Five people move in tandem down a trail as it gets steeper and narrower than the bright orange metal frame connecting them.

This trail, popular with Bend, Oregon, families, is a testing ground for inventor Geoff Babb, and the stakes couldn’t be higher.

One miscalculation about how to navigate the tight squeeze of boulders, and he could topple over the edge toward an ice-cold river below. But, that’s not what worries Babb, who hasn’t walked since a stroke 14 years ago.

“I don’t feel scared on the trail. I trust these guys to figure it out, how to get through those narrow spots without tipping me over,” he said.

As the team lifts him over rocks, Babb focuses on how certain components are working. He’s invested countless hours in this prototype for a new style of an all-terrain wheelchair.