mobility performance evaluation of planetary rover with simi(5)

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VI. Experimental Analysis

Figure 11 shows the results of model experiment while climbing over the step. In this flight, we had carried out the experiment, which reaches two kinds of step (15 [mm] and 30 [mm]), to survey the effects of the mobility system while climbing over the step.

In Fig.11, we express change of the number of revolutions to running time when climbing over the step (30 [mm]). When the models climb over the step of 15 [mm], the both of models with PEGASUS or 4WD could climb over the step smoothly. But, in the step of 30 [mm], the rear wheel of 4WD model slipped and couldn’t climb the step. In the meantime, the Where, r : Wheel radius [mm] ω : Turning angle velocity [rad/s] v : Body velocity [mm/s]

In the case of the 15-degree of grade, the slip ratio in-creased as a model ran, and the both model with 4WD and PEGASUS system had stacked. The slip ratio of the model with PEGASUS was smaller than 4WD to some extent, and PEGASUS had ran a distance longer than 4WD. In the case of the 10-degree of grade, PEGASUS and 4WD system ware able to finish reaching slope because the rapid increase in the slip ratio was not seen although the each wheel was sliding. In model with PEGASUS was able to overcome the step although time was taken. By the result, PEGASUS was better than 4WD because of their load distribution capability.

In the Flight #2 and #3, we carried out the experiment of the sandy slope, which would be the most difficult place while running on the moon surface, and evaluated suspensions relatively on a degree of mobility by the slip ratio of the wheel. Figure 12 and 13 show the results of model experiment while going up a sandy slope. In Fig.12, we calculate the slip ratio of the wheel to mileage from the number of revolutions and the velocity of Flight #2 and #3. The slip ratio λ can be found as follows:

λ=rω vrω

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Fig.11 Result of the number of revolutions of the wheel

at the 0.5G environment

Fig.13, we describe the slip ratio to the difference of gravitational acceleration while running between the unit distances (about 10.0 [cm] from the start) before carrying out a stack. We can guess that the slip ratio becomes small as gravitational acceleration becomes small.

VII. Conclusion The planetary rover needs to be equipped with the mecha-nism which actively or passively improve its mobility because of overcoming its physical limitation. In this paper, we take up a newly developed suspension system called PEGASUS.

In order to research the behavior of the rover when driving on the moon, we should carry out a running test under 1G gravity with 1/6 Model based on similarity laws. However, it's

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Fig.12 Slip ratio at the 0.5G environment

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Fig.13 Change of the slip ratio by the difference of gravity