After investigating the problem with the MPU6050 from last week we found out that all our prototypes have defect MPU6050 sensors :-(. The bias offset values are way out of spec and several of the accelerometer axis is locked to their min or max value. The manufacturer must have dropped the hole batch in the floor or something because we would have expected at least one out of the six prototypes to have a working sensor. Without working sensors it is hard to make a maiden flight, which we are very eager to do. We will have to order new sensors and hopefully we can replace the new sensors without damaging them.
We also finished to patch all our test copters so that they will now be able to fly when we change the sensor:
We don’t have that much new to write about this week. The software clean-up is slowly evolving and we have been working some more on the radio protocol and the ground station.
We hope that the new prototypes will be ready this week so maybe we could make a first flight with them in the beginning of next week :-)
A none return point has been passed as we have put in an order for a shit-load of motors. Now everything has to work out or we will be sitting with a hole bunch of motors and no money to do other fun stuff.
While we are waiting for our prototypes to arrive, the ETA is the 18th of may which is a looong wait, we thought we would play around with the Crazyflie outside now when spring has finally reached the south of Sweden. The drawback with a quadcopter this small is that it doesn’t work that well when it is windy outside but the upside is that it is pretty durable which makes great for some crazy testing :-). This Monday it was very calm outside and we got the idea to throw it in the air and try to make a “throwing start”. From the beginning we thought, no way, but it actually worked better then we thought. Here are some of the clips of the more successful attempts :-)
We also bought one of these very popular key chain spy cameras to try and get some on-board action footage. We removed the electronics from the casing, removed the battery and connected it to our battery instead. We even removed the mini-USB connector to save weight. It all ended up in about 25g including the Crazyflie which is OK. Now it is really starting to look as an insect of some sort…
Frame from onboard video footage
We managed to take a short on-board video but the camera doesn’t handle the battery voltage drop and resets pretty easily as soon as you hit the thrust. Maybe it is possible to power it from our stable 2.8V instead because now it is pretty useless. Also the view-angle is to narrow as well as the framerate being too low to get any good footage. We seem to have gotten the 808 #14 model which isn’t supposed to be the best. At least the Crazyflie is looking pretty mean with it attached :-). Further investigations will be done when we have some time left over.
We wish we had something interesting to write about, but recently we have just been cleaning up and reorganizing the Crazyflie firmware. We are doing this so it would be simpler to further develop the software when it is released. We have also been preparing the new drivers for the digital sensors so they will be ready when the next version of prototypes arrives within the next two weeks.
One funny thing we have though is this little teaser video we put together while testing the speed of the Crazyflie. It is not recommended crashing into something hard at this speed 8O
The last week we have been working hard on finishing the Crazyflie with the digital sensors, MPU-6050, HMC5883L and MS5611-01BA03. We are not so sure that the magnetometer, HMC5883L, will work that well due to the strongly magnetized motors just a few centimeters from the sensor. That will be one of the upcoming tasks to find out.
Within 3-4 weeks we will receive what will hopefully be the final prototype version which later can be used for the first batch of Crazyflies. Until then we have plenty of work with software both on the PC side and the firmware. Now it is pretty late, the clock just passed 00:00 and writing at this hour is hard. We will post some video to compensate for this short post later this week :-)
When we built the latest prototypes we built two different versions. One with the ST accelerometer LIS344ALH and with the ISZ-IDG650 gyros. The other one with BOSH accelerometer BMA145 and with the ISZ-IDG500 gyros. It turned out that the LIS344ALH accelerometer is very vibration sensitive and doesn’t work that well for an application as this. If we would just have spent some time on the Internet we could have found this information in before hand… luckily we made the hardware design work with both and the BMA145 is working pretty well, however now we no longer have an alternative :-(.
The ISZ650 and IDG650 works pretty well even though they are less sensitive with their ±2000deg/s output. We can’t see any direct stability issues compared to the IXX500 versions with ±500deg/s output. Maybe we will stick with the IXX650, that way we don’t limit the flip and loop speed to much. Not that the Crazyflie can do flips/rolls right now but we are very confident it will be able to in the future, judging from its agility.
We have also been working on getting the Crazyflie easier to control for beginners. With some slew rate limiting and thrust control we seem to be getting there. Now even Marcus can fly it without any problem. He used to hit the wall or ceiling all the time before :-).
We had to cancel our weekly Monday meeting due to illnesses but we have at least made some small progress we can write about.
The radio dongle code has been updated to flash either of the two LED’s when sending data or in case of bad transmission.
On our latest prototypes we discovered that the radio transmission went pretty bad on some copters as soon as the motors where turned on. This was not a nice discovery at this time of our project and we had not really seen it before. This kind of problem could require a big re-design of the PCB! After some debugging it turned out to be the PWM switching of the motors causing ripple on the digital supply voltage. It wasn’t that much, about 60mV peak-to-peak but enough to throw the radio off balance. After some tries with different decoupling techniques to get rid of the ripple, which showed only minor improvement, we increased the motor PWM frequency from 17kHz to 280kHz. That made the ripple go away, now about 10mV peak-to-peak, and so did the radio transmission problems, yeay!
It is now Monday evening which is now our official meeting day within the Crazyflie team. From now on we intend to post a progress update every Monday evening here at the Bitcraze blog. First of we can tell you that we have, since two weeks, received our second round of prototypes. For the second round of prototypes we did some small fixes and improvements which unfortunately did not all work.
We fixed an issue with the standby current which was 150uA, due to a misplaced diode, but was supposed to be below 10uA according to our design.
We moved the battery measurement point to the actual battery instead of behind the system off switch so we can measure the battery when it is charging as well. Unfortunately a design mistake made the standby current go up to 250uA instead. Fixed one issue just to introduced another one…
We have discovered a problem with the MAX16054 ON/OFF switch we use to turn the system on and off. If the battery voltage is above 3.5V it refuses to turn on but if it is below it works as expected. We sent a support message to Maxim and hope it can be solved fast. This circuit worked on our first prototypes and it seems to be due to the now removed diode we spoke about in the first bulletin…
Other then that we are getting close to a pretty well working flying PCB.
We have tested a couple of LiPo batteries in different sizes from Fullriver. We decided to go for the 170mAh 25C battery which gives us about 7min of flight time but doesn’t add to much weight.
We have tested a lot of different pager motors in mainly the sizes 6×14 and 6×15 mm. Many of them are not the best quality but we found a good one, 2.5ohm, 6x15mm motor which is of good quality and high performance.
What is left now is the motor mountings which has turned out to be a time consuming task for us since none of us has any direct mechanical/plastic experience. We also have loads of other tasks but let’s take it one step at a time.
There is a short video of the new prototype flying that somebody took when we visited Techfest if you want to have a look.
