The Roomba has an adjustable height feature that automatically compensates for changes in surface composition from e.g., carpet to tile or wood. However, this was insufficient for outside use on grass or tree bark mulch covered with plastic, where the Roomba lost traction. This points out the need for a greater range of vertical motion that will be needed in the desert, where the surface will not be perfectly smooth.
The Roomba’s performance in removing particulate matter from a plastic cover was evaluated in several experiments. A 6 ft x 6 ft test area was constructed by laying 4-mil white construction film on a tile laboratory floor. Wooden boards were used to create a perimeter to keep the Roomba confined. A red clay soil (50g) sieved to below 177 microns used to simulate dust from sand storms was added to the plastic surface by sprinkling it along the back section.
The Roomba removed around 85% of the soil after 10 minutes of operation. Most of the remainder was blown up against the perimeter and some was found trapped in the unit, but not in the particle bin. The Roomba left behind a reddish film over the entire surface, including the front area that was not originally contaminated. This could not be removed by additional vacuuming, effectively reducing the albedo from a nominal 0.8 to around 0.3-0.4.
The unit also left tire tread tracks and circular patterns due to a tread less front wheel. The plastic was cut in several places, but not all the way through. A rubber blade used to sweep particles into the path of the rollers also spread soil across the surface. A wet wiping of the surface removed the residual soil, proving there was no permanent discoloration. However, the surface was never as glossy white as new.
We recommend readers of this research plan view the 26 min VHS video we produced entitled “Maintaining Surface Reflectivity Using Robotic Vacuum Cleaners” in which the performance described above is documented (169).
The discoloration was caused by fine particles, probably <10 microns, which are too small to be vacuumed using this system. The rubber blades and the wheels spread these particles over the entire surface. To solve this problem, the geovac would operate with a vacuum system only and no rotating brushes or sweeping rubber blades. The vacuum head would be located at the front of the geovac and would not touch the surface of the plastic. The wheels would consist of balloon tires to minimize compression and spreading of soil and dust over the rest of the surface. A single pass would be performed also to reduce spreading of soil. Another feature that should be considered is one that would reduce some of the electrostatic attraction of the soil particles to the plastic by offsetting the attractive charges keeping the particles on the surface.
As an example of how some of these features might work, we used the nozzle of the Electrolux conventional vacuum cleaner hose to remove soil freshly deposited on the plastic surface without allowing the wheels to touch the surface. It removed nearly all of the soil without leaving any discoloration due to tracking or spreading. Although this type vacuuming will remove almost 100% of freshly deposited soil, once the dust film has been spread over the surface, it cannot be removed satisfactorily without a wet wiping. Removal of surface contamination from plastic film used as mulch as part of its recycling requires large quantities of water and drying of the plastic is difficult (170).
