Make: Robotic Arms

3-11

57Chapter 3: Inverse Kinematics for 2D Movement

Thanks to the law of cosines, we can solve for Ө

1.2

the same way we solved for C. This time, of the

three law-of-cosines equations, we’ll select the

one that solves for A, as the A variable is in the

same spot as our Ө

1.2

is now:

a = b + c -2bc cos(A)

Just as we did before, let’s rearrange our equation

to solve for cos(A), then plug in our variables and

calculate our value for θ

1.2

:

A = 0.56RAD or 31.96 

With that, we have officially solved for the variable

Ө

1.2

. All that’s left is solving for Ө

1.1

then adding

the two Ө

1

variables together. To solve for Ө

1.1

let’s

take another look at our ...