A one-legged robot that can stand, hop and keep its balance on sloping or unsteady surfaces could offer a cheaper route to bipedal bots and self-balancing exoskeletons. Researchers at the Toyota Technological Institute (TTI) in Nagoya, Japan, built their robot, dubbed TTI Hopper, using simple motors and gears for less than $1000, then created an algorithm that compensates for the limited capabilities of these components. "In robotics, we sometimes use hydraulics, because they can be actuated fast," says Barkan Uğurlu, who is now at Özyeğin University in Istanbul, Turkey. "Or electric actuators that have a special spring arrangement or a strain gauge to measure forces inside. Instead, we used DC motors with gears. We only measure the joint angle, and we only used one very low-cost force sensor at the foot."