MoCap Clusters and Magnetic Markers Set

thingiverse

**MoCap Clusters and Magnetic Markers Set** This is a set of markers, bases, and clusters designed for use with motion capture systems like Qualisys or Vicon. Created at the LABIOMEP: Porto Biomechanics Laboratory, this set was developed to aid data collection in general, but especially in our dual media setup at the swimming pool to analyze swimmers' movements. Water motion capture is challenging, and experience has shown that using glue to hold markers can be a tricky task. Our current solution, which has proven effective, relies on the use of marker clusters to improve system tracking capabilities. This way, even if an anatomical or tracking marker is lost, the segment won't be lost to the system. **MAGNETIC vs SCREW** This set includes both magnetic and screw-based clusters, depending on how and where they are applied. Screw-based clusters are more reliable since markers won't fall from the cluster due to water drag. However, fixing the cluster to the segment can be tricky, as fasteners can slide off the segment and render the cluster useless. Magnetic-based clusters offer an interesting solution since they can be kept in place under a fast-skin suit without puncturing holes in the suit. To avoid this, magnets allow positioning markers over the suit. **CLUSTERS** There are two types of clusters available: T-Shaped and Pelvic. *T-Shaped* T-Shaped clusters are designed to be easily positioned on lower- and upper-limbs. The presence of 6 holes allows users to select their preferred marker configuration. Both magnetic and screw options have cuts to allow fasteners if needed. Screw clusters have some elevation on the marker sites, increasing available distance for screws and improving visibility for system detection. *Pelvic* The Pelvic cluster is a stretchy term, but its first use was to be placed over the sacrum. This 4-hole cluster can be placed over the sacrum or thorax, with a small circle in the center to spare plastic and allow fastener application. Magnetic and screw versions follow the same principle as T-Shaped clusters. **Cluster Thermic Conformation** Clusters should be printed flat as they are. However, if desired curvature is achieved by applying thermic treatment. Simply place the cluster in the oven at a temperature above the glass transition temperature (PLA: 60-65°C) until it becomes malleable. Then, remove it from the oven and apply to a curved surface. **MARKERS & BASES** This set also includes magnetic markers and magnetic bases. The magnetic marker is created by printing two copies of the corresponding file as halves of the marker. There's an indentation for a magnet placement, with a pin and hole for good alignment. Glue should be used to keep them in place. Magnetic bases allow for magnet application and can be used under fast-skin suits, similar to magnetic clusters. An alternative use is to substitute regular glue-based markers. We've had success using the following approach: Place the magnetic base over desired anatomical landmarks/segments and cover with Opsite Flexifix film. This thin, adjustable, and waterproof film adapts perfectly to counters of the base and skin. **MAGNET AND SCREW SIZES** Designs are prepared for neodymium magnets (10mm diameter x 1mm thickness) or M3 screws. We highly recommend using nylon screws due to their resistance to water-chlorine aggression. For magnetic options, neodymium magnets are essential, offering higher attraction. **MAGNET AND SCREW APPLICATION** Magnet holes are ready for press-fit inserts. Simply place the magnet over the hole (with proper orientation) and give a gentle tap with a rubber hammer. Screw insert is straightforward: simply slide them from under the cluster and they'll fit in a groove ready for it.