Post by Wade Vagle
If you are looking for ideas on how to create highly functional mechanical walkers, Professor Joseph Shigley's 1960 feasibility study for the army is a great resource. It combines engineering rigor and sound reasoning to illuminate many of the challenges, and potential capabilities of mechanical walkers.
To meet the requirements of walking tanks, Shigley sought a mechanism that could:
To meet the rugged terrain and speed requirements of tanks, much of Shigley's study focused on the foot-paths of mechanisms. Below is Shigley's diagram of foot-path types, with type E representing his ideal type for rugged terrain and fast speeds.
Shigley's study helped us to develop Strider's mechanism
In his feasibility study, Shigley advised investigating 4-bar linkages as a first step, and referenced Hrones-Nelson's atlas of hundreds of 4-bar linkage coupler curves, which must have been a vital resource for mechanical engineers in the days before personal computers. Below is about the best 4-bar linkage configuration Dr. Shigley found, but it doesn't step high enough for rugged terrain.
Shigley showed how the mechanism could be improved by allowing a joint to slide along a cam groove, but we wanted a mechanism that could be prototyped in LEGO. So, instead we experimented with pairing two 4-bar linkages into a combined 10-bar linkage with front and back legs, such that the rear leg lifted the front foot and vice versa. This increased the step-height significantly, as shown below.
You may have noticed that Strider shares a characteristic with TrotBot - we designed both mechanisms' "hamstrings" to lift high to increase step-height for rugged terrain performance:
Below is this simulated version prototyped in LEGO. To replicate a wheel, the speed of the feet when in contact with the ground should be constant. Strider has nearly constant foot-speed, resulting in a very efficient gait, and is the only mechanism that we've tested which can walk with a 1:1 gear ratio without the LEGO motors stalling:
Strider's linkage dimensions can be found here, and other configurations of Strider can be found here where you can also create your own customized Strider linkage.
Below is Prof Shigley's feasibility study, a 1960 Popular Science article discussing it, and the Hrones Nelson Atlas of four bar linkage coupler curves.
Welcome to DIYWalkers! My name is Ben Vagle, I'm 18 years old and I've been building mechanical walkers since I was 11. 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!