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When motion capture systems and force plates are used together, they become a very powerful tool for various research applications including biomechanical analysis, clinical gait analysis, physiology research, sports performance analysis, and more. The OptiTrack motion capture system can synchronize with force plates to obtain both the kinematic and kinetic data measurements with best accuracy. This page provides a guideline to setting up the AMTI force plates along with the OptiTrack motion capture system; including hardware setup, software setup, synchronization configurations, and the suggestions for post-processing of the recorded data.
For detailed information on specifications and configurations for the force plates, refer to the respective documentation provided by the force plate manufacturer.
(As of Motive 1.9.0 we only support force plate systems with AMTI Gen 5 amplifiers)
Note: Force plates can also be used without wiring to the synchronization hub. However, without the synchronization signals, motion capture data and force plate data may be as many as 1-5 frames off. Learn more about it from the sync configuration section.
When using the Ethernet camera system, connect the eSync 2 to the Gen 5 amplifier(s) for more accurate synchronization.
The eSync 2 has four synchronization output ports which can be connected to separate amplifiers. Use the 50 Ohm BNC Male to 75 Ohm RCA Jack Adapters (included with the eSync 2) and RCA cables to connect the eSync 2 and the Gen 5 amplifiers. Without using the eSync 2, your motion capture and force plate data may be off by few frames.
The following wiring diagram shows how the force plates are integrated into Prime series Ethernet camera system through the eSync 2.
When using a USB based camera system, connect the force plate Gen 5 amplifiers to the OptiHub(s) within the system.
There is one synchronization output port for each OptiHub. Connect a 50 Ohm BNC Male to 75 Ohm RCA Jack Adapter into the output port on the OptiHub(s) and connect each OptiHub to each amplifier using a RCA cable. In this case, you need an OptiHub for each force plate. When integrating multiple force plates, you may use a BNC splitter alternatively to use the OptiHub as a master sync for multiple force plates. (Note: When incorporating more than two force plates into one OptiHub, you may need to use an active BNC splitter, because the signal power will be reduced each time the signal is split.)
The following wiring diagram shows how the force plates are integrated into the Flex series USB system.
(Note: If you have multiple hard drives in the host computer, you may need to move the configuration file to C:\AMTI\CFG\AMTIUsbSetup.cfg. Motive should alert you if this has not been done properly.)
Installation Note: If you install AMTI, then Motive everything should work fine. However, if you install Motive, then AMTI you may run into Visual Studio Redistributed 2010 issues.
1. Start Motive. If the hardware and software for the force plates are setup correctly, Motive will display the detected force plates with number labels (1, 2, etc..). Motive will notify you if it detects an incorrect or nonexistent force plate calibration file.
2. Calibrate cameras. Calibrate the capture volume as normal to get the orientation of cameras (see the Quick Start Guide or Calibration page for more information). The position of the force plate is relative to the center of the volume. So when you re-calibrate or reset the ground plane, you will need to also realign the position of your force plates for best results.
3. Setup CS-400. Pull the force plate alignment tabs out and put the force plate leveling jigs on the bottom of your CS-400 calibration square. 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.
4. Place CS-400 on force plate. Place the Calibration wand on the force plate so that the wand vertex is located at the right corner of the side where the cable input is located (shown in the below image). A correct placement of the calibration square is important because it determines the orientation of the force plate.
5. Set force plate position in Motive. After placing the calibration square, select the CS-400 markers in Motive. Right click on the force plate you want to locate, and click Set Position. You may need to step on the force plate to figure out which force plate the calibration square is on. A force vector will appear as you step on the force plate. Repeat step 4 and 5 for other force plates as well.
6. Zero force plates. After you have set all of your force plate, remove the CS-400. Right click one of your force plates and click Zero (all). This will 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 the force plates.
To view the live force plate data, open the editor from the Timeline Pane. Then, open the Project Pane (or Cameras Pane) and select one of the force plates, and a list of the force plate data will appear at the bottom of the Project Pane. Select one of Fx, Fy, Fz, Mx, My, or Mz to view the live force plate data from the timeline. This is a good way to confirm that your force plates are working.
the project pane (or cameras pane) and timeline pane, then open the editor in the timeline pane. Select your force plate in the project pane (or cameras pane). Then select one of Fx, Fy, Fz, Mx, My, or Mz to view the live force plate data. If the force plates are recording properly, you will see This is a good way to confirm that your force plates are working.
Notes
The force and moment data reflects the coordinate system defined by the force plate manufacturer, which is typically the z-up right-handed coordinate system. Thus, the Fz components represent the vertical force. For more information, refer to the force plate specifications.
The supported force plate sampling rates will also depend on the manufacturer. For the most up-to-date information, consult their documentation. For AMTI force plates, supported frame rates are 2000, 1800, 1500, 1200, 1000, 900, 800, 600, 500, 450, 400, 360, 300, etc...
After these configurations have been applied, the force plate data and the motion capture data will be synchronized. The settings should look something like the following:
After these configurations have been applied, the force plate data and the motion capture data will be synchronized. It should look something like the following:
If you are using the Ethernet system without the eSync, ignore the synchronization configurations. From the Cameras Pane, just make sure that that the force plate sampling rate is a multiple of the tracking frames per second (fps), ex 100fps and 1000fps. Motive will alert you if the sampling rates for cameras and force plates disagree.
Note that without the master synchronization device, recording for the camera system and the force plates will not be triggered exactly at the same time. This can cause problems for longer takes because the sampling timing for mocap data and the force plate data will eventually deviate from each other. If you want your system to be timed perfectly, we recommend synchronizing through the eSync 2.
When the force plate sampling rate is not set to an integer multiple of the camera frame rate, force plate may record improperly; which is shown in the following screenshot.
From Motive, you can export the tracking data and the force plate data into C3D files. Exported C3D files can then be imported into a biomechanics analysis software for further processing. See Data Export page or Data Export: C3D page for more information about C3D export in Motive.
Visual3D which is our recommended bio-mech analysis software. Visual3D offers extensive biomechanics analysis pipelines including biomech skeleton modeling, joint and segment kinematics analysis, and reporting functions. Using the precise marker positional data tracked by the OptiTrack system along with the force plate data, Visual3D can perform the most accurate biomechanical analysis.
To stream the 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. Then you are good to stream into another program. Read more about streaming from the Data Streaming workflow page.
We recommend Visual3D for bio-mechanics streaming as well. When streaming into Visual3D, set the Visual3D Compatible setting to true from the Data Streaming pane. Real-time streaming into Visual3D uses Visual3DServer plugin provided by C-Motion.
For more information on the Visual3DServer, refer to the C-Motion Documentation Wiki: http://www.c-motion.com/v3dwiki/index.php/Visual3DServer_Overview
