#robot #wrist #assembly extended

Here the range of freedom of the wrist can be seen flexing and extending in pitch by at least ninety degrees and yaw by around 30 degrees. In the same way as the human wrist yaw rotation is impinged at the limits of the pitch rotation. Note that the fingers are not rigidly attached to each other in the palm but form one of the two pitch joints of the wrist with tendonous attachment at the knuckles. The second pitch joint is located at the distal end of the forearm. The two joints are torsionally coupled by a ligament that passes through the centre of the wrist joint. Rotation around the long axis of the forearm is provided by the large diameter thin-section bearing that secures the forearm to the lower elbow. The stl files for a sample finger are here: :5384399 The WIP files for the whole hand and forearm are here: :5466653 The last two finger 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 single ligament secured front and back with an M2 screw. 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. Diamond coated steel nail files are a handy tool: Though my favourite diamond file is actually intended for maintaining whetstones, just a nice big expanse to use :-) - Amazon UK: - Amazon FR: - Amazon US: 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 not quite as small or punchy.