Solve 4-bar linkage problem for a robot


New member
Feb 16, 2019
Hi all - I am building a robot and I need to solve the 4-bar linkage equations to determine the robot arm's position in space.

Essentially I have a 4 bar linkage with all 4 link lengths known, and 2 angle measurements known. I am trying to solve the other 2 angle measurements based on these 4 link lengths and 2 angle measurements. If I can figure out an equation for one of the unknown angles based on the known values, the other one should be trivial. But whenever I try to figure out the math the equations "blow up" into more and more terms and I don't know how to develop the problem to get things to cancel out.

I have spent a few months on this and I keep getting stuck, and would appreciate any help. I'm a 36 year old Engineer and am banging my head on the table on this simple problem, so any help would be greatly appreciated. Note that this is a personal project and is not based on homework in any way.


Super Moderator
Staff member
Oct 6, 2005
The labels on the diagram are difficult to read because the current forum software doesn't handle images with large dimensions very well. Hosting that image at instead will provide better results. :cool: