Model the underactuated joints of the ReFlex hand

[Adam Conkey]

Currently the underactuated joints of the ReFlex hand (distal joints with the flex links) are set as fixed joints. This makes grasping in simulation with the hand unrealistic (and probably harder as it'd be easier to get a grip if it flexed). There are different levels to how well this can be modeled:

1. Make actuated and just apply some heuristic for trying to flex the fingers based on the angle of the proximal joint. This would provide some flexing but still not realistic.
2. Create a linear actuator that acts like the tendon pulling on the finger, and actuating the joint with a stiffness controller. This might be more realistic but could be difficult to model the linear actuator well and getting it to map well to the actuation of the proximal joint.
3. Learn a model in a data-driven way by collecting a bunch of data on the real hand and recording data of distal flexion based on actuation of proximal joint and contacts sensed on the hand. This would be the best option I think, but obviously requires a lot of data collection, and it requires this issue to be solved so that you get similar contact sensing in simulation as you did from the data collection.

This package looks like a good place to start: https://github.com/jsbruglie/grasp

‌