VEX Stepper Motor Control Experiments - Part 2
Building the VEX SunBot
By Daniel Ramirez
SunBot II’s mission is to collect critical information eeded from our nearest star — the sun! This insolation data is required to plan for and design the next generation of solar panels and solar cells
that will provide environmentally clean power alternatives to
fossil fuels now and in the foreseeable future. Reducing or
eliminating carbon dioxide (CO2) emissions is important and
solar technologies can play a big part in the solution to this.
SunBot II will be a self-powered, VEX-based robot
whose mission is to track the sun anywhere on earth under
all lighting conditions (during sunny or dark and cloudy
days), using astronomical tables to collect critical solar data
necessary to produce solar power generation systems by
acting as the guide for hundreds of solar panels located
within a one mile radius of it. SunBot also demonstrates
how VEX starter kits can be used to develop prototype
environmentally-friendly products.
Although there are many kinds of solar panels currently
sold worldwide by various vendors, the most common
configuration is the fixed position panel which is typically
positioned facing south and oriented at a 35 to 45 degree
angle facing the sun. This position allows solar cells to
collect sunlight during most of the day, but misses out on
the sun’s direct rays at noon. You see these kinds of panels
in solar powered (PV) homes, businesses, and even along
Ancient Babylonians, Egyptians, Aztecs, Mayans, Greeks, and Stonehenge
Druids have been following the sun, moon, and star positions for centuries.
These vital details gave them seasonal information about when they could
plant and harvest their crops and perform religious ceremonies. It was during
the height of the Renaissance that the planetary orbits and the sun and
moon positions could be computed using the great discoveries in orbital
mechanics and gravitation discovered by Galileo Galilei, Nicolaus Copernicus,
Tycho Brahe, Johannes Kepler, Sir Isaac Newton, and many other
astronomers of that era. These orbital mechanical equations have been
refined over the latest centuries to include the effects of Einstein’s Theory of
Relativity and Einstein’s general theory of relativity so that now mankind can
predict the planetary orbits and the sun’s position with incredible accuracy.
highways.Existing motorized panels are more expensive due
to the motors and controllers required, but they can track
the sun all day long. These types of panels are usually
found in solar energy farms, universities, and energy
research facilities worldwide where sunlight is plentiful all
year long. Commercially sold solar panels usually use two or
more photocells to find the brightest spot in the sky and
track it. Bad weather, cloudy, dark, and rainy days can
cause some of the tracking mechanisms to hunt for the sun
excessively, wasting previously stored battery energy by
having the motors move unnecessarily. So, what does this
project have to do with stepper motors and VEX? With the
Gulf Coast oil disaster now behind us, I believe it’s time to
start thinking more about alternative forms of energy.
The prototype SunBot was assembled using VEX
components (including standard VEX motors) and is
mounted on my VEX-based Gilbert IV Explorer robot shown
in Figure 1. The problem with this prototype was that the
gearing used did not provide enough pointing accuracy
which is why I decided to switch from VEX motors to
stepper motors for the azimuth and elevation drive.
VEX SunBot Features
The Gilbert IV robot shown in Figure 1 is the mobile
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