BrickVista Tech-Notes

As a Rover is a mobile robot, the Mechanical, Thermal and Mobility (MTM) Subsystems are very important to the overall performance of the Rover. The MTM is responsible for:

The physical configuration of the rover

The mobility/suspension design

The mechanisms and motors (actuators) which drive and steer the wheels

the structures which support all electronics and scientific payloads

keeping all electronics and payloads within their safe operating ranges

Mechanical
By necessity, rover design includes several innovative mechanical solutions including:

Low temperature motors - Motors had to operate at –80C

Lightweight Aluminum Structure - Intricate structural design and manufacture:

Chassis components on the Rocky 4 Flight prototype were made light and strong to withstand launch and landing stresses. The design incorporated as many "off the shelf" parts as possible to keep costs down - Where do you wheels like that off the shelf?

Thermal
The Warm Electronics Box (WEB), the body of the rover, is a heated container that protects the rover's vital electronics. It is a low conductivity composite box structure which supports all Rover electronics. The WEB keeps all the components within their design operating range of -40°C to +40°C and is covered in a distinctive gold foil. Without this heated box, extremes of temperature would stress and damage the sensitive electronic components.


A Mars Exploration Rover's WEB - Minus everything else.		Sojourner's WEB formed the body of the Rover supporting all mounted components.

Mobility
A suspension system is how a rover’s wheels are connected to and interact with the rover body.

Both Sojourner, and the Mars Exploration Rovers share a common suspension arrangement referred to as "Rocker-Bogie" suspension.
The rocker-bogie design has no axles or springs, and allows the rover to climb over obstacles (such as rocks) that are up to twice the wheel’s diameter in size while keeping all six wheels on the ground. The suspension enables the rover’s body to withstand a tilt of 45 degrees in any direction without tipping over.

Each of the rover's six wheels has an independent motor. The two front and two rear wheels have individual steering motors, which allow the vehicle to turn in place. Each wheel also has cleats, providing grip for climbing in soft sand and scrambling over rocks

"Rocker-Bogie" suspension was developed by Don Bickler and later patented by JPL in June 1989

ROCKER BOGIE

Rocker Bogie The term "bogie" comes from old railroad systems. A bogie is a train undercarriage with six wheels that can swivel to curve along a track.

The term "rocker" comes from the design of the differential, which keeps the rover body balanced, enabling it to "rock" up or down depending on the various positions of the multiple wheels.

ROVER WHEELS

The Mars Exploration Rovers (MER) use a newer modified wheel design than what was used on the Sojourner Rover. At 26 centimeters in diameter (a little over ten inches), the aluminum wheels of the MER are nearly twice the size of those used on Sojourner and are missing the recognizable sharp cleats.

Chris Voorhees is a mobility engineer working for NASA and is responsible for the development of the MER wheels. He says of the new wheel design that “a big challenge was to be able to get enough traction to get through soil and over rocks of the Martian environment, but also to be able to get off of the lander without getting entangled in the deflated airbags". The new design is "basically like a paddlewheel that is machined onto the outside of the wheel, providing both safety and capability."

Learn more about the MER wheels at the NASA Mars Exploration Rover web site.

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