ME 102: ChalkJET!

The chassis is constructed entirely from ¾” wood. Eight spray chalk cans line across the base of the chassis with nozzles spaced approximately 2” apart. The spraying mechanism consists of a second-class lever mechanism. Levers stretch across the top of the chassis, with their pivot attached to one wall of the chassis. Solenoids are mounted on the opposing wall and attach to ends of the levers by custom-made hooks. When the solenoids pull down on the levers, the spray cans are pushed down and spray. There is a lever advantage because the cans are taking output at a distance between the fulcrum and the input effort. Bolts going through the levers are the point of contact to the spray cans. By advancing the bolts, the spray cans are primed for spraying.

The two differential drive wheels are mounted with acrylic mounting blocks and press-fitted bearings. The output of the wheel rotation is coupled to the encoders with a flexible shaft connector, consisting of heat shrink. Two chair casters mounted at the front balance the chassis. In the picture to the left, the encoder just appears on the left of the picture.

Materials:
Key components:
o       8x Solenoids: Pull type, 12 V, 3 A, modified by removing the spring, $1.50 each
o       8x Temporary Spray Chalk: GoodMark, Inc. Temporary Line Marker, $7.00 each
o       2x 7.2V NiCd Batteries, 2000mAh, $20 each
o       8x TIP120 NPN Transistors, $0.75 each
o       2x Avago HRPG Series Panel Mount Optical Encoders, $50 each
o       2x Wheels: 4.5” diameter, $5 each
o       2x Castor Wheels: 2” diam. Hooded Chair Caster with Black Polyurethane Wheels, $1.50 each

Structural:
o       ¾” Wood: for the frame
o       9/16” x 9/16” Poplar Wood: for the levers
o       ½” Acrylic sheet: for the wheel mounts
o       ¼” Diam. aluminum: for the pivot of the levers
o       Aluminum angle: for the encoder mounts
o       Coat hanger wire: for the solenoid hooks