How do I synchronise multiple motion trackers?
- Date added:
- Tuesday, 14 July 2009
- Last revised:
- never
Answer
All Xsens motion trackers offer options for synchronisation. All motion trackers support sending out a synchonisation pulse to trigger sampling of another device. The MTi and MTx also accept synchronisation pulses to initiate data output. Refer to the User Manual of your device for detailed information of the synchronisation modes, the interface and pinout.
To synchronise recording of multiple motion trackers, you will need to assign one device as master by enabling the sync out and the other units as slave by enabling sync in.Consecutively, set the master device into config mode so it is not sampling data continuously. Set all slave devices in measurement mode.The computers sampling data from the slave devices should be ready to read and log data from the slave motion trackers.Once you put the master device into measurement mode, it will start sampling and sending out sync pulses, initiating the other motion trackers to send data as well. To stop recording set the master device to config mode again.
This warrants not only that each device is sending data at the same time but also that the first and last data package of all devices are identical.
Note the difference between sync modes transmission of latest data and ADC sampling:
In transmission of latest data, the motion tracker will use it's internal clock to initiate sampling at the specified sample rate. Only when the external trigger signal is received, will the device output the latest data package. This allows accurate recording of orientation data at a sample rate lower than 100Hz.
When triggering the ADC sampling, the motion tracker will start the sampling procedure for its internal sensors when a trigger pulse is detected. Data will be sent as soon as it is available. This mode ensures that the instant of sampling is exactly the same for all devices. However, to be able to calculate accurate orientation data, the sample frequency must be at least 100Hz.
The same principles apply to synchronising a motion tracker with third party hardware.
For synchronisation options with an Xbus Kit, refer to the FAQ item "I want to synchronise two Xbus Masters. How does that word?".