IMU Sensor Fusion

Quick Start Guide - Auto Configure

First and foremost, ensure that your tracking volume is setup with optimal conditions and your Calibration is Exceptional.

  1. Power on either a CinePuck or an Active IMU puck.

  2. Set the puck on a level surface and wait until the puck is finished calculating its bias. See below for a description of each indicator light.

  3. Select the markers from the active device and create a Rigid Body Asset.

It is highly recommended to make sure all 8 markers can be tracked with minimal occlusions for the best results when pairing and aligning the Rigid Body to the IMU.

  1. Right click on the Rigid Body in the Assets pane and select Active Tags -> Auto-Configure Active Tag.

  2. Move the CinePuck or IMU Active Puck slowly around at least 3 axes until you see 'IMU Working [Good Optical] %'. You have now successfully paired and aligned your CinePuck with your Rigid Body.

  3. Attach your CinePuck to your cinema camera or your regular IMU Active Puck to an object of your choosing.

  4. Enjoy your sensor fused Puck for seamless and robust tracking.

Motive can automatically recognize a CinePuck and after pairing and aligning a Rigid Body to an IMU Tag, will change the name of the Rigid Body to CinePuck_G### along with its marker constraints.

Active Tag Context Menu Options

The options below can be found both by right clicking a Rigid Body in the Assets pane or by selecting the Rigid Body in the 3D Viewport and right clicking to open the context menu.

The Devices pane has a few redundant options as well under the Active Tag section.

Auto Configure Active Tag

This option will pair and align the Rigid Body to the IMU Tag all in one go. This is the quickest and most preferable option when first getting started.

Set Auto Pair

This will set the Puck to search for an IMU pair. Once paired, this will be indicated in the 3D Viewport IMU visual as 'IMU Paired', the Devices pane Active Tag 'Paired Asset' column, and in the Assets pane's 'Active Tag' column.

Unpair Active Tag

This will remove a paired Tag from the Rigid Body.

Manual Pair

If manually pairing from the Devices pane:

  • Choose the Rigid Body you would like to pair to the selected Tag in the Devices pane.

If manually pairing from the Assets pane:

  • Choose the Active Tag you would like to pair to the selected Rigid Body in the Assets pane.

Align

This allows you to manually align your Tag to your Rigid Body after you have paired.

Remove Alignment

This allows you to remove alignment from your Rigid Body while still paired to the IMU.

Orient Pivot to IMU

If you would like your Pivot orientation to reflect the orientation of your IMU (internal), you can select Orient Pivot to IMU. Motive will recognize the physical orientation of the IMU within the Puck and adjust the Rigid Body pivot bone appropriately.

Assets Pane

Active Tag Column

From the existing Assets pane, you can right click to add columns. For this IMU workflow, you can select Active Tag. The Active Tag column will display either the Paired or fully Paired and Aligned IMU Tag to the Rigid Body Asset. If the Rigid Body is non IMU or is not yet Paired or Aligned, this column will display 'None'.

3D Viewport

In the 3D viewport, just like Labels, you can view the status of the Rigid Body.

Searching for IMU Pair

After either Auto or Manually pairing, the status above your Rigid Body will report 'Searching for IMU Pair'. After moving and rotating your Puck around this should change to 'IMU Paired'.

If it does not, this could mean that an IMU device is not present or is not being recognized. Please check the Devices pane to see if the IMU Device is populated in the table with its Uplink ID. If you are unable to find the Device, please check your RF Channel and Uplink ID using the Active Batch Programmer.

IMU Paired [Optical] %

After your Rigid Body has successfully paired with the IMU Tag, the status will change to IMU Paired [Optical] %.

IMU Working [Optical] %

Once you have either Auto-Configured or Manually Paired and Aligned an Asset, you should see 'IMU Working' appear over your Asset in the 3D viewport.

If you're having issues seeing 'IMU Working,' you may need to rotate the Puck in more axes or try Pairing again and Re-align.

Good Optical: Denotes most markers can be seen and tracked within the volume.

Optical:

Denotes that the minimum markers can be seen and tracked within the volume.

No Optical:

Denotes either below the minimum or no markers can be seen and tracked within the volume.

%:

Percentages denote the amount of IMU packets that an IMU Tag is successfully delivering for every 100 frames. 100% indicates all packets are going through; 80% indicates 20% of IMU packets were dropped.

Devices Pane

Tags that have come into Motive can be viewed in the Devices pane under the Active Tag section. Please see above for context menu options for this pane.

Active Tag Table

Name

By default the Name is set to 'Tag XX:XX'. The XX:XX format denotes the RF Channel and Uplink ID respectively. i.e. Tag 20:00 is on RF Channel 20 and has an Uplink ID of 0.

Paired Asset

When an Asset is paired, this will show the Rigid Body name that will be the same as shown in the Assets pane.

Aligned

The Aligned column will show the Aligned status of the Active Tag.

Properties Pane for Tag and Rigid Body

Properties for both the IMU tag by itself (when selected from Devices pane) and for the sensor fused Rigid Body (when selecting the Rigid Body from either the Assets pane or 3D Viewport) can be found in the Properties pane.

Active Tag Properties

The Active Tag does not have any editable properties but does display a few Details and General properties.

Rigid Body Properties

Rigid Body properties that pertain to IMU specific workflows can be found under the Visuals section.

IMU State

This dropdown allows you to choose how you would like the IMU State to appear in the 3D viewport.

  • None - No visual in the viewport

  • Text - Text visual in viewport

  • Icon - Icon only visual in viewport

Constraints Pane

After pairing a Rigid Body to an IMU Puck, an IMU Constraint with IMU information will be created for the Rigid Body. This along with an update to the names of Constraints based on what Puck type is identified by Motive.

IMU Constraint

As stated above, the IMU Constraint is created when the IMU Tag is paired to a Rigid Body. This not only stores the information after pairing, but also alignment information when the Align action is performed by either Auto-Configure Active Tag or by Manually Aligning.

If this Constraint is removed, this will remove the pair and/or align information from the Rigid Body. You will need to perform another pair and align to re-adhere the sensor fusion data to the Rigid Body once more.

Active Debugging in Info Pane

The Info pane Active Debugging is used as a troubleshooting tool to see the amount of IMU data packets dropped along with the largest gap between IMU data packets being sent.

When either column exceeds the Maximum settings, the text will turn magenta depending on the logic setup in the Maximum settings at the bottom of the pane.

IMU % Drops

This column denotes the number of IMU packet drops that an IMU Tag is encountering over 60 frames.

Max Gap Size

Max Gap Size denotes the number of frames between IMU data packets sent where the IMU packets were dropped. i.e. in the image above on the left, the maximum gap is a 1 frame gap where IMU packets were either not sent or received. The image on the right has a gap of 288 frames where the IMU packets were either not sent or received.

BaseStation Load Capacity

The number of IMUs that can attach to a BaseStation is determined by the system frame rate and the divisor applied to the BaseStation. The table below shows the IMU maximum for common frame rates with a divisor rate of 1, 2, and in some cases 3.

As noted, the table does not include all possible frame rate and divisor combinations. If you are familiar with using Tera Term or PuTTy, you can determine the maximum number of IMUs for any specific frame rate and divisor combination not shown on the table.

  1. Use PuTTy to change the divisor rate on the BaseStation.

  2. Connect an IMU puck to PuTTy.

  3. Attempt to set the ID of the puck to an unrealistically high value. This triggers a warning that includes the current number of slots available for the given frame rate.

  4. Set the IMU puck ID to the highest available slot for the frame rate and confirm that it appears in Motive.

BaseStations have 16 radio frequency (RF) channels available for use (11-26). When adding more than one BaseStation to a system, the IMU count is simply the maximum number of IMUs multiplied by the number of BaseStations (up to 16). For example, in a system with 4 BaseStations running at 90Hz and a divisor rate of 3, the number of allowable IMUs would be 216 (54*4=216).

CinePuck and other IMU Active Puck Indicator Lights

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