Let's Make Robots!

Fish Tank

Drives slowly and nearly unstoppably looking for infrared fish to eat.
FishTank0.3.bas2.87 KB
FishTank0.4.bas3.66 KB


  1. Introducing FishTank
  2. FishTank Update
  3. Fish Tank Meets Piranha Tank


  • ver 0.3 is the basic code with obstacle avoidance and IR following
  • ver 0.4 adds some logic to help when stuck in a corner experiening quick repetitive turns, backing up if too close, and general cleanup


Update 2012-09-20: Nemesis!

Fish Tank is pursued by his nemesis, Piranha Tank!




Update 2012-09-06: Fish Tank finally has some fish food.

I made a couple of little IR beacons built into little plastic fish toys. They have a 3V coin cell battery powering a Radio Shack High-Output Infrared LED (part # 276-0143). A small resistor limits current to the LED. The beacon is turned on when it is placed on the floor and the lead of the resistor contacts the battery.

There's a small neodymium magnet hot glued to the top of each fish, and Fish Tank has a slightly larger but less powerful disk magnet glued to the underside of his IR fish finder.

When Fish Tank drives near one of the beacons, it manuvers into postion and runs straight over the little fish. The neodymium magnet is strong enough to pull the little fish right up to Fish Tank's own magnet. Lunch is served.




Update 2012-08-28: It's a whole new ball game... light finding Fish Tank!

I made a very fun modificaiton to Fish Tank's hardware and programming. Now he can follow light and IR.

I added a DIY Infrared sensor, based on this excellent post on making your own IR obstacle detector by OddBot. I used essentailly the same circuit, with slightly different components.

Of course, my circuit does not include the IR LEDs, because those will be located on separate beacons.

I drilled two holes at the front of the tank's upper deck, which allowed me to neatly mount the new IR sensor with a couple of cable ties. The position of the sensor has the unexpected benefit of helping to keep the battery pack from sliding out of place, which is an issue I ran into. Happy accidents are fun!

The code is still in progress, but version 0.3 is attached, which includes the new behavior.


I learned a lot from OddBot's post on making your own IR sensor.

I'm using essentially two copies of the right side of this schematic in my IR sensor for Fish Tank.


In my version I use the bc337 transistor, just like in the SpurtBot circuit. The IR transistor I'm using are the ones from the Radio Shack Infrared Emitter and Detector pair (part # 276-0142). 

For Fish Tank's beacons, I wanted a stronger IR emitter than what came in the pair, so I used Radio Shack # 276-0143 High-Output Infrared LEDs. 




Update 2012-08-25: Finally added the fish and so this project has been renamed. I'm bringing this guy to Maker Faire.

I'd like to make some little IR beacons that look like tiny fish, and have Fish Tank try to 'eat' them. Maybe also a different IR 'big fish' beacon that someone can wear. Then Fish Tank can run from big fish.



Note: I have posted a review of PropellerHeadGeek's kits on LMR and on my blog.


Good at climbing.


Side view.


Here's lookin' at you, kid.








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Have any plans in the works for it?

I'll add some more detail soon. 

I was thinking about adding some bright blue LEDs, but other than that I'm looking for inspiration.

Maybe something silly, like this.

That would be beyond epic :)

Ridiculously crude mock up of the 'Fish Tank'.


So is the above picture better, or something like this?

I like the way the color scheme lines up here. The tail is motorized and can be made to swish back and forth. I'd mount the whole fish on a servo and embed the Sharp IR sensor in the fish. So turning the fish allows the tank to look left and right for obstacle avoidance.

Well it seemed to turn out pretty close to design specs! :D

love it

That is the happiest looking fish I have ever seen. The orange Tamiya wheels are almost colour matched too. Crazy but sweet.

Thanks, guys!

Now... just let me get my own gold fish... and pimp up a nice ride for it :P