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Difference between revisions of "AMTI Force Plate Setup"

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==Motive Setup==
==Motive Setup==

Revision as of 19:23, 30 January 2017

Main PageAMTI Force Plate Setup


This page provides instructions on integrating an AMTI 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.


Analog Platforms

Analog force plate devices can only be implemented via DAQ devices. Incoming voltage signals can be detected through the data acquisition channels, but force plate related software features (vectors, position calibration, etc.) will not be supported in Motive for the analog platforms. Refer to the NI-DAQ Setup page for detailed instructions on integrating analog devices.

Required Components

  • Supported Amplifier Models: Gen 5,
  • Force platforms that are compatible with the above amplifier models.
  • Prime series Ethernet camera system with the eSync synchronization hub.
  • Motive 1.9 or above.

Hardware Setup

Setup Steps

  1. Connect each force plate into the host PC. For force plate systems with external amplifiers, the platform must be connected to the amplifier which uplinks to the host computer.
  2. Setup the OptiTrack camera system and place the force plate(s) at the desired location(s); ideally, near the center of the volume. See Quick Start Guide or Hardware Setup page for details.
  3. For accurate synchronizations, connect the camera system and the force plate(s) using the eSync 2 synchronization hub. Connect the output ports of the hub to the sync input ports using the BNC cables or RCA cables with matching BNC-RCA adapters.
The eSync 2 output and input ports

Ethernet Camera System + Force Plate

Connect the force plate system through the eSync 2 for more accurate synchronization.

Diagram for Prime Camera System with integrated force plates.
Diagram for Prime Camera System with integrated force plates. (*) Some force plates don't have external amplifiers, but instead, have their amplifiers integrated within the platform. In this case, connect sync cables and the USB cables directly to the host PC.

Camera System Setup

Follow the Quick Start Guide: Getting Started or the Hardware Setup pages for instructions on setting up the camera system.

AMTI Force Plate System Setup

Refer to the AMTI documentation for instructions on setting up the Force Plate system with a host PC.

Wiring the eSync with the Gen 5 Amplifier

The eSync 2 has signal output ports that are used to send out synchronization signals to slave devices. Connect the BNC output ports of the eSync to sync input ports (Genlock/Trigger Input) of force plate amplifiers. If force plate systems have RCA sync ports, use RCA cables along with the 50 Ohm BNC Male to 75 Ohm RCA Jack Adapters included with the eSync 2 to connect the amplifiers. The above wiring diagram shows how force plate systems need to be connected to an Ethernet camera system through the eSync 2.

There are total four output ports on the eSync, and multiple force plates and external devices can be integrated if needed. Consult our Engineers for multiple force plate synchronizations.

Software Setup

Install Plugin

Peripheral Device Module

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.


Installation Note: For integration into Motive, the NI-DAQmx 15.1.1 or later runtime driver must be installed. If you are already using an older version of the NI-DAQmx runtime and Motive is having problems recognizing the connected device, update the driver or uninstall and re-install the packaged version of the driver before contacting Support. In Motive, you can inspect device connection status via the Status Log panel which can be accessed under the View tab in Motive.


Notes on NI-DAQmx version 19.x: There is a known issue with the latest NI-DAQmx version (19.x) where it crashes Motive on startup. If you have this version of the driver installed, please reinstall with the recommended version (15.1.1) provided with the Motive installer.

Installing OptiTrack Peripheral Module. DAQmxInstall.gif

Bertec Customers

In addition to the Peripheral Device module, you may also want to install the Digital Acquire™ from Bertec to verify that the force plates are properly working. Visit the below webpage to download the software, and follow the respective instructions to install. This software installs remaining resources for connecting the Bertec force plates.


Note: You cannot run Digital Acquire and Motive together and have them connected to the plate(s) at the same time.

Motive Setup

1. Start Motive.

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 successfully instantiated in Motive, the Status Log will indicate that the device has been created and loaded.

  • Initial view in Motive after setting up force plates.
    Motive with force plates.

2. Calibrate cameras.

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 relative to the center of the volume, and when you re-calibrate or reset the ground plane, you will need to also realign the position of your force plates for best results.
Motive after setting up force plates and calibration.
Motive with force plates and camera calibration.

3. Setup CS-400.

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.
CS-400 calibration square with force plate force plate parts.
CS-400 calibration square with force plate force plate parts.

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-hand corner of the side where the cable input is located (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 system for force plates are independent of the system used Motive.


AMTI Force Plates

AMTI force plates use the right-hand system. The long arm of CS-400 will define the Y axis, and the short arm will define the X axis of the force plate. Accordingly, Z axis is directed downwards for measuring the vertical force.

Force plate with CS-400 aligned properly.
Force plate with CS-400 aligned properly.

Calibrated force plate position and orientation. X and Y axis is shown.

5. Set force plate position in Motive.

After placing the calibration square on the force plate, select the CS-400 markers in Motive. Right click on the force plate you want to locate, and click Set Position. When there are multiple force plates in a volume, you may need to step on the force plate to find which platform the calibration square is on. In Motive, uncalibrated force plates will light up in green and a force vector will appear when you step on the plate. Repeat step 4 and 5 for other force plates as necessary.
Referencing to the markers on the calibration square, Motive defines the location of the force plate coordinate system within the global coordinate system. Motive uses manufacturer defined X, Y, and Z mechanical-to-electrical center offset when calculating the force vector and the center of pressure. For digital based plates, this information is available from the SDK and also stored in the plate's on-board calibration data.
Setting the position of a force plate in Motive.
Setting the position of a force plate in Motive. The number label on the force plate is inverted because the force plate position and orientation has not been calibrated yet.

6. Zero force plates.

After you have calibrated each of your force plate, remove the CS-400 from the volume. Right click one of your force plates in Motive and click Zero (all). This sets 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.
Set the force plate data to zero for more accurate data.
Set the force plate data to zero for more accurate data.

Force Plate Data in Motive

To view and confirm 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. A list of available channels will appear under each force plate instance. Here, you can confirm that your force plates are working properly. Select Fx, Fy, Fz, Mx, My, or Mz channels to view the live force plate data from the timeline. Multiple channels can be displayed at once. 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.

If you wish to double check the force plate position calibration, you may create a long trackable rigid body and use it to apply force against force plate. If the force plate location is precisely calibrated in Motive, the force vector will go right through the rigid body.

  • Graph of live force plate data.
    Graph of live force plate data.
  • A resultant force vector displayed in Motive.



  • The force and moment data reflects the coordinate system defined by the force plate manufacturer, which is typically the Z-down right-handed coordinate system. Note: This convention is independent of the global coordinate system used in Motive. Thus, the Fz components represent the vertical force. For more in-depth 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...

Synchronization Configuration

Ethernet System Force Plate Sync Configuration


  1. Open the Cameras Pane and the Synchronization pane.
  2. In the Synchronization pane, select the Custom Synchronization mode from the dropdown menu.
  3. Set the Sync Input → Source to Internal Clock.
  4. Set the Sync Input → Clock Freq to 1000 Hz, and set the Sync Input → Input divider to 10.
  5. Set the Sync Output 1-4 → Type to Record Start/Stop Pulse or Recording Gate triggered sync.
  6. Click Apply from the Synchronization pane.
  7. In the Cameras Pane, select the force plates group and double check that the Sync Source is set to Free Run for the force plates.

After these configurations have been applied, the force plate data and the motion capture data will be synchronized via triggering. The settings should look similar to the following:

Example settings in the cameras and synchronization panes for eSync.
Example settings in the cameras and synchronization panes for eSync.

Ethernet System Force Plate without eSync Configuration

If you are using an Ethernet system without an eSync, ignore the synchronization configuration options. From the Cameras Pane, 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.

Without a 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 data may record improperly; which is shown in the following screenshot.

Graph of bad data.
The force plate stops recording when its sampling rate disagrees with the frame rate of the camera system.

How to Validate your Synchronization

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.

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 make the data more obvious for validating the synchronization. Alternately, you can attach a marker on 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 compare when the motion capture data says the ball or foot made contact with the force plate to when the force plate says it made contact.

The following is a example of validating good synchronizations using these methods:

Graphs of good data.
Example of good sync using tests described

The following is a example of validating bad synchronizations using these methods:

Graphs of bad data.
Example of bad sync using tests described

Data Export

The MotionMonitor biomechanics analysis software.
Visual3D biomechanics analysis software provided by C-Motion

We recommend the following programs for analyzing exported data in biomechanics applications:

C3D Export

Motive exports tracking data and force plate data into C3D files. Exported C3D files can then be imported into a biomechanics analysis and visualization software for further processing. See the Data Export or Data Export: C3D page for more information about C3D export in Motive. Note that the coordinate system used in Motive (y-up right-handed) may be different from the convention used in the biomechanics analysis software.

C3D Axes

Common Conventions

C3D export setting for applications using z-up right-handed coordinate systems.

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.

  • X axis in Motive should be configured to positive X
  • Y axis in Motive should be configured to negative Z
  • Z axis in Motive should be configured to positive Y.

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).

CSV Export

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.

Data Streaming

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.


Number of Force Plates

At the time of writing, there is a hard limit on the maximum number of force plate data that can be streamed out from Motive. Please note that only up to 8 force plate data can be streamed out from Motive and received by a NatNet application.