First test of #robot #thumb!

The thumb is more complex than the fingers as it has an additional rotation at the base. Thus it requires four tendons to control it with two passive elastics and one torsional link between the last two joints. The stl files for a sample finger are here: :538... The WIP files for the whole hand and forearm are here: :546... The last two joints are torsionally linked to remove a degree of freedom i.e. both joints always move the same amount relative to each other so effectively operate as a single action. This is achieved with a figure-eight loop of ligament secured front and back, and top and bottom of the last two joints. The thumb is extended by elastic bands tensioned against a bolt that embeds in the knuckle cross and internally rotated by elastic bands between the top proximal end of the first phalange and a support attached to the first finger palm. This support also gives attachment for the upper thumb knuckle tendon. Designed and tested for high speed printing using a diameter nozzle and layer thickness except for the tendon spools (three type of Tendon_Spool_01 supplied, ymmv) and tendon hanger which benefit from printing at layer thickness or better. Test printed in CF nylon. To finish 3d prints to a high standard requires a fine sandpaper or emery board. Use steel ones to avoid breakages: Go with crystal for more durability: Additional components required are listed below. Please consider buying via the Amazon links to help me out! 2mm diameter steel pins - alternatively cut lengths from a wire coat hanger or in Europe order much cheaper from 10mm length: - Amazon UK: - Amazon FR: - Amazon US: 16mm length: - Amazon UK: - Amazon FR: - Amazon US: M2 screws and washers also in Europe from - Amazon UK: - Amazon FR: - Amazon US: M2 brass threaded inserts M2 * 4mm long * Note that the type required has a plain section between the knurled ends to allow attachment of the tendon in the fingertip. - Amazon UK: - Amazon FR: - Amazon US: Kite or fishing line for tendons and ligaments - Sufix 832 is the best I know of for longevity, the 80lbs breaking strength is stiff enough to thread easily and most readily available in the US. - Amazon UK: - Amazon FR: - Amazon US: Ball Bearings 6*10*3 - Need 50, packs of 10 available - Amazon UK: - Amazon FR: - Amazon US: MicroServos like the Emax ES3302 23mm * - 19 needed - Amazon UK: Or search on AliExpress... These are the servos used in the video of the test finger and have an excellent performance characteristic. The next iteration of the hand will be able to fit SC90 servos which are considerably cheaper though of course not as fast, strong or quiet.