This is an adaptive gripper with three flexible fingers. It’s inspired by the Fin Ray Effect, which has been used by many so far. This is my own vision of that concept and it is free to download if you wish to print one for you hobbies and/or university or school assignments. Assembly instructions are found on video:

What you need 

3 pcs of "Clamp.stl" 

3 pcs of "Corrugated_adaptive_Finger.STL" 

1pc of "Front_base.STL" 

1 pc of "Motor_Support.STL" 

1pc of "Worm_Follower.STL" 

1pc of "Worm_gear.STL"

then the hardware shown on the video. Happy printing!!!

Check out the improved version, which has a greater gripping force and a wrist joint.

3D Printed ADAPTIVE GRIPPER-ROBOTIC HAND WITH THREE FINGERS by Adrian_Duran | Pinshape

3D PRINTING SETTINGS

NONE OF THE PARTS NEED SUPPORT. MUST TURN OFF SUPPORTS ON YOUR SLICER.

I have included a thin layer of 0.3mm in the holes of "Motor_Support.STL" to avoid using supports. This thin layer needs to be remove with a 3mm drill bit or similar, so that the holes go through.

All parts are printed in hard material with the exception of the Green finger or "Corrugated_adaptive_Finger.STL" which is of flexible material ( TPU 92 shore A). I have printed  this one  on my Ender 3, which has a Bowden tube.

Printing Settings of TPU flexible material: 

*Print *speed of 20mm/sec. *Retractions need to be turned OFF. *In CURA, under TRAVEL", set the "COMBINE MODE" to ALL, which will make the nozzle to travel inside the printed part only. Failure to do so will result in bits going through the print where they are not supposed to be, which you'll have to cut later with scissors, and is a real pain because the material is flexible.