Tech specs from the project page:
The 3d printed ardumower works on the same principle as its commercial counterparts, which can be bought for a lot of money at most hardware stores. It drives in the inner space of a “boundary wire fence” (BWF). If it comes close to this it stops, turns and then it goes on mowing your lawn continuously. The ardumower is well tested for a lawn size up to 500m². If your lawn is bigger you need a second battery or you should print a second ardumower.
In addition to a 3D printer and the needed filament (ABS and PLA) for printing the parts, only a few tools and resources are needed to build the chassis. These are mainly common hobbyist tools. You do not need a lathe or a milling machine. Every common 3d printer with a build volume of minimum 180mm x 180mm x 60mm (x,y,z) is suitable.
The ardumower is driven by two 12V geared motors. The cutting device is made from a 12V DC-motor and a cutter disc with a diameter of 220mm. The power comes from rechargeable 12V NiMH or 11,1V LiPo batteries.
You can get all the details and purchase the construction manual with all the files for 9,99 euro: