This is where we try to collect the most frequently asked questions and answers to them.

The Crazyflie is controlled with the Crazyradio. It uses the nRF24L01+ 2.4 GHz chip from Nordic Semiconductors which is commonly used in commercial HID devices. We chose this chip because it is low power, low latency, decent range, easy to work with and relatively cheap.

When we where investigating what radio to use, three years ago, we compared several technologies. Here are some of our thoughts

• Wifi
  • + High bandwidth
  • + Wide spread technology
  • + Good range (up to 100-150m)
  • - Complex hardware and software
  • - Power hungry
  • - Can be problems with latency
  • - Expensive
• Bluetooth 2.0 <
  • + Wide spread technology
  • - Short range if using Class 2 device with is common in smartphones etc.
  • - Complex hardware and software
  • - Can be problems with latency
• Bluetooth 4.0 low energy (which was not available 3 years ago)
  • + Can be pretty cheap (e.g. nRF8001)
  • + Low power
  • + Potential to be a wide spread technology
  • o Not so sure about hardware and software complexity but it should be simpler now
  • o Might be short range if using smartphones etc
  • - Can be problems with latency
  • - Low bandwidth
• nRF24L01+
  • + Low power and descent range (up to 100m)
  • + Simple hardware and software
  • + Low latency
  • + Descent bandwidth
  • + Cheap
  • - Not so wide spread technology

The decision fell on the nRF24L01+. There are other comparable radio technology from e.g TI that we also could have used. However there is always the possibility to experiment with another radio technology connected to the expansion header on the Crazyflie.

As with all radio communication it depends. It depends on the environment, radio interference, chip production variations, etc. In a couple of line-of-sight tests outdoor we have gotten from 50 to 80 meters range in the 250 Kbit mode, higher data rate decreases the range.

The Crazyradio has been designed to work as a radio dongle connected to a USB port but has other capabilities.

• We gave it an expansion header and it can work solely from this header, see schematics. The header accepts power up to 16V and could read a PPM signal so it is possible to make it work as a R/C transmitter module, but we have no code for it now and it would be a bit hackish.
• It can be connected to android device with USB host functionality. We are currently working on an android client which is in beta stage. Repository.

The e-sky R/C transmitters use the nRF24L01 chip, compatible with ours, so it would be possible to control the Crazyflie using the e-sky transmitters. No firmware support for this yet but it is planned. Also see “Is a PC required for the Crazyradio”.

The Crazyflie is using the PCB itself as the frame. The PCB is made of FR4 which is a strong and lightweight material. We have tried to find a good thickness for the arms so that it is strong but also flexible. We want it to be flexible so that it bounces during a crash which will reduce the g-force chock imposed on the electronics. It has no problem handling low speed crashes but if you push it too it's limits and you fly 30 km/h into something hard you probably will damage it. Most of the parts can be replaced but if you are very unlucky you break one of the arms. We are working on 3D printed part that can be used to repair the arm in case of an accident such as this.