Page 125 - Robot Builder's Bonanza

94 WORKING WITH PLASTIC

types of plastics are expanded PVC, ABS, high- density polyethylene (HDPE), and polycar-
bonate, in that order. Expanded PVC is used in industry as an alternative to wood (example:
wood molding), and it cuts and drills much like wood.

FOR STARTERS, SEE WOOD BASE DESIGNS
Many of the techniques that you can use with wood to make handsome robot bases also apply
to plastics, especially sheet PVC. Refer to the “Cutting a Base” section in Chapter 7, “Work-
ing with Wood,” for details on how to cut out useful shapes for robot bases.
One exception is the use of a motorized jigsaw. Unless you’re experienced, the jigsaw may
produce too much vibration as it cuts, especially when working with the thinner 1/8″ plastic
sheets. At best, the vibration will cause rough edges in the cut pieces; at worst, the plastic may
crack or even break.
Here are some additional ideas for making bases using plastic sheet.

BASES FROM STRAIGHT CUT PIECES
Chapter 7 detailed the benefit of cutouts for the wheels of your robot— so- called wheel wells
(see Figure 9-5). Because plastic is a bit stronger by thickness than wood, it’s possible to con-
struct bases with wheel wells without fancy cutting. It can be done just with squares and rect-
angles. Figure 9-6 shows the idea, using three separate rectangles of 3mm expanded PVC
plastic.
1. Begin by cutting the center piece. This piece is the full length of the robot, but only as
wide as the inside edges of the wheel wells.
2. Cut two end pieces. These measure the total width of the base, but their length is from
the wheel well to end of the base.
3. Since avoiding square edges is a good idea (when possible), chamfer two corners of
each end piece as shown. You can cut the chamfers with a saw or use a rasp or coarse
sandpaper. If you use a motorized sander, such as a drum or disc sander, push the
plastic in slowly; otherwise, it’ll melt.
4. Assemble the three pieces using glue or fasteners. Ordinary household glue will work,
or you can use contact cement or solvent cement (as discussed later in this chapter)
designed for the plastic you’re using.

Using two 3mm sheets of plastic, the main center portion of the assembled base is 6mm (about
G 1/4″) thick. That’s usually sufficient for bases under about 10″ in size. Note that the corners of
the base are only 1/8″; that’s okay, as the corners aren’t structurally relevant, and you are
unlikely to mount heavy components there.

Cutouts for
wheels
Figure 9-5 Wheel wells are
chunks removed from the base of the
robot to make room for the wheels.

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