Gearboxes exhibit losses that reduce the amount of torque available to the end-effector. Thus, a higher transmission ratio is required for the same torque amplification. There are several types of losses that gearboxes exhibit, including load-independent spin power losses and external torque. Let’s take a look at the most common ones. These losses are caused by the interaction between rotating components in the gearbox and air or oil. BMG gears are cold-resistant and can run without lubricant, which could be an advantage for robots operating in a frozen environment. NASA’s Mars Curiosity rover, for example, wastes a great deal of energy heating up grease lubricant for its gear.
BMG gears also reduce the cost of manufacturing strain wave gears, which are the most common type of gear in expensive robots. Moreover, BMGs are cheaper than standard steel gears, which can be used for robotic applications.
A Planetary Gearbox has a low weight of only four kilograms, and is therefore not a good match for the over dimensioned RG350. However, their efficiencies are similar. Compared to conventional mechanical gears, they are less sensitive to changes in operating conditions and have lower no-load starting torque. These characteristics make them suitable for robotic applications, such as repairing faulty machines. However, there is one drawback to PGTs: the limited torsional stiffness.
Compared to PGTs and Strain Wave Gears, cycloid drives have lower torque-to-weight ratios. However, their peak efficiencies are higher and closer to PGTs. However, cycloid gearboxes are very prone to ratcheting. If you’re considering this type of gear, you should keep in mind that the efficiency of the cycloid gearbox is highly dependent on the operating conditions.
As the versatility of a gearbox is large, direct comparison between the performances of different types is difficult. To compensate for this, design modifications are applied to compensate for the weak points in a gearbox’s design. However, these modifications often result in compromises in size, weight, or cost. It is important to remember that a large Latent Power Ratio indicates a topological disadvantage in efficiency, but may be partially compensated with modifications.
The selection of a gearbox in HRI requires a different approach. Detailed insights on the operation of gearboxes are required to make an educated choice. Scheinman et al. (2016) and Siciliano et al. (2010) provide detailed overviews of high precision gearboxes for robotics applications. Further, Pham and Ahn (2018) provide a comprehensive analysis of different high precision gearboxes. In general, they are suitable for the application of modern robotics in applications that impose lower weight restrictions and higher load capacities.
