Ball Joint Differential for Robot

A method for moving a joint in two degrees of freedom, the method comprising, in any order:

• rotating a first input element around a first axis while rotating a second input element around the first axis in the same direction and in the same amount as the first input element, thereby causing an output link to rotate around the first axis;
• and
• rotating one of the first input element or the second input element around the first axis while rotating the other input element in the opposite direction in the same amount, thereby causing the output link to rotate around a second axis that is orthogonal to and offset from the first axis;
• and
• rotating one of the first input element or the second input element around the first axis while;
• rotating the other input element in the same direction in a different amount;
• or
• rotating the other input element in the opposite direction in a different amount;
• thereby causing the output link to rotate around both the second axis and the first axis.

A non-transitory computer readable medium that is encoded with computer-executable instructions for implementing a target sequence of rotary movements around a first axis and around a second axis that is orthogonal and offset from the first axis, the instructions comprising instructions for:

• receiving the target sequence of rotary movements;
• translating the target sequence of rotary movements to a sequence of motor commands for first and second motors that respectively rotate first and second input elements of a two degree of freedom joint;
• and
• driving the first and second motors according to the sequence of motor commands.