Wheelchairs driven by one wheel - how do they work?

[Mangetout]

I’ve often wondered about this, but only right now thought to ask:

-I’ve seen people in wheelchairs propelling themselves along in a relatively straight line, using only one hand on one wheel - how does this actually work - clearly the wheels are independent when they’re needed to be, as an on-the-spot turn can be executed. Is there some kind of clutch mechanism linking the two wheels so that they can optionally be driven by pushing only one?

[Whack-a-Mole]

Not sure I quite follow this (the actual mechanism) but seems an answer:

One-arm drive enables a user to guide and propel a wheelchair from one side. Two handrims, one smaller than the other, are located on one side of the chair, left or right. On most models the outer, or smaller rim, is connected to the opposite wheel by a folding axle. When both handrims are grasped together, the chair may be propelled forward or backward in a straight line. When either handrim is moved independently, the chair will turn left or right in response to the handrim used. Another alternative is a lever-drive chair that propels the chair forwards by using a lever that is pumped back and forth. Some chairs are also configured to allow the occupant to propel using one or both feet instead of using the rims.

SOURCE: Wheelchair - Wikipedia

[Philster]

One-arm drive connects the two wheels via the axle, rather then letting them be independent.

[yoyodyne]

When there is a slight slope to the pavement perpendicular to the direction of travel the chair wants to turn downslope. This can be counteracted by pushing only on the downslope wheel. Pushing both wheels equally in this situation would result in the chair turning.

The same thing happens when braking, where the upslope wheel is the one slowed.