Considering Slip-Track for Energy-Efficient Paths of Skid-Steer Rovers
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Considering Slip-Track for Energy-Efficient Paths of Skid-Steer Rovers Meysam Effati 1
&
Jean-Sebastien Fiset 1 & Krzysztof Skonieczny 1
Received: 11 July 2019 / Accepted: 9 February 2020 # Springer Nature B.V. 2020
Abstract Skid-steer rovers consume a lot more power in point turns compared to straight line motion. As energy is the integral of power over time, the turning radius should be considered explicitly for this type of rover. Lower instantaneous power consumption for wider arcs must be traded off against shorter traversal distance for tighter arcs by evaluating the total energy consumed when following different paths. This research seeks to find the most energy-efficient path from among Circular arc - Line - Circular arc (CLC) paths, a generalization of Point turn - Line - Point turn (PLP) paths which are the simplest path to execute for a skid-steer rover traversing between general start and end poses. The optimally energy-efficient CLC path on hard ground is found to have circular arcs of radius R′, the turning radius at which a skid-steer rover’s inner wheels are not commanded to turn. The radius corresponds to exactly half the rover’s slip-track. Theoretical, numerical, and experimental evidenceis presented to support this result. Further, important features of the R′ turning radius are explored. Keywords Energy-efficient paths . Skid-steer rovers . Optimization . Power modeling
1 Introduction Skid-steering is a method of steering where four (or more) wheels are not themselves steered, but different velocities are commanded for the left and right wheels in order to maneuver a vehicle. Due to their mechanical simplicity, maneuverability and robustness, skid-steer rovers are widely used for excavation and loading, planetary exploration [1, 2] and other field robotics applications. Energy-efficient navigation is an important aspect of any of these applications, especially when autonomously planning paths in power-starved environments. However, the power consumption for skid-steer rovers can be high, and also highly variable, compared to other steering
* Meysam Effati [email protected]
mechanisms1 due to the torque required to overcome lateral motion resistance while skidding in a turn. A key challenge of skid-steer mobility is thus the power and energy consumption of this steering configuration. Shamah et al. [3] show that during a maneuver the power consumption of a skid-steer rover is generally inversely related to its turning radius, with lowest power consumption during straight line driving and highest during tight turns. For point turns, 2 skid steering can require over twice the power of explicit steering [3]. The difference between the two steering modes drops away with increasing turning radius. Thus, the shortest distance path, which is a Point turn - Line - Point turn (PLP) path, may not be the lowest-energy path. In fact, we show this to be the case. Studying energy efficiency of skid-steer rovers with respect to their turning radii provides insights that are useful for path plan
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