Ultra Low Force and Displacement Assistive Tech Joystick

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Introducing OHMni-stick, an affordable open-source assistive technology solution to address the needs of individuals with disabilities and mobility challenges. This innovative device combines a low force and displacement force-based joystick with pneumatic pressure-sensitive buttons, aiming to enhance accessibility and improve daily living for those who can benefit from it.

Challenge Addressed:

  • OHMni-stick tackles the challenges faced by individuals with disabilities or limited mobility in effectively accessing and controlling technology. Traditional input devices often pose barriers due to their high force requirements and large movements. OHMni-stick aims to provide a comprehensive solution that overcomes these obstacles, enabling users to engage more independently in various activities.

Problem Alleviation:

  • OHMni-stick offers a practical solution to alleviate the challenges faced by individuals with disabilities or mobility limitations. This low force and displacement force-based joystick requires minimal effort and allows for precise control, making it accessible to users with limited strength or dexterity. Additionally, the pneumatic pressure-sensitive buttons provide customizable force sensitivity and tactile feedback, further enhancing control and adaptability for users.

Hardware Solution:

  • OHMni-stick is a hardware solution designed to assist, adapt, and rehabilitate individuals with disabilities or mobility challenges. It aims to enhance learning, working, and daily living by offering a versatile input device. Whether it's aiding in rehabilitation exercises, controlling equipment, or providing a more accessible gaming experience, OHMni-stick is designed to cater to diverse user needs.

The open-source nature of OHMni-stick reflects a commitment to collaboration, knowledge sharing, and community involvement. The project documentation and shared design files encourage further innovation and customization. By fostering an inclusive ecosystem of developers and users, OHMni-stick aims to contribute to the ongoing improvement of assistive technologies. The design is released under GNU General Public License v3.0.

Advantages of the OHMni-Stick:

  • Enhanced Accessibility: Enables individuals with limited muscle strength and range of motion to control devices effortlessly.
  • Low Force and Displacement: Requires minimal force and displacement for operation, accommodating users with extremely limited strength and mobility.
  • Customizable Grips: Interchangeable grips provide personalized comfort and adaptability.
  • Responsive Pneumatic Buttons: Delivers precise and tactile control with adjustable sensitivity.
  • High Sensitivity and Accuracy: Responds to forces as low as a single gram and offers real-time tracking.
  • Open-Source Design: Promotes collaboration, innovation, and continuous improvement within the community.
  • Inclusive Design: Enhances learning, work, and daily living for individuals with disabilities or mobility challenges.
  • Versatile Applications: Suitable for controlling wheelchairs, operating assistive devices, and interacting with technology.

Firmware for the OHMni-Stick, Arduino Framework, PlatformIO Project,

Zip Archive - 76.17 kB - 05/27/2023 at 22:53



Full FreeCAD Model for the OHMni-Stick

fcstd - 5.93 MB - 05/27/2023 at 21:09


  • Pneumatic Pressure-Sensitive Buttons

    oneohm05/29/2023 at 22:10 0 comments

    Early Pressure Button Proof of Concept - Side View
    Early Pressure Button Proof of Concept - Side View

    This update on the OHMni-Stick project focuses on the pneumatic pressure-sensitive buttons. These buttons offer a comfortable and responsive input method, designed to enhance the user experience.

    Each button consists of a silicone tubing "pillow" sealed with RTV silicone at the ends. The sealed ends are securely squeezed between layers of laser-cut acrylic and fastened with M3 screws, ensuring durability and stability. Underneath each button is an affordable and widely available pressure sensor module, snugly pressed into a small hole pierced into the silicone "pillow."

    The sensor modules feature an AVIA HX710B 24-bit ADC module, enabling accurate and reliable pressure detection. This high-resolution ADC module ensures precise measurement and responsiveness, detecting the lightest touch to the heaviest blow.

    One of the key advantages of these buttons is their adjustable sensitivity. By adjusting the activation threshold pressure, users can customize the buttons to their preferences, providing a personalized and comfortable user experience. It is also possible to configure the buttons to respond to multiple pressure levels, for instance light, normal, and firm click modes.

    These pneumatic pressure-sensitive buttons offer a robust and tactile interface, delivering precise control for various applications. They complement the low force and displacement joystick, creating a comprehensive and intuitive control system.

    With the integration of these innovative buttons, the OHMni-Stick empowers individuals with disabilities or limited mobility to interact with technology in a way that is accessible, responsive, and engaging. It opens up new possibilities for enhanced interaction and independence. I am proud to contribute to a more inclusive and accessible world through this project.

  • Objective Force and Displacement Measurements

    oneohm05/26/2023 at 23:54 0 comments

    Now for some objective measurements of the OHMni-Stick's sensitivity, specifically the force and displacement requirements. To accurately assess its performance, I conducted some initial tests using an IMADA DPS-11 digital force gauge in combination with a Mitutoyo SD displacement gauge for precise characterization.

    The current prototype of the OHMni-Stick proved to be highly sensitive and responsive, reliably responding to forces as low as those measurable by the IMADA force gauge (+/-1gram). This means that even individuals with extremely limited muscle strength can effortlessly utilize the OHMni-Stick to control devices and engage in various activities.

    Additionally, the displacement measurements were equally impressive. Even when a force of 1Kg was applied, the recorded displacement was only 0.2mm. This minimal movement requirement is particularly beneficial for individuals with limited range of motion, as it ensures comfortable and efficient operation of the OHMni-Stick.

    In comparison to other "low force" joysticks on the market, the OHMni-Stick outperforms them significantly. While some devices advertise force requirements of 8 grams, 10 grams, 40 grams, or more, the OHMni-Stick sets a new standard by reliably measuring forces as low as a single gram. Additionally, it surpasses these devices in terms of displacement as well, with precise control achieved using a mere 0.2mm of movement.

    It's worth noting that a standard wheelchair joystick typically requires an operation force of about 200 to 250 grams, further highlighting the advantage of the OHMni-Stick's low force requirements.

    These objective measurements demonstrate the remarkable sensitivity of the OHMni-Stick and its potential to significantly improve the daily lives of individuals with limited muscle strength and restricted range of motion. By providing effortless control and reducing physical exertion, the OHMni-Stick empowers users, promoting independence and accessibility.

  • Modular Grips

    oneohm05/26/2023 at 21:30 0 comments

    I'm excited to provide a project update that highlights the modular, swappable grips for the OHMni-Stick. This addition allows for easy interchangeability of grips based on the user's abilities and preferences, offering a personalized and adaptable experience. Let's explore the reasoning behind this design and the advantages it brings:

    The primary motivation for incorporating modular, swappable grips is to cater to the diverse needs of users with varying abilities. By providing multiple grip options, the OHMni-Stick becomes more inclusive and versatile, accommodating individuals with different levels of dexterity, muscle strength, and comfort requirements. Users can simply swap out grips based on their specific needs, ensuring a customized and ergonomic interface.

    The grip-swapping mechanism relies on three powerful magnets that securely hold the grip onto a "push-plate." These magnets are carefully chosen to ensure a robust attachment during normal use. However, they are also designed to reliably detach the grip in the event of an impact, muscle spasm, or any other sudden force that exceeds the maximum rating of the load cells. This safety feature prevents any potential harm to the user or damage to the device.

    The advantages of the modular, swappable grip system are significant. First and foremost, it allows users to tailor the OHMni-Stick to their individual needs and abilities, promoting a sense of control and empowerment. Whether someone prefers a more traditional power chair-style grip, a puck-shaped grip for easy palm control, or a "saddle-style" grip that helps securely hold the user's hand in position, the OHMni-Stick can accommodate their preference. This modularity also allows for future expansion and innovation, as new grip designs can be developed and integrated into the system, keeping the OHMni-Stick up to date with evolving user needs and technology advancements.

  • Alpha Prototype

    oneohm05/26/2023 at 20:45 0 comments

    Here is the OHMni-Stick Alpha prototype, a tangible demonstration of the device's functionality and potential. This prototype features a minimalist design, combining 3D printed components with laser-cut acrylic panels and spacers.

    At the heart of the prototype, three 5kg rated load cells are arranged such that the end mounting points form an equilateral triangle. This configuration allows for precise three-axis (X, Y, Z) force measurement, enabling comprehensive tracking and analysis of user input after signal processing. The handle is fastened to the load cells using reduced shank M4 screws, complemented by protective springs. These springs serve as a safeguard, absorbing any excessive forces and preventing damage the sensitive components.

    For data acquisition, the prototype incorporates a XIAO SAMD21 microcontroller module. The microcontroller interfaces with three HX711 ADC modules, enabling synchronous measurement of the three forces at a maximum sampling rate of 80 samples per second. 

    Throughout the testing of this initial prototype, I was pleasantly surprised by its inherent intuitiveness and ease of use. The OHMni-Stick responded promptly to my commands, and its accuracy and sensitivity truly exceeded my expectations.

    This prototype serves as a compelling glimpse into the capabilities of the OHMni-Stick as an assistive technology solution. 

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