Lecture from the IROS 2021 workshop:
From gears to direct drive: recent trends and opportunities in the field of drive
Website: https://www.ram.eemcs.utwente.nl/gears-direct-drive-recent-trends-and-opportunities-actuation

Abstract:
Despite significant advances in the capabilities of robots, relatively little progress has been made in making them cost-effective enough for widespread acceptance by society. Simply reducing the production costs of existing technology is often not enough; New concepts are needed, combined with modern production techniques. In this talk, I will discuss some of the avenues we are pursuing in cost-effective robotics, with an emphasis on new control concepts: 1) motor control for explosiveness, 2) progressive series elasticity, and 3) a 3D printable low- ratio cycloidal drive.

1. Field Weakening and Fatigue Management for Explosive Robotics. Field weakening is a motor control method to increase their peak speed beyond their conventional voltage-limited limits. This allows robots to achieve significant gains in explosive movements such as jumping. However, significant heating of the engine occurs. By actively managing the heating (fatigue) of the engine during successive movements, maximum performance can be achieved depending on its condition. We show that such strategies are effective in expanding the dynamic performance and explosive movement capabilities of robots.

2. Magnet-based progressive series elastic control. Series elastic actuators provide excellent robustness and interaction control. However, the reliance on precision-machined flexible components reduces their cost-effectiveness. Secondly, research suggests that there are advantages to progressive (stiffening) profiles, which are not easily achieved with mechanical bending. We have developed a non-linear series elastic element based on repulsive magnets. The prototype uses off-the-shelf magnets with a 3D printed housing to achieve progressive stiffness with negligible hysteresis.

3. Robust, cost-effective robotics with 3D-printable low-reduction cycloidal drives. Most modern robots use planetary gears or harmonic drives to increase output torque. Planetary gears have gained popularity recently, following the trend towards lower gear ratios. However, cycloidal drives also have excellent properties for modern robots, such as high (shock/impact) robustness, torque capacity and efficiency. They are ideally suited to be 3D printed, while remaining robust due to their large contact surface for force transmission. We have developed a compact, low-reduction cycloidal drive gearbox that is low-cost, 3D-printable and uses off-the-shelf components, while maintaining good performance characteristics.

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