IHMC Robotics Lab

First prototype Fast Runner with segmented leg design, knee-ankle coupling, dual state stance control locking knee, pelvis with elastics configured so that leg swings are dually sensitive to both horizontal and vertical spinal oscillations. Horizontal oscillations swing the legs in opposite phase. Vertical oscillations swing the legs together in unison.

In this configuration, the intent is to demonstrate that throttle modulation can be achieved by moving the desired driving ellipse trajectory forward or backward relative to the main body, which remains suspended vertically beneath the MetaCentric Hub.

The blue GRF direction extensions graphically show convergence near the MetaCentric Hub when seen from the side - but here the intent is to see the lateral components. Strict planarization requires extremely high lateral GRF components - so nature is deliberately NOT strictly planar - with good reason.

In this video we really get a visual sense of how much the ground actually speeds beneath the robot with each flying stride - and a better sense of the lateral GRF modulations as they occur. Lateral GRF excursions were further minimized by raking the hub axes rearward for three degrees of toe divergence - again similar to the femur geometry.

On Thursday May 22, 2014 in Pensacola, we made a successful launch at 1:52 PM, of the large HexRunner, and it went to world record speed for a legged robot, demonstrating stability, and the concept that stability at these speeds is geometric, not a matter of traditional control methods.

In this FastRunner leg simulation, the control point is attached to an IlioTibial linkage, which pivots about a point above and slightly behind the hip. When the linkage locks at maximum length, the resulting foot path is constrained by this geometry to follow a circle centered correspondingly above the robot - at or slightly forward of the MetaCentric GRF Convergence Hub, based on throttle setting.

By slowly moving the IlioTibial pivot point rearward, we advance throttle, and the foot path contours are inclined to slope upward, causing the robot to lean forward and accelerate - or correspondingly accommodate an uphill incline in the terrain. Moving the point forward reverses throttle to decelerate or accommodate downhill slopes.

Video demonstrating the inherent stability of the HexRunner as it runs over a variety of terrains - slopes, rolling hills, gravel - easily clearing obstacles up to one quarter spoke length. This performance dynamically matches the extreme performance of running birds - observed to easily clear obstacles up to half the leg height - with running speed undiminished.

Shown here is a video of the running ostrich from the side at slow to intermediate running speeds. Stability of posture and speed, and stability in phase space, are both achievable in our elastic segmented leg design, even at these slow to intermediate speeds, when the mechanism is tuned for nonlinear autoresonance as a Warminski class oscillator.

Running the Hydraulic Test Bed Planar FastRunner through its paces at less than half speed with only Fourier 1 wave driving.

Initial runs with the HexRunner were actually overspeeded for the number of spokes - recall that in nature the idea, as our current research has shown, is to have maximum ground and obstacle clearance for every given speed - with the number of spokes being the fewest possible - just on the verge of instability.

A major landmark in fast running simulation - without sensory feedback or terrain information whatsoever, we achieved highly robust stable running over this rough terrain with obstacles up to half as high as the main body - matching the extreme performance observed in nature with birds running on treadmills [Monica Daly] - but now in a reciprocating context.

This slow motion video shows the HexRunner exhibiting yaw and roll oscillations of the main body with each step while maintaining essentially steady throttle angle forward. [See VIDEO 03 for yaw and pitch oscillations in the reciprocating context]

In this planar simulation - we are approaching the natural limit in fast running as observed in the running ostrich - at these speeds the correct number of spokes is only two - and the performance is surprisingly stable and robust - shown here slowing down to the point of instability and vaulting

At 20 mph the hex configuration has too many spokes for its speed - note in this video the dramatic increase in ground clearance for the same forward ground speed. At speeds over 20 mph we are nearing the range where running on only two spokes would be appropriate and feasible.

For all tasks, we generate waves through the robot geometry. In this demonstration the task is to move the end effector by a given distance and stop there with no residual motions. The technique is to send a wave of amplitude half of the intended displacement.

Here an elastic pantograph is driven to phase space stable autoresonance with characteristic period two oscillations over a range of speeds. The shape size and frequency of the period two oscillation curves respond quickly to changes in throttle setting, immediately reaching stable period two steady state oscillation.

In a typical differential - the slipping tire gets all the power, leaving no power to drive the tire with traction. A similar situation occurs in the reciprocating case. We overcame that problem with this drive that applies power between the traction leg and main body directly.

Simulation shows promise that the planar hydraulic FastRunner robot can complete its full mission - with the addition or modification of the following elements: - Software to NonLinear Spring compensation - Full Fourier driving in software - IlioTibial Linkage, Modulator, Lock - Forward IlioTibial Lift Spring - Fore and aft

In this planar simulation of a two-spoked running robot, the only control performed is maintaining a desired constant velocity between the suspended main body (white) and the spoke assembly. The open-loop dynamics of the robot automatically adjust hopping height in order to maintain stability.

Locking the knee at any position near instantaneously and allowing for free swinging upon release required special development. Our hydraulic FastRunner employed a metal solenoid activated locking system - reliability and metal grinding to powder issues were overcome with this innovative robust elastopolymer based mechanically actuated design - essentially a dual state strap wrench We will use this device to lock the IlioTibial linkage 'knee' as an alternate to locking the kinematic knee directly, in order to augment GRF convergence to MetaCenter.