View source for AMTI Force Plate Setup

[[Category: Biomechanics]]
[[Category: Peripheral Devices]]
[[Category: Device Synchronization]]
 [[OptiTrack Documentation Wiki|Main Page]] &rarr; [[AMTI Force Plate Setup|AMTI Force Plate Setup]]
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'''Scope'''
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This page provides instructions on integrating an AMTI Force plate system with an OptiTrack motion capture system.
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'''Overview'''
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{{ForcePlateIntro}}
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'''Required Components'''
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* Supported Amplifier Models: AMTI Gen 5, AMTI Optima.
* 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.
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=Hardware Setup=
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==Component Wiring (AMTI)==
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====AMTI Force Plate System Setup====
: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.  For detailed instructions on setting up the Force Plate system with a host PC, refer to the AMTI documentation.

====Camera System Setup====
: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.

====Wiring the eSync with the Gen 5 Amplifier====
:For accurate synchronizations, the [http://optitrack.com/products/esync-2/ eSync 2 synchronization hub] must be used. 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.

====Multiple Devices Sync====
:There are total four output ports on the eSync 2, and multiple force plates and external devices can be integrated if needed. Consult our [http://optitrack.com/support/ Engineers] for multiple force plate synchronizations.

====Hot Plugging====
{{Indent|{{HotPlugging}}}}

<center>
<li class="thumblist">[[Image:FP_EthernetWiring.png|thumb|alt=Diagram for Prime Camera System with integrated force plates.|650px|center|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.]]</li>
<li class="thumblist">[[Image:eSync2.jpg|thumb|center|The eSync 2 output and input ports]]</li>
</center>
</div>

=Software Setup=
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==AMTI Software Setup==
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Before setting up the force plates in Motive, make sure software components required by the force plate system is installed on the computer. AMTI's software (e.g. AMTINetForce) must be able to detect and initialize the connected devices in order for the force plates to be properly initialized and used in Motive. Once this has been confirmed working, start setting up Motive. Please refer to manufacturer documentation for more information.

[[Image:AMTI_NetForce_20.png|center|thumb|550px|Optima amplifier detected in the NetForce software.]]
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==Peripheral Device Module==
{{#lst:Bertec Force Plate Setup|peripheralmodulesetup}}

==Force Plate Setup in Motive==
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====1. Start Motive====
{{#lst:Bertec Force Plate Setup|setupstepone}}
</ul></center>

====2. Calibrate Cameras====
{{#lsth:Bertec Force Plate Setup|2. Calibrate Cameras}}

====3. Setup CS-400====
{{#lsth:Bertec Force Plate Setup|3. Setup CS-400}}

====4. Place CS-400 on force plate====
{{#lst:Bertec Force Plate Setup|setupstepfour}}
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{{Info|'''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.}}
</div>

<center>
<li class="thumblist">[[Image:FP_WandFP.jpg|thumb|alt=Force plate with CS-400 aligned properly.|450px|center|Force plate with CS-400 aligned properly.]]</li>
<li class="thumblist">[[Image:FP_ForcePlateCoordinateAxis.png|thumb|300 px|Calibrated force plate position and orientation. X and Y axis is shown.]]</li>
</center>

====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.

[[Image:FP_SetPosition.png|thumb|alt=Setting the position of a force plate in Motive.|600px|center|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.====
{{#lst:Bertec Force Plate Setup|setupstepsix}}
[[Image:FP_Zero.png|thumb|alt=Set the force plate data to zero for more accurate data.|750px|center|Set the force plate data to zero for more accurate data.]]

====7. Set sampling rate====
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Sampling rate of force plates is configured through the synchronization setup which will be covered in the following section. You can sync the force plates either through the ''reference clock sync'' or through the ''triggered sync''. Please note that only specific sampling rates may be supported depending on the amplifier models. 

{{Info2|
'''Supported force plate sampling rates: '''

For AMTI force plates support the following sampling rates depending on the amplifier used. For the most up-to-date information, consult their documentation. The supported sampling rates (Hz) are the following:

:*'''AMTI Gen 5 Amplifier:''' 2000, 1800, 1500, 1200, 1000, 900, 800, 600, 500, 450, 400, 360, 300, etc...
:*'''AMTI Optima Amplifier:''' 1000, 600, 500, 300, 250, 200, 150, 125, 120, 100, 60, 50, 30, 25, 15, 10.}}

[[Image:AMTI_Device_Multiplier_21.png|thumb|350px|center|Configuring force plate sampling rate from [[Devices pane]].]]
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=Synchronization Configuration=
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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.  

==Sync Configuration Steps: eSync==
<tabs>
<tab name="Reference Clock Sync" style="padding:0 1em 0 1em;">
====Reference Clock Sync Setup Steps====
# Open the [[Devices pane]] and the [[Properties pane]]. 
# In the [[Devices pane]], select the eSync among the listed devices. This will list out the synchronization settings in the properties pane for the selected eSync.
# In the [[Properties pane]], under '''Sync Input Settings''' section, set the '''Source''' to '''Internal Clock'''.
# Next, to the '''Clock Frequency''' section, input the sampling rate that you wish the run the force plates in. This clock signal will be eventually outputted to the force plate system to control the sampling rate. For this guide, let's set this to 1200 Hz. 
# Once the clock frequency is set, apply the '''Input Divider/Multiplier''' to the clock frequency to set the framerate of the camera system. For example, if you set the '''Input Divider''' to 10 and the ''Input Multiplier'' to 2 with internal clock frequency running at 1200 Hz, the camera system will be running at 240 FPS.  The resulting frame rate of the camera system will be displayed in the '''Camera Rate''' section. 
# Next step is to configure the output signal so that the clock signal can be sent to the force plate system. Under the ''Outputs'' section, enable the corresponding output port of the eSync which the force plate system is connected to.
# Set the ''Output 1-4 &rarr; Type'' to [[External_Device_Sync_Guide:_eSync#Gated_Internal_Clock|Gated Internal Clock]]. 
# Now that the eSync has been configured, you need to configure the force plate properties in Motive. While the force plate(s) is selected in Motive, access the Properties pane to view the [[Properties: Force Plates|force plate properties]]. Here, set the following properties:
::*Record Trigger &rarr; ''False''
::*Reference Clock Sync &rarr; ''True'' 
::*eSync Output Channel &rarr; output port used on the eSync.
::Once this is set, the force plate system will start sampling at the frequency of the clock signal configured on the eSync, and this rate will be displayed on the [[Devices pane]] as well.

<center><ul>
<li class="thumblist">[[Image:AMTI_eSyncClockSyncProperties_21.png|thumb|370px|alt=Example settings in the cameras and synchronization panes for eSync.|Example eSync properties for clock sync.]]</li>
<li class="thumblist">[[Image:AMTI_FPClockSyncProperties_21.png|thumb|370px|alt=Example settings in the cameras and synchronization panes for eSync.|Example force plate properties for clock sync.]]</li>
</ul></center>

{{Indent|{{Info2|*When force plates are synchronized through ''Gated Internal Clock'', the force data may not be available in the Live mode because the signal gets outputted only when Motive is recording. If you need to see the data in Live mode, use the triggered sync setup.
}}}}
</tab>
<tab name="Triggered Sync" style="padding:0 1em 0 1em;">
====Triggered Sync Setup Steps====
#  Open the [[Devices pane]] and the [[Properties pane]]. 
#  The final frame rate of the camera system will be displayed at the very top of the [[Devices pane]].
#  In the [[Devices pane]], select the eSync among the listed devices. This will list out the synchronization settings in the Properties pane for the selected eSync.
#  Set up the output signal so that the recording trigger signal can be sent to the force plate system. In the ''Outputs'' section, enable and configure the corresponding output port of the eSync which the force plate system is connected to.
#  Set the ''Output 1-4 &rarr; Type'' to [[External_Device_Sync_Guide:_eSync#Recording_Gate_.26_Recording_Start.2FStop_Pulse|Recording Gate]].
#  Now that the eSync has been configured, you need to configure the properties of the force plates. While the force plate(s) is selected in Motive, access the Properties pane to view the [[Properties: Force Plates|force plate properties]]. Here, set the following properties:
::*Record Trigger &rarr; ''Device''
::*Reference Clock Sync &rarr; ''False'' 
::*eSync Output Channel &rarr; output port used on the eSync.

::Once this is done, the force plate system will synchronize to the recording trigger signal when Motive starts collecting data, and the force plates will free-run after the initial sync trigger. You can configure the sampling rate of the force plates by modifying the ''Multiplier'' values in [[Devices pane]] to sample at a whole multiple of the camera system frame rate.

<center><ul>
<li class="thumblist">[[Image:AMTI_eSyncTrigSyncProperties_21.png|thumb|370px|alt=Example settings in the cameras and synchronization panes for eSync.|Example eSync properties for triggered sync.]]</li>
<li class="thumblist">[[Image:AMTI_FPTrigSyncProperties_21.png|thumb|370px|alt=Example settings in the cameras and synchronization panes for eSync.|Example force plate properties for triggered sync.]]</li>
</ul></center>

{{Indent|{{Info2|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.}}

{{Info|
====ReSynch====
[[Image:ForcePlate_ReSynch.png|thumb|300 px|Re-aligning initial sampling timing of the force plate.]]
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|Devices pane]] or the [[View pane#3D Perspective View|perspective view]], and select Resynch from the context menu to realign the sampling timing of both systems.
}}}}
</tab>
</tabs>

==How to Validate your Synchronization==
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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 &mdash; closest to the marker &mdash; 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. [[#top|↑]]

The following is an example of validating good synchronization outcomes:

[[Image:AMTI_Goodsync_20.png|thumb|center|600px|Good synchronization]]
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=Device Settings Profile=
{{#lsth:Bertec Force Plate Setup|Device Settings Profile}}

=Force Plate Data in Motive=
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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.

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====Live Force Plate Data====
: For plotting live force plate data, the graph ''View Style'' of the corresponding graph must be configured to ''Live''.

{{Info|'''Notes'''

* 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.}}

<center><ul>
<li class="thumblist">[[Image:FP_FPGraph_20.png|thumb|alt=Graph of live force plate data.|600px|center|Graph of live force plate data.]]</li>
<li class="thumblist">[[Image:FP_graphview_20.png|thumb|alt=Layout configuration.|center|150px|Graph view pane layout configuration.]]</li>
</ul></center>
</div>

=Data Export=
{{#lsth:Bertec Force Plate Setup|Data Export}}