Bettlebot

SCIENCE

DIY

SCIENCE

BEETLEBOT
Ultra-simple bugbot navigates obstacles with feelers and switches. By Jérôme Demers
The Beetlebot is a very simple little robot that avoids obstacles on the floor without using any silicon chip — not even an op-amp, and certainly nothing programmable. Two motors propel the bugbot forward, and when one of its feelers hits an obstacle, the bot reverses itsopposite motor to rotate around and avoid it. The project uses only 2 switches, 2 motors, and 1 battery holder, and it costs less than $10 in materials (or free, with some scrounging). 2. Glue the SPDT switches to the back of the battery holder, at the end with the wires. The switches should angle out at the 2 corners with their levers angled in toward each other, as shown in Figure C. Also, thecontacts farthest from the buttons on each (the normally closed contacts) should touch. This will be the front end of our bugbot. 3. Cut the metal strip, mark enough length at each end to hold a motor, and bend each end in at about a 45° angle. This is your motor plate. 4. Examine or test your motors to determine their polarity. Tape the motors onto opposite ends of the motor plate so that theirshafts point down and angle out. Orient their positive and negative contacts so that they’ll spin in opposite directions.
Photography by Jérôme Demers

Beetlebot in 10 Easy Steps
1. Cut pieces of heat-shrink tubing and use a heat gun or other high-heat source to shrink them onto the motor shafts. Trim the tubing evenly, with a little bit running past the ends of the shafts. These will act astires, improving traction (Figure B).
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A

B

C

D

Fig. A: Diagram of Beetlebot running free, not bumped into anything; both motors draw current from the right battery only. Fig. B: Heat-shrink tubing acts as tires, giving traction to the motor shafts.

Fig. C: Switches and motor plate glued to the back of the battery holder. Fig. D: Bent paper clip threaded through abead and glued to the rear end of the battery holder to make a rolling caster.

MATERIALS 1.5V motors (2) You can often scavenge these from toys, dollar store fans, etc. SPDT (single pole double throw) momentary switches with metal tabs (2) You can scrounge these from an old VCR or mouse, or buy new ones for $1–$4 apiece. Electrical wire around 22 gauge AA batteries (2) You can also use AAAs.AA battery holder Spherical bead plastic or wood Heat-shrink tubing to shrink to the widths of the motor shafts and the antennae connectors Black electrical tape Terminal connectors, spade type, small (2) 1"×3" piece of scrap metal plate I used aluminum. Paper clips (4) Cyanoacrylate (Super/Krazy) glue or epoxy Soldering iron and solder Toggle switch (optional) for on/off switch FOR THE SHELL(OPTIONAL) Round plastic lid I used a lid from a container of hair gel, but you can also use a peanut butter jar lid or anything similar. Auto body filler putty or epoxy glue Black and red enamel paint and primer Clear varnish Small, thin magnets (2) to attach shell to body

5. Use cyanoacrylate glue or epoxy to glue the motor plate down onto the back of the battery holder, just behind the switches(Figure C). Orient the motors so that the left motor spins counterclockwise as you view it from below, and the right one spins clockwise. For aesthetics, I then covered the plate with black electrical tape. 6. Unbend a paper clip, slip it through the bead, and bend it symmetrically on either side to make a caster (Figure D). Attach each end of the clip to the corners of the battery holder at theback. I used hot glue — not very professional. You could also try bending the clip ends under and soldering them to the battery connection tabs, but if you apply too much heat to the tabs, you might melt the plastic and ruin your battery holder. Beware! Next we’ll wire up the circuit, but first, an explanation: the key is that the 2 batteries work separately. Battery holders usually connect cells...