WARNING:
The instructions here are intended for adult users who are familiar
with basic principles and safety procedures for DC circuits and low-power
lasers. DO NOT ATTEMPT THIS PROJECT UNLESS YOU ARE QUALIFIED OR PROPERLY
SUPERVISED. Even battery-powered circuits can cause fires, injury or
damage.
ELECTRICAL CONNECTIONS:
We recommend that you use a 6-volt battery pack (such as 4 AA batteries)
to power the servo motor. It MAY be possible to power the motor directly
from the 5-V output on Vernier's SensorDAQ, but we've seen that overload
the SensorDAQ and cause it to shut down. Note that the motor will consume
current even when it is running, so it must be disconnected when not
in use. You might want to add a switch. To control the servo motor,
the required connections are
- Connect the battery pack's positive to the motor's positive (usually
red)
- Connect the battery pack's negative to the motor's ground wire (usually
black) AND to pin 5 on the SensorDAQ's Aux I/O port
- Connect the motor's signal line (usually white) to the high-precision
counter line, pin 7, on the SensorDAQ's Aux I/O port
The software program below can also control the SensorDAQ's 4 data
lines (pins 1-4) to activate a laser module, buzzers, lights and other
DC devices. We much prefer to use an external 6-V power pack to power
these devices and normally use a ULN2003A integrated circuit as an electronic
switch. WIth a single ULN2003A, the small output currents from the SensorDAQ
can control currents of 300 mA or more to each of 4 channels. See the
Circuit Diagram for more details.
SOFTWARE DOWNLOADS:
Zipped
Servo Control software (2.0 MB, updated Sept 7, 2009) from Math
Machines. Once unzipped to a convenient location on your PC computer,
it should be ready to run--provided that the free runtime engines
for LabVIEW 8.6.1 and NI-DAQmx 8.9 have also been installed on your
computer.
Unless the full versions of LabVIEW 8.6.1 and NI-DAQmx are installed
on your computer, you must download and install the runtime engines
for both. They are available free from National Instruments. LabVIEW
8.6.1 Runtime is available at http://joule.ni.com/nidu/cds/view/p/id/1244/lang/en
and NI-DAQmx 8.9 Runtime is available at http://joule.ni.com/nidu/cds/view/p/id/1221/lang/en.
SUGGESTED MOTORS:
Hobby servo motors are available at a wide range of prices from many
hobby shops and from many internet supplies. These motors are typically
used to steer radio-controlled cars, boats and airplanes and they typically
have a range of movement from roughly -90° to +90°. They have
an internal potentiometer to provide feedback as to its actual orientation.
Signals to these motors cause them to move to a specific position. The
signals are sent in the form of square pulses, delivered about once
every 20 ms. The width of the pulse (typically ranging between about
1 and 2 ms determines the position to which the motor will move.
We have generally had good success with "standard" servos,
which cost around $10 each. Most often, we have used the Futaba S3003
(shown above) or Tower Hobbies STD TS-53. Both are available at www.towerhobbies.com.
STEP-BY-STEP BUILDING
INSTRUCTIONS
OTHER RESOURCES:
Formula Strings partial list
of functions and syntax for formula strings in Servo Control
Science
Laboratory Safety Manual, by Linda M. Stroud, 408 pp. Science &
Safety Consulting Services, Inc. Raleigh, NC, 2008, ISBN: 9780978879617
Vernier Software
and Technology. Follow this link for information about the SensorDAQ,
including instruction on controlling a hobby servo motor that are written
for LabVIEW programmers.
Under construction. Check back later or email fred.thomas@mathmachines.net
with questions or suggestions.
