This doctoral thesis extends analytical terramechanic modelling for small
lightweight mobile robots operating on sandy soil. Previous terramechanic
models were designed to capture and predict the mean values of the forces
and sinkage that a wheel may experience. However, these models do not
capture the fluctuations in the forces and sinkage that were observed in
experimental data.
The model developed through the course of this research enhances existing
terramechanic models by proposing and validating a new pressure-sinkage
relationship. The resulting two-dimensional model was validated with a
unique high fidelity single-wheel testbed (SWTB) which was installed on a
Blohm Planomat 408 computer-numerically controlled creepfeed grinding
machine. The new SWTB translates the terrain in the horizontal direction
while the drivetrain and wheel support systems are constrained in the
horizontal direction but allowed to freely move in the vertical direction.
The design of the SWTB allowed for a counterbalance to be installed and, as
a result, low normal loads could be examined. The design also took advantage
of the grinding machine's high load capacity and precise velocity control.
Experiments were carried out with the new SWTB and predictable repeating
ridges were found in the track of a smooth rigid wheel operating in sandy
soil. To ensure that these ridges were not an artifact of the new SWTB a
mobile robot was used to validate the SWTB findings, which it did. The new
SWTB is a viable method for investigating fundamental terramechanic issues.
A series of experiments at different slip ratios and normal loads were
carried out on the SWTB to validate the new pressure-sinkage relationship
which explicitly captures and predicts the oscillations about the mean
values for the forces and sinkage values for both a smooth wheel and a wheel
with grousers. The new pressure-sinkage relationship adds two new
dimensionless empirical factors to the well known pressure-sinkage
relationship for a rigid wheel. The first new factor accounts for changes in
the local density of the terrain around the wheel and the second factor
accounts for the effects grousers have on the forces and sinkage.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/14233 |
| Date | 08 August 2011 |
| Creators | Irani, Rishad |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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