  Tensegrity robots are a class of compliant robots that have many desirable
traits when designing mass efficient systems that must interact with uncertain
environments. Various promising control approaches have been proposed for
tensegrity systems in simulation. Unfortunately, state estimation methods for
tensegrity robots have not yet been thoroughly studied.
  In this paper, we present the design and evaluation of a state estimator for
tensegrity robots. This state estimator will enable existing and future control
algorithms to transfer from simulation to hardware. Our approach is based on
the unscented Kalman filter (UKF) and combines inertial measurements, ultra
wideband time-of-flight ranging measurements, and actuator state information.
  We evaluate the effectiveness of our method on the SUPERball, a tensegrity
based planetary exploration robotic prototype. In particular, we conduct tests
for evaluating both the robot's success in estimating global position in
relation to fixed ranging base stations during rolling maneuvers as well as
local behavior due to small-amplitude deformations induced by cable actuation.
