For vehicle using tire model 0, The tractive forces are applied as longitudinal force at the spindle. This is due to the simplicity of this tire model. To account for gyroscopic effects and proper graphics in the simulation, it is important to maintain proper wheel rotational velocities. In order to keep the wheel rotational velocities consistent with the longitudinal velocity of the ground under the wheel, a torque is applied to the wheel parts. This torque is controlled via a user routine which measures actual and desired rotational velocity of the wheel parts. The torques are applied by using a custom user written ACTIONONLY SFORCE:
SFORCE/id, I=toram, J=toram, ROTATION, ACTIONONLY,
, FUN = USER (1100,wnum,trad,maxt,maxve,wcgm )
where:
toram | = | MARKER located at the wheel center with the z axis pointed along the axis of positive rotation (right-hand rule) |
wnum | = | tire number 1 = left front 2 = right front ... n = (up to 40 tires) |
trad | = | tire free rolling radius (mm) |
maxt | = | maximum allowable torque (N-mm) |
maxve | = | maximum velocity error (mph) |
wcgm | = | wheel CG MARKER number |
An example of an Adams vehicle file with wheel torques is:
M/2114, QP=1528, -739.6, 517.4, EU= 0, 90, 0 LEFT FRONT WHEEL
SFORCE/0003, I=2114, J=2114, ROT, ACTION, LEFT FRONT WHEEL
, FU = USER( 1100, 1, 334.0, 650.0, 1.0, 2100 )
M/2215, QP=1528, 739.6, 517.4, EU= 0, 90, 0 RIGHT FRONT WHEEL
SFORCE/0004, I=2215, J=2215, ROT, ACTION, RIGHT FRONT WHEEL
, FU = USER( 1100, 2, 334.0, 650.0, 1.0, 2200 )
M/6753, QP=4277, -739.6, 511.0, EU= 0, 90, 0 LEFT REAR WHEEL
SFORCE/1001, I=6753, J=6753, ROT, ACTION, LEFT REAR WHEEL
, FU = USER( 1100, 3, 334.0, 650.0, 1.0, 6700 )
M/6853, QP=1528, 739.6, 511.0, EU= 0, 90, 0 RIGHT REAR WHEEL
SFORCE/1002, I=6853, J=6853, ROT, ACTION, RIGHT REAR WHEEL
, FU = USER( 1100, 4, 334.0, 650.0, 1.0, 6800 )
The magnitude of the torque is dependent on the velocity error, delta-omega, which is calculated as follows:
delta_omega = omega_desired - omega_actual
omega_desired = vel_long_ground / load_tire_rad
omega_actual = wheel_rotational_velocity {dot} wheel_axis
load_tire_rad = abs ( wheel_center_displacement {dot} radial_dir)
radial_dir = long_direction {cross} wheel_rotational_axis
long_direction = axis_of_wheel {cross} global_Z_direction
vel_long_ground = wheel_translational_velocity {dot} long_direction
where {cross} and {dot} are the cross and dot products of two vectors respectively.