/ / INTRODUCTION
The Vibrobot is a BEAM device. The solar cells power the motor and the motor moves the device. When the device bumps into something, it tilts in a new direction and moves on.
Solar cells provide a fraction of the power of a regular AA battery,
which makes it almost impossible to run motors off a solar cell.
So what is one to do?
If you create a solarengine circuit, you can release stored energy in bursts of usable energy.
Characteristics of Solarengines
- They store energy
- They decide when to dump energy, then they dump it
- They repeat the process
To store the energy you attach the solar cell to a capacitor or a rechargeable battery. If you use a small capacitor (1000µF), it will take only a few seconds of lamp light to charge. If you use a
large capacitor (1F), you will have to wait minutes. A rechargeable battery will take hours.
A solarengine can use time, voltage or current to decide when to dump.
Types of Solarengines
Most solarengines use a
voltage-based activation circuit. That means the circuit uses the volts stored in the capacitor to determine when to activate.
Voltage-based circuits are simple to build and are efficient to use (they don't eat a lot of the power to do what they do).
Another type uses a
built-in activation timer. These timer-based solarengines dump the stored power after a certain amount of time, even if the capacitor is only half full.
These solarengines eat up more power to do what they do because the electronic timer uses power.
The third type of solarengine watches the power flow into the capacitor. When it can't push more power in, it dumps the power. This gives the best performance, but is less simple to build.
/ / DESCRIPTION
This Vibrobot uses the FLED (Flashing LED) version of a
voltage-based activation circuit.
Parts
- Pager Motor with weight still attached
- Solar cell that puts out a minimum of 3.0V.
- 1 capacitor (4700uF )
- 2.2KΩ resistor
- 2N3904 NPN transistor
- 2N3906 PNP transistor
- 1 Flashing LED
- Copper paper clip or wire
- Electrical hook-up wire
- Heat Shrink Tubing
- Guitar String
Before you solder anything, wire up the circuit on a breadboard:
If you shine a light on the solar panel, the motor should start to pulse (within a ten second range).
Things to keep in mind
The LED is sensitive to light. Keep it covered by the solar cell or black tape.
If the LED is flashing, the resistor value is too low.
If you hear a high-pitched whine from the motor, the solarengine is having trouble turning on (latching).
To fix this, replace the resistor with one of a lower value.
If you hooked up your solar cell backwards, the capacitor won't store power.
If your motor is not hooked up, the solarengine will not be able to charge.
If it just isn't working, try another motor.
/ / BUILDING IT
The two transistors and resistors are arranged in what is called a SCR latch (a switch that when it is turned on, stays on).
The Flashing LED flips the switch to turn it on. Once it is on, it stays on until all the power has run out.
How does it do this, you may ask?
The flashing LED has a tiny chip in it that tries to light up the LED every second.
Every time it tries, it also tries to activate the switch circuit.
But only when there is enough power stored up in the capacitor, will the circuit kick into operation.
- Start with the transistors.
To identify the leads, hold the transistors up, flat face toward you, pins down.
From left to right, you have the emitter, the base and
the collector:
The pins control the flow of electron holes
through the component. Think of the emitter as the input and the
collector as the output. The
base is
like a valve that controls the flow.
- Take the 2N3904 and starting near the transistor body, bend the emitter, the
left lead, 90 ° out to the left side and the collector 90° up
- Take the 2N3906 and bend the emitter, the
left lead, 90 ° out to the left side and the base 90° up so it's pointing up at you.
- Solder the leads you did not bend together (a base and a collector)
- Add the resistor to the collector of the 2N3904 and base of 2N3906
- Trim the excess part of the resistor
- Indentify the leads of the LED
- Cover the LED with tape or heat shrink
- Take the cathode lead of the LED (flat side) and bend it so that you can solder
it to the emitter of the 2N3904.
-
Solder the anode lead to
to the base of the 2N3906 (this is also soldered to the resistor)
- You have now completed the solarengine circuit.
Zach DeBord's Tips
The key to a good Vibrobot is to keep it as lightweight as possible so the motor can really jiggle it around when it fires.
Play around with leg placement. Having only a couple of the legs touching the ground at the same time can create some interesting movement patterns.
An assortment pack of heat shrink tubing goes a long way. Not only are your bots more interesting-looking, but you can use the tubing in key places to reinforce weak joints.
- Solder short lengths of wire to the solar cell (one to each pad).
- Glue the wires down to the back of the solar cell after you finish soldering
- Solder the emitter of the 2N3904 to the black lead of the solar cell.
- Solder the emitter of the 2N3906 to the red lead of the solar cell
- Solder the emitter of the 2N3906 to the positive lead of the capacitor
- Solder the red (positive lead) from the solar cell to the positive lead of the capacitor.
- Solder the black (ground lead) from the solar cell to the ground lead of the capacitor.
- Solder the red motor wire to the collector of the 2N3904 transistor.
- Solder the black motor wire to emiter of the 2N3906 which should be connected to the positive lead of the capacitor.