The race is on to create an ebike motor that adds the least amount of weight and bulk as physically possible, disappearing away into the bike where it's barely seen or heard but is felt on every pedal stroke. The latest contender is the Magnetic Gear Motor (MGM) from Chinese ebike component supplier Star Union. As its name implies, this electric motor drive swaps out physical gears in favor of a magnetic gear system that compacts the core while cutting friction. The drive is then able to put out a serious punch from a tiny, incognito package.
Last week, we looked at how TQ's latest electric bike drive is able to cut weight and bulk by using a Harmonic Pin Ring gearing system that places two gears inside each other, rather than laid out laterally as in a larger ebike drive. Star Union uses a similar gear-in-gear layout, albeit without the need for mechanical power transmission between physical gear teeth.
Star Union isn't the first to explore the idea of magnetic gearing, but it does claim to be the first to apply it to an electric bike drive. Its permanent magnet-based gears transmit torque via a magnetic coupling that eliminates physical contact. The contactless transmission, in turn, cuts friction down around nil, resulting in an optimized power transmission Star Union estimates at 90% maximum efficiency.
"Virtually no energy is wasted as heat from friction, meaning more of the battery power translates into wheel torque," summarizes Zhi Pan, Star Union director. "Riders can expect better range and sustained output."
With that level of efficiency and the snug, concentric configuration of gears, Star Union is able to ensure potent performance from a very compact drive package. The MGM's outer casing measures in at 4.7 x 4 x 3.5 in (12 x 10 x 9 cm), which isn't quite as grabbable as a 3.8-in-diameter (9.7-cm) softball, but the photo up top does show it fitting rather comfortably in the hand.
More importantly, the 5-lb (2.3-kg) MGM fits quite neatly and inconspicuously in the bike's bottom bracket, improving ground clearance and delivering aesthetics that are about as clean as any we've seen. It also gives bike manufacturers more flexibility in placement and overall frame design.
Beyond those big advantages, the magnetic transmission system cuts out noise associated with the physical grinding of gear teeth and the accompanying wear and tear of mechanical transmission. As for the potential of magnetic decoupling and slippage, Star Union is confident it has designed the MGM e-drive to prevent such problems.
"There are fewer points of mechanical stress, and the magnetic coupling can ‘slip’ harmlessly if overloaded, avoiding damage," explains Zhi Pan. "Of course, the MGM motor doesn't slip because we understand the torque limits of magnetic gears and can control the current accordingly."
The good news about major components like this one is that the ebike industry will have the chance to fully vet Star Union's claims before integrating the drive into the actual bikes that will be staring at consumers through the windows of local shops. After showing the Magnetic Gear Motor at Eurobike 2024, Star Union will be offering hands-on demonstrations and test rides for the first time at this year's Eurobike show later this month.
The 2025 MGM produces a claimed 80 Nm (59 lb-ft) of peak torque, up from the 75 Nm (55 lb-ft) of last year's drive. Star Union says it was able to bump the torque up without adding any weight or size to the package. The drive has a continuous power of 250 watts and has been tested to 580 watts of peak power.
Star Union has developed several packages for road and mountain bikes with 48-V batteries ranging between 160 and 480 Wh. It says it's been working with and talking to several ebike OEMs in Asia and Europe on development of MGM-powered products and plans to begin mass production of the mid-drive in the fourth quarter of this year.
Source: Star Union
