When two linked bars are nearly parallel their connecting joint can easily flip orientations and cause the linkage to lock. This phenomena is known as a "Dead Point". Here's an example:
The below right picture is near the Dead Point, where two bars highlighted in red are nearly parallel:
Due to the force on the foot, the joint can "flip" as shown below, which causes the linkage to lock::
Linkages need to prevent joints from ‘flipping' at these Dead Points. Below are two methods I've used to prevent joints from flipping in my LEGO builds.
This solution for my Klann Ver 1 simply blocked the joint from flipping by the addition of a red LEGO beam:
My Strider build encounters the same problem as shown below:
This solution for my Strider build uses an additional linkage on the inside of the joint that allows the joint to bend toward the robot, but prevents bending away from the robot:
Welcome to DIYWalkers! My name is Ben Vagle, I'm 17 years old and I've been building mechanical walkers for the past 4 years, at both LEGO-scale, and SUV-scale. I started this blog to share what I've learned, and to collaborate with you. Let's see if we can take walkers to the next level!