Testing sensors

2012-03-13 | Tobias | 6 Comments

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 :-).

A little bit further

2012-02-28 | Tobias | 12 Comments

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!

Screenshots of the PC side user interface

2012-02-06 | Marcus | 1 Comment

As promised here’s a new Monday post. Below are some screenshots of our PC side/ground station software written in Python using pyUSB, pyGame and PyQt4. It’s far from finished but it’s good enough for us to get real-time plots of flight data and control parameters. Unfortunatly we did not have a flying prototype at hand while writing this post so the data is somewhat fake but good enough to show the concept.