Cheap Easy Solar Powered Robot

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Introduction: Cheap Easy Solar Powered Robot

Make a very cheap, relatively easy to construct robot which will wake up any time you shine a desk lamp on it. There are no sensors on it, although I suppose the solar panel can be called a sensor. I plan on adding solar panels and another motor, and making it controlled by a PIC microcontroller in the future.

http://www.youtube.com/watch?v=BQjmZaHMCZ8

Step 1: The Circuit

The circuit for the robot is very simple, it has no digital electronics. It's called a 'miller solar engine' (http://solarbotics.net/library/circuits/se_t1_mse.html) and it allows a small solar panel to power a motor.

The solar panel stores energy over time by charging the capacitor in the circuit.

When enough energy is stored (this is sensed by the '1381' part) the energy is allowed to flow through the motor and the robot moves.

Then the whole process repeats.

In the circuit diagram, C1 is a capacitor, D1 is a diode, R1 is a resistor, and the circled M is the motor.

#####################################
############--Purchasing--###########
#####################################

If you buy from www.digikey.com, here are the part numbers for 1381 chips (they 'turn on'/'become active' at different voltage levels):

2v: MN1381-C-ND
2.6v: MN1381-J-ND
3v: MN1381-L-ND
3.4v: MN1381-N-ND
4.2v: MN1381-S-ND
4.6v: MN1381-U-ND

here is the part number for a 2N3904 and 2N3906

2N3904-ND
2N3906FS-ND

I got my solar cell from here:

http://www.flexsolarcells.com/OEM_Components.htm

================================================
If you can't find the stuff at those sources try these:
mouser.com
jameco.com
allelectronics.com
or do a google search for BEAM hobby stores.

Step 2: Prototype It

To make you robot correctly you'll have to use appropriate components. Depending on the motor you use, the optimal component values will differ, so you should buy a range of values for each component.

After getting a nice assortment of component values make a little prototyping circuit so you can easily swap in and out different part values. You can do this on a breadboard but I made a permanent circuit to test future robots.

#######################################
#######--things to vary--##############
#######################################
You can use different versions of the 1381 part so that it will wait for different voltages before triggering (and sending power to the motor). Get one that will trigger at a voltage appropriate for you motor and which your solar panel can handle (your solar panel should be able to supply more than the voltage it triggers at)

Also, varying the either of the capacitors and the resistor will alter how much power goes to the motor and how long the time is in between motor movements.

#######################################
########--My Components--##############
#######################################
I got my motor from a CD-walkman, it works nicely with:

Two 3V 25mA solar panels in parallel (since they're in parallel the current sums so adds up to 3V 50mA power supply). I got them from here: http://www.flexsolarcells.com/OEM_Components.htm

A 100 ohm resistor, a 3300uf capacitor and a 0.22uf capacitor, and some random 'signal' diode I found (it's not that important).
get them from here:
www.digikey.com or www.jameco.com or www.mouser.com, or some other place.

Step 3: Build It

I used wire wrap (http://en.wikipedia.org/wiki/Wire_wrap) to connect all the components appropriately (component leads in general fit into the hole of a manual wire wrap tool), then once I was sure it was working I soldered the wire wrap connections.

The motor is being held by the legs of the big capacitor, and the two back legs of the robot are just the bent legs of the smaller capacitor. The tire is a rubbery offset thing from the same CD-walkman that I got the motor from. The offsets help reduce vibration in old portable music players.

This robot is pretty crappy, it was just a proof of concept. It has no sensors and ony one motor, but more power/motors/sensors can be added once you get a nice base working and you get the feel for everything.

This is a good resource for these types of robots:
http://www.solarbotics.net/library/circuits/se_t1_mse.html

Here is a good, cheap book on this type of robotics:
BEAM robotics book

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64 Comments

Hey, U mean by flashing lamp light it works? Okay i am a tyro in this so please bear with me...If u find a way so that u can continuously flash light then the robot will work without stopping ryt? And anyway i can find a way to power a micro-controller with the solar panel??? Thanks a lot!

flashing light would work too, but a steady light would work better. Yes, if you put it under the light it will keep running until the light goes out. To have the solar power run a microcontroller you would have to have the solar panel charge a battery which is used to provide the microcontroller with a steady electrical current (microcontrollers don't work on little bursts of current).

Wait a minute, if the 1381 chip goes off at at a certain voltage, wouldn't the thing go off constantly because its connected to the solar panel, or does C1 give it a time delay so that when it gets fully charged the chip aahhh, opens(?) the transistor????

it would'nt go off constantly because the solar cell's current is too low. Anyway the schematic is wrong, there needs to be a diode in series with the cap and cell

The extra diode isn't needed in this circuit. The function of the diode when used in a typical battery charging circuit is to stop the battery discharging through the solar cell when there is not enough light to power the solar cell. Because this solar powered circuit only works when the sun is on the cell, the diode is superfluous. It would also, in this case, lose some of the voltage generated by the solar cell in the diode drop voltage and therefore make it more inefficient.

But, the charging current will disharge through the solar cell and cause inneficency. But the diode is not manditory

This circuit is designed to work only when the solar cell is actually in light, so the cell is always "powered up" and therefore effectively at a greater voltage than the capacitor, so there is no charging current to discharge through the solar cell as such. This circuit does not demand that the capacitor retains its charge when the solar cell isn't in light and so the diode isn't needed and there is no inefficiency without it in this case. However, if you were using a battery or supercap which you wanted to retain its charge when the solar cell was in the dark, it would be necessary.

Exactly {O{_{O{

 theres so many different types of diodes which one did you use?

...Just use a high speed skotchy (spelling plz) diode. I would reccomend getting 3 in parralel so that there is almost no current loss.