Spitter: A Very Picky Eater

Sivan Toledo, December 2006

March 2007 update: see below for a relative of Spitter

What can I say? This hungry little fellow is a picky eater. He is very hungry. If you don't feed him often, he asks for food. Clearly, the most appropriate food for him is paper pellets. But whenever I feed him, he objects and spits it out.

Spitter and his food		He's hungry: you must feed him
But when he senses the food in his mounth, he gets upset and his wheels start spinning		He tries to swallow (you can see the throat openning), but then spits his food

If you are looking for a bot with a strong personality, you have found your match.

More seriously, I built it to demonstrate the NXT to students and colleagues. I felt that a rude robot would be more memorable than a polite one. That meant one thing: throwing paper pellets at them. Throwing something that was either dangerous or valuable was out of the question, but paper pellets are fine. For the Lego purists: you can make even the pellets from genuine Lego, but you'll have to sacrifice a few instruction booklets... 

I wanted it to be compact, which ruled out using large trebuchet or a catapult. When searching for Lego robots that throw things, I found Philo's amazing Hammerhead. I used the same throwing principle, but a different feeding mechanism. It detects the white pellets using the light sensor (this is why the throat area is completely black, to make the pellets easily visible. Once it sees a pellet in its mouth, it starts spinning the wheels, waits for them to spin fast, and then opens his throat. The pellet falls into the spinning wheels and gets thrown out. 

Spitter is very reliable, even though the pellets are not identical. If you feed him more than one pellet, they usually all get ejected. A two-year old niece tested it very thoroughly. Most of the time, he did not disappoint her. (My kids are older, so they got bored more quickly than her.)

Here are a few more pictures of the construction. 

Complete building instructions (21MB PDF file) and the NXC program that Spitter runs is also availale.

Front view		Side view
The other side, with a closed throat		and with an open throat
The back side		The underside

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Thomas Midtskog built a variant of Spitter and sent me this description and picture: I found your robot on the net, and have tried building a similar robot, and after a bit of work due to some buggy compiler, I've now finally made it work.Here is a photo of the robot. I made some changes to the throat-mechanism as I didn't have the same pieces as you made it from, and I had no black parts at all. What I did to make up for this was cut out a small piece of black paper and put it against the wall where the light sensor works. I also found out that the robot was having problems operating in bright daylight. I'm sure this could be corrected by adjusting the light level where the robot reacts to the white paper pellet though. It's been very popular with the employees here, so perhaps we might work a bit further on it and make it into some kind of dispenser, including the use of the touch button in some way or another.

© 2006, Sivan Toledo