Mini robots waiting for chance to attack Mars

A pint-sized robot that uses special wires and springs to move about rather than gears and motors promises a novel new way to explore the solar system. Teams of the devices, about the size of a shoebox, could be dispatched to travel the surface of Mars, sending back a wealth of data.

The robot, known as a BiRoD for "Biomorphic Robot with Distributed power", makes use of metal alloy wires that respond to an electrical current by contracting. This allows the BiRoD to be light, simple and durable, and ideally suited to planetary exploration according to its designer.

"We are trying to imitate biological systems," said Prof Kumar Ramohalli, who heads the project in the Space Engineering Research Centre at the University of Arizona, Tucson. "BiRoDs are much simpler than robots you have seen in the past."

The BiRoD does not depend on the usual mix of gears, servomotors and other complex mechanical systems. It uses nickeltitanium alloy wires and springs which mimic the actions of muscles by contracting when exposed to a current. The resultant movement "is extremely predictable and is extremely fatigue resistant", Prof Ramohalli explained.

Muscle wires respond in milliseconds and remarkably can carry 17,000 times their weight. The wire returns to its original length as it cools and can be recycled through millions of contractions without wearing out.

The Arizona team has several prototypes which have been used to demonstrate the technology. They have featured on US television and are regularly taken out to local secondary schools in an effort to spark the interest of students in possible careers in the sciences and engineering.

The first BiRoD had two "walking" legs at the front and two unpowered wheels at the rear, but later versions used four of the mechanical legs. This version is better at striding over obstacles and can turn 360 degrees within its own body length.

There are a few kinks to iron out, Prof Ramohalli said. "Stability has never been a problem," he said, but speed has. "It has always been very slow. I don't think that is a negative factor because it wouldn't have to be fast on Mars."

Its wires heat when a current is applied and so its speed is dependent on cooling the wires after contraction. This can be aided by using a fan, but on the frigid surface of Mars, where Prof Ramohalli would really like to test his robot, cooling would be much faster.

BiRoD takes a two-centimetre stride at each step. Its speed could be improved by increasing the number of wires applied to each joint and then contract the wires sequentially, but this would greatly add to its complexity and the BiRoD's simplicity is its greatest advantage over existing robots.

It can also unfortunately be quite temperamental and will work one day and not the next. This seems to be associated with bugs in the software that controls its movement, however, and not with its propulsion systems and so should be something that will be corrected over time.

The BiRoD carries high technology devices. Its stripped down version is fitted with infra red "vision" that enables it to avoid obstacles even in the dark and a laser range finder could be added to achieve distance measurement.

Its great lifting and carrying power would allow onboard experiments and another dimension that Prof Ramohalli wants to build into future versions is energy autonomy that would allow truly automated exploration.

"We are hoping to marry it with ISPP - in situ propellant production," he said. The BiRoD would land and then be expected to use materials available in the soil, atmosphere or perhaps in crushed rocks that would give it fuel to carry out its mission.

It would also give more options for a "power surge", he said, actions which periodically require much higher levels of energy. Examples might be when an onboard oven heats to test a sample or when a robot "arm" is used to crush and sample rock.

BiRoD can already do this now, unlike existing robot systems, but energy storage could become a problem. If the robot could find its own local energy supplies, however, it could operate for longer and carry out more experiments.

The existing BiRoD design is light and compact. For example 25 BiRoDs would have fit in the space required for the Sojourner robot used on the Mars Pathfinder mission. Even if one or two or a dozen BiRoDs failed to survive the journey there would still be plenty left to carry out a successful mission.

The BiRoD design has been protected under a NASA Novel technology Report and Prof Ramohalli has been in discussion with a number of companies. The work has involved two graduate students and two under-graduates, but he has high hopes for his robot and awaits the day when it takes its first steps on Mars.