Wheel assembly

A wheel assembly comprising a wheel, a deformable chamber containing a transition substance comprising jamming particles and an interstitial gas, and an actuator configured to transform the transition substance between:

• a fluid state in which the deformable chamber can deform into a conformal state as the wheel encounters an obstacle during use;
• and,
• a rigid state in which the transition substance is rigidified by evacuation of the interstitial gas, wherein the interstitial gas is evacuated to lock the jamming particles together in the rigid state within the chamber to maintain the deformable chamber in said conformal state to provide increased purchase on said obstacle.