SRI International robotics engineers have developed the first new rotary transmission design since Harmonic Drive introduced its gear system, based on a mechanism known as a strain wave gear, in the 1960s. Harmonic gears are compact, have high gear ratios, and don’t have backlash, but they are also expensive. Harmonic Drive is a partner in the new project - the company has licensed the Abacus design from SRI and is collaborating with them to commercialize it. The new Abacus drive is a pure rolling transmission - there are no parts that rub or slide against each other, only parts rolling against other parts. Rubbing and sliding result in wasted energy, and conventional transmissions are typically only 50 percent efficient. SRI International researchers say the new drive has efficiency in the high 90s. The Abacus drive has beads that roll in and out of a groove with a variable diameter, which causes the beads to effectively change their diameters depending on where in the groove they are.