I teach Astronomy and Space Science. Wishing to teach students
about the difficulties of manned vs. robotic exploration, it occurred
to me that it would be nice if I could simulate a deep-space
rover.
The basic idea is simple: Use a radio controlled car to drive
around a video camera, which will transmit live video to a wireless
receiver connected to a computer and VCR.
This article is aimed at those who might need to be shown how to
connect the wires. Not everyone is a tinkerer. However, this system
is simple and reliable. It should work for you the first time with a
minimum of adjustment.
Why Build LEMMY
With such a device, you could demonstrate that first-person
maneuvering is not the same as third-person (the robot's view is
different than the view from an external source). Time delays would
mean careful planning of the excursion is necessary. The primary
limitation of robotic explorers can be demonstrated (large power
supply needs which are extremely time-limited).
We did one main demonstration with LEMMY in the classroom. First,
I had one student watch the video monitor while the other held the
controls and looked out the window. This introduced a time delay not
unlike the delay which would occur for real-time drivers of lunar
rovers. Also, it soon became apparent that conventions for left,
right, slow, and fast were needed.
Students complained of the narrow field of view, even though the
camera was zoomed as wide as it would go. Also, the signal would
intermittently fade in and out as the angle between the transmitter
and receiver changed and metal table legs got in the way. Once, the
camera shut itself off (it was in standby mode, not recording), and I
noted the similarity between this and robotic probes tendency to go
into safe mode when something goes wrong. One of the Russian probes
to Mars was accidentally turned off when it arrived in orbit; without
a safe mode to restart itself at a preset time, it was essentially
lost.
Gathering Parts
Unlike the iBorg over at MacAddict, I never intended (read: didn't
know how) to make LEMMY web-accessible, so that gave me the added
bonus of actually being able to get mine to work. Also, I used only
parts on hand, so I didn't invest in a LEGO Mindstorms kit, for
example.
In time-honored Low End Mac and science teacher tradition, I
started scrounging around to see what I could find to accomplish my
mission. Here is what I eventually came up with. You don't really
need all this stuff; this is just how I chose to do it. It
also includes the gear necessary to display the video on the
classroom TV.
LEMMY parts
1 Radio Shack BlackHawk R/C car (a basic car with independent
4 wheel suspension, 2 channel R/C for drive and steering) +
transmitter
1 Sony Hi-8 Video Camera
1 Recoton wireless TV remote extension (lets you transmit
standard video over wireless connection) includes one transmit and
one receive unit
3 9V batteries
8 AA batteries
1 6.3V Lithium battery + charger
Sony battery for video camera
1 RCA type video patch cable
Video gear
1 Cable TV coaxial cable
another RCA video patch cable
1 extra-long Mac keyboard cable
cable-ready VCR
1 PowerMac G3/233 with A/V card installed (input/output for
video)
TV with S-video input
Assembling LEMMY
First, I removed the Radio Shack car's stylish cover, because it
wasn't flat and didn't look space-probish enough. Four Phillips
screws later, I had a chassis that worked fine. (It occurs to me they
probably have just a few chassis that they stick different covers
on.)
Next, I duck-taped my Sony camcorder on top of the car.
I then attached the Recoton transmitter to the back of the car as
shown in the photo. Since all this equipment is borrowed and not
dedicated to the project, tape is best. This transmitter/receiver
pair I picked up several years ago from Damark. Although there is
still a page for it on Recoton's
Web site, it is apparently not in their current catalog. A modern
alternative might be one of those secret X-10
"wireless spy cams" they advertise all over the Web. (Hey you
guys, if you send me one, I'll tell how it worked for LEMMY II).
The Recoton transmitter requires 18 volts of electricity, but it
would kind of ruin the effect to use an extension cord. Therefore
I took two 9V batteries and connected the + terminal to the -
terminal of the other; then I cut the power supply cord to the
transmitter and attached one lead to each side of my battery.
5. Finally, I connected the video camera's RCA - out port to the
RCA-in port of the transmitter.
After charging the car's battery and replacing all the batteries
in the transmitter and camera, LEMMY was complete.
Video Hookup
At the receiver end ("Mission Control") I had the Recotron
receiver connected to the VCR through a standard cable-TV coax cable.
(Odd
how the transmitter and receiver have different assumptions about how
they connect to different devices.)
The VCR output was routed to the video-in card on the computer via
another RCA cable.
The VCR could have been directly connected to the TV of course,
but that requires a manual switch to make the TV switch from the
closed circuit in-house TV to the VCR, and to leave things connected
simply, I chose to route the S-video output from the video card
directly to the TV via an old Mac keyboard cable. This leaves the VCR
connected to the TV through coax all the time, and no cable switching
is necessary.
TIP 1: In case you missed it, there's a
little tip buried in there: Mac keyboard cables are exactly the
same thing as S-video cables, so they can be swapped one for the
other. One of these days I'm going over to Fry's to get a 20 foot
cable for my keyboard so I can run presentations from across the
room. But I digress.
Driving LEMMY
The educational purpose for LEMMY was achieved by illustrating the
frustrations involved in remote sensing with a time delay. A Martian
rover could have a time delay of 10 minutes (minimum) for a signal to
get to the rover and the return video to arrive back on Earth - and
typically it would be longer, as much as 45 minutes or so. Thus, in
one class period you could essentially send one command - "Turn Left"
- and see the results if you were attempting to drive the car
"live." This makes the point that real-time remote exploration just
isn't going to happen on Mars.
On the moon, however, it might work if the drivers can learn to
"look ahead" about a second and a half. To introduce this sort of a
time delay, I asked one student to stand at a doorway and look out
the window while another looked at the TV monitor. Neither student
was allowed to look at the car itself. The observer then relayed
instructions to the driver, who tried to execute them. The goal was
to simply maneuver around the room and find a little rocket I put on
the floor.
This allowed me to make the point that an autonomous,
reprogrammable rover, such as was used for Pathfinder, is the best
tool for this type of exploration, but even such a tool is extremely
limited and slow compared to the admittedly more expensive human
explorers.
I used Apple Video Player application to display the video. I
powered everything up and immediately got a picture. This application
also lets you capture the video signal to a QT file, so I did that
and recorded a short driving session.
Finally, I turned video mirroring on via the control strip and
tuned the TV to S-video input (which is a whole 'nother story), and
the class could finally see what LEMMY was up to.
The
video shows a student driving the car for a couple of minutes
after class has ended.
TIP 2: Once the video was captured, I
compressed and saved it using a copy of the QuickTime video
player. Being a hoarder of old versions of software (who at LEM
isn't?) I have discovered tip 02. Old versions (pre-Pro versions)
of the QuickTime movie player can access the codecs and special
effects installed for the new version. However, installing the new
version of the player deletes the old one - unless you
change the name of the older player to something different! Mine
is called "QuickTime Player That Can Edit." This tip enables you
to avoid paying the QuickTime Pro fee. Thus I was able to load the
original 120 MB file and trim it down to 286 KB.
Supporting LEMMY
LEMMY needs your help. First, the wife says the video camera
cannot be zooming around on a R/C car driven by teenagers. I also
need to learn more interfacing so I can have the car programmable
instead of just remotely operated. So I've got to buy one of those
wireless spy cam thingummies and a MindStorms set. For LEMMY to grow,
you have to support Low End Mac!
Hop on over to Amazon.com and show your appreciation. Heck, the tips
in this article alone could save you $30 or more - and you get the
bonus of my entertaining writing style and effortless wit. ;-)
Jeff Adkins is a science teacher who isn't afraid to state his preferences in computing platforms. In his classroom he has everything from a beige All-in-One to a a G4 XServe, and they all work together nicely. He calls himself the "poster child for technology integration" in the classroom. He was the 2006 Outstanding Educator of the Year for the California Computer Using Educators (CUE) organization. He also maintains a site for astronomy teachers at www.AstronomyTeacher.com.
Mac of the Day: Quadra 700, Oct. 1991 - The successor to the Mac IIci ran a 'wicked fast' 25 MHz 68040 processor.
List of the Day: Apple TV List The Apple TV List is a forum to discuss the Apple TV.
August 29 in LEM history: 00: My lowest low-end Mac - 01: Uncluttered organization - Microsoft wins over Mac user - 02: Salute to SatireWire - 03: Wireless Internet popping up everywhere - 05: World domination, online or off - A 3-dimensional Dock replacement - 06: Productive at the low end - PowerPC vs. Intel - Secure wireless
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LEMMY
Therefore
I took two 9V batteries and connected the + terminal to the -
terminal of the other; then I cut the power supply cord to the
transmitter and attached one lead to each side of my battery.
(Odd
how the transmitter and receiver have different assumptions about how
they connect to different devices.)
