The giant (by radio control standards) servos above are shown adjacent to a Nokia 3310 mobile phone to give an idea of the scale. The arms are 12cm long – perfect for lifting a bank of solar panels (wing).
Our local Model Aerodrome in Seaside Road, Eastbourne, supplied these beauties, taking the trouble to source one unit from afar – not the kind of thing you are asked for every day. Thanks to Dave and Steve for helping us out of a tough spot. The Model Aerodrome were also able to match a reduction gearbox shown elsewhere on this site under catamaran model drive-train.
On this page we also look at two electronic design solutions for control of our wing angle. One is an analogue comparator based circuit, the other a digital computer chip based circuit. They both do the same thing, but with different features.
LM339 COMPARATOR BASED SUN TRACKER
There are many ways of arranging for an array of panels to track the sun. The description below is for a DIY control board that seems to work quite well. But there are dozens of designs from enthusiastic roboteers. See the links below.
LM339 BASED SUN TRACKER DIY COMPONENT LIST
dU1/U2 – LM339 quad comparator
Q1 – TIP42C Power Transistor
Q2 – TIP41C Power Transistor
Q3 – 2N3906 Transistor
Q4 – 2N3904 Transistor
R1 – 1meg ohm
R2 – 1k ohm trim pot
R3 – 10k ohm
R4 – 10k ohm
R5 – 10k ohm
R6 – 4.7k ohm
R7 – 2.7k ohm
C1 – 10n ceramic capacitor
M – DC motor up to 1amp
LEDs – 5mm 563nm Hi Green Water Clear
The LED arrangement in the LM339 circuit below uses two rows of three LEDs with each LED connected in parallel, the two rows are connected in parallel but reversed polarity. The sensor array is made with three west LEDs and three east LEDs. A 1meg resistor and a 10n ceramic capacitor (103z) are also in parallel with the sensor. The sensor LEDs provide input voltage for two comparators on the LM339 chip with the variable resistor R2 providing a “dead zone” or sensitivity adjustment. Each comparator output is fed into a transistor Darlington pair which in turn drives the DC motor. The rail voltages are provided by two batteries connected in series with the center tap providing the ground reference.
The developers at Green Watts have tested this circuit with 2 single cell lithium-ion batteries providing +/- 4.2 volts and two 12 volt lead batteries, the LM339 is rated for input voltages from +/- 2 volts to +/- 18 volts.
MMT SCIENTIFIC KIT
This special COMPUTER CHIP CONTROLLED SOLAR TRACKER CIRCUIT KIT (Catalog #ST2-HD-PIX) from MTM Scientific is a new product they are making available on a limited basis for advanced electronic hobbyists. Identical in function to their other Solar Tracker Kits, this kit contains all the electrical components for building the circuit (shown above) to automatically find and follow the sun across the sky.
Just like their other kits, this tracker circuit finds the sun at dawn, follows the sun during the day, and resets to home at nightfall for the next day. This kit is ideal for driving a single axis solar tracker with a 12 VDC gear motor or linear actuator that they don’t provide. Also included, but not shown, are the same 2 photocell sensors, 2 limit switches and 20+ page booklet they include with all their Solar Tracker Kits.
So what is different about this kit? This new version of our Solar Tracker Kit is controlled by a PIC micro-controller running a computer program written in PICAXE BASIC. Much more information about the Picaxe family of micro-controllers is available at Phil Anderson’s website (www.phanderson.com). The Picaxe Chip can be reprogrammed using the serial port of your computer using the Picaxe Development Platform Software (Download and Installation required). Obviously that would be a project for advanced hobbyists capable of reading and writing computer line code and reading circuit diagrams. Note: We provide the Picaxe chip already programmed for this kit.
For more detail: SUN TRACKER’S WINGS