Wednesday, 28 November 2012

Design for a robot vacuum

My dog makes lots of hair. Seriously, you can hoover the kitchen and five minutes later there's fluff all over. I want a robotic vacuum to keep it under control, but I'm not willing to spend £300+ on a roomba

So I'm going to build one.


First issue I can see is navigation - there are a lot of posts and designs that use ultrasonic sensors, IR, GPS :) and all kinds of expensive, fiddly kit that needs a hefty processor to calculate position ...

Well, my kitchen has a tiled floor. Surely I can use that grid for really simple navigation with no floating point maths or stats, all running on an 8-bit microcontroller of choice?

My intitial thoughts are:

Two bog-standard DC motors driving differential steering and forward/backward motion. This should allow the robot to swivel on the spot.

Three light sensors mounted on the underside of the robot will pick up the lines of the grout and determine if the robot is staying straight on the grid line, and detect when it crosses another line.

A bumper sensor (basically a switch) to detect when the robot hits an obstacle

Oh, and a modified hand-held hoover...

Possibly a charging dock also...

Sunday, 11 November 2012

Mantis-a-like CNC milling machine - update

I've been working on the Mantis CNC build recently to get the X-Y table up and running. Previously, I'd posted the design. I was working on a motor driver board based on an ATMEGA328P running the Arduino bootloader and three L293 motor driver chips. After a few months on-again-off-again (I/O pun) work on the board I gave up trying to get it working :( Instead I bought 3x Easy Driver boards.

These are really easy to use - just two pins are used to step the motor and tell it which direction to turn. They support bi-polar (4,6 and 8 wire steppers) motors and have a trim pot for varying the current supply.

So I wired an Easy Driver running on a PC PSU 12V supply into an Airpax stepper motor that I found a pair of on Ebay. It made a few noises and tick-tocked, but spectacularly failed to spin. I suspect these motors need more voltage/current to run. Oh well. In my box-o-junk I had a stepper from a 99p Ebay printer. Wiring that up and tweaking the step speed gave good results so I fitted this motor to the X-axis drive shaft on my mill. Now we're in business: