Welcome to the fifth installment of the Make It Last Build #3, the Drawbot, sponsored by Microchip and Energizer. The goal this week is to build and rig all of the mechanical parts on your drawing machine. By next week you should also have a more permanent version of the controller and stepper drivers soldered onto protoboard. See the landing page for full details, prizes, and info about the first two builds in the series. And get your progress pictures up on the MAKE Flickr pool (tagged: makeitlast). Entries must be received by 11:59 p.m. PST on March 3, 2011 to be eligible for the prize drawing. Any pics are eligible for the drawing, they don’t have to be finished Drawbots. We’d love to see your progress images.
Build the Spools
First, we’re going to make two spools and mount them directly to the shaft of the stepper motors. Make the spools however you like; I’m going to use the spools from some intercom wire. Cut a 1″ diameter wooden dowel down to 2.5″ and drill a hole for the stepper motor shaft. Unwind the wire and insert the dowel into the spool. Use hot glue to secure it if it is not a tight friction fit. Then attach the spool directly to the shaft of the stepper motor: 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. Repeat.
Make the mounting brackets
Now, cut two pieces of wood 2.5″H x 4.25″W out of thin plywood. Cut or drill holes as in the photo. I used a laser cutter and this design for mine. The slots are to hold the stepper motors with zip ties. The exact placement doesn’t matter; just make sure there’s 2″ between them for the motor.
Next, loop some long zip ties through the slots and tighten them around the motors. Two zip ties should be enough, but you can always wrap a third around the middle of the motor if you are worried about the stability.
Lay out the Control Lines
As we discussed in previous newsletters, a unipolar motor typically requires six control lines, 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.
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. The Drawbot scales to very long walls, but the example program will be using a 6′ x 4′ drawing area, as shown in the illustration above.
Splice the Control Lines
As discussed last week, 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. If you want, you can use heatshrink tubing to cover the soldered wire connections. Cut the heatshrink into eight lengths (four for each motor) and fit the tubing over each of the wires on the motor side (before you splice them together!)
Next, twist the following wires together:
Cable GREEN to Motor GREEN
Cable RED to Motor BLACK
Cable BLACK to Motor RED
Cable WHITE to Motor BLUE
If you’re going to be moving this around a lot, it may be a good idea to get stranded wire instead of the solid wire that was speced. Eventually the solid wire will break if it is twisted a lot.
Run the monofilament and hang on wall
Add a short 1.25″ (or so) screw-in eyelet to the bracket. This will help keep the line parallel to the wall and help pull the Sharpie against the wall.
Cut a length of monofilament and attach it to the spool. Thread one side of the monofilament through the wire eyelet. Use a small piece of tape to secure the string to the spool. Wind it counterclockwise for the left motor and clockwise for the right motor.
Next, attach the motor holders to the wall. You can put four drywall screws through the corner 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″ apart and the Sharpie should start 48″ down at the center point between the holders. This starting point at (W/2, H) will be referred to as the home position. Of course, these dimensions can be changed if you want to scale up the drawing area.
Make the Clip Stabilizer
If your drawing area is very wide (say ten feet or more), there will be enough tension in the line that the binder clip holding the Sharpie can be tied directly to either end of the monofilament. However, on shorter spans, you may need to make the assembly a bit more rigid. I drew a little clip stabilizer that I cut out of Masonite (see drawing above for how to thread the holes). The clip stabilizer holds the binder clip and helps to make sure each wire tugs evenly on the marker.
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 a binder clip and hang it on the clip stabilizer. We’re almost ready to begin drawing!
Next Steps:
For next week, start transferring your breadboard prototype to a more permanent form on protoboard. I’m using the Wired Breadboard from Modern Device that mirrors the layout of a wireless breadboard (see above).
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