Main Page → Kistler Force Plate Setup
This page provides instructions on how to integrate a Kistler force plate system with an OptiTrack motion capture system.
When a motion capture system is used in conjunction with force plates, they work together as an efficient tool for various research applications including biomechanical analysis, clinical gait analysis, physiology research, sports performance research, and many more. An OptiTrack motion capture system can synchronize with force plates to obtain both kinematic and kinetic measurements. Note that force plate integration is supported only with a Prime camera system using the eSync synchronization hub. This page provides quick guidelines for setting up and configuring force plates — with digital outputs — along with the OptiTrack motion capture system.
For detailed information on specifications and configurations on the force plates, refer to the documentation provided by the force plate manufacturer.
Hot plugging is not supported with the integration. When a new device is connected to the system, you must re-start Motive to instantiate it.
Before setting up the force plates in Motive, make sure all of the required software components are set up on the computer. First of all, Kistler's software must be installed and configured, and it should be able to detect and initialize the connected devices in order for the force plates to be used in Motive. This requires the Kistler BioWare software and the device driver (InstaCal) as well as other required software components to be installed.
Once they are all installed, launch the BioWare software and register each force plate. During this process, you will need to input the model and serial number as well as other specs of each platform to configure the device. For more information, please refer to manufacturer documentation.
In order to integrate force plate systems with Motive, you will need to setup the required drivers and plugins. Motive installer is packaged with the Peripheral Device module which can be added. During the Motive installation, a list of program features will be shown in the Custom Setup section. Here, change the setting for the Peripheral Device module, as shown in the below image, so that the module is installed along with Motive Files.
Note : Even if you are not using NI-DAQ, it is still necessary to install NI-DAQmx drivers that come up next in the installer.
Kistler system also requires Microsoft Visual C++ 2010 Redistributable - x64 to be installed on the computer. If it is not already on the computer, you will get prompted to set this up during Motive installation process. Please make sure to have this installed as well.
After registering the force plate in BioWare, next step is to export out the device configuration XML file. In BioWare, go to the Setup → Save DataServer Configuration File to export out the configuration XML file. To add the Kistler force plates in Motive, this XML file containing the force plate information must be added to the Motive directory. Copy-and-paste the Configuration.xml file into the C:\ProgramData\OptiTrack\Motive\DeviceProfiles directory, and then rename the file to Kistler.xml. Once this is done, Motive should initialize the force plates that are detected by computer and that are registered within the XML file.
If the hardware and software for the force plates are configured and successfully recognized, Motive will list out the detected force plates with number labels (1, 2, etc..). Motive will notify you of incorrect or nonexistent force plate calibration files. When the devices are properly instantiated in Motive, the following status messages will be shown under that Status Log.
Calibrate the capture volume as normal to get the orientation of the cameras (see the Quick Start Guide or Calibration page for more information). The position of the force plate is about the center of the volume, and when you recalibrate or reset the ground plane, you will need to also realign the position of your force plates for best results.
On the CS-400 calibration square, pull the force plate alignment tabs out and put the force plate leveling jigs at the bottom. The leveling jigs align the calibration square to the surface of your force plate. The alignment tabs allow you to put the CS-400 flush against the sides of your force plate giving the most accurate alignment.
Place the calibration wand on the force plate so that vertex of the wand is located at the left-hand corner of the side where the cable input is located (as shown in the image below). A correct placement of the calibration square is important because it determines the orientation of the force plate and its local coordinate axis within the global system. The coordinate systems for force plates are independent of the system used Motive.
After you have calibrated each of your force plates, remove the CS-400 from the volume. Right click one of your force plates in Motive and click Zero (all). This will tare the scale and set the current force on the plate data to 0. This will account for a small constant amount of measurement offset from the force plate. Remember that it zeros all of the force plates at once. So make sure there are no objects on any of the force plates.
Sampling rate of force plates is configured through the synchronization settings, which will be covered in the following section.
Supported force plate sampling rates: Kistler plates support rates sampling rates between 10~2000 Hz. Make sure the synchronization is configured that the force plates sample at the supported speed.
There are two synchronization approaches you could take: Synchronization through clock signal or through recording trigger signal.
Synchronization via clock signal utilizes the internal clock signal of the eSync to synchronize the sampling of the force plates on per-frame basis. However, when there is another device (e.g. NI-DAQ) being synchronized to the clock signal frequency, the sampling rate cannot be set for each individual device. In that case, triggered sync must be used for synchronizing the initial recording trigger. Synchronization via trigger signal utilizes the recording trigger in Motive to align the initial samples from both systems. After the initial sync, both systems run freely at their own sampling rate. If the force plates are running at whole multiples of the camera system, the collected samples will be aligned. However, since the sampling clocks are not perfectly accurate, alignment of the samples may slowly drift over time. Thus, when synchronizing via recording trigger, it is better to keep the record times short.
When synchronizing through the eSync, use the following steps to configure the sync settings in Motive. This will allow both systems to be triggered simultaneously with reference to the master synchronization device, the eSync.
For free run sync setups, sampling rates of force plates can be set from the Devices pane, but the sampling rate of force plates must be configured to a whole multiple of the camera system's framerate. By adjusting the Rate Multiplier values in the Devices pane, sampling rates of the force plates can be modified. First, pick a frame rate of the camera system and then adjust the rate multiplier values to set force plates to the desired sampling rate.
When two systems are synchronized by recording trigger signals (Recording Gate or Recording Pulse), both systems are in Free Run Mode. This means that the recording of both the mocap system and the force plate system are triggered simultaneously at the same time and each system runs at its own rate.
Two systems, however, are synchronized at the recording trigger but not by per frame basis. For this reason, alignment of the mocap data and the force plate data may gradually drift from each other for longer captures. But this is not a problem since the sync chain will always be re-synchronized each time recording in Motive is triggered. Furthermore, Takes in general do not last too long for this drift to take effect on the data.
However, this could be an issue when live-streaming the data since recording is never initiated and two systems will be synchronized only when Motive first launches. To zero out the drift, the ReSynch feature can be used. Right-click on force plates from either the Devices pane or the perspective view, and select Resynch from the context menu to realign the sampling timing of both systems.
Before you start recording, you may want to validate that the camera and force plate data are in sync. There are some tests you can do to examine this.
The first method is to record dropping a retroreflective ball/marker onto the platform few times. The bouncing ball produces a sharp transition when it hits the surface of the platform, and it makes the data more obvious for validating the synchronization. Alternately, you can attach a marker on a tip of the foot and step on and off the force plate. Make sure that your toe — closest to the marker — strikes the platform first, otherwise the data will seem off even when it is not. You can then monitor the precise timing of the ball or the foot impacting the force plate and compare them between the mocap data and the force plate data. ↑
The following is an example of validating good synchronization outcomes:
All of the configured device settings, including the calibration, get saved on Device Profile XML files. When you exit out of Motive, updated device profiles will be saved under the program data directory (C:\ProgramData\OptiTrack\Motive\DeviceProfiles), and this file gets loaded again when you restart Motive. The persistent settings folder can be accessed through Help → Application Folders → Persistent Setting. This XML file ensures that all of the device settings are persisted each time you close and restart Motive.
Force plate data can be monitored from the Graph View pane. You will need to configure a custom graph layouts to show force plate data. As shown in the images, make sure the desired force plate data channels (Fx, Fy, Fz, Mx, My, or Mz) are selected to be plotted. Then, when you select a force plate in Motive, and the data from the corresponding channels will be plotted on the graphs. When both reconstructed markers and force plate channels are selected, the force plot will be sub-sampled in order to be plotted along with trajectory data. For more information about how to configure graph layouts, read through the Graph View pane page.
We recommend the following programs for analyzing exported data in biomechanics applications:
Since Motive uses a different coordinate system than the system used in common biomechanics applications, it is necessary to modify the coordinate axis to a compatible convention in the C3D exporter settings. For biomechanics applications using z-up right-handed convention (e.g. Visual3D), the following changes must be made under the custom axis.
This will convert the coordinate axis of the exported data so that the x-axis represents the anteroposterior axis (left/right), the y-axis represents the mediolateral axis (front/back), and the z-axis represents the longitudinal axis (up/down).
Force plate data and the tracking data can be exported into CSV files as well. When a Take file is exported into a CSV file. Separate CSV files will be saved for each force plate and it will contain the force, moment, and center of pressure data. Exported CSV file can be imported for analysis.
To stream tracking data along with the force plate data, open the Data Streaming Pane and check the Broadcast Frame Data, and make sure that you are not streaming over the camera network. Read more about streaming from the Data Streaming workflow page.
Motive can stream the tracking data and the force plate data into various applications — including Matlab — using NatNet Streaming protocol. Find more about NatNet streaming from the User's Guide included in the download.