Dynamic modeling of a heavy-duty skid-steer mobile robot
Puolakka, Lassi (2025)
2025
Automaatiotekniikan DI-ohjelma - Master's Programme in Automation Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2025-03-24
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202503242986
https://urn.fi/URN:NBN:fi:tuni-202503242986
Tiivistelmä
The trend towards autonomy in heavy-duty mobile work machines used in e.g. construction, forestry, and mining has been significant in recent years. Precise driving is an important aspect of the autonomous operation of these machines. To ensure accurate path-following control, a model-based control architecture is often the choice. For passenger vehicles, kinematic models are usually valid up to a certain velocity. However, the forces and torques in heavy-duty off-road vehicles are significantly higher already at low speeds, leaving no option but to use dynamic models to obtain sufficient accuracy.
This thesis aimed to develop a dynamic model concerning the driving aspects of a heavy-duty skid-steer mobile robot. The goal was to develop a model that could be used in, for example, model-based path-following control. The starting point was the analytic support force calculation and the Magic Formula (MF) tire model with a reduced number of parameters developed previously at the research group.
The tire support force calculation was improved by allowing the center of mass (COM) location of the vehicle to change with respect to the wheels due to the orientation of the suspension. Also, the suspension cylinder forces were projected to tire support forces. The calculation of the rolling resistance moment was added to the MF model, which determines the torques of the wheels at constant-speed operation and cannot therefore be ignored. The components of the hydrostatic transmission (HST) were modeled using steady-state equations. The model also included the pressure dynamics in the hoses. The results from the tire forces and torques were combined into the wheel rotational dynamics to obtain a relationship between the torque from the HST and the tire force and torque from the MF model. In addition, the validity of the model needed to be tested for a whole new kind of driving structure, the skid-steer. The theory for modeling six-degrees-of-freedom (DoF) vehicle dynamics was presented but could not be validated at this stage due to poor accuracy.
The results proved good accuracy during pure longitudinal motion and reasonable accuracy on a curved trajectory. The experimental and simulated results from the Simscape Multibody model were compared for the trajectory and velocities of the vehicle. The analytic torques and angular speeds were validated with experimental data simultaneously. The results also presented the validity of the tire support force on uneven terrain. Overall, the dynamic vehicle model developed in the thesis could be used in designing model-based controls that improve the driving performance of heavy-duty mobile robots.
This thesis aimed to develop a dynamic model concerning the driving aspects of a heavy-duty skid-steer mobile robot. The goal was to develop a model that could be used in, for example, model-based path-following control. The starting point was the analytic support force calculation and the Magic Formula (MF) tire model with a reduced number of parameters developed previously at the research group.
The tire support force calculation was improved by allowing the center of mass (COM) location of the vehicle to change with respect to the wheels due to the orientation of the suspension. Also, the suspension cylinder forces were projected to tire support forces. The calculation of the rolling resistance moment was added to the MF model, which determines the torques of the wheels at constant-speed operation and cannot therefore be ignored. The components of the hydrostatic transmission (HST) were modeled using steady-state equations. The model also included the pressure dynamics in the hoses. The results from the tire forces and torques were combined into the wheel rotational dynamics to obtain a relationship between the torque from the HST and the tire force and torque from the MF model. In addition, the validity of the model needed to be tested for a whole new kind of driving structure, the skid-steer. The theory for modeling six-degrees-of-freedom (DoF) vehicle dynamics was presented but could not be validated at this stage due to poor accuracy.
The results proved good accuracy during pure longitudinal motion and reasonable accuracy on a curved trajectory. The experimental and simulated results from the Simscape Multibody model were compared for the trajectory and velocities of the vehicle. The analytic torques and angular speeds were validated with experimental data simultaneously. The results also presented the validity of the tire support force on uneven terrain. Overall, the dynamic vehicle model developed in the thesis could be used in designing model-based controls that improve the driving performance of heavy-duty mobile robots.