Since September, it seems that things at Bitcraze are progressing at an incredible speed. A lot of stuff is happening, and this blog post will try to talk about why we feel excited about the changes coming up… With some teasers!
Changes in the office
One of the reason we picked the office we’re at now is the big flight space, commonly known as the arena. It’s a pretty huge area (around 100m2), separated from the office space, with a high ceiling. It’s perfect for flying. But when we moved here in 2019 we always dreamed about the space that our next-door had, which could be a perfect extension of the flight lab. And, after years of daydreaming, our wish actually came true! So our flight lab is now in the process of getting significantly bigger. I’ll tease you with some before/during photos, to show what the status is right now, but we expect to have a majestic area to fly in quite soon.
Behind the curtain
If you have ideas on how to name it, a name that feels a little more majestic than “arena”, you’re welcome to share it in the comments!
Changes in the products
We have a list of products that we’re working on that we’re really excited about. You know already some of those if you have read our blog posts, and they are a big part of what we’re spending time with, but they’re not the only ones ! Here is a list of the projects we can reveal:
The brushless is in the pipes! We’re getting help to make it as sturdy as possible.
We’re working on an “upgraded” Crazyflie offer, with the longer battery pins and the 47-17 propellers.
There’s a new software release that should come out soon.
Most of our development work the past couple of months have been dedicated to a new deck for flying with more than 4 lighthouse base stations…
And of course, there are always prototypes laying around that look promising!
Of course, that’s just a hint of what lies ahead, and for right now, we can’t really say more until we’re sure everything is on the right tracks.
Other exciting stuff
I know I said this time and time again, but we’re actively looking for new Bitcrazers to add to the team. We hope that some changes will come soon and of course, we will share if we have some big news!
We’ve also partnered with Droneblocks to provide a drone education program for students in the US. The Crazyflie has been integrated into their STEM classroom bundle, complete with a coding curriculum and a dedicated software to introduce young minds to the world of drones. It’s a privilege for us to contribute the Crazyflie to this significant educational endeavor!
We plan to have everything coming together for an epic Christmas video with some new hardware, in our new flight lab… Of course, nothing is certain, but one thing is sure: it’s an adventure being at Bitcraze right now!
When we originally wrote the TDoA3 implementation for the Loco Positioning System back in 2017 we had the idea of adding functionality to also enable the Crazyflies to send UWB packets in some situations, AKA TDoA3 Hybrid mode. We did not have the time to implement that idea back then, but through the years there have been some interest in the functionality and recently I finally got around to do it as a Fun Friday project. Annoying enough it was not that complicated and only took a couple of hours, I should have done it earlier!
We wrote a bit about the hybrid mode in an earlier blog post and there is also a github issue with some discussions on the topic. The short version of the functionality is that a Crazyflie at selected times switches from only passively receiving UWB packets from the anchors, to also actively transmitting packets and doing Two Way Ranging (TWR) with the peers in the network.
One use case is for a Crazyflie to simply participate in the TWR traffic to give it ranging information for improved position estimation. This can for instance be useful when flying outside the convex hull where TDoA positioning degrades rapidly while TWR works pretty well.
Another funky use case is to extend a Loco positioning system by using TWR to fly outside the convex hull and land somewhere. At this point the Crazyflie switches role and acts as an anchor instead by including its position in the transmitted packets and enabling other Crazyflies to use the transmissions for TDoA or TWR position estimation.
It is also possible to go even more dynamic and transmit the estimated position while flying and thus act as a flying anchor. There are complications when doing this with multiple Crazyflies as they use information from each other and the estimated positions probably will diverge if errors are not handled in a proper way, but at least there is now a framework where this type of functionality could be added. See the references to research in the area in the previous blog post.
The implementation is very experimental and has not been merged to master yet, but if you are interested you can find it in the krichardsson/hybrid-mode branch (PR #1330). There are a few new parameters that changes the behavior such as turning on/off transmissions, using TDoA or TWR data for position estimation and what to include in transmitted packets. Please see the implementation and documentation for details. Also note that the hybrid mode functionality is not compiled by default and must be enabled in the build configuration to be available.
It’s been cooking on the slow burner for a long time now, the Crazyflie 2.1-Brushless, or CF21-BL in short. Ever since we got inspired by the tinypepper 1-cell brushless motor controller which showed us a small brushless ESC could be made, we got the idea of integrating brushless ESCs into the Crazyflie. Integrating the ESCs turned out to be easier then we though, but we hade more ideas, we wanted it to be efficient. Due to the FPV market and the toothpick sized category plenty of appropriate size components exist, however none is really optimized for efficiency. So we had to go back to the drawing board, contact suppliers and work with them to try and improve efficiency. This turned out to be a very time consuming task and we are now at a stage where we think we have gotten as far as we can with the resources we have.
Why go brushless?
A brushless setup is better in most aspects but it has some downsides, such as cost and complexity. The brushless motors requires a more complex design and is therefore more expensive to manufacture. It also requires a more sophisticated motor driver that also needs a larger PCB board space. On the upside we have better power to weight ratio, better longevity and efficiency to name a few. For the tiny type of brushless motors that are interesting here the efficiency gain is not so obvious though. This is mainly because it is hard to make an efficient motor driver due to the low inductance in the motors and this can definitely be further improved, perhaps with software upgrade of the ESC firmware in the future.
Let’s dive into the current specification!
After many prototypes this is where we are at now:
Crazyflie 2.1 base design using the PCB as the frame.
4 x integrated 1-cell 5A ESCs running BLHeli_S/Bluejay
Weight: 32 grams ( including 350mA battery)
4 x 08028-10000KV high-quality motors generating up to 30 grams thrust each
Custom-designed and optimized 55mm propellers with 35mm pitch
Over 10 min hover time in 32-gram configuration (~5g/W efficency)
The added thrust and the longevity of the brushless motors are probably the key features of the CF21-BL. This will improve payload capability or agility for applications where this is needed as well as the robustness. It will come at the expense of a higher price tag though.
The Crazyflie 2.1-Brushless has come a long way but there are still many things that have to be done before it will be available in the store and it is too early to talk about any timeline, but the goal is to release it during 2024!
It seems that many of you are very interested in simulation. We might have gotten the hint when we noticed that our July’s development meeting had our best attendance so far! Therefore, we will be planning a new developer meeting to discuss the upcoming plans for supporting simulation for the Crazyflie.
Getting Started with Simulation tutorial
Perhaps you are not aware, but there is actually a Getting Started tutorial for simulation that has been available for a little over 2 months now. Unfortunately, circumstances prevented us from writing a blog post about it, but we’ve noticed that not all of you are aware of it yet!
The getting-started tutorial demonstrates how to set up the Webots simulator, which already includes Crazyflie models and some cool examples:
An example that you can control the Crazyflie with the keyboard
An example that the Crazyflie does wall following autonomously
The tutorial concludes with instructions on how to edit these controllers. Alternatively, you can choose to run the files directly from the crazyflie-simulation repository. After completing the tutorial, you can explore the simulation repository documentation for more information and to access additional examples.
Upcoming plans
With so many plans and so little time! This is a common phrase at Bitcraze, and it’s a symptom of being an overly ambitious, but too small, team. By the way, we are still looking for more people :). Nonetheless, we have big plans to take our Crazyflie simulation to the next level:
ROS 2 Crazyflie model for Webots: The Crazyflie has been a part of the Webots standard robots for 2 years now, but we still need to implement the Crazyflie into the Webots ROS 2 repository.
Better (new) Gazebo support: Currently, we only have a very simple example for Gazebo, which is limited to motors with no control input. Working with the C++ API can be a bit challenging, so it might be worth considering the use of ROS 2 in the loop here. Let’s see what comes out of it.
Integration into Crazyswarm2: Once the Webots ROS2 node has been released, integrating the Crazyflie simulation into Crazyswarm2 will become more straightforward.
Improvement to the Python bindings: We’ve had Python bindings for controllers and the high-level commander for a while. Recently, we also added Python bindings for the estimator (currently for loco positioning only). However, there are still some issues to address with the Python bindings for the controllers due to timing issues with the simulators.
Linking with our CFLIB: Currently, both Webots and the Crazyflie Python library use entirely different APIs. This means that these scripts are not compatible and you’ll need to be creative not to reuse new code. However, wouldn’t it be nice to use a python example from the python library with a --sim and that it would actually control the Crazyflie in the simulator instead?
Of course, there are probably more improvements that we haven’t thought of yet, but that’s why we have developer meetings!
Come and join us at the Developer meeting.
We will be hosting another developer meeting on November 1st at 15:00 Central European Time (accounting for the time-shift from summer to autumn). You can find details on how to join in the discussion thread here.
Just for your information, I (Kimberly) am the main driving force behind our simulation efforts. However, I’m currently on partial sick leave and will soon be on full leave for a while. I kindly ask for your patience with the pace of ongoing developments. Remember, it’s an open-source project, so if you’d like to contribute and help out, we would greatly appreciate it :)
Today, Suryansh Sharma from TU Delft presents the open-source Gimbal they devised. Enjoy!
Crazyflies (and other drones in this weight class) are extremely fun to fly and prototype with! But if you are also a scientist or tinkerer and not a well-skilled drone pilot then you might struggle with flying these platforms especially when testing new control loops or experimental code. While crashing also teaches a lot about the behavior of the system, sometimes we are interested in seeing the system dynamics without breaking the drone.
Currently, doing this for such small drones is not easy. We need something lightweight and still accessible. To solve this, we made Open Gimbal: a specially designed 3 degrees of freedom (DoF) platform that caters to the unique requirements of these tiny drones. We make two versions, (a) Tripod version which can be mounted on a camera / light tripod with a screw thread of sizes 1/4-20 UNC or 3/8-16 UNC (b) Desktop version which can be placed on a table top.
Tripod VersionDesktop VersionCAD models of the different Open Gimbal versions you can 3D print and use.
Our approach focuses on simplicity and accessibility. We developed an open-source, 3-D printable electro-mechanical design that has minimal size and low complexity. This design facilitates easy replication and customization, making it widely accessible to researchers and developers. The platform allows for unrestricted and free rotational motion, enabling comprehensive experimentation and evaluation. You can see the movement from the CAD version below:
Degrees of Rotational freedom that Open Gimbal provides
You can also check out the interactive CAD model and see how the gimbal moves here. All of the 3D model files as well as the BOM and instructions for assembly can be found in our repository here.
In our publication, we also address the challenges of sensing flight dynamics at a small scale. To do so, we have devised an integrated wireless batteryless sensor subsystem. Our innovative solution eliminates the need for complex wiring and instead uses wireless power transfer for sensor data reception. You can read all about how we do this in our paper here.
If you do end up using the platform for research then you can cite us using the details below:
@ARTICLE{10225720, author={Sharma, Suryansh and Dijkstra, Tristan and Prasad, Ranga Venkatesha}, journal={IEEE Sensors Letters}, title={Open Gimbal: A 3 Degrees of Freedom Open Source Sensing and Testing Platform for Nano- and Micro-UAVs}, year={2023}, volume={7}, number={9}, pages={1-4}, doi={10.1109/LSENS.2023.3307121}}
Open Gimbal at European Robotics Forum 2023 in DenmarkOpen Gimbal in use at Prof. Leszek’s lab in PolandOpen Gimbal at TU Delft, NetherlandsOpen Gimbals with Crazyflies mounted in the wild!
I hope that you find the Open Gimbal useful! Feel free to reach out to me at Suryansh.Sharma@tudelft.nl if you have any ideas/questions or if you end up making an Open Gimbal yourself!
It’s been some time now that we’ve tried to grow the Bitcraze team. Since we’re a small team, it’s been hard to put the time and energy into recruiting; and even though we’ve been looking for a new Bitcrazer for a long time, things haven’t progressed as much as we liked.
That’s why we’ve got some help. We are now working with a recruitment agency to help us reach the right people, and their insights and advice have been of great value in us figuring out exactly what kind of person we wanted, and how to phrase it in the right way to get the right person.
So we now have a new job post, that you can read here in its entirety, but which I will summarize here:
We’re looking for a production and quality manager – embedded developer. Someone that is not only a skilled embedded developer, but is also interested in our products’ production: running it, synchronizing with our partner in China, developing production tests… Having a passion for technology, production and quality is a big plus.
As usual, no roles is set in stones here at Bitcraze. Being part of a small company means that everyone has the opportunity to be involved in all parts of it ; we get to build the company we work in. With that comes freedom and responsibility! The way we work is unlike any other, and we know from the Covid experience that working remotely is nearly impossible for our process. That’s why that person should be ready to move to Malmö, Sweden. But, as I’ve explained in a precedent blogpost, coming to work at Bitcraze comes with great advantages.
While this role is one that we’re currently actively trying to fill, you’re always welcome to openly apply for a job at Bitcraze. Don’t hesitate to send us an email at jobs@bitcraze.io and tell us who you are!
One detail that has its importance: unfortunately, hiring someone from outside the EU takes time and energy; with a lot of paperwork and a much longer timeframe. That’s why we’d prefer if the person we hire has EU citizenship.
Dev meeting
Next week is already time for our next dev meeting! This time, we will talk about how to handle the increasing complexity of the expansion decks. We’ve seen some issues with the increasing complexity of the expansion decks, and had some ideas for solutions moving forward that we want to share!
Lately we have been thinking about and using the Rust programming language more at Bitcraze. In this blog post we will talk a bit about our current use, current experiments and potentially future use and how it will affect our ecosystem.
Rust is a system programming language that has good performance, is reliable and productive. Practically it means that it can be used to run small and fast code (well suited for embedded systems for example), be quite fun to write, and be reasonably sure that if it compiles, it works.
On servers
Over the year we have written and maintained a server system to handle a lot of things related to production and sales. This system is the one generating shipping quote when you order in our store, telling us that there is an order, printing packing lists and shipping labels for the order as well as keeping track of stock and telling us when it is time to order a new batch of product.
This system is used every day and has been invaluable to how we work at Bitcraze. It is mostly implemented as NodeJS micro services.
We have started writing new functionality for it in Rust instead of in a new monolithic service. This has been a great experience, not always easy, but the bonus is that once it compiles there has been almost no run-time error. This has allowed us to gain experience with Rust in an environment that is well documented: servers on PC.
In test rigs
Every manufactured product must be tested: there is no guarantee a board will work when it exits the re-flow oven. This test usually happens in a test-rig that measures and affects various signals on the board (look under your favorite Bitcraze deck and you will see test-points: round pads designed to enter in contact with test probes). Attached to this test-rig is a computer running our test software. We have used a Python-implemented test software for all our products so far and this system started showing its age by being harder and harder to work with and, most importantly, hard to deploy on computers in the factory.
For Crazyradio 2.0, we decided to completely re-write our test software, in Rust of course :-). The design of the test framework is very inspired by OpenHTF: the framework provides the basic architecture of the test and the executor, tests are implemented in Rust and implement all the required test phases. Test statuses are streamed to a web browser as well as to our server (to one of the newer parts of our server system written in Rust). There are two big advantages of using Rust in this application: making sure the test software works reliably and without errors saves a lot of time during manufacturing and helps make sure no bad board leaves the factory. Rust is also awesome to deploy and distribute: the software written on our Linux machine can be compiled for Windows/Mac/Linux on any architecture, no more Python environment to set up!
As for the deployment we actually choose to deploy the test software on a Raspberry pie managed by Balena cloud. This means that we can remotely update the test rig software and we are always sure that the right version is running in production. Rust has allowed that to be painless: we develop on our amd64 PCs and it compiles out-of-the-box and works on the ARM64 Raspberry Pi.
In embedded systems
Now we are coming to our more experimental use of Rust, until now on fun-Fridays project but soon on prototypes. We have been playing with Rust on embedded for quite a while: I have re-written the Crazyflie2’s stm32 boot-loader in Rust, we have experimented with Rust on a couple of our ESP32-based prototypes. Embedded systems are never as easy as programming on PC and the way Rust libs are organized to guarantee good usage of the peripheral does not always yield good error messages from the compiler. But, for sure, it does not feel good and it feels very scary to come back to C: the Rust compiler checks so many things that it makes programming fun, with C, any small mistake will bite hard a couple of weeks later.
We have just started working seriously on a new deck (more about it in a future blog post ;-) and we have started in Rust. We do still take that as an experiment: we keep our options open to coming back to C if there is any hiccup. But so far it looks quite good.
In the Crazyflie lib?
That is a future plan, that we have not started to work on seriously at all, but that we are planning for the future. We are planning to write a new version of the Crazyflie lib in Rust with binding to other languages.
According to our experience so far, Rust is safe, fun to write, and very easy to distribute to all the systems we currently support with the Python lib and more. On top of Windows/Mac/Linux, Rust would enable support of our official lib on the web, in embedded systems (ie. ESP32), as well as on iPhone and Android.
The plan would be to have the low level of the lib, ie. communication with Crazyradio and the Crazyflie and subsystems drivers, implemented in Rust. Then binding to Python, C++, Ros, Javascript, … can be made to allow usage of the lib in these languages. This would have the advantage of allowing every current user to use the official lib without having to re-implement their own special-purpose version. On the Python side, nothing would change, in the sense that a Rust-implemented lib can be installed with “pip install cflib” …
Conclusion
This blog post is a request for comments: if you are a user of the Crazyflie and have strong opinions for or against Rust we would like to hear about it. We want to make it clear that we are not planning on porting the Crazyflie firmware to Rust: the Crazyflie is designed as a development platform and we are aware that Rust is not yet as used or well-known as C or Python. However, the firmware running on a deck CPU or in the bottom of the lib would benefit a lot from Rust’s advantages and do not need to be modified so often outside Bitcraze (it is of course always open-source and we encourage contributions :-D).
We will keep you updated if we make more progress on the new deck and the lib, in the meantime we will keep having fun experimenting :-).
The python client is based on Qt and we have been using version 5 so far. Qt5 has been replaced by Qt6 quite some time ago and as Qt5 is not really maintained any more, we have been looking at switching to Qt6 for a long time. Finally we have taken the step, this blog post will outline what has changed.
The switch to PyQt6 is not that complicated for the majority of the client code base, apart from some minor changes in various classes, the biggest update is that enumerations are handled differently. If you check out the changes in the pull request you will see that imports have changed for obvious reasons
The main blocker for doing this change has been that the Qualisys tab was using a library that used to be available in PyQt5 but that has not been added to PyQt6, we ended up removing the Qualisys tab to be able to move on. The Qualisys tab was originally contributed by Qualisys for demo purposes and it had two nice areas of functionality that we would like to re-implement:
Motion capture positioning. It was very easy to connect a Qualisys mocap system and feed the position information to the Crazyflie for automated flight.
Trajectory support. It was possible to fly some simple trajectories, for instance a circle which is nice for testing and demos.
The idea is to re-implement the mocap connectivity using the libmotioncapture library from Crazyswarm2, as an extra bonus this would support all major mocap systems. For the trajectory part, we would like to add this as a new tab that can be used by any positioning systems, mocap, Loco, Lighthouse or flow deck. If you are interested in helping out with this, let us know!
The state of the code
The changes for PyQt6 have been merged into the master branch. It seems to work but we have not tested all functionality yet, please let us know if you run into any problems or weird behavior.
When you have pulled in the code from github you will also have to re-install all dependencies by running
Last week our brand new 47-17 (47mm diameter, 17mm pitch) Crazyflie 2.X propeller became available in black and green in the shop! It is a custom designed propeller for the 0.8mm shaft, 7×16 coreless brushed motor, that comes with the Crazyflie 2.X. The improved design boosts the efficiency, both flight time and maximum thrust is increased with up to 15%. It is made in polycarbonate (PC) which makes it more durable so that it will withstand crashes better. The new propeller is better then the stock 45-17 in almost all areas except in noise where the new 47-17 propeller runs at a higher RPM. Below is a graph comparing the two propellers using the thrust stand we previously built. The graph is a bit messy but hopefully you can figure it out! The big takeaway is that the 45-35 propeller tops at ~4 g/W while the 47-17 tops at ~4.7 g/W using the stock 7×16 motor.
The Crazyflie 2.1 kit will continue to be shipped with the “stock” 45-35 propeller. At some point we want to switch to the new propeller in the kit. We don’t know when this will happen yet and will of course announce it here at that point :-).
After a nice (but rainy) summer, everyone is back at the office and we’re coming back to business as usual at Bitcraze. This blog post is dedicated to various bits of news, in order to get you caught up on what’s been happening during the summer.
Dev meeting theme
There were no dev meetings in August to allow everyone to rest and enjoy their vacations, but after this hiatus, we’re back in the saddle! The dev meeting will happen, as usual, on the first Wednesday of the month, so the 6th of September, at 15.00 CEST.
This month, Arnaud is going to talk about the lib: what is its current status, its architecture, and some hopes we have for the future. As usual, we’ll have a short presentation, and then a discussion; you can also join if you have more general questions or feedback. If you’re interested and willing to take part in this discussion, you can check the information on Github: https://github.com/orgs/bitcraze/discussions/884
Chargers out of stock
Some items were out of stock during the summer (like the HQ propellers) that we thankfully received soon after we came back. Unfortunately, one product is still not available: the battery charger. Since it’s part of the Swarm bundles, it also means that the bundles are out of stock too. But the wait for their restocking shouldn’t be too long, as they are scheduled to arrive around the end of next week. We’re hoping it’s not a big inconvenience for you and we thank you for your patience!
Problems with payment
We’ve noticed that some of you had some problems getting their payment through in our shop. If you’re one of the unlucky ones who faced this issue, we apologize for the inconvenience, and we want you to know we’re working with our payment provider to figure out a solution. This, unfortunately, can take some time because of the number of parties involved (there’s us, the payment provider, different banks, so the situation gets quite complex quickly). In the meantime, if you should encounter such a problem, don’t hesitate to send us an email at contact@bitcraze.se and we can help out. It would also help us to know who is facing this issue.
