Drawbot Assembly Instructions

Here are the instructions for building the drawbot kit. You should have received the following parts:

(1) AC/DC transformer 6V, 2.5A, center-positive
(2) wall mount boards
(2) long string guides
(2) short string guides
parts for (2) spools
(4) zip ties
(1) binder clip
(1) binder clip stabilizer
25' or so of monofilament
20' of Green/Red/Black/White intercomm wire
(1) Sharpie
heat shrink tubing
(1) Drawbot circuit board, assembled
(2) Vestax stepper motors, .9 degrees per step, 4V, .6A

You'll also need the following tools:

soldering iron
a little solder
wire snips and/or strippers
screwdriver
measuring tape
hot glue gun
small screwdriver

Build the Spools and Motor Holder

First, put the spools together. The masonite rings should fit pretty tightly around the top and bottom of the pine dowel, but you may want to put a drop of glue around the edge of the dowel to keep them together.

Glue the string guides (the masonite brackets holding the white nylon spacers) to the motor holders. The long one is closer to the spool, as shown in the photo.

Attach the Motors

Attach the motors to the holders using the provided zip ties as shown in the photo. Make sure the zip ties go through the slots, otherwise they won't be long enough to tighten correctly. Make sure the zip ties don't rub against the motor shaft.

Attach the Control Wires

Each of the motors is a stepper motor; these particular ones are Unipolar motors with 400 steps per rotation. A unipolar motor typically requires 6 control lines (the colored wires sticking out of the motor housing), but the drawbot circuit drives the motors as bipolar stepper motors using only four control lines. The next step is to attach the provided green/red/black/white (I'll call it GRBW) cable to the four control lines of each motor.

The provided spool of wire is only 20 feet long. Now is the time to sketch out the placement of the motors and the drawbot board so we can cut the wire to an appropriate length. We'll need one length of GRBW cable to run from the drawbot circuit board to each of the motors. Here's how to position the motors for the default program running on the drawbot:

UNwind the GRBW wire and cut it into two appropriate lengths, or two 10' sections if you are unsure exactly how you want to mount it. Note that the drawbot scales very well to much larger walls (in our lab we routinely have it drawing on a 20' x 8' wall). To increase the drawing area, you'll have to get more wire. The 4-pair GRBW wire is available at Radio Shack as Intercomm wire (part #278-858).

We're only going to use the Black, Red, Blue, and Green wires of each motor. Trim them back to 3" or so and tie the unused yellow and white wires to keep them out of the way.

Next, strip about .75" of the insulator from the ends of the GRBW wire and the motor wire. In the box you'll find a short length of heat shrink tubing that we'll use to cover the soldered wire connections. Cut it into eight lengths (four for each motor) and fit the tubing over each of the wires on the motor side:

Next, twist the wires together as shown in the photo. Connect the following wires to each other:

Cable GREEN to Motor GREEN
Cable RED to Motor BLACK
Cable BLACK to Motor RED
Cable WHITE to Motor BLUE

Yes, that is a bad GIMP job there; I soldered the wrong color wires in the original photo!

Shrink the heat tubing around the joint using your solder iron:

The other side of the GRBW wire can be stripped (shorter this time, like 1/8" or so) and inserted into the green screwdown blocks on the circuit board. The wires should be inserted in the order (L to R):

Cable GREEN (control line 1)
Cable RED (control line 2)
Cable BLACK (control line 3)
Cable WHITE (control line 4)

The screwdown block on the left is for the left motor, and the right for the right motor. Repeat for both motors.

Attach the spools to the motor. I was hoping a friction fit would be enough, but it is not; put a dab of hot glue in the hole of the spool and push it on the motor shaft to secure it. Leave about 1/4" space between the motor casing and the spool.

Next, attach the monofilament to the spool after cutting the full length in half. Thread one side of the monofilament through the two white nylon string guides, as in the photo. Use a small piece of tape to secure the string to the spool, the wind it counterclockwise for the left motor and clockwise for the right motor.

Hang on the Wall

First attach the motor holders to the wall. You can put two drywall screws through the center holes.

Important: the distance between the holders and the starting location of the Sharpie are hard-coded into the controller. The holders need to be 72 inches apart and the Sharpie should start 48 inches down at the center point between the holders. Here's the setup diagram again:

Of course, these dimensions can be changed if you want to scale up the drawing area, but you'll need to reprogram the controller (see "Programming the Drawbot" below).

Next, tie the dangling monofilament to each side of the clip stabilizer. Thread the stabilizer like this:

It is important for the clip stabilizer to remain parallel to the wall as it is being tugged back and forth. You may need to fuss with it a little, or use a dab of hot glue to secure the strings. One of our biggest sources of error will be a clip that tilts back and forth and is tugged unevenly.

Put the Sharpie in the binder clip and hang it on the clip stabilizer, as shown in the photo:

Often I will attach the drawbot circuit board directly to the wall with some thick double-sided tape. One thing to consider is that the motor regulator and the motor driver heat sinks can get uncomfortably warm, so try to keep them away from things and exposed to air.

The motor regulator is rated for 4A and is providing about 1.6A. It's a linear regulator, though, so it is kind of hot and inefficient. If you like, you can bolt a little heat sink on the motor regulator to help dissipate the heat. I actually have a drawerful of them, so let me know if you would like a heatsink!

Using the Drawbot

Here are the important bits of the drawbot:

POWER IN: Plug in the AC/DC transformer (i.e., wall plug) here. You can conceivably run the drawbot off of batteries in the 6-9V range, but remember that the motors draw a not insignificant amount of current, so they may not last very long.

POWER ON/OFF: Turns it on. Up is OFF, down is ON. Actually, it switches power from between the transformer input and the power provided from the USB programming cable. See more about this is the Programming section.

MOTOR POWER JUMPER: Disconnects the power from the two motors. Useful for troubleshooting sometimes.

AUTO RESET JUMPER: If this is disconnected, you will have to manually push the reset button (the white pushbutton) before uploading a program to the drawbot.

PROGRAMMING HEADER: This is where you plug in the special 6-pin FTDI programming cable (see below).

When you turn on the drawbot, it has no memory of what has happened in the past, so it assumes that it is at the point (w/2, h), where w is the distance between the two motor holders (72 inches to start) and h is the distance down from the motor holders to the starting point of the Sharpie.

Troubleshooting

I'll use this space to collect the answers to installation problems as we hit them.

How to Program

Sample code