver is held in a normal way, pointing into a drone, it emits almost no signal in this direction. This and an additional single whip antenna on the receiver makes it virtually impossible to have a good radio range.

So, I’ve decided to fix that and install external antenna that would work with vertical linear polarization and actually emits some power in drone’s direction.
This tutorial shows how to do it for UDI 829A, but will work almost all cheap drones. Their transmitters are very similar inside and as long as there is antenna pad or connector, it can be done. Continue reading “Improving cheap radio range” »

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iNav: RTH with land mission

This video was taken last weekend during tests of latest changes implemented in iNav, as well as new GPS module Beitian BN-880 I shortly described here.
Mission plan:

  • Take off in Angle mode,
  • Engage 3D Position Hold
  • Fly away 100m
  • Return to Position Hold
  • Engage Return To Home mode

Summary:

  • Beitian BN-880 performed well. Quadcopter returned home with 1m accuracy. Constant fix on 15 sats all the time and HDOP at 1.2
  • No problems with magnetometer inside GPS module
  • No bigger problems during whole mission. I still have to work on yaw behavior. At the moment FP-PID and linear mixer from Betaflight can cause some strange yaw behavior on bigger quads. Fix should be available soon

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Battery C rate: do I need a lot of it?

One of the values that describe LiPo batteries used in RC crafts is so called C rating. For example: 3S 1300mAh 45-90C. Or 3S 5000mAh 25-30C. Or 4S 1300mAh 65-95C. S is simple, it tells the voltage. mAh or Ah tell capacity.

But what about C rate? According to Wikipedia is can be described as:

The C-rate is a measure of the rate at which a battery is being discharged. It is defined as the discharge current divided by the theoretical current draw under which the battery would deliver its nominal rated capacity in one hour. A 1C discharge rate would deliver the battery’s rated capacity in 1 hour. A 2C discharge rate means it will discharge twice as fast (30 minutes). A 1C discharge rate on a 1.6 Ah battery means a discharge current of 1.6 A. A 2C rate would mean a discharge current of 3.2 A.

So, if we take a look at Turnigy Nano-tech 3S 1300mAh 45-90C we will know that:

  • Constant discharge current on 45C is 58.5A
  • Burst discharge current (10 seconds) on 90C is 117A

Neat, yeah? Almost 60A constant current! That gives 15A per motor. And that a lot on 250 or smaller quad. So, I should be fine! Continue reading “Battery C rate: do I need a lot of it?” »

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Hands-on: Turnigy Graphene LiPo batteries

LiPo battery life is hard. Charged, discharged, beaten in a crash, charged, discharged and so on. Because last week I had to utilize few of my old Turnigy Nano-tech LiPos, I’ve decided to try something “better” this time. Turnigy Graphene 1300mAh 3S 65C. Package came today and this is what I got:

Turnigy Graphene LiPo in box

Turnigy Graphene LiPo there is even a bag inside

Turnigy Graphene LiPo Battery

Turnigy Graphene LiPo

  • Box is huge. Really, it would fit 3 LiPos, not just one. Kind of waste. But box is nice enough to reuse for something else
  • Black is the color of choice here. Black and red. I like this combination
  • They are noticeably heavier than 1300mAh 3S Nano-tech LiPos. But they have 20C more, so that was predictable

More after the weekend when I should be able to give them a first try.

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