Boston Dynamics drops the pinky from Atlas to save three actuators per hand

A nail gun has a grip and a trigger, and the person using one holds the grip while one finger works the trigger. Boston Dynamics lists nail guns with drills, grinders, torque drivers and welding torches among the tools its new Atlas hand is designed to handle ^[12]. The hand is roughly the size of a large human hand because Atlas is meant to use human-scale tools and equipment ^[13].

Humanoids are increasingly designed to work in places built for people ^[15]. The easy next step is to copy the person down to the fifth finger. Boston Dynamics tested the copy against the job. Adding a pinky would have been relatively straightforward, the company said, so the team checked whether its tasks needed one ^[4]. A fifth finger would have meant three more actuators, adding cost, size and potential failure points ^[6].

The report gives enough to estimate the parts count. The joints are directly actuated ^[16], each finger other than the thumb has three degrees of freedom ^[3], and a fifth finger would add three actuators ^[6]. If each degree of freedom has its own actuator, as those figures suggest, the hand has 13 and a five-finger version would have 16, about 23 percent more ^[20].

The second design target is training. The transmissions are backdrivable, so outside forces can move the joints and Atlas can sense its own joint positions and motion ^[8]. Boston Dynamics said that, with controls that compensate for friction and motor cogging, this lets the hand be modeled with high dynamic fidelity ^[11]. Pressure-sensitive tactile sensors across the fingertips and palm add contact information ^[9].

The strength figure needs adjusting before it goes into a work-cell plan. The company said the hand can carry a loaded mini-fridge weighing more than 100 pounds ^[17]. The production Atlas is rated for an instantaneous payload of 110 pounds and a sustained payload of 66 ^[18]. The fridge sits within 10 pounds of the peak rating and at least 34 pounds above the sustained one ^[19].

Every figure here comes from Boston Dynamics through one report by Interesting Engineering, and it covers one company's hand ^[1]. On that evidence, Boston Dynamics put parts count and simulation fidelity ahead of anatomy. Whether other humanoid makers are doing the same is outside what the report covers. It does not include a price, an actuator count or failure data from deployed robots.

The test Boston Dynamics ran on the pinky works on any humanoid shortlist. Take the tasks planned for the robot's first month and sort them on two questions: do the parts arrive in a controlled orientation, and does the job need a tool trigger or in-hand reorientation. Controlled parts with neither need are work a conventional gripper already does well ^[14]. Varied parts with a trigger are the case Boston Dynamics built this hand for ^[12]. In my view, every joint a vendor adds beyond that should come with the name of the task that fails without it.