It did take much longer than anticipated, but we finally managed to get the AI-deck 1.1 back in stock! We had some difficulties with the post-production testing and Chinese new year was also a main contributor to the delay, but we are now very happy that we have a batch of AI-deck’s which are ready to ship!
There are only minor changes between the AI-deck 1.0 and 1.1 which can be read about in the “AI-deck product update” blog post. Since the AI-deck 1.1 is now using the gray-scale version of the camera module and the AI-deck 1.0 was using the Bayer RGB version, we now also offer the camera modules as stand-alone products for those that rather have the other variant.
For those of you that already have the previous AI-deck 1.0 and rather wished for the gray-scale camera module, please send us an email at contact@bitcraze.io, and we will work something out!
The AI-deck 1.1 is still a early access product, so remember to post any question or problems you have on our forum in the AIdeck group or to check out examples / documentation on the Github Repo. We also are planning to organize an online workshop / tutorial for the AI-deck in the coming months. We will hopefully have more information about that soon, so keep an eye out on the blogposts!
The lithium polymer battery we use, as with basically all rechargeable batteries, suffers from degradation. That means that when using it, and as time goes by, its energy capacity as well as performance will degrade. The performance, which is very related to the batteries internal resistance, will result in that the Crazyflie will not be able to produce the same maximum thrust and it will not be able to carry as much payload. The loss of capacity is due to ageing and charge cycles, results in that the flight time will decrease. A common solution to monitor the degradation is to have a BMS, or Battery Management System, that constantly monitors the battery health. For the small type of battery that is used in the Crazyflie, this is not yet viable, but maybe there is something we can do to test part of the battery health anyway?
Theory
Since the internal resistance will result in a larger voltage drop during load we can exploit this property and measure it. We will however not only measure the batteries internal resistance but the resistance of the complete power path as a result of the components we have at hand on the Crazyflie.
Power path block diagram
So what we do is to activate the switch (mosfet) so the load (motor) will pull power from the battery. The power drawn will result in a voltage drop compared to a no-load situation, which we can measure and compare to a healthy setup. Since the measurement point is at the PCB traces, any of the components before that point can be causing the voltage drop, however the battery and connector are most likely of doing so as they are most prone to ageing.
Implementation
The load is achieved by, for a very short time, activate the motors at full thrust. We don’t want the Crazyflie to fly away as that would be a bit unhandy. Before activating the motors we measure the idle voltage and during load we measure the minimum voltage so we can calculate the voltage drop. This is pretty easy to do, the problem is to find a good level where we can distinguish a good battery from bad battery. Therefore this feature is pretty experimental. We tested many batteries and good batteries tend to yield a voltage drop between 0.60V – 0.85V while bad batteries go above 1.0V. Therefore the current threshold is set to 0.95V but it would be good to have more data so if you use this feature please give us feedback if the level is wrong. The testing was run on a “stock” setup with the standard battery, propeller and motors, and it is for these the level is set. A different setup will probably not work well and needs a different threshold. Also keep in mind that the connector can also be a “bad” guy as oxide can build up and result in a higher resistance. Often this can be solved with some e.g. WD-40 solvent or un-connecting/connecting the connector several times.
Usage
This is not in the 2021.01 release so one would have to run the latest on the master branch on both the crazyflie-firmware and the Crazyfie-clients-python. The simplest way to test this feature is to launch the cflient, connect to the Crazyflie, open the console tab and press the battery test button.
cfclient console tab after running battery test
When pressing the button the propellers will shortly spin and there will be an output in the console as highlighted in red. If the sag value is below 0.95V it will yield [OK] and if it is above it will say [FAIL].
A probably more useful use case is to test this automatically before taking of with e.g. a swarm. This can be done by setting the parameter health.startBatTest to 1 and after around 0.5s readout the result in the log variable health.batteryPass to check that it is set to 1. The health.batterySag log variable will contain the latest sag (voltage drop) measurement. Hopefully this experimental feature will be a good way of increasing reliability of flights.
Li-Ion batteries have packed more energy per gram for a long time compared to Li-Po batteries. The problem for UAV applications has been that Li-Ion can’t deliver enough current, something that is starting to change. Now there are cells that are supposed to be able to deliver 30-35A continuously in the 18650 series, at least according to the specs. Therefor we thought it was time to do some testing and decided to build a 1 cell Li-Ion drone using the Crazyflie Bolt as base.
Since a 18650 battery is 18mm in diameter and 65mm long, the size would affect the design but we still wanted to keep the drone small and lightweight. The battery is below 20mm wide which means we can run the deck connectors around it, that is nice. We chose to use our 3D printer to build the frame and use off the shelf ESCs, motors and props. After a couple of hours of research we selected 3″ propellers, 1202.5 11500kv motors and tiny 1-2s single ESCs for our first prototype.
Parts list:
1 x Custom designed 130mm 3D printed frame
1 x Crazyflie Bolt flight controller
4 x Eachine 3020 propeller (2xCW + 2xCCW)
4 x Flywoo ROBO RB 1202.5 11500 Kv motors
4 x Flash hobby 7A 1-2S ESC
1 x Li-Ion Sony 18650 VTC6 3000mAh 30A
Screws, anti vib. spacers, zipties, etc.
The custom designed frame was developed in iterations, and can still be much improved, but at this stage it is small, lightweight and rigid enough. We wanted the battery to be as central as possible while keeping it all compact.
Prototype frame designed in FreeCAD.
Assembly and tuning
The 3D printed frame came out quite well and weighed in at 13g. After soldering the bolt connectors to the ESCs, attaching motors and props, adjusting battery cable and soldering a XT30 to the Li-Ion battery it all weighed ~103g and then the battery is 45g of these. It feels quite heavy compared to the Crazyflie 2.1 and we had a lot of respect when we test flew it the first time. Before we took off we reduced the pitch and roll PID gains to roughly half and luckily it flew without problems and quite nicely. Well it sounds a lot but that is kind of expected. After increasing the gains a bit we felt quite pleased with:
This would be good enough for what we really wanted to try, the endurance with a Li-Ion battery. A quick measurement of the current consumption at hover, 5.8A, we estimated up to ~30 min flight time on a 3000mAh Li-Ion battery, wow, but first a real test…
Hover test
For the hover test we used lighthouse 2 which is starting to work quite well. We had to change the weight and thrust constants in estimator_kalman.c for the autonomous flight to work:
#define CRAZYFLIE_WEIGHT_grams (100.0f)
//thrust is thrust mapped for 65536 <==> 250 GRAMS!
#define CONTROL_TO_ACC (GRAVITY_MAGNITUDE*250.0f/CRAZYFLIE_WEIGHT_grams/65536.0f)
After doing that and creating a hover script that hovers at 0.5m height and was set to land when the voltage reached 3.0V. We leaned back with excitement, behind a safety net, and started the script… after 19 min it landed… good but not what we hoped for and quite far from the calculated 30 min. Maybe Li-Ion isn’t that good when it needs to provide more current…? A quick internet search and we could find that Li-Ion can run all the way down to 2.5V, but we have to stop at 3.0V because of electronics and loosing thrust, so we are missing quite a bit of energy… Further investigations are needed.
Lighthouse 2 flight test
As a final test we launched some flight scripts to fly in a square and in a spiral so we would get a feel for Lighthouse 2 + Bolt with PID controller combination. We think it turned out quite nicely, and this with almost no optimization effort:
Summary
Li-Ion felt like it could be a game changer when it comes to flight time but was not as promising as we hoped for. It doesn’t mean we can’t get there though. More research and development is required.
For a long time issue #270 has been bugging us. It caused the µSD-card logging to fail in combination when using either the flow or loco deck, or actually any deck that uses the deck SPI bus. Several attempts has been made to fix this issue over time and recently we decided to really dig in to it. There has been some workaround to move the µSD-card to a different SPI bus but that was tedious and required patching the deck. So it was time to fix this for good, or at least know why it doesn’t work. A SPI bus is designed to be a multi-bus so it should be possible… Timing problems is still tricky but that is another story.
The problem
The SPI driver is protecting the bus with a mutex to prevent several clients to access it at the same time. After some digging we found that the FatFs integration layer was bugged and that SPI bus handling wasn’t well done. After comparing this to some other open implementations we found that this needed to be rewritten.
The solution
After rewriting part of the integration layer to have clear path of when the SPI bus was taken, and when it was released, we immediately got some good results. µSD-card logging with flow and loco deck worked, hooray! There is of course a limit to this and as we mentioned earlier the bus is a shared resource and if it is to congested, things will slow down, or stop working. This is currently the case when LPS is put in TWR mode. The TWR is very chatty and causes around 15k transactions per seconds on the SPI bus, and since it has higher priority than the µSD-card logging, the µSD-card write task starves, causing the logging to fail.
µSD and LPS SPI bus captured with a logic analyzer, over 50msµSD and LPS SPI bus captured with a logic analyzer, over 6ms
So if you stay away from LPS in TWR mode µSD-card logging should now work fine. I’m pretty sure there is a workaround for the TWR mode as well. First guess is that you would need to slow down the TWR update rate which is now at its maximum.
The summer has reached Sweden but this summer is not an ordinary summer. Coming from a pandemic spring, and not really knowing what the world is going to be like next, is not a situation we are used to. The covid situation in Sweden is looking a lot better now but we still have to be cautious and travel around as little as possible. That mean we will have a “homecation” or “hemester” as we say in Swedish.
We will recharge our batteries and get new inspiration and will try to embrace the “homecation”. During this time the pace at the Bitcraze office will be a bit slower but we will continue to ship products, answer emails, help you in the forum etc as usual all summer. The remaining time will be spent mainly on cleaning up as we normally do during summer. This includes bug fixing, documentation improvements, finishing small things that never gets done, etc. To summarize, improvements in general.
Who knew propellers would be that hard? Already from the very beginning with the Crazyflie 1.0, we had problems with very unbalanced propellers resulting in reduced flight performance. The fix at that time was to manually test and sort out the bad propellers. This worked well until the manufacturer’s injection mould got too worn down and we had to reject a lot of propellers. The manufacturer didn’t want to continue selling us the propellers unless we accepted them all. The hunt for a new manufacturer begun and after trying several, we finally, just in time for the Crazyflie 2.1, found one that could deliver well balanced propellers.
That could have been the end of a happy story but recently we found out that the new propellers tend to break too easily. The root cause seems to be that the center hole is too tight, causing tension in the plastic which makes it more fragile and prone to break.
Typically broken propeller
We don’t fully understand when this started but it looks like it was not that frequent in the beginning when the Crazyflie 2.1 was released and that it has increased from the batch manufactured in the end of July 2019. We don’t have data on how many propellers are bad but our estimation is around 20-40% and it is booth CW and CCW propellers. It also includes the spare part bundles manufactured in the second half of 2019.
Currently out main focus is to fix this propeller manufacturing issue. As soon as we have done so, we will lunch some form of replacement propeller program so that those of you that have gotten many bad propellers can get new ones for free. We don’t have any time estimate right now, and due to the world covid-19 crisis we have a feeling it can take a while. We are very sorry about this!
Insert propeller so it sits firmly, but not further
Workaround
There is an easy, but not ideal, workaround for this and that is to not push the propeller all the way down on the shaft. Instead stop when force is getting high and it holds the propeller in place. This will prevent the tension in the propeller to become big enough to break.
For those that have ordered after the 16th of March we have fixed the propellers by drilling the center hole slightly larger. This solves the problem for those units until we have fixed the root cause at the manufacturer.
When there is a possibility to name a release with only two’s and zero’s one has to take that opportunity right! Adding to that, it was about time to make a new release, and there is actually another reason. As we wrote about in the “What’s up 2020” blog post, it’s time to look back, finish up and make things more stable. This includes improving documentation, more examples/tutorials etc. With this release we create a good baseline to start this work from.
After a couple of delays we are happy to announce the Crazyflie Bolt is now stocked and ready to ship out. For those of you that are new to the Bolt, it is basically a Crazyflie 2.1 control board, but built to fit a bigger package. We have blogged about it a couple of times before, so if you would like to catch up you can start from the first idea, to maturing and finally changing name from RZR to Bolt. Another way to describe the Bolt is: Crazyflie 2.1 + Big-quad deck in one which doesn’t hog any deck expansion pins. Thus combinations such as Bolt + Led-ring + Lighthouse-4 is now possible or e.g. Bolt + Flow v2 + LPS.
Keep in mind that the Bolt is an early access product so you will most likely have to dig in to the code to hard-code PID-tuning parameters etc. Also trowing a warning finger, heavier drones can be very dangerous so be sure to keep safe!
The Crazyflie Bolt is delivered as a stand alone control board. Frame, motors, propellers and battery needs to be added, for details check out the wiki. Unfortunately we don’t have a good reference kit to recommend at the moment. If you happen to have built a good one, please share.
As pointed out in Daniele’s blog post about the PULP-DroNet we are collaborating on a AI-deck built around the new GAP8 RISC-V multi-core MCU. In the blog post you can find all the details around DroNet while here we will talk a bit about the AI-deck hardware. The AI-deck is similar to the PULP-Shield but with some optimizations. One of the HyperFlash memory spots has been removed, the communication interface slimmed down and a ESP32 (NINA module) has been added for WiFi connectivity.
Latest AI-deck prototype
So all together this a pretty good platform to develop low power AI on the edge for a drone.
Features:
GAP8 – Ultra low power 9 core RISC-V MCU
Himax HM01B0 – Ultra low power 320×320 greyscale camera.
512 Mbit HyperFlash and 64 Mbit HyperRAM
ESP32 for WiFi and more (NINA-W102)
2 x JTAG for GAP8 and ESP32
Currently we are doing the final testing of the hardware and hopefully we will launch production in the end of October. If production goes according to plan we hope we can offer it as an early access product just before X-mas. Make sure to come back and check the blog for more information about the progress as well as pricing.
We have now come to a the point were we will start manufacturing of the Crazyflie Bolt, Formally known as the RZR. You might wonder why we changed the name… Well the RZR more implies it is a Racer quad and it really isn’t. This is mainly because of the design in power distribution which is limited to around 8A per motor. However by using your own PDB it will work well for that too. But that is not the intention, it is more intended to have the strengths of the Crazyflie 2.1 but in a slightly bit bigger package. Therefore we wanted a better name for it and after a brainstorming session we came up with the name, Bolt. Both as it is a Crazyflie building block, a bolt used to fasten things, but also because it has the potential to be fast, as in a lightning bolt. Great name right :-)
The CF-Bolt development has been pushed back many times because of other more promising products, but finally it is getting here. If things goes according to plan, the Crazyflie Bolt should be in our shop in Aug-Sept. If you want to read up on the history and what it is all about read about the first flight to the almost-final prototype here.
A quick recap of the features:
Fully compatible with the CF2 firmware, expansion decks as well as radio.
Connectors to attach motor controllers (also possible to solder though) so it is easy to build and repair.
Power distributions built into controller board. (Max ~8A per motor controller) with XT30 connector.
Motor controllers can be switched off by the system (MOSFET) so the system can go into deep sleep and only consume around 50uA.
Voltage input 1S-4S (3V to 17V).
Standard mounting (M3 mounting holes spaced 30.5mm in a square).
