As a naming convention the forearm parts consist of a bulk, a split, inserts and shells - the stl files are in the Post CES 2023 folder.
The bulk is typically the larger of the forearm prints and houses the servos and other components.
The split is typically smaller and is effectively a lid though may also incorporate structural supports for components and other print inserts inside the forearm.
Inserts are detachable pieces necessary to assemble pieces inside the structure beneath other components.
Shells are thin coverings that cover over openings in the main structure.
Print all the files in the Post CES 2023 folder to make the forearm. The battery cover is optional and in practice the bulk shell seals all the components adequately if well printed.
Some minor updates still required to finalise the tendon routing in the forearm and hand.
There are two main forearm structure files, Bulk and Split and additionally two shells, one to cover the servos in the palm and a pair to cover the outside of the forearm and seal over the electronics and battery compartment.
The Split print has mounting holes for the battery springs and an external hole to mount a 16mm latching push button switch to turn the hand on and off.
To download the stl files click the green button above on the right to drop down the Code menu. At the bottom click Download Zip.
The hand is made entirely by 3dprinting with additional total cost of components required for the hand around $300 USD.
The cad for the arm and hand is freely and publically available down to a parasolid level at:
The forearm and hand can operate as a stand-alone unit allowing unlimited axial rotation for rotational tasks like scrubbing.
Some notes on printing:
Designed and tested for high speed printing using a 0.6mm diameter nozzle and 0.4mm layer thickness except for the tendon spools and split parts of the palm sections which benefit from printing at 0.3mm layer thickness or better.
Test printed in PETG and CF nylon with 0.6mm nozzle and 0.4mm layer for structural components.
To finish 3d prints to a high standard requires a fine sandpaper or emery board.
The amazon links below will open to product pages that are related to building high quality robots. Please consider buying via the Amazon links where available to help fund the robot development.
Diamond coated steel nail files are a handy tool: https://amzn.to/3VBBsOX
Though my favourite diamond file is actually intended for maintaining whetstones, just a nice big expanse of diamond to use :-)
- Amazon UK: https://amzn.to/3gj1ExD
- Amazon FR: https://amzn.to/3EU3pM2
- Amazon US: https://amzn.to/3eN3bvo
Additional components required are listed below.
The biggest cost item are the servos:
16 slim microservos like the Emax ES3301 (approx $6.6) are needed for a total of approx 100 - 200 bucks.
The hand in the video uses Emax ES3302 but any slim micro servo that fits inside the envelope of 23.29.224.1 will do.
Emax themselves make four variants at this size with plastic or metal gears and using either digital or analog control technology.
ES3301 (approx $6.6) ES3302 (approx $9.2) ES3351 (approx $8.5) ES3352 (approx $12)
Official website: https://emaxmodel.com
2 micro servos needed for wrist flexion and extension (required).
Feetech SCS2332 - https://feetechrc.com/product-name_55... are recommended.
These are serial bus driven servos over allowing a greater range of controlled rotation.
They cost around 35 bucks each plus delivery obvs.
If you prefer to use a traditional servo for simplicity they can be substituted by any servo that fits inside the envelope 23.212.128.5mm.
The trade off is the reduction of the powered range of motion of the wrist to about half.
1 standard servo needed for axial wrist rotation (optional) Feetech SCS15 - https://feetechrc.com/6v-15kg-digital... or any servo that fits inside the envelope 402040.5mm. Reduces powered range of motion to about half and the loss of a continuous rotation option.
The rest of the components are relatively inexpensive:
2mm diameter steel pins - alternatively cut lengths from a wire coat hanger or in Europe order direct from https://www.visseriefixations.fr/goup...
Otherwise kits are available on Amazon:
M2 screw and washer kits, or also in Europe from https://www.visseriefixations.fr
M2 brass threaded inserts M2 x 4mm long x 3.5mm Note that the type required has a plain section between the knurled ends to allow attachment of the tendon in the fingertip.
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.
Ball Bearings 6103 - Need 50 for a hand, packs of 10 available which are enough for the sample finger.
Ball Bearings 2x6x3 or 2x6x2.5 - Need 6 for a wrist.
Ball Bearings 15x21x4 - Need 4 for a wrist.
ptfe tubing 2mm OD 1mm ID, sold for 3dprinters, a metre will do if you're careful.