Working at Bitcraze means designing electronics as well as writing software for it, but there is also a lot of other things going-on and managing servers is one of them.

Originally, in 2011 we had a virtual server in the cloud (a VPS like it was called back then). We carefully setup and configured this server and we maintained it over the years. This was easy and served us well but it was also very ‘manual’: any updates where done on the production machine directly and we where doing all changes directly in the production machine.

In 2015, when Kristoffer joined Bitcraze, he revamped completly the server setup. Suddenly we had not only one server but two, one production and one staging. And all servers running on these machines where running in docker containers. This means that the servers where nothing more than a well configured machine to run docker, and all important software and configuration are in docker images and are launched using docker-compose. This is the architecture we are still using today, a great description was written by Kristoffer in a previous blog post.

The docker architecture has worked well but we still have one major problem, we still have servers to take care of. They are still configured manually, needs to be kept up to date and happy at all time. We have been wanting to get rid of these servers and “just” run our containers.

Now enter Kubernetes. Kubernetes is a container Orchestrator originally made by Google that abstracts the servers and allows to run containers independently of handling servers. We had heard of Kubernetes back when we started working with Docker but deemed it overkill: we did not want to setup and handle a cluster of server by ourselves and back then it was not clear that how long Kubernetes would be around. Over time though Kubernetes has had support by all major cloud providers and there is managed offers that would allow us to not handle any servers ourselves.

We are not there yet, but we have been working over the summer at converting our infrastructure to Kubernetes and we are very close to deployment. One of the main parts is our internal Jenkins build server that currently build and deploy services by ssh-in into servers. With Kubernetes this deployment phase will be much simpler and will allow us to update the website without downtime, this is a welcome functionality now that the documentation is moved from the wiki to the main website.

With lightweight Kubernetes distributions like K3S there is also an opportunity to run containers in more domains. For instance we have been talking about making automated hardware system test-bench for a while to test every commit against the real hardware. With K3S and a couple of raspberry-pi that could be achieved quite easily. This is a subject for future fun Fridays though … :-).

We have briefly mentioned the Active marker deck earlier in our blog and in this post we will describe how it works and what it is all about.

The Active marker deck is a result of our collaboration with Qualisys, a Swedish manufacturer of high end optical tracking systems. Optical tracking systems are often referred to as motion capture (mocap) systems and are using cameras to track markers on an object. By using multiple cameras it is possible to calculate the 3D position of the markers and the object they are attached to with very high precision and accuracy. It is common to use mocap systems in robotic labs to track the position and orientation of robots, for instance quadrotors.

Passive markers

The most common marker type is the passive marker, that is reflective spheres that are attached to the robot. By using infrared flashes on the cameras, the visibility of the markers is maximized and it makes it easier for the system to detect and track them. We are selling the Motion capture marker deck to make it easy to attach markers to a Crazyflie.

To get the full pose (position, roll, pitch, yaw) of a robot, the markers must be placed in a configuration that makes it possible for the mocap system to identify the orientation. This means that there must be some asymmetry in the marker positions to understand what is front, back, up, down and so on.

With a swarm of Crazyflies, unique marker configurations makes it possible to distinguish one individual from another and track all drones simultaneously. With a larger number of robots it becomes cumbersome though to place markers in unique configurations, and one approach to solving this problem is to have known start positions for all individuals and keep track of their motions over time instead. This solution is used in the Crazyswarm for instance and all Crazyflies can use the same marker configuration in this setup. Another approach is to make it possible to distinguish one marker from another, enter the Active marker deck.

Active markers

It is possible to use infrared LEDs instead of the passive markers, this is called active markers. The LEDs are triggered by the flash from the cameras and they are easily detected as strong points of light. Since they are emitting light they can be detected further away from the camera than a passive marker and the smaller physical size also keeps them more separated when they are far away and only a few pixels are available to detect them in the camera.

Furthermore Qualisys has a technology that makes it possible to assign an id to each marker and that enables the tracking system to identify individual markers and thus uniquely identify individuals in a swarm. With different IDs on the markers, there is no need have asymmetrical configurations and the marker layout can be the same on all drones. It also reduces the risk of errors in the estimated pose, since there is more information available.

The deck

The Active marker deck is designed to go on top of the Crazyflie and has four arms with one LED each. The arms are as long as possible to maximize the signal/noise ratio in the cameras, while still short enough to be protected from crashes by the motors. There is a STM32 F0 on the deck that takes care of the LEDs and handling of IDs and the main Crazyflie CPU does not have to spend any time on this.

The status of the deck is that the hardware is fully functional (we might want to move something around before we produce it though) and that there is a basic implementation of the firmware. IDs are assigned to the markers using parameters in the standard parameter framework in the client or from a script.

We will start production of the deck in the near future and it will be available in the store this autumn. Qualisys added support for rigid bodies using active markers in V2019.3 of the QTM tracking software.

We have a busy schedule in the fall, since we are planning to travel all around the world for all kinds of awesome conferences and symposia. Here is a quick overview of where we are planning to go in October and November.

IMAV Madrid 1/10-4/10

We will attend the IMAV 2019, and this time it is in Madrid (Spain) from the 1th to the 4th of October. This is a conference for anything related to micro-aerial vehicles and also includes an awesome indoor and outdoor competition. Arnaud and Kimberly will be present at both the indoor and outdoor fair, where we will show some demos with the lighthouse system and show off our new Crazyflie Bolt!

Symposium Seoul 14/10 – 15/10

In collaboration with our partner CLRobur, we will have a symposium in Seoul (Korea) on the 14th and 15th of October. Kristoffer will explain the attendees all about positioning systems, and show off the LPS and our new lighthouse deck.

Sign up here or send an email to

IROS Macau 4/11-8/11

Last but not least, we will be there at IROS 2019 as well! This is one of the flagship robotics conferences of IEEE. In Macau (China) from the 4th till the 8th of November, Marcus and Tobias will show some awesome demos with the lighthouse system and hopefully we will present the new AI deck!

We have so many interesting things we want to do, but too little time to do it. Now we are looking for more talented people to join our team to help us create awesomeness!

We don’t have a clear description of exactly what we are looking for but there are some properties that we think are important:

  • You are interested in technology
  • You are passionate
  • You want to learn new things and evolve your skills

Head over to our jobs page for more information.

Hello everyone, I’m Victor and you probably haven’t heard of me yet but I’ve got the awesome opportunity to spend some weeks during this summer working at Bitcraze. Working… Well, I’ve spent the majority of my time here getting invaluable experience, programming, flying with drones, eating incredible falafel and having fun so it’s really been a pleasure.

I’m quite new to both programming and electronics, so while I haven’t created any huge masterpieces of code yet, I did make a small program with a GUI that let you test the health of motors and propellers of the Crazyflie. You can run multiple ones simultaneously (I’ve tried up to 8, which works fine, even with a single radio, and you should be able to run many more) and it relies on using either Lighthouse or a Flow deck for positioning.
The propeller-test is essentially the same test as the one integrated with the cfclient, however the motor-test checks the thrust-levels of the motors (by hovering in the air for x seconds) to see if any of them are off and ranks them as good/bad. The default threshold is 15% but can be changed according to needs. The program is written in Python and uses tkinter to run the GUI application and the cflib to communicate with the Crazyflie. The script can be found here.

In the end of August I’m going to study Computer Science and Engineering which I’m extremely thrilled about and this has really been a perfect preparation for that! In the future I hope to contribute to the Crazyflie projects and learn more from the great team here at Bitcraze.

So until next time, fly safe!

The High-level Commander has been part of the Crazyflie firmware since the 2018.10 release. In combination with a positioning system, it can fly the Crazyflie along a trajectory that is either defined in the firmware or uploaded through the python lib. It originates from the Crazyswarm project and we have used it in various demos since it is possible to make trajectories that are very fluid and looks really cool. The trajectories are defined as 7th degree polynomials describing segments executed one after each other.

The controller gives full control of position, velocity, acceleration and jerk, the only problem is that it is non-trivial to generate the polynomials. We have wanted to simplify the creation of trajectories for a long time and have finally had some time to play with it. In this blog post we will describe how it can be done with Bezier curves and show some examples.

Each segment in a High-level commander trajectory is defined by four 7 degree polynomials, one for x, y, z and yaw. There is also a scaling parameter that tells the controller the time scale to use when executing the segment. Using polynomials of degree 7 makes it possible to design trajectories that are continuous in position, velocity, acceleration and jerk when changing from one segment to the next, which is important to get a smooth and controlled flight.

Bezier curves are common in many graphics applications and are probably known to most users. They are parametric curves defined by control points, usually three or four. Bezier curves can also be expressed as a polynomial, and this is what we will use in this case. To get a correct mapping to the desired polynomials we need some more control points and will use 8 per segment. The basic idea is to define the trajectory as Bezier curves and make sure the control points are placed in such a way that the continuity requirements are satisfied.

Bezier curve with 8 control points

On this page from University of Cambridge, there is a good explanation on continuity across the joins between curves and formulas for c0, c1 and c2 continuity. We also need c3 continuity which can be calculated in the same manner

With these formulas it is possible to set the handles of the Bezier curves to make sure we get a smooth ride.

We have added a python example that implements the ideas above. You can find it in crazyflie-lib-python/examples/positioning/ The design is based on Nodes that represents the connection points between bezier curves (called Segments). The Nodes has a set of handles that are shared between the Segments that use the Node. If not all handles are set the implementation will set them to appropriate values, see the comments in the code for more details. The Node API only allows the user to set handles on one of the Segments, the handles for the other segment are automatically set to generate a continuous trajectory.

The example uses nodes in the corners of a square and contains three parts:

No velocity in the nodes. The Crazyflie stops in the Nodes. Similar to calling go-to in the HL commander.
Velocity in the nodes. A fluid motion all the way around.

Velocity in the nodes. A fluid motion all the way around.

A bit more aggressive settings to get a little action.

Finally a video showing the full sequence, we use the Lighthouse for positioning.

A lot of you are using our forum on a regular basis. From our point of view, we prefer giving support and guidance on our forum instead of by email, since solutions we provide to our users can be found by others as well. However, we are experiencing some spam-related issues with the forum!

Somewhere last week, our forum started getting some weird posts, including some links to websites that are…. not exactly Bitcraze or Crazyflie related… We didn’t think about it too much, so we cleaned the forum, deleted the users responsible and moved on. But the very next day more spam post appeared, and it was getting so bad that we changed our sign-up from the regular security question to Captcha. Unfortunately, spambots are way too smart these days, so that didn’t work either… By the end of the weekend we had to remove over an hundred spam accounts and 500 spam posts!

The forum is experiencing a major spam attack at the moment and the usual security measures are not helping. Since yesterday, we enabled manual activation of new users (meaning that we physically need to approve each account), since currently this is the only way to catch the dodgy new accounts (we already caught over 100 in one day alone !!). This week we will look into other measures and plugins to better secure our forum, so we don’t have to manually go through all the newly registered users to see if they are not spam bots. We heard about Cleantalk by one of our users, so we probably will give that a go!

However, please be contact us if the following occurred or is occurring to you in our spam removing frenzy:

  • If we accidentally removed a post of you
  • If we removed or banned your account
  • If we are not activating your new account

Also make our lives a bit easier this week, and send us an email straight away if you have just have made a new account on the forum. Send an email to: with your username and a sentence about why you are using the Crazyflie (so we know that you are real).

This is only a temporary solution, so hopefully at the end of this week or the next we will not need to worry about this anymore :).

Improving the flow of information

Our usual blog posts usually consists of the awesome new products and demos that we make here at Bitcraze, but now we will talk about… documentation! Alright alright, it is maybe not the most thrilling topic, however you should be excited about it! Good documentation about the Crazyflie and its tools will not only enable you to recreate the demos and the work of others, but also to implement your own ideas and to contribute to our open-source firmware.

In the years that Bitcraze has been around, there has been quite the build-up of information, which can be either found on the main website, the wiki, the github repositories, and in bits & pieces on the forum. Although we try to provide all the information necessary for getting started with development, it is currently quite a clutter. If we at Bitcraze already have difficulty of finding and maintaining all the documentation, we can only imagine how difficult it would be for a starting developer. We therefore would like to improve the flow of information dramatically!

Here are some ideas of what we would like to do with the documentation:

Moving product information to the shop.

LED ring expansion deck in the main website, shop, and wiki.

Currently there are three different locations where you can find information about physical Crazyflie, localization systems or expansion decks, which is the main website, the online store and the wiki. We see that a lot of electronic and hardware shops usually put all the details of the product directly on the product page of their shops. We aim to do that as well, since there will only be one page for users to go to for schematics, specifications, instructions and more, and for us it will be also easier to maintain and update any product information

Moving Software Info to GitHub

There is a lot of bits and pieces of information to handle the firmware on the Crazyflie and all the tools in the tutorials on our main website, wiki and Github repository. This again makes a lot of duplicate information, which is difficult for us to maintain and therefore gets easily outdated. We could put all the information on the wiki, but what if somebody changes something in the code which requires a change in the procedure as well?

It would be the best to keep all the information about the firmware as close to the source as possible, therefore we think is best to move everything to the github repositories. For instance, the wiki cfclient instructions can be moved to the documentation of the cfclient repostitory, or Onchip debugging instructions can go to crazyflie firmware repostitory To keep it all manageable we will:

  • Create a /doc folder on the repositories to better structure all the information
  • Add more Doxygen comments to all the function in the the codes and automatically generate documentation for this.

Restructuring the Wiki Content

After moving all the hardware- related content to the shop, and moving all the firmwar- related info to the Github repositories, we will need to think about what we want to do with the Wiki! You would think that there is nothing left to put on the wiki anymore after the replacement of the earlier documentation, but we beg to differ! For instance, there is so many Github repositories that there is a really a need for an overview. The wiki can educate developers on which tools we have an how to properly use them. Of course, we already have the getting started tutorials, but we want to also provide a more in-depth explanation of the overall structure and how the different repositories would need tho work together, like this .

This does mean that we would need to restructure the wiki entirely and only focusing on topics like:

  • System Architecture Crazyflie
  • Communication protocol between STM and the NRF
  • Communication protocol between the Python library and the Client
  • Overview Github-repositories
  • Projects and hacks
  • etc etc

What do you think?!

Of course we can change all we want in the documentation, but you guys are the ones who actually use it! We are very curious of what what you think of the plans and give us more tips or suggestions on how to improve the overall documentation experience. Please leave a message below or express your opinion on this forum thread.

Two weeks ago we posted about the demo we did for our new office move-in party. There has been multiple requests to share the script but unfortunately this is a hacked old script that is not going to be useful at all as an example. So, last week, we made an example that could run a synchronized swarm sequence.

The example has been pushed in the example folder of the Crazyflie-lib-python project. It is called Running this example unmodified with 3 Crazyflies in a positioning system will give you this result. (Like the previous demo, this was done in a lighthouse system.)

One of the key design of the example is that it is based on a single control loop that can be synchronized with an outside system: in this example, there is a simple sleep of one seconds between each step of the sequence but it could for example be changed into a midi clock receiver to synchronize the sequence with music.

The example was developed with the help of Victor, a student we have hired to help-out during the summer. He has then played around a little bit to make a 9 Crazyflies sequence that is more impressive:

I uploaded Victor’s sequence in a github gist as it can be good for inspiration. One bit of warning though: as is, the sequence contains some vertical movements that are quite aggressive and the part where Crazyflies fly directly on top of each-other is more to be considered as a stress test.