TDoA 3 is part of the official Crazyflie and LPS Node firmware releases since 2018.10.
The Crazyflie will automatically detect that the positioning system is using TDoA3 and switch to the correct mode. If you want to force the Crazyflie to use TDoA3 on startup, use the LPS_TDOA3_ENABLE=1 compile option
The LPS Nodes
- Configure the Nodes as anchors, and set the mode to TDoA 3
- Set anchor positions, see below.
Setting anchor positions
Anchor positions can be set by the python client or the tool in the lps-node-firmware repo. You might have to move the Crazyflie close to all anchors to transfer the positions from the Crazyflie.
All the anchors work in the same coordinate system, so you need to choose a common origin for your system. Try to expand your system step by step, testing it at each step to catch problem when they start to happen.
2D positioning
TDoA 3 supports 2D positioning as well. In this mode all anchors can be placed in the same plane. The tag (LPS deck) is expected to move in the XY-plane at a fixed Z.
Recompile the Crazyflie firmware using the LPS_2D_POSITION_HEIGHT
compile flag set to the desired Z. For instance
make "EXTRA_CFLAGS=-DLPS_2D_POSITION_HEIGHT=1.2" if the tag will be
located at 1.2 meters height.
Longer range and lower bitrate
Note: this is experimental functionality that is not fully tested or might not work as expected.
In this mode the UWB bitrate is lower and the data of messages can be read at a longer distance. The packet rate will be reduced though.
Recompile the Crazyflie firmware with the LPS_LONGER_RANGE compile flag.
Example: make "EXTRA_CFLAGS=-DLPS_LONGER_RANGE"
There is a setting for the bitrate in the Anchor configuration when connecting using USB.
Longer preamble
Note: this is experimental functionality that is not fully tested or might not work as expected.
It is possible to use a longer preamble, this will also reduce packet rate. There is no compile flag for this setting, it requires some code modifications in the Crazyflie and the anchors. The preamble is used by the anchor radios to detect messages and a longer preamble increase the probability and thus the useful distance. Note that the radios might detect the preamble but fail at reading the data of the packet (see lower bitrate above). The "SFD" LED on the anchor indicates if a preamble has been detected by the radio.
The Crazyflie
- Find the src/deck/drivers/src/locodeck.c file
- Locate the call to dwEnableMode()
- Change the second argument to MODE_LONGDATA_MID_ACCURACY
- Compile and flash
The LPS Nodes
- There is a configuration setting for the preamble length
Sniffing
Sniffing the system is useful when you want to start digging into the radio messages exchanged between the anchor. It is a debug functionality.
If an anchor is configured to act as a sniffer, it can be used to listen to the UWB messages in the system. To set an anchor to sniffer mode, connect via USB and configure it to sniffer mode.
Basic sniffing
Connect the sniffer via USB and check in /dev which port that it uses.
Use this as the first argument The second argument is the output format,
use yaml example:
python3 tools/sniffer/sniffer_binary.py /dev/tty.usbmodem1421 yaml
TDoA 3 parsing
Pipe the yaml into the TDoA 3 decoder to see TDoA 3 data unpacked
example:
python3 tools/sniffer/sniffer_binary.py /dev/tty.usbmodem1421 yaml | python3 tools/sniffer/tdoa3_decoder.py
This will show all data that the sniffer receives. To limit the output it is possible to filter which anchors to show. Add one or more ids at the end to only show data from only these anchors.
example:
python3 tools/sniffer/sniffer_binary.py /dev/tty.usbmodem1421 yaml | python3 tools/sniffer/tdoa3_decoder.py 2 3
Time of flight and anchor to anchor distance
By piping the TDoA 3 data into the TOF tool, the measured anchor to anchor distances will be displayed. By adding the 'm' argument the output will be in meters instead of UWB clock ticks.
example:
python3 tools/sniffer/sniffer_binary.py /dev/tty.usbmodem1421 yaml | python3 tools/sniffer/tdoa3_decoder.py | python3 tools/sniffer/tdoa3_tof.py m