CCW propeller replacement

2015-02-16 | Tobias | 9 Comments

We have finally managed together with Seeedstudio to improve the CCW propellers and to setup a process to acquire a free set of CCW replacement props. As continuing from this post we have discovered that many of the CCW propellers from the first batch of Crazyflie 2.0 where a bit too unbalanced. Too be a bit more technical the tolerance distribution for the CCW propellers was a bit offset, so instead of the majority being decently balanced, many where unbalanced and needed balancing. This is not really a big issue and can pretty easily be corrected by balancing them with some tape according to this guide and we still recommend them to be balanced to get the best flight performance. We however think there where to many unbalanced propellers so we offer every one that bought a Crazyflie 2.0 kit from the first batch a free set of CCW propellers including shipping from China. To acquire a free set of CCW propellers please fill in this form.

Measuring propeller RPM: Part 3

2015-02-09 | Tobias | 7 Comments

Finally here is the last, and probably most interesting part of the “Measuring propeller RPM” series, see part 1 and part 2 to catch up. Now it is time to gather some data and display what we get.

As described in part 2 we are now able to measure each propeller RPM with the expansion board we made and with the code we added. This can, as been described in part 2, be logged to a csv file using the cfclient. Next thing would be to do something useful with it. To do that we use Octave (very similar to Matlab but open source). The first thing that could be interesting to know is the step response for a motor and propeller. This was acquired by altering the Crazyflie 2.0 firmware a bit to do a step from zero to max trust and then to zero again. It was done on M1 with a fully charged battery.

The motor goes from zero to 25k rpm in about 180ms, quite impressive. What is also interesting is that the falling slope in the range 15k to 20k rpm is quite similar to the rising slope in the same region. The inertia of the turning parts of the motor and the propeller is quite low so this energy will quickly be consumed when the motor and propeller starts to coast. This is good as it will lead to better maneuverability.

cf2 thrust fixture Knowing the RPM is great but it is the thrust that is most interesting. So to get this we need a rig where we can measure it. We made one out of a bottle to which we glued a prototype board on that we put on a scale, not a perfect rig but simple and probably good enough. Then we made a program that ramped up the PWM from 0% to 93.75% in 16 steps with stabilization disabled. We also connected the Crazyflie 2.0 to a power box where we could measure the current. The program would increase the thrust in 16 steps and during each step we took a reading of the thrust and current. The RPM, voltage and PWM was logged over the cfclient at the same time. Some manual work was needed afterwards to correlate the data and get it into a table. While in the table a lot of interesting plots could be graphed.

The first one would be the rpm and thrust as this transfer function is interesting. By using the Octave polyfit function the second order fit could be found. It is a pretty accurate fit and with this fit it is easier to get the thrust, as the rpm is the only variable needed, which is easier to measure. The fitting function returned by polyfit is:

Thrust (in gram) = 1.0942e-07*rpm² – 2.1059e-04*rpm + 0.15417.

Here is a combined plot of some other interesting parameters. Notice that the voltage graph is ~quadratic, the current ~square-root and the power linear. From the power graph one can find out that the thrust efficiency is about 3.8 gram/W. Not super good but pretty good for a quad of the Crazyflie 2.0 size.

Another interesting graph is the graph of the flight time. Since we know the power consumption and the battery characteristics we can plot a graph of an estimated flight time depending on the battery size. This graph makes the assumption the battery capacity per weight is 32mAh/g.

And finally the transfer function we set out to find, the PWM to thrust. The problem with this is that motors are controlled by voltage (PWM) and the voltage comes from the battery, which varies with the power taken from the battery due to internal resistance. Therefor we made two fitting functions, one based on measured battery voltage while applying PWM, and one based on the PWM. Looking at the graph one interesting thing is that the polyfit is making a better fit (red curve) for the PWM. I would have expected the opposite. Something that we will have to investigate further. Or maybe one of our readers have the answer?

On the wiki we will update this analysis with some more details and the raw data so if you are interested please have a look! Hopefully using this information we can make the Crazyflie 2.0 fly even better.

On the news side there is a new version of the Android client available on Google play, thanks Fred! Also Fred has uploaded the slides of his Crazyflie lightning talk at Fosdem 2015.

Measuring propeller RPM: Part 2

2015-02-02 | Tobias | Leave a comment

We finally got some time to follow up on the previous blog post Measuring propeller RPM: Part 1. In this post we will continue where we left of and describe a little about the software we have implemented.

The sensor output, as showed in the scope picture, can be connected directly to a digital input. We connected them to the expansion port signals TX2, RX2, IO2 and IO3 as they are all internally connected to a timer with capture capability, TIM5_CH3, TIM5_CH4, TIM3_CH2, TIM3_CH1 respectively. With the capture functionality it is possible to trigger a timer read on events like a pin change. Thus it is not that difficult to calculate the period time of the input signal which can be used to calculate the rpm. Setting up the timer to run at 1us tick was a bit tricky but manageable. With 1us tick it will wrap around, it’s a 16 bit timer, so after 1us * 65536 = 65.5ms. This means the slowest rpm that can be measured is about 458 rpm (1/(2*65.5ms)*60). The division by 2 is because there are 2 blades on the prop. Since hovering happens way over 458 rpm it doesn’t matter much that we can’t measure any slower speed.

Next thing was to setup the capture compare. The ST library already provides the basic API, TIM_ICInitStructure, so it was more or less just a matter of finding how to configure it. The capture part of the timer can do quite fancy things but in the end we decided it was easiest to just use it the simple way, were it stores the timer value in the corresponding capture compare register on a predefined edge. As the register values will be overwritten when the next pulse comes we setup a interrupt handler to take care of the result. What the interrupt handler ended up to do was to copy the timer value, use that to calculate the rpm and then save the result in a variable. It turned out to be good to do an average of the two latest values as the pulses was not fully symmetrical because of the two blades. This was then done the same way for each propeller input and, voilà, rpm measurements was taken. (Well, there certainly was a bit of hair pulling before it all worked but in the end it worked! Love that feeling)

Getting it down to a cfclient was a piece of cake using the logging framework. We just defined the variables to be logged, setup the logging in the cfclient and it could all be plotted. The variables was defined using the macros below.

LOG_GROUP_START(rpm)
LOG_ADD(LOG_UINT16, m1, &m1rpm)
LOG_ADD(LOG_UINT16, m2, &m2rpm)
LOG_ADD(LOG_UINT16, m3, &m3rpm)
LOG_ADD(LOG_UINT16, m4, &m4rpm)
LOG_GROUP_STOP(rpm)

Then by connecting the the Crazyflie a log configuration could be created called “motor” containing the rpm values as well as voltage and PWM.

After that by opening the Log Blocks tab the “motor” log configuration could be enabled a written to files. The data log output folder can be opened from the menu by selecting “Settings -> Open config folder”. In my case in “logdata/20150202T17-29-49/motor-20150202T17-35-09.csv”. This CSV file can then be imported to a program such as Octave, Matlab, Spreadsheet etc for further analysis.

The data can also be plotted in real-time using the plotter as in the picture below. Hmmm, interesting, the Crazyflie 2.0 seems to hover at about 19000 rpm with the RPM measurement board attached.

The idea was to do the analysis part in this post as well but it turned out to be a little bit to much, therefore stay tuned for the final analyzing part!

Refocusing for 2015

2015-01-26 | Marcus | 5 Comments

During the last week there’s been lots of work, but we don’t have that much to show for it. We’ve spent a lot of time discussing what we should do during 2015. Last year there was a clear focus: develop, release and ship the Crazyflie 2.0. But up until now we haven’t really discussed what the goals for 2015 are. It’s not that we don’t have ideas, there’s always lots of ideas. It’s more about finding a common focus to work towards. It’s still ongoing, but there’s a few points that we know. We will of course continue the development (firmware, software, clients) of the Crazyflie as well as creating more expansions for the Crazyflie 2.0. For the expansion boards we’ve already talked a bit about it before, but for the firmware/software side we haven’t communicated our plan. The reason for this is simple, there’s not really been a plan for this. The main focus has been stabilization and creating clients for iPhone and Android. But now that it’s done we need to move forward with new features. If you have any feedback on this please let us know. Something that we are hoping to work on is ROS integration. (Edit: well, what do you know, this has already been started by Wolfgang Hoenig, the power of open source! Here’s a link) Once we figure out the plan we will let you now :-)

Fred, the main developer of the Crazyflie Android client, is doing a presentation about the Crazyflie at FOSDEM next weekend. Arnaud will be attending as well so if you would like to meet up, let us know!

But a few things happened during last week:

There’s a new release of the Android Client (thanks Fred!), so make sure to upgrade your apps!
We’ve added LED-ring settings to the FlighTab in the latest version on the develop branch of the client.
We released a bug-fix version of the python client. This new version fixes Crazyflie 2.0 configuration.
We added a some guideline for contributing to the client. We hope to streamline the contribution process to be more efficient at it. Tell us if you have any comments.

As for the RPM measurements and analysis we’re working on it, but it’s not ready yet… We are however making progress and it’s been very interesting, have a look at the thrust fixture we made :-).

Working on a new input device architecture

2015-01-19 | Marcus | 4 Comments

Today we were supposed to post the next part of the RPM measurements. But since we are’t finished with the analysis yet we thought that we would post some info on what we are working on. Since Christmas we have been working on and off on a new architecture for the input devices in the Crazyflie Python client. A while back we started discussing the possibility of “hooking in” different backends that could be used for input data like LeapMotion, Gamepads, sockets and so on. It’s something that we have been wanting to do for a while, but other things have always been prioritized. But during Christmas a forum request triggered the work. Users wanted to be able to change the LED-ring effects directly from the controller. We had some code for this lying around, but since the switch from PyGame to PySDL and Linux devices this wouldn’t merge easily. So we thought we might as well take this opportunity to implement what we wanted :-)

Below is a brief overview of the architecture and a description of the different parts:

Crazyflie Python client input device architecture

Each backend is implemented as a single Python file in the directory /lib/cfclient/utils/inputreaders. When the application starts up each of the files are picked up and initialized, so for anyone that wants to create their own backend it’s pretty easy. A list of successfully initialized backends is created. Once the application is started a scan of the input devices will be requested. Each of the backends will do it’s own scanning and together a big list of available devices will be created. Each of these implement a specific API for opening, closing, scanning and reading the device by using their respective backends. The higher layer (Input) now has a list of available devices that it can open and read. But to make sense of the data read from the devices a mapping needs to be created to set which axes/buttons effect what parameters. There’s a number of parameters that can be changed, the main ones being roll/pitch/yaw/thrurst for controlling the Crazyflie. In order to make the mappings as flexible as possible each mapping has a scale and offset. It’s also possible to split axis, so two axis on the device can effect the same parameters (like having yaw on bumper buttons). Normally (for PySDL2 and linuxjsdev) all axis are between -1 and 1 and buttons are either 0 or 1. But using the mappings it’s possible to have other values, like for the LeapMotion. When the LeapMotion is read it return the roll/pitch/yaw/height as read from the device. Using the mappings offset and scaling these values are transformed into usable values for roll/pitch/yaw/thrust. Here’s a step by step walkthough of how a device is read:

Input: Each 10 ms the open device is read
InputDevice: Asks the backend for reading the device
Backend: When read two arrays are updated, one for the buttons and one for the axes. If the device is event based all the events are consumed before updating
InputDevice: Takes the raw values from the backend, iterates though them and updates a list of highlevel parameters accordingly. This returns a dictionary with keys like roll/pitch/yaw/thrust
Input: Pre-processes the values of the parameters, like only calling callbacks when there’s a state shift (button 0->1 or 1->0), slew-rate limiting the thrust, dead-band and trimming
Input: Calls special callbacks (such as alternative functions and emergency stop)
Input: Calls callbacks registered for control data (roll/pitch/yaw/thrust). For this there are two registered callbacks, the UI and the Crazyflie object (crazyflie.commander.send_setpoint(…))

So how does this help the original problem of setting parameters from buttons? In this change we have also included two new buttons, alt1 and alt2. These can be mapped just like any other buttons in the configuration dialog. When these buttons are toggled (0->1 and 1->0) all the registered callbacks are called. The idea is not mapping them graphically to specific parameters, it’s for enabling users to easily (with one line of code) register for these and be able to act on them. For instance setting the LED-ring headlights on/off or changing the effect of the LED-ring.

When we are poking around in the code we are also looking at fixing some other issues, like how to handle when Bluetooth controllers go out of range (see this topic in the forum). We are hoping that everything will be finished and merged when the next release of the client. Also a big thanks to everyone that’s contributed code for the input reading, it’s made things a lot easier!

Today we also released new firmware for the Crazyflie 1.0 and a new Crazyflie Python Client. We have now fixed the client compatibility issues between the Crazyflie 1.0 and 2.0. We are also happy to report that next week the LED-ring and the Crazyradio PA should be back in stock.

Measuring propeller RPM: Part 1

2015-01-12 | Tobias | 1 Comment

We have had numerous request to get a transfer function from the motor PWM output to propeller RPM. The next step would then be to get the propeller RPM to thrust transfer function as well. With that it is easier to do calculations on the system and mathematical models. So this and probably next post will be about how to obtain this function and also give a bit of insight in how one can do development with the Crazyflie 2.0.

First thing how do one do propeller RPM measurement? A quick search on the internet and you will find that using an optical switch is a common method. I also found this guide written for Arduino which was a great start. Since I preferable wanted to measure the RPM while flying the switch needed to be small and lightweight. I found two types that could be useful. A slotted type and a reflective type. The reflective type, QRD1114, is small and promising but would it work? I got some of each type just in case.

[Show as slideshow]

Now the optical switch needs interfacing and power. Sparkfun made a good tutorial using the QRD1114 sensor so I will not go into details. Since we use 3V instead I adjusted the resistor for the LED to 82 ohms instead. This will give me ~20mA emitter current. I also played a bit with the sensor output pull-up resistor. If you go with a to strong pull-up, the sensor will need a lot of light to pull it down and if it is to week, it will rise to slow. 12k pull-up seams like a good compromise in my lighting conditions.

As a first thing I wired it up on a breadboard using the Crazyflie 2.0 breakout board to get a sense if it would work or not. My finding by measuring the output signal with a multimeter is that it is pretty sensitive to surrounding light but that could be solved by flying in a dim room since it is mainly intended to be used for research.

[Show as slideshow]

Now it was time to build a circuit using the prototyping expansion board. I also multiplied the circuit 4 times so I can measure all 4 motors. The inputs I use was TX2, RX2, IO2 and IO3. This because they are all connected to timers so I could use the input capture timer functionality later when I get to the software part. Bending the legs on the QRD1114 was a pretty fiddly job but worth it as it came out so cool in the end. Before I connected it to the Crazyflie 2.0 I measured the current draw and it all seamed OK, ~80mA (4 x 20mA). I also double checked all the connections since it is easy to put a lot of time thinking it is a software fault later if things aren’t working as they should.

[Show as slideshow]

As a first test I just turned on one of the motors at a PWM of 10000 and measuerd the sensor output with a scope. The black color of the propeller wasn’t so good so I searched around in the office and found some reflective paint we used a while ago. I painted the backside of the propeller and it made a big difference. In the pictures below you can find the scope picture using a 12k pull-up and some pictures of the painted props.

[Show as slideshow]

Next part I will start doing the software and analysis so stay tuned!

Crazyflie 2.0 radio communication

2015-01-05 | Arnaud | 1 Comment

The Crazyflie 2.0 supports two types of radio protocols out of the box: ESB (Enhanced ShockBurst) for Crazyradio/Crazyradio PA USB dongle compatibility and Bluetooth LE for mobile devices. All Crazyflie 2.0’s are shipped with a radio bootloader, able to update virtually all the different parts of the firmware running in Crazyflie 2.0. We thought we would do a post to explain a bit further how it all fits together. Even though the Crazyflie 2.0 supports Bluetooth LE, the preferred way is to use the Crazyradio/Crazyradio PA when doing development. Flying via Bluetooth is very practical since there’s no additional hardware needed except for a mobile device, but the Crazyradio/Crazyradio PA has minimal latency, more bandwidth and works easily with computer. This makes it ideal for development and other advanced usage.

(On a side note, some of our products are currently out of stock (like the Crazyradio PA and LED-ring). We have started the next batches, so they should arrive soon. Until then have a look at our distributor page to find our products.)

Crazyflie 2.0 architecture

For the radio of Crazyflie 2.0 we choose the nRF51822. The great thing with this chip is that it integrates a radio compatible with our existing Crazyradio USB dongle as well as with Bluetooth Low Energy. The nRF51 also integrates an ARM Cortex-M0 MCU enabling radio protocols to be implemented directly in the chip. However this MCU is not powerful enough to be used by itself in our quadcopter development platform, so we put a powerful STM32F4 Cortex-M4 168MHz on the side to do the heavy work.

The nRF51 mainly handles radio and power management and the STM32F4 handles all the rest: flight control, expansion port, log, param, etc. As far as the radio is concerned the nRF51 act as a bridge: CRTP packets are received by the nRF51 and sent unmodified to the STM32F4 and the STM32F4 sends raw CRTP packets to the nRF51 that transmit it by the radio. This means that the STM32 firmware is unaware of the physical communication protocol, it can be Bluetooth, Shockburst or something else, it makes no difference it is still CRTP packets. CRTP is the protocol used to control Crazyflie, it encapsulates all commands and messages exchanged between the client and the Crazyflie.

Enhanced Shockburst (ESB)

Enhanced Shockburst is a radio physical protocol implemented in some Nordic Semiconductor 2.4GHz radio chips. In the nRF24 chip, used by Crazyradio (PA) and the original Crazyflie, this protocol is implemented in hardware and we have little control over it. The nRF51 used in Crazyflie 2.0 offers more control on the radio physical packet and ESB since it’s implemented in software instead.

ESB handles ack and retries: The Crazyradio sends a packet on a given channel and waits for an ack. If a Crazyflie receives the packet without error it sends an ack packet. If an ack is received, the Crazyradio can send the next packet. If no ack is received Crazyradio will automatically retry by sending the same packet again. The current implementation will retry to send a packet forever, so all packet are guaranteed to be transmitted as long as a Crazyflie is in range. Packets are sent back by the Crazyflie by adding a data payload to the ack packet. Close to 80 different channel can be used and every packet is sent with an access address, so more than one Crazyflie could share the same channel.

Enhanced Shockburst using the Crazyradio (PA) offers the lowest latency that can be expected. The minimum latency to send a packet is estimated to about 2ms (1ms minimum for USB and 1ms measured latency for the radio at 2Mbps without any retries). With the Crazyflie 2.0 and the Crazyradio PA it also offers the maximum range with 20dBm power output.

For the original Crazyflie there is an implementation of the E-sky RC transmitter protocol. This permits controlling the Crazyflie directly from an RC transmitter. It is technically possible to implement this protocol in the Crazyflie 2.0 nRF51, but it hasn’t been done yet.

Bluetooth Low Energy

In the Crazyflie 2.0 Bluetooth low energy is implemented as a CRTP bridge: CRTP packet are written and read using Bluetooth. This simplifies greatly the implementation, but does not make full use of the Bluetooth LE functionality. It is planned to add more Bluetooth capabilities for things like communicating the battery status and being able to switch ON or OFF the Crazyflie with a mobile devices.

On the nRF51 side the Bluetooth functionality is implemented using the Nordic Semiconductor S110 Bluetooth stack. This stack runs independently of the firmware. Nordic calls this a softdevice and it’s a fitting description of how it works. It almost looks like a hardware device from the firmware point of view as it is not linked into the main firmware.

However we do not currently have the right to distribute the supporting files for the stack, so unfortunately you will have to download them yourself if you want to compile your own nRF51 Bluetooth firmware. To do so you must own a Nordic Semiconductor development kit. Even though some of the kits are pretty cheap, we do not like this situation at all so we are working on solving it. However we made sure that it is possible to compile the nmRF51 firmware without Bluetooth, to avoid the added dependencies. This means that you can still build your own nRF51 firmware to work with a Crazyradio/Crazyradio PA.

Bootloader/firmware upgrade

The Crazyflie 2.0, like the original Crazyflie, is upgradable wirelessly with radio. The radio bootloader has been enhanced to work both with ESB and Bluetooth LE. Both nRF51 and STM32F4 can be upgraded and it is even possible to upgrade the nRF51 Bluetooth stack and bootloader.

Currently the bootloader is working with Crazyradio on ESB. Bluetooth implementation for iPhone and Android is still work in progress. The STM32F4 can also be upgraded via USB and so, for people that does not have a Crazyradio, the first Crazyflie 2.0 firmware upgrade has been released for USB DFU as well as the classical radio bootloader update package.

Looking forward to 2015

2014-12-29 | Tobias | Leave a comment

Well its hard to believe that yet another year has passed. Maybe because it’s been such an hectic year for us at Bitcraze things has been moving so fast. It has not only been hectic but very exiting as well, we managed to release the Crazyflie 2.0 platform just in time for Christmas. That was our goal when we started working on it in March and we can’t really believe we made it. Sure, there are still lot’s of things to be done but now we can all unleash our creativity and start having fun while creating the future for small drones. So what does that mean? Well we don’t know what you have planned but we can at least share some of our ideas for 2015

Improve documentation and instructions
Develop new expansion boards where GPS and Camera are on top of the wish list
Improve the smartphone apps
Master thesis in dynamic mesh networks
Improve firmware and merge it with Crazyflie 1.0
Support for on-board scripting languages such as micro-python and Lua.
Improved ROS support
And much more!

With that said we thank you all for your support and wish you all a great 2015.

xmas_2014_cf2

Expansion board Architecture and Bluetooth firmware

2014-12-22 | Arnaud | 3 Comments

It seems that many have received their Crazyflie 2.0 now. It is a very exciting time for us, tell us what you think about your Crazylie 2.0 and if you have any problems. We wish you Merry Christmas, a Happy New Year, and a lot of fun with your new Crazyflie 2.0!

Getting started

The instructions and documentation are not really as finished as we would like them to be but we hope it is good enough for everyone to get started. For convenience we have put together a sets of links to find the information easier.

Crazyflie 2.0 – Getting started
Crazyflie 2.0 – Wiki
Crazyflie 2.0 – FAQ
Crazyradio/Crazyradio PA – Wiki
Crazyradio/Crazyradio PA – Windows driver installation
Android App
iOS App

Expansion port

The expansion port is a core functionality and it is important that it is easy to work with. The hardware part of the expansion port allows to easily attach custom electronic to the Crazyflie 2.0, making it a very versatile platform. We want to bring this convenience to the firmware and software development as well. We are not really there yet but would like to share our ideas of how we think, but also as an inspiration and to get valuable feedback.

As you might know we have added One-Wire memories on all our expansion board so that CF2 is able to detect which expansion board is connected. The intent is to automatically initialize the expansion board driver when a board is detected so that the firmware can contain all the expansion board drivers. Other benefits are that the resources easier can be shared but also blocked if there are conflicts between boards.

Currently we are in a state where we have made a prototype of how we want the driver to look like and work. The example/mock-up driver we have put together is for the traffic light hack we have written about earlier. The driver would just declare which expansion board it is supporting and it would be loaded automatically. Also some enhancement to the parameter API would allow for more declarative and short code.

Things will be a little bit slow here at Bitcraze during Christmas period as we are focusing on support and on our families. This is however definitely one or our focus when we start 2015. We will create issues to track this work in the Crazyflie firmware bug tracker, contributions are welcome :).

Bluetooth support

We have also published the rest of the Crazyflie firmware, the nRF51 has firmware, bootloader and a ‘Master Boot Switch’. The STM32F4 has bootloader and firmware. The nRF51 bootloader and firmware supports bluetooth low energy using a proprietary stack from Nordic Semiconductor. This stack architecture should play well with open source software as it is completly isolated from the firmware, it runs on the background and is interfaced with syscall (ie. the same way a program communicates with an OS in computers), Nordic call that a Softdevice. The problem is that the supporting libs that allows to access the softdevice is currently proprietary and we do not have the right to publish it.

Currently you can compile the nRF51 firmware in ESB (Enhanced Shock Burst) mode (ie. to communicate with Crazyradio) out of the box. To compile with BLE support you should download the S110 Softdevice and nrf51_sdk from Nordic Semiconductor and this requires you to have one of the Nordic kit. We are in communication with Nordic to fix this situation and will keep you updated. One nice thing about the nRF51 is that the radio is well documented so one way or another this is going to be solved: either we can distribute supporting files for the Nordic stack, or we make our own stack ;-).

Virtual machine

The virtual machine for the Crazyflie 2.0 is on its way, but as we have run into some problems, it has been delayed a bit. Now most of the problems has been fixed and we hope to release it any day now.

New Crazyflie 2.0 firmware and updated Android client

2014-12-16 | Arnaud | Leave a comment

The workload is still huge and now it is starting to take its toll, we are really looking forward to a short vacation around Christmas! But even though we will be off, we will still be checking the support forum. Meanwhile we are doing our best to continue to march on and we managed to write some new documentation and also pushed some new releases. Please have a look at last week post which we have updated and will continue to update as we push them out.

Unbalanced CCW propellers

After receiving the final production version we have found that many of the CCW propellers (not marked with an A) shipped with Crazyflie 2.0 are a bit too unbalanced. This might cause vibration that will affects the flight performance. To get the best flight performance the propellers, especially CCW, might need to be balanced. Balancing the propellers is pretty easy, all you need is a needle and some office tape. We have put together a step by step guide on how to balance them and also updated the general assembly instructions to include balancing. We are currently investigating this with the propeller manufacturer and we will keep updating about it. If you have any questions or concerns drop by our support forum.

Firmware update

Yesterday we released a new version of the Crazyflie 2.0 firmware. This version fixes an issue that was triggered by the motor PWM frequency interfering with the one of the voltage regulators causing the Crazyflie 2.0 to shut-off if the thrust increased too fast. Doubling the PWM frequency fixed this issue completely. We also adjusted the gyro and accelerometer low pass filters a bit to handle vibrations from unbalanced propellers a bit better.

Crazyflie 2.0 can be updated with Crazyradio using the latest version of the Crazyflie client, with the update zip. Documentation of the update process is on the wiki. We also made a USB dfu update zip for people that do not have the Crazyradio. Instruction for the DFU is in the README.txt file in the zip file. In the future it will be possible to update Crazyflie 2.0 with the Android and iPhone client as well. This time around the update is for Crazyflie 2.0 only but the plan is to merge both Crazyflie firmware together in order to release everything at the same time.

New Android release

The Android client is also going forward thanks to Fred. This evening we are releasing an update that enhance the GUI and allow the app to run full screen on Android 4.4+. The update is going to be released on the play store.

Feedback

We are really eager to hear what you think about the new Crazyflie 2.0, the instructions and everything else around it. So please drop by our feedback topic in the forum, or post your feedback here, to let us know what you think.