[Alex] posted up build details of his robot, Halfbot, on Tinkerlog. We’ve been big fans of his work ever since his Synchronizing Fireflies Instructable way back in the day. [Alex’s] work usually combines an unconventional idea with minimalistic design and precise execution, and Halfbot is no exception.
You’ll have to watch the video (embedded below the break) to fully appreciate the way it moves. The two big front legs alternate with the small front pads to make an always-stable tripod with the caster wheel at the back. It lifts itself up, moves a bit forward, and then rests itself down on the pads again while the legs get in position for the next step. It’s not going to win any speed tournaments, but it’s a great-looking gait.
The head unit also has two degrees of freedom, allowing it to scan around with its ultrasonic rangefinder unit, and adding a bit more personality to the whole affair.
[Alex] mentions that he’d recently gotten a lathe and then a CNC mill. So it’s no surprise that he made all the parts from scratch just to give the machines a workout. We think he did a great job with the overall aesthetics, and in particular the battery pack.
We’re excited to see how [Alex] adds new behaviors as he develops the firmware. No pressure!




As unique as the X axis is, the Y sure gives it a run for its money. No linear rails are used, two lead screws are the only things that maintain the gantry’s position. To prevent gravity from pulling the gantry down and bending the Y axis lead screws, there are a couple of bearings on either side that ride along the bed of the machine. The frame material also hits the cheap target, it’s made from blank PCB board. A PIC16F877 microcontroller and a handful of mosfets control the motors. [msassa11] built this control circuit but admits it’s performance is not that great, it’s noisy and loses torque at high speed.

The project started off with some stock Shapeoko 2 parts. Achieving the deck-cutting size required shortening the X Axis and tripling the length of the Y Axis resulting in a 250 x 1200mm work envelope. The DC spindle used accepts ER16 collets and has a fully variable speed control. The stand alone selectable 24/48 volt power supply has a neat DIY handle to ease transportation. Even though the router itself has skateboard trucks, it also has a handle at the front so it’s easy to grab and drag behind you.
CAD programs might be a little too foreboding for someone just getting into the world of CNC, so Inventables has created their own design program called