Hoser: A Squirting Mobile Robot


Hoser is an autonomous mobile robot with an on board motorized water gun. It is able to move around avoiding obstacles while seeking people out and squirting them with its water gun. As far as I know, it was the first autonomous mobile robot with a water gun. It was completed in May 1989 for a class taught by Professor Rodney Brooks at MIT.


Hoser was built out of the Mobile Armatron toy from Radio Shack. The robot was about 15" long, 9" wide, and stood 15" high. I modified the toy and added electronics, sensors, and the guts of a motorized toy water gun to make it do its stuff. Hoser's brain is a 6811 microcontroller programmed in assembly language. It has a ring of eight IR proximity sensors which it uses for obstacle avoidance. It uses two pyroelectric sensors to detect people. One sensor is mounted on top of a Futaba servo at the top of the robot and scans back and forth looking for people. Once the sensor detects a person, the robot lifts its arm and pivots its body in the direction of the person. The robot then uses the second sensor mounted on the arm with the water gun to detect the target. When that sensor is triggered, it turns on the water gun and pans it back and forth in the direction of the target. For more detail on Hoser's operation and construction please refer to the paper I wrote for Rod's course.

[Hoser Front View Image]
Hoser arm assembly. White pyro lens is visible in the center of the gripper. Water gun nozzle is white area immediately above. The nozzle is connected by the tube on the right to the water gun module mounted on arm. [Hoser Arm Image] [Hoser Head Image] Hoser head assembly. White pyro lens is visible mounted on top of black servo. The Polaroid sonar unit was never functional.


Hoser is a lot of fun. Kids just love the robot, they try to get it to turn their way and then run away when it starts to squirt. There's something about the water gun that makes it interesting. The robot is in your face, if it notices you and squirts you, you know it's there, you can't ignore it. One time I took it to a robot show at the Exploratorium in San Francisco and the kids couldn't get enough. Probably the most memorable run was the first time I ever demo'ed it, for Rod's class. I took it out to a lobby at MIT and turned it on. It immediately turned around and started heading away from my classmates and towards a pair of old ladies sitting on a bench. I had to chase after it and catch it, it had started to take aim and was about to give the nice old ladies a bath.

[Hoser Side View Image]

How well did it really work? It worked pretty well. Aiming was never all that accurate, but the panning back and forth action made up for that. The biggest problem was with the toy's mobility base. The toy's mechanical system wasn't very robust over even smooth terrain or over long periods of time.

A Rose by Any Other Name

This robot's original name was "Wet Dream", but the name was changed to "Hoser" for the sake of the politically correct.

[Wet Dream Cover Page]

Product Placement

People always got a kick out of the fact that the water reservoir was a "Liquid Neutrogena" bottle.

[Neutrogena Bottle Image]

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Author: Charles Rosenberg, chuck@cs.cmu.edu
Last Update: 9/20/97