Path Follower Example
A recognized problem in the use of either simulation models or full-scale testing in relation to investigation of automobile dynamics is the manner of guiding and controlling the vehicle. For research we performed for FHWA with the Highway vehicle Object Simulation Model (HVSOM) (see HVOSM Curve Study paper, 3 megs) we created an driver model and wagon tongue steer contol to permit path following through various roadway geometrics. The same path follower has been implemented in the msmac program
The Path Follower Example is an illustration of the path follower working with either vehicle 1 or vehicle 2. There are 2 smac input files in the project,
o Demo_Path_Follower_Sample.si5,
o which uses the path follower with vehicle number 1
o Demo_Path_Follower_Sample_veh2.si5,
o which uses the path follower with vehicle number 2
In each of the samples, a vehicle follows a curved path which culminates in a circular path. The simulation runs are 50 seconds long and include paths which the vehicle can not follow but which it does ultimately follow after running wide. In on of the examples, the vehicle has a 0.1 g-unit acceleration during the circular path for which it will find it’s critical speed to maintain the path.
The path follower inputs are on cards 403-405.
o The main difference between the two runs is the 1st field of card 402 is the designation of the vehicle number.
o Please refer to the msmac input file for a description of the inputs to the path follower and wagon tongue path follower.
Driver Model TIPS and NOTES:
o When setting up a path, run a simulation for 0 seconds! Then as you make change and click run, the path will be displayed on you scene diagram or whatever additional background you have. The path specification includes distance along path and radius, and a judicious choice of changes can affect the transitions. The software can spiral between different radii, or have abrupt changed in the path radius.
o Be sure to start the vehicle on or near the path.
o The initial path location and heading are specified on input card 403
o The path is specified on input card(s) 404, where pairs of radius and distance along path are specified from which a path is generated.
o You can also view the generated path in the View menu, item 1, Input Echo, which lists the path curvature information.
o When setting up a path, run a simulation for 0 seconds!
o Since the path is automatically displayed in the graphics and animation files
o The path display can be turned off by selecting the Options On/Off button in the pop-up dialog, which is opened from graphics or animation by electing the right mouse button.
o The wagon tongue steer samples an extension of the longitudinal axis of the vehicle
o probe length, card 405, field 3
o The path follower samples at specific intervals of time, and times between samples
o initial probe time, input card 405, field 1
o time between samples, input card 405, field 2
o At the end of that extension the distance to the desired path is determined
o an acceptable error can be specified on input card 405, field 4.
o The steering gain and damping are used to calculate a corrective steer response based on the error from desired path.
o Steering gain, input card 405, field 7
o Steering Damping, input card 405, field 8
o You can also impose limits the vehicle acceleration and steering velocity
o Maximum acceleration, input card 405, field 5, which if exceeded will limit steering
o Maximum steering velocity, input card 405, field 6, which limits the change rate of the steer
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