THE MARS ROVER & LANDER UNDER CONSTRUCTION!

What do You Want to See? Rover Construction Details Lander Construction Details The Rover Exhibit in Action

On this page Bob Martino (Former Perkins staff member) details the development of the Perkins Observatory Mars Rover Exhibit. Interested persons can duplicate his work for their own museums or classrooms. Contact us if you need additional information or details.

Inspiration

The basic design was inspired by NASA's Sojourner Rover, of course. Also, the Planetary Society and the LEGO company created an educational software and hardware suite called "Red Rover, Red Rover." This allowed children to build LEGO robots that carried small video cameras. The robots would explore small "Mars Yards" using only the eyes of the camera. This is what I wanted to do as a permanent exhibit.

Red Rover, Red Rover control screen.		A typical Rover

But there were some problems with this approach. First, the robots were quite small and so were the Mars Yards. Typically a whole set-up could fit on top of a large table. This wouldn't make for a very good exhibit. More importantly, the robots were always tethered to computers using wires. NASA Mars missions don't trail behind 50 million mile long wires. More to the point, I saw these Mars Rovers in action on two occasions and the wires were constantly getting tangled up on the rocks. We needed something completely wireless, reliable, and big.

Exploration Mars

Enter the Mindstorms system system from LEGO and its "Exploration Mars" expansion set. Mindstorms is centered around a "programmable brick" (actually a very small computer) called the RCX. The RCX has input ports for sensors and output ports which can drive motors. It is programmable and endlessly versatile.

	The rover design that came with Exploration Mars looked a lot like what I wanted to create. However, it was not large enough to carry the wireless camera I had selected. Thus the design had to be scaled up. This is not as simple as it sounds at first.
The Basic Design RCX on top, six wheels, two motors. Very simple. Simple is good.		Undercarriage With the RCX removed one can see how the motors are placed (arrow). They turn worm gears which step-down the motor for lots of torque. These drove the center wheels.

Early Attempts

Version 2.1 A very early attempt. I was trying to get the camera completely enclosed. The RCX sat on top of the motors and the wheels are too small. The whole thing was so top-heavy that the slightest slope would cause it to roll over on its back.	Version 3.0 Better. The center of gravity is lower so it doesn't flip at the slightest provocation. However, the wheels are still too small for the size of the rover. It looks bad.	Version 3.3 Success! I obtained six nice large (and high-tech looking) wheels from an older LEGO set. The set also included many other useful pieces. I also stopped trying to completely enclose the camera, which helped a lot.

Construction of the Rover was an iterative process. Build, test, rebuild, test again until you have what you want. I tried several different designs, but the one I settled on was very simple, low-slung, and rugged. There were countless little problems to solve which at first glance one would never think could cause trouble. The exhibit currently uses version 3.4 of the Rover.

Slip Steering Military tanks use slip steering when they change their facing. So does the Rover. In order to change facing, all the wheels on one side of the Rover turn in one direction while the wheels on the other side turn in the opposite direction. Thus, the Rover (or a tank) sits still and spins in place. This gives it a turning radius of zero. The real Sojourner Rover used a slightly different form of slip steering. The wheels in the front and rear actually did rotate before the Rover turned. While this is more efficient, it would have been impractical to duplicate.

Note the black electrical tape on the Rover wheels. This is to reduce friction when the Rover turns (see "Slip Steering" below). By reducing friction the Rover turns a little faster and he RCX batteries last longer.

The camera has been removed to show the cavity where it sits. It was built to hold the camera nice and snug in its spot. The small red thing at the bottom is a LEGO magnet. It is intended to simulate the Alpha Proton X-Ray Spectrometer carried on the Sojourner Rover.

This view is from the front with the camera removed. Note that the two Gray motors are mounted beside the RCX rather than underneath as is shown in the "Exploration Mars" basic design. This allowed the RCX to be placed lower, giving a more sleek and elegant design with a lower center of gravity.

Costs

So, you want to make a rover, do you? Expect to spend about $930 on parts for the Rover, not including the Mars Yard, computer, or labor costs. Any computer able to run Windows 95 will work. How much you spend on the Mars Yard depends on your facility, size, resourcefulness, and budget. The largest expense will be labor, as it takes quite a bit of time, effort, skill and luck to get a good design. Good luck.

E-mail us if you would like my help in making a similar set-up for your school or science education facility!

WORKING ON MARS

It takes a lot of work to make a planet. It takes even more to make a good LEGO robot. Here are a few images of the construction of the Mars Yard and the Rover.

The Mars Yard is a walled-off portion of a room in the new exhibit area. It measures 8' x 12'. The yard is completely enclosed on three sides, with a rail on the fourth so that visitors can look in. The person driving the rover cannot directly see what he or she is doing, but rather must rely on the rover camera to navigate. The IR tower which controls the rover is 8 feet off the floor. Nevertheless it gives excellent coverage for all parts of the Mars Yard.

Bob Pushes Rocks It takes a few hundred pounds of rocks to make a good Mars, and they all have to be in just the right spot. We used several plastic grocery bags full of red volcanic "score," and several brown river stones (These "brown" stones are nice and reddish, just like the rocks on Mars).

Our rocks were provided free of charge by Lang Stone of Columbus (Thank you so much!). Next time you want to create Mars on Earth, why not get your rocks from Lang Stone?

FOAM VOLCANOES

One of the more interesting parts of the exhibit's creation involved the making of phony cinder cones. This was accomplished by building up the general shape with cut pieces of blue foam board insulation (sort of like a 3-D topographic map). These were then covered with spray-on foam insulation from a can. After drying for a couple of days, the whole mess was painted red. Sand was added for realism. This wasn't the best method, however. If you want to try this yourself, use plaster.

Pretty Little Lisa

Lisa Blakeslee was the Observatory's summer helper. When she was not riding the lawn mower endlessly around the yard in circles she was painting rocks and volcanoes. She did a great job on the backdrop surrounding the Mars Yard, giving the rover drivers something to look at other than a blank wall. Lisa helped with the volcanoes as well.

The Lander

was added about six months after the Rover was up and running. Adding a Lander was always one of the long-term goals for the Mars Yard, but funding was not available until NASA came through with a grant (this grant also helped with a lot of other projects around the observatory as well).

Watching children use the Mars Yard really drove home the need for a Lander and second work station. Kids at the Rover Work Station would click the buttons to tell the Rover what to do. They would then jump up and run around the wall to look into the Mars Yard to watch the Rover move. Obviously this destroys the immersive experience since real NASA engineers cannot go to Mars and watch their robot move around.

But NASA also didn't have to rely on just one camera to see what was happening on Mars. The Sojourner Rover carried a camera, but so did the Pathfinder Lander. Engineers and Mission Planners used both. This is the experience Bob Martino wanted to create.

INSPIRATION

Obviously, NASA's Pathfinder Mission was the source of inspiration for the entire Perkins Observatory Mars Yard. Therefore the first attempt at creating a Lander for the Perkins Mars Yard was to duplicate the Pathfinder design.

However, two problems quickly became apparent. Bob had intended to use blue LEGO base plates to simulate the solar panels on the Pathfinder Lander. But the base plates are square while Pathfinder's solar arrays were more triangular. Also, when he tried building something that looked like the instrument package for Pathfinder, it looked like a ziggurat.

We have no images of this first Lander design since it didn't last more than a couple of hours. On to Plan B.

LUNOKHOD Lunokhod was the robotic lunar rover sent to the Moon by the Soviet Union in November 1970. Not very many Americans are familiar with it. The mission consisted of a lander with a robotic rover sitting on top. After the successful landing a set of ramps deployed and the Lunar Rover drove down them to the surface of the Moon. A second improved rover was sent to the Moon in January 1973.

Mission Profile

As a side note, the Soviet Union also returned several lunar samples using robots. Landers were sent to the Moon which were almost identical to the Lunokhod landers. Instead of a rover on top, however, the landers each carried a rocket which launched soil samples back to Earth. Three successful sample return missions were sent (along with a few failures). They returned a total of 320 grams of lunar material. This type of design and mission profile is almost identical to what is being planned for unmanned Martian sample returns by NASA.

Lunokhod was thus the inspiration for the Lander built for the Perkins Observatory Mars Yard. Bob envisioned a future Mars Mission with a Lunokhod-style lander delivering a Sojourner-style rover.

In a nut shell, the Lander consists of four major parts:

• The Landing Legs
• The Fuel Tanks
• The Road Bed and Ramps (which sit on top of the fuel tanks)
• The Camera Mast (which attaches to the back of the road bed)

Lander Legs

Legs Each leg is built mainly from parts contained in LEGO set number 7146. The flexible hose and gantry structure was part of the display stand for the set. The feet were also made from this set.	Star Wars Tie Fighter Set number 7146 We bought four of these (at $20 each). Each set contained just one display stand. However, many of the black base plates were used to construct the road bed and ramps. Smaller pieces became decorations on the Lander and the Satellite.	Legs and a Tank Two legs are attached to a white fuel tank. This set the scale of how large to make the tanks and how long to make the legs. The legs bend quite a bit to allow for rough terrain.

Fuel Tanks

The Fuel Tanks were almost entirely made from ordinary LEGO bricks. 2x4, 2x2, 2x1, and 1x1 bricks were all used. A few slopes were used on the light gray tanks, many were used on the small yellow tanks, and none were used on the large white tanks (because of cost considerations). We bought four of the blue tubs in order to have plenty of pieces to work with. Nevertheless, many more white bricks were still needed which were ordered directly from LEGO Shop at Home in bulk. No light gray pieces come in the blue tubs, unfortunately, so these were all ordered in bulk as well.

"Rounding the Square" is the term used by LEGO builders to refer to making objects with curved surfaces out of bricks that are all squares or rectangles. The slopes really helped for the smaller tanks. Because a lot of slopes were needed , most had to be ordered from Bricklink.

	What's in the Tanks? A spacecraft engine needs rocket fuel, of course. But it must also carry an oxidizer because there is no air in space. The oxidizer might be pure liquid oxygen or perhaps a compound with a lot of oxygen molecules bound into its chemical structure. That makes two types of liquids to carry. But the Mars Lander has three different types of tanks. What's in the little yellow tanks? Umm... Errr... QUICK! Here comes your boss! Get back to work!

Road Bed

Humble Beginnings

This is the work area for Lander construction. It is, in fact, Bob's dining room table. It was occupied off and on by Lander construction work over a period of about five months. Some of these delays were because new materials needed to be ordered. Some were because the project fried his brain --ask anyone.

The black base plates seen lined up in two rows here are the beginnings of the road bed. The two rows are exactly as wide as the Mars Rover's wheel base. The little wheeled cart in the upper left of the photo is a stand-in for the real rover.

Road Bed from Behind The black road bed used 16 of the 4x12 black base plates from set 7146. Each side uses 8 plates in side by side pairs making the road bed 8x48. A good many blue Technic beams from set 8462 were used as connectors and supports. Sticking out of the side of the road bed are the places where the landing legs attach.	Road Bed on Tanks Here is how the road bed sits on the tanks. The white tanks are an earlier version, however. The actual white tanks used are a bit longer than shown here. To the left are the ramps which the Rover drives down to get to the Martian surface (these ramps are also shorter than those in the final version).	Road Bed Details This close-up of the road bed shows off some of the details. These are the older tanks once again. The decorative parts come from the Tie Fighter, set 7146. In the final version of the lander the white tanks are separated by a greater distance as well.	Road Bed Final Version Here is the completed road bed. It is unchanged from the photo to the far left. The white tanks are longer and so are the ramps (not shown). In the back one can see red and white translucent bricks which light up when the camera is panning and tilting. Part of the camera base is visible also.

Camera Mast

Camera Mast The antenna to the left and satellite dishes to the right of the camera mast are just for show. The red and green translucent LEGO bricks at the bottom light up when the camera pans or tilts.

This component was, beyond any doubt, the most difficult part of the entire project. A motor rotates the camera left and right through a 90º angle. Another motor tilts it up and down through about 45º. The limits were set to prevent children from turning the camera around so they could see themselves outside of the Mars Yard. Had they been able to, they would have just turned the camera so they could see themselves dancing about. Obviously, this isn't the purpose of the exhibit. The camera had to turn up to a certain limit and then stop. Continued use of the motor to try and turn past this point could not be allowed to damage the camera mechanism or motor. Then it then had to be able to turn back the other way quickly and easily when required. This proved to be enormously difficult. For left-right turning, a LEGO turntable and a gear designed to slip teeth when too much torque is applied was finally successful. Actual physical stops were constructed which the camera bumps up against when the limits are reached. The motor's output was stepped-down using a worm gear and some small-to-large gear ratios.

Lander from Rear A rear view of the lander. The camera is at the top and its wire can be seen leading away from it. At the bottom are two wires which connect to the camera mast motors.

The limits to the tilting of the camera were the most difficult to solve. Initially Bob had intended to use LEGO's Vision Command camera (9731) for the lander. Unfortunately the camera turned out to be too large and heavy. It also had a thick, relatively inflexible wire coming out of it. Instead, an "Anaconda" camera from X-10.com was used. This is similar to the X-Cam 2. However, it outputs its signal over a wire and not through a radio transmitter. This makes the camera much smaller and lighter. The set of wheels seen in the picture (above, left) steps-down the motor's output since a worm gear proved to be impractical for this location. The camera's tilt is halted at its limits by the slipping of a rubber band on the drive wheels. Getting this rubber band to slip when desired but hold tight when needed resulted in many a sleepless night.

Because the camera and motors use wires to operate, we had to drill a hole through the wall of the Mars Yard to get the wires in. They run along the base of the wall, hidden by rocks.

A Few More Images

Close-up of the side of the Lander. One can see the legs clearly as well as the fuel tanks and the road bed.	The yellow tanks are seen here. There are four sets of three tanks each, one set at each corner. Above it all is the Rover, just starting to drive down the ramp.	Lander and Rover in their new home. The Rover has been here for awhile but the Lander is new. It is possible to drive the rover up and down the ramp.

Rover In Action!

A ROBOT ON MARS

The Perkins Observatory Mars Yard is home to a little toy robot. This robot uses the LEGO RCX as its brain and a wireless camera as its eyes. Visitors to Perkins Observatory can control the rover and use it to explore our simulated Martian environment.

The Mars Yard includes a "Lander" (also made of LEGO bricks) with an additional camera. The whole set-up is modeled after NASA's highly successful Pathfinder Mission with its Sojourner Rover.

Rover and Lander Movie

We now have two QuickTime movies to show you.

Rover up Close and Personal

EXPLORATION MARS ROVER

The fundamental rover design came from the Exploration Mars LEGO package. This image is from the Constructopedia included with the package. A lot of modifications were necessary for a variety of reasons. See Rover Construction Details for more information on how it was built.

Rover Run Here is an early shot of the Rover in action. Just a few of the larger rocks have been placed to lay out the basic Mars Yard design for testing.	Redhead on the Red Planet This shot gives some idea of the size of the Rover and the Mars Yard. The "Cute Little Redheaded Girl" in the photo is Celeste Martino, daughter of Bob Martino. Bob was Assistant Director of Perkins and the Chief Designer of the Mars Exhibit.	Rover Run 2 The brown river rocks seen here look particularly good through the eyes of the camera.

Mission Control On the left is the computer controlling the Rover. To the right is the work station for the Lander. Marvin keeps a close eye on everyone (to avoid treaty violations).	Girl Scouts This is the very first group of children to play with the Rover. This shot is from inside the Mars Yard looking out. Unfortunately the nice open rail proved to be impractical. Later on a "Child Proof Force Field" (made of plexiglass) was installed to keep intruders out.	Budding Scientists Boy Scouts use Mission Control to drive the Rover and explore the Mars Yard. Because of the wall (on the left in this photo) those at Mission Control cannot see into the Mars Yard. They only have the eyes of the two cameras to guide them.

The Lander and the Rover

The Rover, as you can see here, is completely wireless.

The Lander is NOT without wires. The camera is physically wired to the Lander Work Station so images can be displayed on the monitor. The camera can pan left and right through 90º and can also tilt up and down about 45º. The two motors controlling this motion are also physically wired to the Lander Work Station. These wires are hidden under the rocks running along the wall at the top of the photo.

Control Issues

The Rover receives its instructions from the computer work station thanks to infrared signals (exactly like those used in TV remote controls). The computer passes instructions through a wire to an "Infrared Tower" which then talks to the Rover.

The software used for this purpose is called Red Rover, Red Rover. It was developed by the Planetary Society in conjunction with the LEGO company.

"Satellite" The IR Tower for the Perkins Mars Exhibit has been made to look like a satellite thanks to the magic of LEGO bricks. Yes, it cost a whole lot less than a real NASA probe. Then again, those plastic parts wouldn't really do very well in the vacuum of space.	Satellite in Place 1 The "Satellite" hangs from the ceiling above the Mars Yard. It is attached to a convinent pipe as seen here. Just pretend it's really orbiting 300 miles above the planet Mars and relaying signals from Earth, 50 million miles away.	Satellite in Place 2 Here you can see the wire connecting the IR Tower to the computer. Even though the Mars Yard measures 8' x 12' and the IR Tower is 8 feet above the floor, signal coverage is very good. No part of the Mars Yard is a "dead zone" for the IR signals.	Satellite Details A nice shot of the satellite. Extra LEGO odds and ends were used to give the IR Tower that high-tech look. All the signals pass through the little windows seen in the top center of this photo.

The RCX talks to the Satellite using IR signals (The RCX is the big yellow "brick" seen here). But the video signals are handled seperately. The wireless camera has a radio transmitter that sends its output to a receiver which is plugged into a video card in the Rover Work Station Computer. The image from the camera appears on the screen along with point-and-click buttons which control the Rover.

One Final Note

 

Real radio signals going to or from any planet are limited by the speed of light. Even travelling at 186,000 miles per second, it can take more than 5 minutes for an instruction to travel from Earth to a probe on Mars. Then, it would take just as long for the reply from the probe to reach Earth. Since most 10-year-olds wouldn't like to sit there and wait 10 minutes for the results of each and every instruction to be seen, we decided to not try and simulate this delay.

Postcards from the Red Planet

Here are a few photos detailing the "Mars Mission" as it has been envisioned by the exhibit designer.

Just Landed The Lander with Rover on top has just landed on Mars. Good thing it missed all those rocks! The egress ramps for the Rover have successfully deployed. (These ramps don't actually move in the exhibit. However, the Rover can drive up and down them.)	First Look The Lander's camera takes a careful look around its environment. When Mission Control is assured that all is well, the "Go" is given for Rover Deployment.	Rover Deployment The Rover rolls down the ramp. The surface is not at all like scientists back on Earth had anticipated. (It's actually red, tight-weave, office-style carpeting. Just don't tell NASA.)

Almost Down A front view of the Rover as it leaves the ramp. By the way, who's holding the camera for this shot? There shouldn't be any intelligent life here!	Success! A close-up view of the Rover as it executes a left turn for a quick look around. Break out the champaign and start selling those Hotwheels Toys.	Off to Explore The Rover Moves away from the lander to begin its mission. There are actually several little things in the Mars Yard for visitors to find.

If you wish to contact us, send e-mail at perkinsw (at symbol here) owu (period here) edu or call us at (740) 363-1257