Description

This is an open-source design by Engineer Mat Bowtell – Free3DHands.org (https://free3dhands.org) – Australia. Kinetic Arm can also be found on Thingiverse (https://www.thingiverse.com/thing:6736769) From the moment you see this design, it’s evident that the Kinetic Arm is a game changer compared to most open-source prosthetic solutions. Unlike many community-driven designs, this device was engineered by highly skilled professionals who dedicated countless hours to brainstorming, designing, refining, and stress-testing every component. The result is a prosthetic arm that sets a new standard in functionality, durability, and user comfort—truly elevating what is possible within the open-source assistive technology community. The Kinetic Arm is designed to suit trans-radial arm differences. In order to operate a Kinetic Arm, the user's residual limb should have a length of 15–70% of the unaffected forearm length. Residual limb lengths that lie outside of this range may be unable to operate the Kinetic Arm. Free 3D Hands is an Australian charity that designs and provides high-quality, low-cost assistive devices for people with upper limb differences. They share all of their designs under open-source licenses, enabling people worldwide to create and repair their own devices. This approach not only democratizes access to assistive technology but also encourages further innovation in this field. Rotating Wrist The Palm can be rotated into four positions to allow the Kinetic Arm to grasp a wide range of objects. For example, the Palm facing downwards assists with grasping a handlebar, while the Palm facing sideways assists with holding a cup. Wrist Locking Mechanism Once the fingers are closed, the wrist locks into position under the tension of the Tendons through the Locking Mechanism. This ensures the palm doesn’t rotate whilst holding an object or performing a task. Improved Scalability The Kinetic Arm has been tested successfully between scales of 50% and 100% of the CAD model, which is designed at the scale of a large adult. We recommend 50% as the minimum scale to use for part strength and ease of assembly. Multiple Forearm Variants To allow for comfortable and functional wear, six Forearm component variants have been created. These Forearm variants share equal heights but vary in elbow widths, accommodating a wide range of body shapes. Forearm Tongue Using the same principle as shoe fitment, four variants of a flexible Tongue have been added for a secure Kinetic Arm fitment. The Tongue’s reinforced centre channel, combined with tightened Velcro straps, improves the user's ability to actuate the arm. Flexible Tensioners The Tensioners, made from elastic TPU, allow each finger to close independently, ensuring even grip distribution across different object shapes. With no inter-finger connections, individual fingers can come to a close while other fingers continue to travel. Elastic recoil in the Tensioners allows fingers to straighten naturally after contraction. Silent Operation The Finger and Elbow Hinges are designed to prevent any contact between rigid parts, allowing for silent operation. Increased Durability The combination of rigid parts with flexible hinges allows for very impact-resistant joints. This greatly improves long-term durability. Split Hinges The Hinges are designed to insert from one side and stretch fit to the other. This prevents the Hinge from sliding out laterally without requiring glue. The hinges provide structural support to the fingers whilst offering an ideal amount of elasticity to allow the fingers to close. Neoprene Liner Scalable templates are included to cut out neoprene (wetsuit material) liners for maximized comfort. Dual Tendons The need to tie Tendon knots in the fingers has been eliminated, with Tendons looping back through the arm, being tied off only once in the Upper Arm. Adjustable Tensioner Positions Tensioner positions can be adjusted under the Upper Arm Cover. This allows for the way each finger opens and closes to be individually adjusted to suit the user’s preference. Moulded Silicone Finger Grips and Silicone Palm Using scalable 3D printed moulds, Silicone Finger Grips and the Silicone Palm allow for a wide range of objects to be grasped easily. This also eliminates the need to use commercial grip strength alternatives, such as Lee Tippi Micro-Gel Finger Grips, which are hard to source, expensive, and limited to only a few sizes. Part Numbering All of the Finger Components, Hinges and Grips are individually numbered to assist in assembly, ensuring correct part position and orientation. Printing Support Elimination All parts have been designed and oriented to eliminate the need for printing supports. Smooth Part Surfaces The parts have been oriented to minimize the appearance of 3D print layers, whilst maintaining strength in design. Eased Fitting Tolerances Regardless of scale and size, the flexible Hinges are designed to fit tightly with no need for fitting tol