3 The hardware build

As I previously indicated, the heart of the vision code will work with a variety of builds.

I based my robot on "Charlie the Chess Robot" (EV3 version) by Darrous Hadi; info on that page says how to get the build instructions. The parts list is here

I modified the robot in a couple of ways.

1. The grabber. This did not work for me. The gears slipped, so I added additional Lego pieces to prevent that. And then when the crane was lowered it would often jam, so I added a Watt's linkage to prevent that.

Here is the grabber in action, showing the modified linkage:


2. The original build uses the Lego Mindstorms EV3 processor, but I use a Raspberry Pi, which makes it easy to use Python.

3. I use a Raspberry Pi 3 Model B.

4. In order to interface the RPi to the Lego, I use BrickPi3 from Dexter Industries. The BrickPi attaches to the Raspberry Pi and together they replace the LEGO Mindstorms NXT or EV3 Brick.

When you have the Lego Digital Designer file, then there is the question of getting the LEGO pieces. You can get bricks direct from the LEGO shop, and this is the cheapest way to obtain them. However, they will not have everything you need, and the bricks may take a couple of weeks or more to arrive.

You can also use Rebrickable: open an account, upload the LDD file and from that get a list of sellers.

Another good source is Bricklink.