## 4 Experimental Results
### Experiments with \"Dyjob\" Moving over a Step  
The analysis in Section 3 indicated that _[PERSON]_ should shift the movable mass to the furthest possible point backward in Step 1 and Step 3 and the furthest point forward in Step 2. We first conducted experiments with _[PERSON]_ moving over a step. _[PERSON]_ could successfully traverse a step of 180 mm high, which is the same height as _[PERSON]_ itself, and 400 mm deep. A movie of this experiment is presented in the Supplementary Video S1. Figure 9 shows some snapshots of the movie. The magenta and light green lines in Figure 10 show _[PERSON]_'s tilt and the movable mass position in the experiment. The tilt \(\theta\), the same as in Figure 7, is positive when the vehicle tilts backward. The movable mass position is zero when it is placed at the center of _Dyjob_ and positive when it moves forward. Each circled number in Figure 10 shows the time of the corresponding snapshot in Figure 9.  
Figure 8: Assumed step heights that _”[PERSON]”_ can climb with the tilt in Step 2, as calculated with Equation (6) by a geometric analysis.  
In Step 1, the tracks slipped on the ground and the step wall with the movable mass kept in the center, thus preventing _Dyjob_ from lifting its front end onto the step. Moving the movable mass the furthest backward, as shown in No. 1 in Figure 9, allowed the front end of _Dyjob_ to move up onto the step, as shown in No. 2. It is similarly observed in Figure 10 that because the movable mass was placed the furthest backward between No. 1 and 2, _Dyjob_ was able to tilt up to approximately 0.6 rad.  
Figure 10: Experimental results for _Dyjob_ traversing a step. Each circled number shows the moment of the corresponding snapshot in Figure 9.  
Figure 9: Snapshots of _“Dyjob”_ traversing a step.  
For Step 2, the operator moved the movable mass the furthest forward while _Dyjob_ was tilted up, as observed between No. 2 and 3 of Figure 10. Consequently, after _Dyjob_ was tilted up by approximately 0.8 rad, the tilt steeply dropped to zero, as shown in No. 4 of Figure 10, and the vehicle landed on the step (see No. 4 in Figure 9). Without moving the movable mass the furthest forward, _[PERSON]_ was not able to achieve Step 2.  
For Step 3, the operator moved the movable mass the furthest backward between No. 4 and 5 of Figures 9 and 10 to safely land _Dyjob_ on the ground. Subsequently, _Dyjob_ moved forward, and the front end landed on the ground without the vehicle turning over, as shown in No. 6 of Figure 9. In the case that _Dyjob_ proceeded while keeping the movable mass forward, as shown in No. 4 of Figure 9, _[PERSON]_ was vertically tilted down in No. 6 of Figure 9, thereby flipping over. If the rear end falls from the step while the movable mass was kept backward, as shown in No. 6 of Figure 9, the devices in the mass will be damaged. Therefore, the operator moved the mass forward, as shown in No. 7 of Figure 9, and _[PERSON]_ safely landed on the ground, as shown in No. 8 of Figure 9.  
_[PERSON]_ with the adjusted COG position could traverse a step of up to 180 mm high, while without COG adjustment it could traverse a step of up to 120 mm high. The results are similar to our analytical results shown in Figure 8, although the _Dyjob_ experiments were occasionally dynamic.