Introduction and Background
Even with the advent of faster computers and efforts to improve artificial intelligence, the ability of humans to make decisions and adapt to new environments still far exceed those of any machines built to date. As a result, there are still strong advantages for the construction of human-machine systems over purely autonomous systems. These devices utilize the intelligence and adaptive abilities of the human operator, while using the machine to provide increased strength, speed, and endurance.
The goal of this project was to create a simple and rugged device of this nature in the form of a power assisted pogo stick, which is capable of maintaining a constant bounce height of several inches, without requiring any jumping effort by the user. The knowledge gained from the design and control of this device could then provide the foundation for a running exoskeleton robot consisting of a similar mass-spring-actuator system for each leg.
A pneumatic cylinder was chosen as the actuator for the pogo stick. There has been much research on electric linear actuators and jumping machines,
but the power density of batteries is dismally low and the exoskeleton requires a high energy density. Hydraulics are incompressible and would not allow a pneumatic spring effect in the actuator. Hydraulics are also bulky and messy.
There was some question whether to put the actuator in series or parallel with the spring on the pogo. Most of the technical papers to date use electric or hydraulic actuators in series with a spring, and the control of such devices is well documented. The Pogomatic uses its actuator in parallel since this produces a much smaller loading of the actuator while bouncing. If the actuator were in series with the spring, it would see the entire load of the rider. The parallel arrangement lets the spring take the majority of the load while the actuator sees only a fraction.