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.