Let's Make Robots!

FRED solar roller

Solar Roller:Charges capacitor(s) until sufficient charge is reached, then discharges.

I have started finished work on my second robot. It uses a FRED solar engine, and is a really simple circuit; I salvaged a belt and pulley from a cassette player, and I am using it as the body; The belt will be used as the back wheel. A pinch roller I found in the same cassette will be used as a front wheel.  It has been soldered directly to the motor.  This has proven ineffective because the wheel is delicate and never stays put.  Instead, I used some 16 gauge solid core wire to poke through two holes in the pinch roller.  This was soldered in place.  The other end of the wire was soldered on the motor where the wheel used to be.  This new setup is much more stable and easier to adjust with pliers.  I am in the process of getting the resistors soldered in.  I have finished soldering the resistors in.  It took a while because I was free forming it directly onto the body of the robot.  I used the metal frame itself as ground.  I have tested it with lamp light, and then in direct sunlight.  I am pleased with its performance.

The parts I am used are:

1 - 2N3904 NPN transistor

1 - 2N3906 PNP transistor

3 - 1000uF capacitors

1 - 4.0V, 3 mA solar cell

1 - red flashing LED

1 - 0.47uF capacitor

1 - 330 10% tolerance resistor*

1 - 3,300 10% tolerance resistor*

  - A whole lotta duck tape



Pictures of the robot:

side view of the robot

*these resistors are 20-30 years old; they have been in my grandpa's basement all this time.  Which is why they are 10% tolerance


Credit for this solar engine goes to Ben Hitchcock.

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yeah, some pictures would be good. I am having trouble building mine. I am not sure what I am doing wrong.

can you post a picture of the robot that isn't working?  or, tell me which one it is so I can search for it?

mine isnt really a "robot" yet. Its just the engine right now. I found that the motor seems to spin lot fasters when I use the FLED setup instead of the FRED setup. I dont have a 0.47uF capacitor so I have been using a 1uF. I am not sure if thats the problem though. Also, it's mentioned here that the FLED are photo sensitive. I am not sure if that has anything to do with it. But its worth mentioning.

Yes it is photo sensitive.  I have the same book you do, and I have even tried to build the same thing you did.  Mine would not work, I think because of the LED will cause the solar engine to stop working if the light is too bright.  I have not had any problems like that with this engine.  The photo popper actually takes advantage of the light sensitivity to make light following robots.  I think they are called photopoppers.  I think the capacitor might have to be polar.

Good luck, can you get some pictures up of the build in progress? I love BEAM bots!

ok I will tonight.