Work Done By-SANDEEP GILL

Wanna build your first simple solar roller using discrete and easily available electronic components(R,C,diodes etc.). Here is where you begin. Solar Roller is a beam-dragster robot that utilizes sunlight as a source of energy. Mostly in all solar competitions this being quite a popular event, wherein two solar bots are placed side by side on a track and they have to travel a distance of 1 meter in shortest time using light source coming from overhead high watt bulbs. So, let’s try and build a simple solar roller.

Check out these links for problem statements of the solar roller competitions

http://techfest.org/nexus/photoroller/

http://www.robotgames.net/robotgames/pdf/2002%20solar%20roller.pdf

Component List:

1 Solar Panel- 4 V, 90 mA

1 Storage Capacitor 0.047F, 5.5V

1 3V3 Zener diode

1 mini DC motor with sleeves

Two Transistors –2N2222A & 2N2907A

1 Resistor- 50 K

Two small wheels (taken from mechano parts) without rims

A foam board body design

Construction Details:

1. Body design: Cut a piece of foam board in a rectangular shape and attach two small wheels at the front side. The wheels are screwed to the foam board via 90degree clamps with an axle passing through them.

2. Attaching the Motor

Mini DC motor

Put on a sleeve onto the motor and attach it to the rear side of the foam body with the help of a mechano strip bended at an angle of 45-60 degree to touch the ground so that it is as close as possible to centre of body.

This is how the whole body will look:

3. Solar Engine:

Working: This is a Zener based SE. This design uses a Zener diode as means of determining the trigger voltage. The reverse bias operating voltage of the Zener is used as means of triggering point in the circuit. You can also use LED’s or diodes in series to accomplish the same trigger voltage. For further readings:

http://www.beam-wiki.org/wiki/index.php?title=Zener-based_Solar_Engines

http://faq.solarbotics.net/oscillate.html.

You could veroboard the circuit like this:

Attach the solar engine to the centre of foam body with help of a double sided tape and connect the motor to the berg terminals.

4. Attaching the Solar panel

Take out two wires from the solar panel for giving the supply to the solar engine.

Just place the solar panel at the rear side of the foam body with help of a rubber band or a double sided tape.

5. Complete Solar Bot:

Results: Testing our newly built solar roller under light gave us quite good results. The solar roller was working in longer bursts – less frequent rate mode i.e. travelling a distance around 25-30 cm during his burst cycles of 3-4 sec occurring every 15-20 seconds. The solar bot was placed on a table and driven by a source of 100W light bulb from a distance of 20-30 cm from the table. We took 3-4 readings holding the light bulb at varied distances from the table and the approximate time to travel a distance of 1meter varied from 47 seconds to a little more than a minute.

Further Modifications:

Mechanical design modifications: Though this design is quite light weight, there is a little problem with the roller it slightly keeps deviating from the straight track i.e. because of the front wheels are not properly locked and also the motor shaft is little offset from the centre (motor tilt angle is changed). So you could try building a design where in the motor is attached to an axle driving two idler wheels and you attach a third pint of contact via a skid or and idler wheel. Also try using even smaller wheels to cut down the torque even further.

Circuit modifications: 1. Try varying the trigger voltage by using a Zener of higher or lower value which will decide duration of bursts as well as their rate of occurring.

2. Try varying the storage capacitor value. Since we have already used a large capacitor you could test the circuit a smaller cap around 4700-10000 microfarad and work with shorter bursts – more frequent rates.

3. Try varying the feedback resistor will help in making the bot tolerant to motor variants & inefficiency, it also helps in decreasing the charge time of capacitor little bit.

4. Try varying the size or current ratings of solar panel. Higher current ratings will help in giving in more current for motor runs but the solar panel size is going to increase.

Further readings:

http://www.solarbotics.com/assets/documentation/solarbotics_solarspeeder2_kit_may022007.pdf

http://library.solarbotics.net/apocrypha/pix/solaroller_mechanics.gif

http://library.solarbotics.net/apocrypha/pix/solaroller_circuits.gif

http://www.robotgames.net/RobotGames/Event_Rules/2002-BEAM-solaroller.html

http://www.beam-online.com/Robots/Galleria_other/solarollers.html