The Arduino Inventor's Guide (38 page)

FIGURE 7-21:
Four sides of the greenhouse complete

On our template, we made a small cutout for the servo motor as close as possible to the pivot point of the window, to maximize the amount the window opens when the servo horn moves. Disconnect the servo from your circuit, and attach a horn to the end of the servo if there isn’t one already there. We’d recommend using the single-sided horn, because it’s easier to tell where the servo is pointing. Gently rotate the servo clockwise with your fingers until it stops to set the motor at the 180-degree position. This is the position where the horn will be when the window is fully open. Remove and reposition the servo horn so that it is pointing up in the opposite direction from the wires that come out of the back of the servo, as shown in
Figure 7-22
.

FIGURE 7-22:
Servo horn in the 180-degree position— rotated clockwise

Now feed the servo through the hole in the template from the inside of the greenhouse so that the wires are pointing down and the servo horn is on the inside pointing up (see
Figure 7-23
).

FIGURE 7-23:
Placing the servo into the greenhouse

The tabs of the servo should sit flush with the cardboard. You can screw in the servo using the screws that come with it and the two small screw holes in our template, or use a few dabs of hot glue to secure it in place.

As in
Project 6
, you’ll need a linkage to connect the servo horn to the window. Take a medium-size paper clip and straighten out all but the small hook on the end. Now, grab a ruler and add a sharp 90-degree bend about 1 1/8 inches from the small hook end, pointing away from the hook, as shown in
Figure 7-24
.

FIGURE 7-24:
Bending the paper clip linkage

The roof piece is a rectangular piece of cardboard. Cut out the windows, and score the centerline of the roof, as shown in
Figure 7-25
. The scored edge will form a hinge for the window flap to open and close.

FIGURE 7-25:
The roof piece

Position the greenhouse so that the servo is on the left side. One half of the roof will be secured down with glue, and the other half will form a window flap that opens and closes. Using a small bead of hot glue, attach one half of the roof structure to the greenhouse. Only glue down three edges of the roof (that is, one half of the six edges) so that there’s still a flap that can open. Make sure that the side that opens coincides with the side that the servo horn moves against, as shown in
Figure 7-26
.

FIGURE 7-26:
Gluing in the roof. Be sure to only glue one half of the roof so that the other side can open.

Hook the paper clip linkage around the last hole in the servo horn, as shown in
Figure 7-27
, with the rounded hook attached to the servo. Make sure that the opposing bend is pointing back toward the servo motor. This will hook into the frame of the roof piece.

FIGURE 7-27:
Servo horn and paper clip linkage

Keeping the window flap open, rotate the paper clip until you can insert it into the side of the frame through the cardboard itself. If the paper clip isn’t long enough to reach, you can either rebend it or reposition the servo horn at an angle rotated slightly higher to extend the reach of the linkage. It may be helpful to lift the greenhouse structure and reposition the servo horn from underneath. Once you’ve positioned the servo horn so it will reach, insert the end of the paper clip into the side of the window frame, as shown in
Figure 7-28
.

FIGURE 7-28:
Servo arm linkage connected to the window flap

Bend the portion of the paper clip that protrudes from the other side to create a hook so that the linkage does not fall out (see
Figure 7-29
), and cut the remaining end off. Now carefully move the servo back and forth; you should be able to open and close the lid of your greenhouse!

FIGURE 7-29:
Bending the hook in the servo linkage

With the mechanism complete, you can glue or tape the transparency windows for the top of the greenhouse. A small dab of glue on the four corners will be just enough to hold the window pane down. The window panes should go on the outside of the greenhouse roof to allow room for the linkage to open and close the lid. Next, you’ll build a box to hold the motor and fan.

The motor will serve as a fan to move air around when the greenhouse gets too warm. To prevent the motor from moving as it spins and vibrates, we designed a small cardboard box to hold it in. The template has a design for a five-sided box with a small hole to allow the motor wires to come through, shown in
Figure 7-30
.

Cut out this template from a piece of cardboard, and carefully score the dashed lines so that it can fold up into a box. Using either tape or hot glue, secure the four sides of the box so that it will hold the motor snugly (see
Figure 7-31
).

To build a fan blade, you’ll glue a small piece of cardstock onto the end of the motor. Cut the fan blade so that it is no more than 1.25 inches wide. To help the fan move more air, fold the edges of the cardstock as shown in
Figure 7-32
.