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 of what Klann Ver 1 experienced, since it used a configuration of the linkage where the "knee" joint came close to being straight :
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 a few ideas to prevent joints from flipping in LEGO builds.
This solution for Klann Ver 1 simply blocked the joint from flipping by the addition of a 2-hole red LEGO beam:
As shown below, Strandbeest's knee joint can also flip:
Strider's knee joint also has a dead point that needs to be managed. Strider Ver 3 uses a blue LEGO pin to prevent flipping of the knee joint. However, as you can see in the video below, when 10 pounds are added to Strider, the blue pins bend, causing the robot to drop in height and the gait to become bumpy. To better handle loads, a stronger blocking option is needed for Strider.
Strider Ver 2 also has a dead point that needs to be managed:
Below is another possible solution that uses an additional linkage on the inside of the joint that allows the knee joint to bend toward the robot, but prevents bending away from the robot.
Below is another variation of Strider where Dead Point flipping is blocked by a 2x4 L-shaped part:
Welcome to DIYWalkers! I'm Ben Vagle, and I've been building mechanical walkers since I was 11 years old, both big and small. 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!