Budgets and Experiments

GOALS: to provide the students with an insight into the problems that need to be solved when designing a rover. To design a rover within budgetary and experimental limits, to produce a protoype model from a construction systems, such as Lego or Fischer-technik.

KEY CONCEPTS: What difficulty does the distance between Earth and Mars present? What problems on the Martian surface will the rover have to deal with? What steps must be taken to ensure the rover's survival and continued functioning?

OVERVIEW: Mars is further away from the Sun than Earth. Although it can approach close to the Earth in its orbit, it never gets closer than about 56 million kilometres (35 million miles). This huge distance means that radio signals, travelling at 300,000 kilometres per second (186,000 miles a second), can take up to 20 minutes to reach the planet, and another 20 minutes for any answer to return to Earth (when the Mars is at its greatest distance from Earth). This means that direct control of the rover from Earth is not possible. The exercise in this unit is meant to show the students how they deal with performing tasks when taking the role of the rover, and how this can feed back into their designs. Students may proceed to building rovers of verying complexity, dependent on available materials. Various testing procedures may be planned.

MATERIALS: Room with tables, wooden boxes, slopes, various obstacles; stopwatches or ordinary watches; optional blindfold, cassette recorder. Construction materials [ junk, construction kits, electronic components: tilt switches, push-to-make switches, control software].

PROCEDURE: Arrange a variety of obstacles in a room, gymnasium or outside; these should include slopes, objects to negotiate around or through; items to pick up. Get into pairs, a "Rover" and a "Controller". The Controller needs to examine the arrangement of items, and set tasks for the Rover to perform. The Controller guides the Rover around the obstacle course via spoken commands. However, the Rover cannot perform any of the tasks until an agreed time delay [30 seconds to a minute] has elapsed. The Rover must do exactly what the Controller says, even if this means bumping into things. It is the Controller's job to give the Rover precise instructions in adequate time to avoid obstacles. the Rover performs any task that the Controller sets. This same activity may be performed with the Rover blindfold. This time, the time delay need not be observed. The Rover should however relay to the Controller any information on slope, evenness of surface etc. Alternatively, the Controller can plan the route s/he wants the Rover to follow, and record it on audio cassette. The Rover then follows the exact sequence of pre-recorded commands. During this activity, changes may be made to the arrangement of obstacles by a third person, to simulate unexpected events on the planet [landslides etc].

ANALYSIS: The information relayed by the Rover should give the Mission Designers some ideas about sensors that the mechanical rover might need: contact sensors, tilt sensors etc. It should also highlight the need for some form of on-board intelligence to deal with unexpected events - after all, the rover needs to be able to avoid danger before it receives a command from a far-away Earth. Rover design can now proceed. Should tracks be used, or wheels? How can this be tested for?

Experiments have been designed and selected, and planned for installation on the rover. The rover may now be constructed in prototype form, either as a drawing, or a model, or a working model, dependent on the sophistication of available facilities. The old-fashioned "cotton reel tank" provides a good simple power source for a low-tech rover model. Access to electronics will allow for a complex rover which will perform tasks set for it under computer control. Note that a very simple computer is all that is required.

Interesting work can be done designing test tracks for the rovers, and having "Rover Races". Sand, talcum powder, flower, gravel etc can provide useful "Martian" surfaces for testing the rovers

CONCLUSION: at the end of these modules, the students should have acquired a basic knowledge of Martian conditions, and an awareness of the nature of the experiments that should be taken to Mars. They should have realised that there are limitations on the effectiveness of autonomous rovers, due to physical, technological, human and budgetary factors.

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