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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Hello, I know this is a kinda old post but, I dont think it hurts to ask, im makig a robot with the same tamiya tracks configuration, and i plan on using wood to make a wooden platform instead of using the tamiya universal, and im looking for informations about  the spacing of the wheel holes in the platform you are using, if that is possible, thank you.

Fish tank! that is precious, i laughed hard at that one, nice ignoblegnome =D

That's a unique concept using an old toy and turning it into an awesome fish tank! (lol) It would be even more intersting if somehow you could put a water tight coating around the chassis, and then you could put it in shallow water to make it look like its moving on top of the water! 

Ha ha. That'd be pretty cool, but this chassis will never be water proof. The fish toy originally was, but it'll never be the same since I hacked it. ; j

Thanks for the complements. I'm glad you like it.

I am commenting on my own robot, mostly so I don't forget these ideas. It's like a blog/robot page thing. Whatever.

The Fish Tank totally needs to be able to play music and dance to it. Like a one fish homage to the Sashimi Tabernacle Choir.

Hi IG,

I know you've talked before about the ratio's of track size to distance, etc.  and, just visually, it seems like you've nailed it on this bot.  - they just look right!   can you tell us the dimensions and ratio's you used to get this design?

thanks, Paul


Firstly, all credit for the design goes to propellerheadgeek, not to me!

Here are some of the dimentions.

  • Wheel base (length of road wheels from axle to axle): 72mm
  • Track (width from center of tread to center of tread along the axle): 90mm

So you see that even though the robot body is fairly long, the actual track in contact with the ground is shorter front to back than it is side to side.

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.

Ridiculously crude mock up of the 'Fish Tank'.