Hex 565

Timing Diagram
Timing Diagram

HEX565 is a six legged pneumatic walker, also called a hexapod. Each leg has two pistons: one to lift and drop the leg, and the other to move the leg forward and back. HEX565 always has at least 5 feet on the ground at a time. It starts with all 6 feet back and on the ground. It then lifts the front right leg, moves it forward and the puts the foot down. It does the same lift, forward drop process with the front left leg, followed by the mid right, mid left, back right, and finally back left leg. Once all the legs are forward, they all push back at the same time. Once all the legs are back, the one leg at a time lift, forward back process repeats.
The timing diagram shows a drawing that describes how the pistons change shape to control the walking sequence. On the left side of the diagram you see the letters A through M. The lines to the right of the letters represent the piston's timing of changing shape. Each piston starts out contracted, and then expands and then contracts. Horizontal lines means the piston's shape is not changing. Diagonal lines starting low and moving up right indicate a piston is expanding. Diagonals starting high and move down right indicate a piston is contracting. Pistons A and B control the front right leg, C and D control the front left leg. These piston pairs continue for the mid right and left legs, and the back right and left leg.
For each of the piston pairs in a leg, the first piston is the up/down piston, and the second piston is the forward backward piston.
Reading the timing diagram from left to right you can see that piston A changes shape first, lifting the front right leg. Next, piston B changes shape, driving the front right leg forward, then piston A changes shape again, putting the foot back down. Next the front left leg (using pistons C and D) do the same thing. This pattern repeats through the rest of the legs.
I always try to have all the pistons in a design play the role of muscles that change the shape of the LEGO model, as well as play a role as part of the timing control. Each leg's up/down and forward/back pistons are both muscle and timing pistons. But because of the nature of the leg movement, I needed one timing only piston that comes into play after all the legs have individually moved forward. It makes all the of the legs move back at the same time. This timing only piston is piston M in the timing diagram.
In the timing diagram, the arced arrows show the relationships between the pistons. An arced arrow indicates that a piston change causes another piston to change. The arrow head identifies the piston being changed. The arrow tail identifies the pistons that is causing the change. Also in the timing diagram, vertical bars identify things that have to all complete before we can continue through the diagram. You can see this at the end of the diagram, where we cannot start lifting the front right leg, until all the legs have moved back.
Each piston is mechanically hooked to switches, so that the switches flip back and forth when the pistons expand and contract. The arched arrows in the timing diagram map to outputs of switches going into the inputs of pistons. The vertical bars identify that outputs of switches have to go to input of other switches. This leads to the schematic diagram <schematic.jpg> showing the pistons and switches and how they are connected together using pneumatic hoses. The squares with letters in them represent pistons. The squares with three dots in them represent switches. The curved lines represent hoses.
Sadly I do not have a movie of this walking. I designed this model in 2005, and videos were not so easy to record and save back then like they are today.