Wouldn't you enjoy building and utilizing a robot that draws abstract art to use in your art and craft projects? The Lego Multigraph, even if it had no practical applications, is fun both to build and to operate! This is an iteration on my Lego Spirograph project (see it HERE).
I call this the "Lego Multigraph" simply because it can draw various things. It could also be called Lego Spirograph V2.0. It's capable of achieving radial symmetry (like a Spirograph) or drawing basic or complex non-symmetrical or bi-symmetrical shapes. The possibilities are nearly endless, depending on your ability to program the machine. This Instructable explains how to build the robot and comes with some basic demo programs written in RobotC. I would love to hear back from you on programs or modifications that you make!
Step 1: Paper Pad
Start by building a pad for the paper that can be rotated. It's made of regular 1 by X Lego bricks with a turntable and some rubber grips.
Dimensions: 28 studs wide, 24 bricks high.
You'll need some Lego Technic bricks to which to attach the Technic beams.
Step 2: Rotation Base Part 1
To build a base that will hold and rotate the pad, you will need one servo motor, 3 large wheels for feet, a couple rubber bands, and several Technic elements.
In this step, we build the Base, the Servo Assembly, and the Pin Assemblies.
Build the separate parts shown in the pictures here - we will put them together in the next step.
Step 3: Rotation Base Part 2
Put it together!
1. Place the Base face-up (ooo that rhymes)
2. Place the Pin Assemblies in the spot pictured.
3. Hold them there while you flip the Base over and attach the rubber bands.
4. Push the pins in towards the centre all the way.
5. Attach the wheels and Servo Assembly to the bottom of the Base as shown.
6. Don't forget the small gear on top.
Step 4: Main Base
For this part, you need 2 big wheels for feet, 2 servos, and the NXT.
Build the base as shown in the pictures.
Step 5: Interchangeable Pens
For each pen, you will need two 3X1 Technic beams, 2 long pins (the ones with the 'cap'), 2 axel-pin connectors, and 2 rubber bands.
Step 6: Drawing Arms
You will need some long beams and low-friction connectors to make these arms.
Make as shown.
Step 7: Put It All Together
Now it's time to put it all together!
1. Connect the Rotation Base and the Main Base using the Technic Pins (they are green in mine).
2. Place the Paper Pad in position and pull back the 2 pins to let it drop in place.
3. Attach the Arms and a pen.
Step 8: Programming
I've included 3 programs written in RobotC. You will need to upload the RobotC firmware onto your NXT before you can use them. Or you can write your own programs using any language.
Multigraph.c - Asks the user questions and draws a picture accordingly.
MultiManual.c - Allows you to set the motor speeds manually.
MultiDemo.c - Draws a particular design for demonstration purposes (what I used in the video).
Note that the gears I'm using in this model have the following ratios.
For each rotating arm, the ratio is 3:1. This means the servo motor will rotate a total of 3 times in order to rotate the arm once.
For the rotating paper pad, the ratio is 7:1 (small gear to turntable gear). So the servo will spin 7 full rotations in the time the pad will spin once around.