The key features we need to create our drawing machine are a pair of variable speed motor drives and an armature to move the pen across the paper. The two drives rotate at different speeds, pushing the armature (and the connected pen) along a repeating, yet slightly changing path.
There are nearly limitless ways to do this with LEGO blocks and Technics parts. You can adapt this to work with parts you have on hand, or follow these instructions to build one that uses very few parts, most of them easily obtainable in a moderate sized Technics set and a few pick-a-bricks.
This gear reduction section is the key to slowing down the fast motion of the TT motor and increasing the torque. Without this, the machine would draw way to fast, get out of control, and probably tear itself to pieces! You can use actual gears to accomplish this, but pulley wheels and belts are easier to connect, more forgiving of slop, and dampen the motion a bit.
Watch this video for a CG timelapse build of the parts.
This video provides step-by-step build info.
If you'd like to take a close look at the model, download the files below and open them in Lego Digital Designer or any LDraw compliant program!
This is the Bill of Materials (BOM) for the parts used:
Most of these parts can be found in any larger Technic-based kit. If you have any trouble finding certain parts, you have a few choices. First, search for them on the LEGO Pick-a-Brick site or at a LEGO store.
If you have access to a 3D printer, you can 3d print them -- just search for the part on a 3D model hosting site such as Thingiverse. Here's a very nice looking collection of the key components.
You can also purchase them on an aftermarket brick site, such as Bricklink.
Following the video build instructions above, build the base of the machine. The two stacks hold the axles for the drive and the gear reduction pulleys, which will be connected to the TT motor later.
Again, following the build instruction video, make the scissor armature as shown. You can then set it onto the two drives with the short axles. You can use pegs, but this makes it harder to lift the arm on and off, which you'll do every time you want to cap your pen!
In order to introduce our Crickit controlled TT motors into the world of LEGO, we'll need to do two things:
- Mount the TT motor chassis to a 2x2 flat tile
- Adapt the motor shaft to LEGO cross axle
TT to LEGO Tile Mount
Some LEGO purists will dislike this next step, and for that we are sorry. But one of the best ways to bridge the worlds of electronics and LEGO is to sacrifice some tiles and glue them to your non-LEGO parts!
Now, this motor can attach to the baseplate of the drawing machine -- or any other LEGO for that matter!
Adapt the Shaft
This couldn't be easier -- simply press fit the LEGO cross axle adapter onto the shaft!
Now, it's ready to connect to any cross axle compatible part, such as gears, wheels, pulleys, and half bushings, such as the one shown here that we'll use to drive the machine.
Mount the Motors to the Base
This step is optional, but very stylish! You can 3D print (or have 3D printed by a company) a Crickit-to-LEGO plate using the instructions in this tutorial. I'm using only the lego-base-plate-tubes.stl part here, and then connecting it with M2.5 nylon screws and standoffs.
The pen needs to be connected securely to the armature. You can place it in the holder and then wrap rubber bands or Technic belts around it to hold it tightly in place.
Now, plug in the 5V 2A power plug to the Crickit and get ready to program the Circuit Playground Express in MakeCode!