When you’re building robots, gears are essential. But if you’re building a robot that can grip ledges or climb mountains, you won’t find a gear that fits your needs in a hardware store. Instead, NASA technologist Douglas Hofmann is building better gears from bulk metallic glass. He uses a specially crafted alloy called BMG. In addition to being cheaper to produce, BMG gears run smoother even without lubricant.
In addition to its low weight, gearheads are also less sensitive to operating conditions. RG350s are more efficient but also have larger diameters and shorter lengths. The torque-to-weight ratios are similar for both solutions, but the gearheads have a significant advantage in efficiencies. Their low starting torques are ideal for robotics, but their low efficiencies make them less flexible under changing conditions. High-ratio gearboxes are also more expensive.
Strain-wave gears are extremely light and can serve cobot needs well. They’re dominant in the field of cobots and are a cost-effective solution for many tasks. Compared to traditional gears, they offer high torque at low speeds, which is critical for pHRI robotic tasks. Despite this, the topology of the Strain Wave gear is similar. Instead of a flexspline, the system incorporates a Teeth Carrier that includes two rows of individual teeth. In addition to a Poligon Shaft, the system uses a circular spline as a wave generator.
The NuGear structure resembles a two-stage Wolfrom PGT. Each stage uses a carrier as an input and is paired with two Wolfrom PGTs. This corresponds to two stages in Barbagelata et al. (2016). This structure implies a high Latent Power Ratio, assuming a 1:10 gain on each stage. The high Latent Power Ratios of this geartrain indicate the possibility of high efficiency.
A gearbox with a Wolfrom topology is a very high-efficiency gear with low topological efficiency. Its low topological efficiency is due to the loss of contact between the gear-teeth and ring rollers. Its high Latent Power Ratio is supposed to compensate for this by transferring torque from the planet to the ring rollers. However, the manufacturers haven’t released any official data to prove its efficiency.
Another type of gear is the planetary gearbox. The PGT has high input speed but low output speed. Moreover, it has low torsional stiffness. Despite its drawbacks, this gear is highly versatile, efficient, and affordable. Its versatility has also drawn the attention of roboticists. There are a few types of high-ratio PGT configurations. The Wolfrom topology, for example, offers a better meshing efficiency by replacing teeth with rolling contacts.
Backdrivability is a measure of the efficiency of a gearbox. It involves the combined effects of reflected inertia, reflected damping, and Coulomb friction. Backdrivability is closely related to the efficiency of the gearbox. If a gearbox is able to backdrive a motor, then it is highly efficient. However, this type of gearboxes is not as effective for applications with heavy loads.
