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Inverse Kinematics Help

**idee17**:

I have little experience with trigonometric functions, and was seeing if anyone can help me get some algorithms running for inverse kinematics. I have read of the robot arm tutorial with the inverse kinematics stuff and understood most of it, except the part with "psi" and "theta". I thought that those words are like variables that values assigned too (more programming experience then trig), if that's right, what symbol do they correspond to? Just one more thing, I'll be running the algorithms that are processing intense on my computer.

psi = arccos((x^2 + y^2 - L1^2 - L2^2) / (2 * L1 * L2))

theta = arcsin((y * (L1 + L2 * c2) - x * L2 * s2) / (x^2 + y^2))

where c2 = (x^2 + y^2 - L1^2 - L2^2) / (2 * L1 * L2);

and s2 = sqrt(1 - c2^2);

~Thanks Idan

**Joker94**:

Psi and theta are just Greek letters that are commonly used to represent angles when applying equations to a geometry scenario, such as you posted. There is not set value for this letter, essentially it is just a variable that can be used to represent an angle.It is more so convention that Greek letters are used to label angles.

When you are writing programs you don't have to use these symbols, you can use any unique letter in your program. For example Psi could be swapped for A and theta could be swapped for B to make programming simpler.

Cheers,

Joker94

**newInRobotics**:

Θ - theta

Ψ - psi

**idee17**:

Thanks for the fast responses guys, this will really help me out.

**idee17**:

I realized a couple days ago that I would need a robot arm with 4 DOF instead of the 3 DOF arm example. I have looked at various websites and haven't found the equations that do what is needed. Also, the base angle could be ignore and have the inverse kinematics work in 2D. If anyone knows how to do this or could point me in the right direction it would be appreciated.

The FBD is attached...

~Thanks Idan

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