Robot Log

Bought items total £34.72. No soldering: a servo plug is three female sockets, so male-to-male jumpers join it to the breadboard or the Uno.

Tutorial followed for the first sweep: Using an SG90 servo motor with Arduino (electronics-lab.com).

1. Base plate on standoffs. Servo 1's body hangs through a window in it, with its tabs resting on top.
2. Arm 1 (110 x 24 mm) on servo 1's horn. Servo 2 sits in a window at the far end, with its tabs resting on top of arm 1.
3. Arm 2 (80 x 16 mm) on servo 2's horn.
4. Fine-liner pen through a 9 mm hole near the end of arm 2, tip on the paper. The pen stays down, so the line is continuous.

How the paper arm fixes to the servo

1. The servo's own small silver screw goes down through the paper arm and the horn into the shaft. In the latest file the hole in the arm is 2.4 mm, so the screw head clamps the paper to the horn.
2. The white plastic horn pushes onto the servo shaft. Choose the single-arm horn; the cross-shaped one gets in the way, and a two-arm horn can be trimmed.
3. The shaft turns when the servo moves.
4. The servo body hangs below the plate, with its tabs resting on top.

Measurements

Each layer is cut separately and then glued, with screws through the layer holes to keep them aligned. This worked better than cutting a glued stack.

Cricut Design Space settings

• Design Space reads the millimetre values in the file as inches, so the upload comes in far too large.
• Select all, keep the padlock locked, and set the height to 5.51 in. The width follows.
• Check that the holes and windows show as empty, and do a test cut on scrap first.
• Mat: 12 x 12 in.

How the file changed

Check before plugging in

• The 5V jumper goes to the + rail only, and the GND jumper to the − rail only.
• All three wires are in for each servo, and no red wire is in the − rail or brown wire in the + rail.
• Nothing connects the + rail to the − rail.

Setting up the Arduino IDE

• Arduino IDE 2.3.10. Board: Arduino Uno. Select the USB port the Uno appears on.
• The sketches need the Servo library. The first upload failed with Servo.h: No such file or directory. Fix: Tools, Manage Libraries, search for "Servo" and install the one by Michael Margolis, Arduino.

Sketch 1: centre a servo

#include <Servo.h>

Servo servo;

void setup() {
  servo.attach(8);   // servo 1 signal wire is on pin 8
  servo.write(90);   // go to the middle of the range
}

void loop() {
  // nothing to repeat
}

Sets servo 1 to 90 degrees, the middle of its range, so the horn can be fitted pointing the right way. Use this before putting the horn on.

Sketch 2: two-servo test

#include <Servo.h>      // library for driving hobby servos

Servo s1;                // servo 1 (base), signal on pin 8
Servo s2;                // servo 2 (in arm 1), signal on pin 9

void setup() {
  s1.attach(8);
  s2.attach(9);
  s1.write(90);          // hold servo 1 in the middle
  s2.write(90);
}

void loop() {
  for (int a = 60; a <= 120; a++) {   // sweep servo 2 from 60 to 120 degrees
    s2.write(a);
    delay(20);                        // wait 20 ms per degree
  }
  for (int a = 120; a >= 60; a--) {   // and back again
    s2.write(a);
    delay(20);
  }
}

Holds servo 1 at 90 degrees and sweeps servo 2 between 60 and 120. At 20 ms per degree, each sweep takes about 1.2 seconds. This sketch was supplied by Claude for this test; the code that follows will be my own.

Earlier sketch

The first sweep, from the tutorial above: one servo on pin 8, sweeping from 10 to 180 degrees with a 15 ms delay per degree. Pin 8 is not a PWM pin and does not need to be, because the Servo library handles the timing. Saved as sketch_oct13a.