MoCap Clusters and Magnetic Markers Set

thingiverse

**MoCap Clusters and Magnetic Markers Set** This is a set of markers, bases and clusters to be used with a motion capture system such as Qualisys or Vicon. This was created at the LABIOMEP: Porto Biomechanics Laboratory to assist data collections in general, but specially in our dual media setup at the swimming pool to analyse the swimmer's movement. Water motion capture is challenging, and by our experience the use of glues to hold marker is a tricky experience. Our current solution, that has proven quite effective, is to relly on the use of marker clusters to improve the tracking capability of the system. This way, even when loosing an anatomical, or even tracking marker, the segment will not be lost to the system. *MAGNETIC vs SCREW* This set includes both magnetic and screw-based clusters. This depends on how and where to apply them. - Screw-based clusters are more reliable since the marker will not fall from the cluster due to the water drag. However the fixation of the cluster to the segment is trickier since we have to rely on fastners that can slide from the segment and therefore rendering the cluster useless. - Magnetic-based clusters are an interesting solution since they can be kept in place under a fast-skin suit. In order no to puncture holes on the suit, the magnets allow to position the markers over the suit. *CLUSTERS* There are available two types of clusters: T-Shaped and Pelvic. >- T-Shaped The T-Shaped are designed to be easily positioned over lower- and upper-limbs. The presence of 6 holes allow the user to select the prefered marker configuration. Both magnetic and screw option have some cuts to allow passing a fastner if needed. The screw cluster has some elevation on the marker sites. This serves a double purpose: increase the available distance for the screw in order not to pass through the marker, but also to improve the visibility of the bottom of the marker and therefore detection by the system even in difficult angles. >- Pelvic Calling pelvic is a little stretch, but its first use was to be placed over the sacrum. This is a 4-hole cluster that can be placed over the sacrum of the thorax. It has a small circle in the center to spare plastic, but also allows the application of a fastner. The magnetic and screw versions follow the same principle of the t-shaped cluster. >Cluster thermic conformation The clusters should be printed flat as they are. However, if you want to give them a nice curvature to better adapt to the segment on which wil be applied, you can perform some thermic treatment. Just place in in the oven for a while, at a temperature above the glass transition temperature (PLA: 60-65ºC) until it becames malleable. Then, remove it from the oven and apply on a curved surface. A PVC tube or a tree log will work just fine. *MARKERS & BASES* Also in this set is a magnetic marker and magnetic bases. The magnetic marker is created by printing two copies of the corresponding file as they are two halves of the marker. There is an indentation where a magnet can be placed, and the pin and hole allow for a good alignement of the halves. Glue should be used to keep them in place. The magnetic based allow for the application of one magnet, and they can be used under a fastskin suit, in a similiar fashion to the magnetic cluster. An alternative use of this magnetic bases is to substitute the regular glue-based marker. We have been using the following approach with much success: Place the magnetic base over desired anatomical landmark/segment and cover it with a film such as Opsite Flexifix. This is a somewhat streatchable, thin and adjustable film that will adapt perfetly to the counters of the base and to the skin. It is also waterproof, and if properly applied water won't get under the film and peal it off. This has been shown to work better and longer than glues or tapes. *MAGNET AND SCREW SIZES* This designs are prepared for neodymium magnets with a diameter of 10mm and thickness of 1mm, or M3 screws. I higly recomend the use of nylon screws since they are resistent to the water-chlorine agression. If you are going for the magnetic option, neodymium magnets are essencial, since they possess a higher attraction. Be carefull not to chip the magnet, since that may cause some oxidation. *MAGNET AND SCREW APPLICATION* The magnet holes are ready for a press-fit insert. Just put the magnet over the hole (with the appropriate orientation) and give a gentle tap with a rubber hammer. The screw insert is straight-forward. Just slide them from under the cluster and it will fit in a groove ready for it. **More info:** http://www.labiomep.up.pt https://www.facebook.com/LABIOMEP/ Or contact me by PM