Results 2010–2013
- Better Contact Model:
Morteza and Roy developed a new nonlinear model of compliant contact that
reproduces published experimental measurements of contact behaviour between
solids ranging from cork to cast iron more accurately than any previous
model. See publications 1, 5 and 6.
- Ability to Balance:
Roy invented a new quantitative measure of a robot's ability to balance,
called velocity gain, which can be used to help design new robots
(like Skippy), analyse existing ones, and choose good balancing
behaviours. See publications 3, 9 and 13.
- Balance Control (2D):
Morteza developed a new balance control system that was as good as the best
published balance control systems. He implemented it on planar
inverted double pendulums and demonstrated good balancing behaviour on both
sharp points and rolling contacts. The new controller makes the robot
track commanded motion trajectories while simultaneously maintaining the
robot's balance, both tasks being performed by a single actuator. See
publications 2, 6 and 12.
- Single Hops (2D):
Morteza demonstrated inverted double pendulums making single hops to a
specified landing point, the motion beginning and ending in a balanced
configuration. Specifically, the robot leans forward, crouches down,
launches itself into the air, controls its foot motion during flight, lands
on a specified spot, recovers its balance, and finishes in an upright
position. All aspects of the motion were performed using Morteza's
balance controller, which demonstrates just how versatile it is. See
publications 4 and 6, and this video.
- Balancing in 3D—Bend Swivel Control:
Roy invented, and Morteza implemented, a new strategy for balancing in 3D,
in which the task is decomposed into two subtasks: balancing in the robot's
saggital plane (bend control) and keeping the plane vertical
(swivel control). The swivel controller also rotates the plane,
so that the robot can face in any desired direction. Morteza's
controller works well, but there is room for improvement because swivelling
interferes with bending due to gyroscopic forces. See publications 6
and 8, and this video. The robot in
the video is following a trajectory that specifies the angle between the
upper and lower links (the bend angle) and the orientation of the saggital
plane (the yaw angle, or heading) while simultaneously maintaining the
robot's balance in 3D; and it is doing all this with only two actuators.
Results 2014–2018
- Ring Screw Mechanism:
It became apparent at an early early stage that the speed limit on the ball
screw would be the limiting factor on Skippy's performance. This
prompted Roy to invent a new mechanism, called
the ring screw mechanism, which
performs the same function as a ball screw but at higher speeds. This
mechanism has now been patented; and a Masters student called Elco Heijmink
tested a prototype at speeds of up to 16,000rpm and mesured efficiencies (at
lower speeds) of up to 91%.
- New Balance Controller (2D):
Roy has invented a new planar balance controller, inspired by Morteza's
controller, which has similar performance to Morteza's controller but is
simpler and more easily applied to general planar mechanisms. The key
step was to study the physics of balancing first, and then design a
controller that controls balancing behaviour in an abstract sense, thereby
exploiting the fact that the physics of balancing is the same for all planar
mechanisms. See publications 10 and 13 and talk 1.
- Leaning in Anticipation (2D):
Roy discovered a new and very simple way to make a robot lean in
anticipation of the balance disturbances expected to be caused by the
robot's immediate future motions. It involves passing a preview of the
motion command signal through a simple first-order low-pass filter
running backwards in time, and feeding the output of the filter to the
balance controller. This simple technique improves the speed, accuracy
and robustness of the controller to such a great extent that it is now good
enough for Skippy. (So the next step will be to try and replicate this
level of performance in 3D.) See publication 13.
- Experimental Demonstration of Balancing:
Antony and Roodra implemented and demonstrated the simplest case of Roy's
new balance controller on balancing machine called Tippy, configured as a
reaction-wheel pendulum. We found that Tippy was much too wobbly to
reach the bandwidth we were aiming for, and had to be clamped in a specially
made stiffening brace, which raised the performance to an acceptable
level. We also had some trouble with the servo control of the
harmonic drive around zero velocity. Nevertheless, the balance
controller worked very well. See publication 15
and this video.