The Swiss precision drive manufacturer maxon motor has developed a coaxial gearhead that combines worm and planetary gears to deliver high levels of torque in almost total silence – even with high input loads. The 32mm-diameter Koaxdrive KD 32 delivers up to 6.5Nm of torque and is aimed at demanding, noise-sensitive applications.

The innovation is in the first gear stage, where peripheral speeds are the highest and where most noise is usually produced. A worm-formed helical motor pinion drives three offset plastic planetary wheels which interlock with an internal gear with straight-cut teeth. A patented sliding mechanism takes axial load off the motor shaft, reducing contact noise dramatically and allowing the gearhead to operate at up to 8,000 rpm.

The other stages are arranged as in a standard straight-cut planetary gearhead, producing reduction ratios in the range 11:1 to 1091:1.

The gearhead’s combination of high power, small size and low noise is expected to open up new applications. The luxury car industry is already showing an interest, as is the medical sector, where the development could result in silent surgical instruments.

Paul Williams, senior sales engineer at maxon motor uk, admits it is unusual to find real innovation in gearing, “but with the Koaxdrive, we’ve pioneered a genuinely new concept”.

“When I describe this technology to design engineers,” he says, “their eyes light up. We’re giving them the solution to an age-old problem: generating power without noise.”