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How much does wrist DoF count actually matter for real tasks?

Posted: Mon Mar 31, 2025 10:48 pm
by matthew43
Curious what people here think about this. Bimanual manipulation - two arms coordinating on one task - is harder than it looks mostly because of the added degrees of freedom and the timing/force coordination required; a lot of 'two-handed' demos are actually closer to two independent single-hand tasks done in sequence. Figure's fourth-generation Dexterous Hand (on Figure 02/03) reportedly offers 16 degrees of freedom per hand with sensors integrated into each finger, aimed at fine force control tasks like handling small electronic components without crushing them. Would appreciate any first-hand accounts.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Tue Apr 01, 2025 3:56 am
by sarah.santos3
I dealt with almost this exact situation. A lot of the manipulation shown in production demos still leans heavily on teleoperation, particularly for anything involving fine force control or novel objects - autonomous grasp success rates on genuinely unstructured, previously-unseen clutter are still well below what teleoperation can achieve. Vision-based grasp confidence estimation (predicting success before attempting a grasp) and tactile-based confirmation (confirming after contact) are complementary rather than competing - vision helps you choose a grasp, tactile tells you if it actually worked.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Tue Apr 01, 2025 9:34 am
by jwang
@sarah.santos3 Pretty much this. One thing to add: In-hand reorientation (repositioning a grasped object without setting it down) is one of the more advanced manipulation skills, requiring either a highly dexterous hand with enough DoF or clever use of gravity and controlled slipping - it's an active research area rather than a solved problem.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Tue Apr 01, 2025 12:41 pm
by sarah.santos3
@jwang Small correction on one detail: Grasp planning for deformable or non-rigid objects (bags, cables, cloth) remains one of the genuinely unsolved problems in manipulation - rigid-body grasp models simply don't capture how the object will behave once contact starts.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Tue Apr 01, 2025 5:07 pm
by kwilliams
Pretty much this. One thing to add: Cable routing through a wrist joint with multiple degrees of freedom is a genuinely tricky mechanical design problem - tendons and wiring both need enough slack to avoid binding through the full range of motion without tangling or fraying over thousands of cycles. Wet, oily, or otherwise low-friction objects are still a genuine edge case for most current hands, since tactile sensing and grasp-force controllers are typically tuned and validated on dry, higher-friction test objects.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Tue Apr 01, 2025 7:20 pm
by sarah.santos3
@kwilliams Worth being a little skeptical of the marketing angle here. Tendon-driven fingers let you move the heavier actuators back into the palm or forearm, keeping the fingers themselves light and fast, but they introduce cable routing, tensioning, and long-term wear problems that direct-actuated fingers don't have.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Tue Apr 01, 2025 11:58 pm
by williams84
@sarah.santos3 Counterpoint: Underactuated hands (fewer actuators than joints, using mechanical coupling to shape the grasp) are a reasonable engineering compromise for robust power grasps on a budget, but they generally can't do fine in-hand manipulation the way a fully actuated hand can.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Thu Apr 03, 2025 8:26 pm
by sarah.santos3
This matches what I've seen too. Payload-to-hand-weight ratio varies a lot across current dexterous hands, and it's a meaningful tradeoff - more DoF and finer sensing generally means more actuators and mass in the hand itself, which eats into the arm's usable payload budget. Palm sensing gets less attention than fingertip sensing, but a lot of power grasps (holding a box, a tool handle) rely more on palm and lateral finger contact than fingertip contact, so under-sensing the palm can leave a real blind spot in grasp confidence.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Sat Apr 05, 2025 12:54 pm
by jonathan.rao1
Short answer: Imitation learning from human demonstration video (without robot teleoperation data) is an appealing way to scale up training data cheaply, but it runs into the embodiment gap - human hand kinematics and force profiles don't map directly onto a robot hand's very different mechanism. Object occlusion by the robot's own hand during the final approach to a grasp is a common and annoying perception problem - the closer the hand gets to a good grasp position, the more it blocks the camera's view of exactly what it's about to grab.

Re: How much does wrist DoF count actually matter for real tasks?

Posted: Sat Apr 05, 2025 2:23 pm
by pierregreen
Yeah, this tracks with what I've read as well. Bimanual manipulation - two arms coordinating on one task - is harder than it looks mostly because of the added degrees of freedom and the timing/force coordination required; a lot of 'two-handed' demos are actually closer to two independent single-hand tasks done in sequence. Payload-to-hand-weight ratio varies a lot across current dexterous hands, and it's a meaningful tradeoff - more DoF and finer sensing generally means more actuators and mass in the hand itself, which eats into the arm's usable payload budget.