Ik Formulas for Flowstone

Lynxmotion Robot Arms
1

Hey guys,

I’ve been working on IK for a little bit and I’m having some issues with getting it to work correctly.

I took a look at Mike Keesling’s xls file from the projects & how-to’s section on the lynxmotion site. I recreated his formulas in Flowstone to get the same angles from the original xls document. The problem is when I applied the math to my AL5A arm. When i change the target on the X axis only the arm moves as expected and stays at a constant level while moving horizontally. However when I change the target on the Y axis only the arm moves up and down with and arc motion. For example, starting at the bottom of the movement range and going up the gripper will move backwards about an inch even though the X target did not change. This behavior continues even on a different arm so i think there must be a problem in the math. Any help would be greatly appreciated!

Here’s a link to the xls sheet: lynxmotion.com/images/html/proj057.htm

And attached is my Flowstone file
IK.fsm (33 KB)

2

Here’s all the math I got from the xls file.

M = sqrt(X²+Y²) //distance of a line between the base and wrist

A1 = arctan(Y/X)

A2 = Arccos((A²-B²+M²)/((A*2)*M))

Shldr = A1 + A2

Elbow = Arccos((A²+B²-M²)/((A*2)*B))

A = Length between base and elbow

B = Length between Elbow and wrist

Target = (x,y) This target is for the wrist! not the end of the gripper.

3

Okay! We’ve made a lot of progress very shortly. the IK works great now. The next problem is how to get an angle for the wrist.