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The open-source software uses an Ubuntu image which can be downloaded from our repository. This image contains the operating system and code that will run on the Rasberry Pi. Once downloaded, unzip the image file. Insert your microSD card into your computer using the SD card adapter. We will transfer the Ubuntu image to the microSD card using a free program called balenaEtcher. Install this software and open it. Select the image location that you downloaded, select the microSD card as the drive to install to, and click “Flash!”. Once this has completed, you can eject the microSD card and insert it into the Raspberry Pi. You have finished installing the software and are ready to assemble the hardware.
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How to Assemble the Hardware
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Fig 1. The components and default IMU orientations of the OpenSense Real-time System. (A) An IMU on the pelvis is required and acts as the base in order to compute the relative orientation of other sensors. The OpenSense Real-time System accommodates a variable number of additional IMUs to customize which kinematics are measured. To monitor movement of the upper body, three IMUs may be placed on each arm (upper arm, forearm, and hand). An additional IMU can be placed on the torso. The orientation frame with axes shown in red, green, and blue are used to orient the x, y, and z axes defined on each IMU. These individual body frames should align with the world reference frames of the fore-aft, mediolateral, and vertical axes, while the subject’s joint segments are aligned in a neutral standing (or other known) position. (B) The lower-limb IMU placements also require the pelvis IMU as a base and include three IMUs on each lower limb, measuring the thigh, shank and foot. Any number of upper and lower limb IMUs can be combined and measured simultaneously. (C) A zoomed in view of the system components shows the microcontroller, battery, button (for starting and stopping recordings), IMU connector, and pelvis IMU.
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Customizing the OpenSenseRT System to Track Specific Body Segments
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The third line of the settings.txt file is the computation frequency, the maximum frequency that can be computed depends on how many IMUs are in use. The recommended frequencies based on the number of IMUs is detailed in the research paper. The fourth line denotes whether the system will run in real-time using the “online” mode or simply save the raw IMU data for computing later in the “offline” mode. The fifth line defines the name of the folder where the recorded kinematics will be saved. The sixth line defines what the maximum recording length can be before the recording is automatically ended. The seventh line acts as a way to calibrate the system for a new IMU configuration. The first time a new IMU setup is used, the word “calibrate” should be added to automatically remove the bias in measurements from the gyroscopes. This line will be automatically deleted from the file after calibration is complete, so the system does not need to be recalibrated for each use.
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Using the OpenSenseRT System
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The motion files are saved numerically for each run with the raw IMU data in a numpy ‘.npy’ file, the kinematics motion data in a ‘.mot’ file, and the timestamps of each sample in a ‘.npy’ file. The motion files can be visualized using OpenSim. See the introductory information for setting up OpenSim and loading a motion file.
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We suggest testing your initial setup by assembling the device as previously discussed and performing a short data collection and visualizing the result to ensure the system is performing as expected. Errors in the system are challenging to debug due to the use of hardware and software components. See the instructional video for more information.
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Learn More
The current version of the OpenSenseRT System is our first step in open-sourcing both hardware and software components to provide accurate, low-cost, and wearable IMU-based biomechanics tools to the research community. This system can be customized for specific research applications by modifying the provided Python code. The main code directory is the Github repository, which contains the Python files that can be modified. While we currently won’t be able to support customized projects, we’ve provided the additional information about the system to allow you to access and modify the code as needed. These steps assume you have completed the previous setup instructions.
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For additional modifications I recommend you look at the Raspberry Pi webpage and forums and look at the configuration file for the Raspberry Pi: /boot/firmware/config.txt
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