This project allows you to make your own electric screwdriver like Xiaomi Wowstick.

Print both parts with flat side down. The Tsang model should be printed vertically.

The screwdriver body guts consist of four main blocks.

First: The charger board
The CB I used is a LiIon charger from China with indicator LEDs and undercharge protection. In the right side of the body there is a well for charge state indicators (red/blue). It can be filled with some transparent hot glue or plugged with a piece of acrylic window. I left it as is.
Example: http://www.ebay.com/itm/1A-Micro-USB-18650-Lithium-Battery-Charging-Module-LED-Charger-Board-Protection-/112520617292

Second: LiIon 18650 cell
Here you can use almost any 18650 cell, for example from old laptop battery. The capacity of cell will effect the working time of screwdriver. In my case the consumption was around 30-100 mA, so it will work very long.

Third: The Switch
You will need a DPDT ON-OFF-ON switch with 6 pins to make the screwdriver work both directions and wil be possible to turn it off.
Example: http://www.ebay.com/itm/20Pcs-AC-125V-6A-ON-OFF-ON-DPDT-Locking-Mini-Toggle-Switch-Blue-6mm-K4G4-/262846034205

Fourth: The motor
In my project a micro DC motor with metal gearbox and speed reduction is used.
You will need a motor for 3v or 6v with 160-300 RPM. The lower RPM is the higher is the torque, but you can fall asleep while the screw will come out. I used 160 rpm 6v motor, but is is neither powerful enough to loosen a screw nor fast enough to make it good. I upgraded the model with a brake button so it is now possible to put a 300 RPM motor for fast working and use brakes to tighten or loosen nuts and screws.
Example: http://www.ebay.com/itm/DC3V-6V-12V-N20-Micro-Speed-Reduction-Gear-DC-Motor-with-Metal-Gearbox-Wheel-New-/172018005599