Homemade Waveguide Antenna for FPV Racing Timing Gate

In the past few years, FPV racing has quickly grown into a competitive sport. As a result, it has become necessary to keep track of lap times. Time-keeping is usually done using IR transmitters and receivers. However, this timing can be done without adding extra IR or RF beacons. By making use of the already present video transmitter on each vehicle, it is possible to keep track of every everyone in the race using their specific video channel frequency. However, there are some problems associated with using the 5.8 GHz emissions to track the vehicles. The first is the spatial accuracy where a timing event is triggered; the second is the effort needed to monitor the full FPV RF band continuously. The first problem in realising such a system is to design the receiving antenna.

A straightforward and cheap solution exists for the antenna. Using some cardboard, foil and aluminium or copper tape it is possible to build a high-gain waveguide antenna at 5.8 GHz. A slotted waveguide antenna has a thin disc shape antenna pattern which is ideally suited for use as a timing gate. Below are some photos showing the construction of the antenna.

Cardboard structure

Cardboard structure

Adding the feed structure

Adding the feed structure

Feed in place

Feed in place

Wrapping the rest of the waveguide in foil

Wrapping the rest of the waveguide in foil

Cutting waveguide slots

Cutting waveguide slots

Testing the antenna

Testing the antenna

The receiver needs to be broadband to be able to monitor all of the vehicles at the same time. For this, I would suggest mixing down the antenna signal to below 1 GHz and use multiple RTL-SDR dongles as a low-cost solution for monitoring all of the multi-copters in real-time.

Unfortunately, I have run out of time to work on the receiver. I will upload further data if there is interest in reproducing the antenna or continuing the project.

FPV Quadcopter Racing

After slipping into the world of quadcopters a few years ago, mostly for research purposes, I recently stumbled across a sport called FPV racing. This activity most commonly involves a small quadcopter equipped with a forward facing camera. The pilot then straps a monitor to his face and attempts to fly a designated race track. Think Red Bull Air racing, less expensive and less dangerous.

I built a 3D printed quadcopter based on the MHQ 2.0 on Thingiverse. All of the electronics were sourced from bandgood.com which made this probably the cheapest racer on the planet. Instead of buying the expensive Fatshark FPV goggles, I equipped myself with a Boscam transmitter and receiver along with Quanum foam goggles (Poor mans FPV option). In the end, I became comfortable with this setup with no regrets.

Yesterday I took part in the first race of the first official FPV racing competition in South Africa. My 3D printed underdog even made it past the first heat.

Below are some photos of my 3D printed FPV quad and South Africa first historical FPV race:

Pilots flying Race start image2

Smug face after coming second in my first heat.

The Intelligent Ski-Course

Last year I started building an intelligent ski-course, which was basically a set of buoy drones that would swim to there positions in a public river to form a ski course. This would then allow tons of interesting possibilities such as easy setup and effortlessly changing the shape of the course. Most of the project is documented on hackaday.io. As I am a very eager slalom skier in dire need of a course I would very much like to finish this project. However, I find myself without time working on finishing my PhD. I will one day restart my efforts, if anyone is interested in developing the project from where I left it, you are more that welcome, just keep me in the loop.

The state of the project:

  1. Most of the code has been written.
  2. The electronics for the buoy and base station has been mostly finalized
  3. 3D printed parts needs to be revised
  4. Propulsion system needs to be tested

Birth of FEMU 2.0

As part of my PhD research, involving the characterisation of the propagation environment at the SKA Karoo, time was spent developing a multi-copter RF metrology vehicle. A dramatic autopilot failure in our early prototype caused a the multi-copter to fly away forever. This event gave us a clean slate to do a full redesign upon what we have learned. One of the main problems with RF metrology using a multi-copter is the effect of the multi-copter itself on the measurement, which at this point has not been adequately addressed in research. Therefore, we set out to design a vehicle that could be appropriately de-embedded from a measurement.

The performance of antennas onboard these vehicles are in most cases unknown or assumed. These antennas have a specific characteristic pattern which could cause significant fluctuations in the measured signal, depending on its orientation. Even if the orientation was kept constant, the antenna patterns are sensitive to changes in metallic structures of the vehicle. An excellent example of this is the replacement of batteries after a flight. The replacement battery might have slightly different dimensions, position and will most certainly perturb some of the ubiquitous wires in the system.

Our approach was to shield all of the subsystems of the vehicle in a metallic enclosure. This shielding gave us a platform which had a predictable antenna pattern. Also, by closing the complex metallic environment, accurate antenna simulations have been made possible. Additionally, FEMU 2.0 also boasts a quasi-isotropic antenna pattern and a bandwidth of 260 MHz to 960MHz (See the paper for more information on this).

Hopefully, this will pave the way for RF metrology using multi-copters. If done correctly this could significantly speed up measurement time and deliver measurements that are spatially continuous. The entire vehicle has been constructed from 3D printed parts and local hardware supplies. The electronics, receiver and antenna systems can all be made available if another research group is interested in further developing the project.

Below are two images showing FEMU 2.0 during setup and measurement.

Setting up FEMU 2.0 before flight

 

Don’t Leave Me…

Since the last post, we have completed a year of successfully RF measurement campaigns. Sadly, the quadcopter featuring in the previous post (FEMU 1.0) underwent an autopilot failure during a measurement dry-run which caused it to fly straight up into the air until its battery died. It has never been seen since. This forced us to build FEMU 1.5 in 3 days. Being a temporary vehicle, FEMU 1.5 was decommissioned shortly after his first measurement campaign (25 flights). All this happened in the earlier part of the year and gave us the opportunity to do a complete redesign which will be discussed in the next post. This redesign formed a large part of my PhD degree and made attempts to break new ground in RF metrology using Multicopters.

Reward if found poster for the disappearance of FEMU 1.0

Reward if found poster for the disappearance of FEMU 1.0

This was also the start of our quest to 3D print antennas, see the 900 MHz antenna mounted at the bottom.

FEMU 1.5 with a 900 MHz antenna

FEMU 1.5 with a 900 MHz antenna

Python in Eclipse

A short brief walk-through on setting up a python environment in Eclipse with the necessary libraries. Note that all installers need to be of the same architecture namely 32bit or 64bit. This walktrhough will focus on the 64bit case.

1. Install the latest java runtime environment

2. Install the latest python distribution

3. Install the latest eclipse environment

4. Follow the instructions on the pydev site to install and setup the pydev module

5. Install the fundamental libraries from this site, below is a list of packages I would recommend:

  1. SciPy
  2. Numpy
  3. Matplotlib

I would recommend looking for the latest versions of the linked applications.