TABLE 1. Bill of Materials that I used for assembling the
SunBot II project. You may substitute parts as necessary.
The VEX quadrature optical encoders are optional and will
be used in a future article to calibrate the stepper motor
commands to azimuth and elevation positions.
ITEM
QT Y
1
1
2
1
3
2
4
1
5
1
6
4
7
2
8
1
9
1
10
1
11
1
12
2
13
1
14
1
DESCRIPTION SOURCE
VEX microcontroller Innovation First, Inc. www.vexforum.com
12 volt SLA battery RadioShack www.radioshack.com
SparkFun EasyDriver
stepper controllers
SparkFun
www.sparkfun.com
Wire-wrap cable RadioShack www.radioshack.com
Package of
jumper cables
SparkFun
www.sparkfun.com
VEX limit switches Innovation First, Inc. www.vexforum.com
VEX quadrature
optical encoders
Innovation First, Inc.
www.vexforum.com
VEX structural
components
Innovation First, Inc.
www.vexforum.com
VEX 9. 6 volt
battery
Innovation First, Inc.
www.vexforum.com
VEX RC transmitter Innovation First, Inc. www.vexforum.com
VEX receiver Innovation First, Inc. www.vexforum.com
Geared stepper
motors
All Electronics
www.allelectronics.com
Heavy duty 12 volt
marine solar panel
All Electronics
www.allelectronics.com
Recycled tin can
(cylinder)
issues were probably caused by backlash from the gears
and also by not detecting the hard stops accurately using
the VEX limit switches.
Some of these problems could be corrected by
calibrating the movements, or by using a different stepper
motor drive mechanism other than gears. Timing belts and
direct drive are possible alternatives to fix this problem. In
addition, the VEX firmware needs more work to be able to
track the sun correctly, once the mechanical problems have
been ironed out.
Wrap-Up
Using simple VEX hardware with some PIC18 C
firmware, precise and repeatable movements are possible
for your next robotics or automation project, using the
information in this article. Stepper motors need not remain
a mystery to use if you build the SunBot II or similar
applications. The SunBot II robot demonstrates very
complicated micro-stepping used to aim a solar panel at the
sun using stepper motors.
In the next installment, I plan to show a PIC18 C
application that I actually used to move the solar panel, and
some issues that I encountered with it. I will also cover
using the quadrature optical encoders and limit switches,
and calibrating the stepper motors which you will need to
start tracking the sun with your own SunBot II.
Until next time, happy stepping! SV
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SERVO 12.2010 65