I based this off of this really nice instructables.com post for building a water bottle boat, with some additions for obstacle avoidance and light-guided control. I used Arduino as a microcontroller, an ultrasonic sensor in the front, a few simple switches on the side of the boat, and a few light sensors on either side. See here for a few more photos or here for a pdf step by step.
This simple little floating boat bounces off walls, can be steered with a flashlight, and won’t hit something head-on.
Step 1: MATERIALS
hot glue + glue gun (silicon optional)
two small DC motors
two water bottles
two small propellors
arduino + USB cable + computer
a plastic box
a 9V battery + a connector
a power diode (like 1n4004)
a soldering iron + solder
a MOSFET transistor or TIP 120
2 few switches + 2 photocells
Step 2: Put the motor in the cap
1. Take off the top of both water bottles
2. Poke a hole in each cap
3. Apply hot glue to the inside of the cap, but not on the hole. Slip the motor shaft through the hole. When dry, the shaft should spin freely.
Do this with both bottle caps and motors.
Step 3: Tape the water bottles together
Use two or three strips of tape to tape the water bottles together, sort of like a raft.
Step 4: Solder leads to the dc motors if there are none
The motors are now attached to the bottle caps.
Solder on long (about 10″) leads to the motors, if there aren’t any.
Step 5: Cut a slit in the water bottle
Cut a small slit in each water bottle.
This is the hole through which the wires from the motors will poke through.
Step 6: Put on the cap and feed through the wires
Put the cap on the bottle and feed the wires into the bottle opening, then out the slit that you just made. If you have trouble screwing on the cap, use some hot glue to secure it.
Step 7: Make the Electronics House
Now, put a bit of hot glue on the holes you made in the bottles to make sure the bottles are watertight.