| 摘要 |
The wheel &c carries at least one peripheral roller (16) which forms at least part of the ground engagement surface and which is arranged so that the wheel &c is capable of moving forward or sliding sideways. Peripheral rollers (16), preferably having surfaces conforming to the ground engagement locus for smooth ground contact, extend around part or all of the wheel &c periphery. Two rows of rollers (16) may be provided, each roller of one row being aligned with a gap in the other row. Each roller may be mounted for retraction radially and controlled for selected free rotation, frictional resistance to rotation and braked against rotation.
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