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Adams/Car Tutorial

Modifying Suspension Hardpoints

Overview

In ADAMS/Car hardpoints are the building blocks for larger components. The hardpoints are

essentially the joint locations for the parts of the vehicle. In ADAMS/Car you will move

suspension hardpoints to change suspension kinematics, steering hardpoints to change steering

characteristics, etc. For example, you can move the outer steering tierod connection to the

upright to adjust Ackermann steering. When you move a hardpoint, ADAMS/Car moves the

joint location to the position you specify. The actual connections at the hardpoints are modeled

as ideal joints with specified degrees of freedom or bushings with 6 degrees of freedom and joint

stiffnesses.

The FSAE and Mini-Baja frames have no role in defining hardpoint locations. Hardpoints

mounted to the frame are all connected to a rigid chassis. The image of the frame has no

structural role in ADAMS/Car.

Common abbreviations found while modifying the suspension are found below.

hp[lr] hardpoint left or right

arb anti roll bar

lca lower control arm

prod push rod

uca upper control arm

Control Arm Hardpoints

The suspension control arm geometry defines suspension properties such as roll center, motion

ratio and camber profile. With ADAMS/Car you can adjust the control arm geometry by

adjusting hardpoints and then simulate wheel travel to determine the kinematics for the new

geometry. The FSAE model has independent suspensions front and rear. The Mini-Baja model

has independent front suspension and an independent or rear swing arm suspension. To modify

the control arm of an open suspension subsystem click Adjust>Hardpoint>Table and the

Hardpoint Modification Table will appear.

Warning: Remember to change your working directory before you begin this lesson. If you do not,

Adams may not work correctly. Also remember to move everything you wish to keep from the working

directory before you log off. See the Opening Files tutorial for more information.

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Below are the hardpoint tables for the FSAE and Mini-Baja front suspensions with the upper and

lower control arm hardpoints highlighted.

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Mini-Baja Swing Arm

The swing arm found on the Mini-Baja can not be simulated by its self. A full vehicle assembly

must be opened to simulate swing arm motion.

Pushrod, Bellcrank & Shock Hardpoints (FSAE)

When modifying the bell crank placement on the FSAE model you must enter the position of the

joint connection to the chassis (hpl_bellcrank_pivot) and a point to define the rotation axis

(hpl_bellcrank_pivot_orient). The other points defining the bell crank are the pushrod, anti-roll

bar and shock connections (hpl_prod_to bellcrank and hpl_shock_to_bellcrank). The

connection of the pushrod to the upright is hpl_prod_outer. The shock connection to the chassis

is hpl_shock_to_chassis. If you wish to design a pullrod suspension converting the pushrod

system is simply a matter of changing the geometry of the components. The image of the

bellcrank is defined by the positions of the bellcrank pivot, pushrod location, and anti-roll bar.

When these connections move the image of the bellcrank will update.

The Mini-Baja has a simpler suspension design and the shocks mount directly to the

control/swingarm and chassis. The shock is modeled with two hardpoints; one to the control

arm or swing arm and one to the chassis.

Anti-Roll Bar Hardpoints (FSAE)

The hardpoints of the anti-roll bar geometry is modified using the fsae_front_arb subsystem with

the exception of the connection to the bell crank (hpl_ arblink_to_bellcrank) which is modified

on the fsae_front_susp subsystem. The anti-roll bar bushing mount (hpl_arb_bushing_mount) is

listed in the fsae_front_susp subsystem but cannot be modified there. You will need to move the

hardpoint hpl_arb_bushing to coincide with the anti-roll bar system to insure the system works

properly. Having hardpoints hpl_arb_bushing and hpl_arb_bend at the same point works well.

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Steering Hardpoints

In the FSAE steering system the steering rack placement is defined by the location of the inner

tierods found on the front suspension subsystem. When the inner tierod positons move the rack

moves with them. The pinion and rack do no have to coincide to work properly. ADAMS uses

input and output communicators to relay the displacement information. The model has two

joints between the steering wheel and pinion, and can be placed with creating an angle between

intermediate shafts.

hpl_arb_bend

hpl_arb_middle

hpl_arb_bushing

hpl_droplink_to_arb

hpl_arblink_to_bellcrank

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The Mini-Baja steering shaft must be straight from the pinion (hps_pinion_pivot) to the steering

wheel center (hps_steering_wheel_center). Between the pinion and steering wheel center are

two intermediate points (hps_intermediate_shaft_forward and

hps_intermediate_shaft_rearward). You will need to move these points to create a straight

steering shaft from the steering wheel to the pinion. The shaft must be straight in order for the

steering to work properly. In the template the pinion and rack are coincident. This does not have

to be the case. You could move the steering rack and inner tierods forward and leave the pinion

Steering intermediate

joints

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and steering shaft in its original position. There does not have to be a visible connection between

the pinion and the rack.

hps_intermediate_shaft_forward

hps_intermediate_shaft_rearward

Pinion and rack are

coincident in template

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Modifying the FSAE Front Suspension

Obtain and save the FSAE template. Open ADAMS/Car and add the database to the session by

clicking Tools>Database Management>Add to Session. Navigate to the location you have

saved the FSAE template to add.

Open the FSAE front suspension assembly by clicking File>Open>Assembly. Navigate to the

FSAE assemblies.tbl folder and select fsae_front_with_steer.

The default units for the FSAE model are millimeter, kilogram, and newtons. Change the units

to inches, pounds mass, and pounds force by going to Settings>Units.

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Click the IPS button at the bottom of the window to change the units. Click OK.

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From the menu select Modify> Adjust> Table.

The Hardpoint Modification Table will appear. Click the arrow in the top center to see the

subsystems that have hardpoints that you can adjust. Notice the front suspension, steering, and

anti-roll bar subsystems make up this assembly and have hardpoints you can modify. The origin

for the assembly is at an arbitrary location. Placement of the hardpoints will need to be made

relative to other hardpoints in the suspension.

Subsystems

Hardpoints to show

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At the bottom left of the Hardpoint Modification Table you have the option to view the left,

right, or both sides of the vehicle. If left or right is selected then you will be entering changes for

that side of the vehicle but changing both sides symmetrically. To modify the hardpoints for the

front suspension make sure fsae_front_susp is selected and simply enter a new value for the

loc_x, loc_y, or loc_z positions. Then click OK or Apply to make the changes.

Six points determine the control arm geometry at one wheel. For the upper and lower control

arms there are outer, front and rear hardpoint locations. The names for theses hardpoints are

hpl_lca_front, hpl_lca_outer, hpl_lca_rear, hpl_uca_front, hpl_uca_outer, and hpl_uca_rear.

New position values can be entered into the table.

Looking at the model space, notice the coordinate axes at the bottom left-hand corner of the

window has the positive x-direction towards the rear and the positive y-direction towards the

right from the driver’s perspective. Obtain a front view of the assembly by right clicking on the

workspace and selecting Front. With the Hardpoint Modification Table open change the loc_y

values for hpl_uca_front and hpl_uca_rear from -7.876 to -12 and click Apply. Notice that the

inboard upper control arm connections have been moved outward from the center of the vehicle

thus shortening them.

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Now adjust the outboard lower control arm connection changing both the kingpin and caster

angles. Reduce the kingpin angle by making the loc_y value for hpl_lca_outer -26 and observe

the change in kingpin. Now obtain a side view of the assembly by holding “r” + left mouse

button to rotate. Change the loc_x position for hpl_lca_outer to -23, click Apply and observe the

increase in caster angle.

The pushrod, bellcrank, and shock parts in the template are not planar at the design position and

the pivot orient is not perpendicular to the face of the bellcrank. Make the following changes to

the system to create a planar system with a perpendicular pivot orient. When done making

changes click Apply. Rotate the system to confirm the pushrod, bellcrank, and shock are planar.

hpl_prod_outer (-18.2, 27.1, 0.1), hpl_prod_to_bellcrank (-17.2, -9.9, 17.4),

hpl_ bellcrank_pivot (-14.2, -10, 17.1), hpl_bellcrank_pivot_orient (-14.6, -2.9, 10.1),

hpl_shock_to_bellcrank(-15.2, -8.3, 18.9), hpl_shock_to_chassis (-5.2, -8, -18.7),

hpl_arblink_to_bellcrank( -15.2,-8.3,-18.9).

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Adjust the steering tierod by making the following modifications. Click Apply and notice that the

steering rack moves with the placement of the inner tierod.

hpl_tierod_inner (-14, -12, 3), hpl_tierod_outer (-18,-23, 3)

Move the wheel center to the following position. Click Apply and observe the change in wheel

position.

hpl_wheel_center (-21.5 -27.6, 6)

Select the anti-roll bar subsystem in the Hardpoint Modification Table. View the anti-rollbar

subsystem be clicking View>Subsytem, and selecting fsae_front_arb. To insure the system

works properly you will need to move the hardpoint hpl_arb_bushing to coincide with the anti-

roll bar system. Move the anti-roll bar to the following positions and click Apply.

hpl_arb_bend (-20.2, -8.3, 23), hpl_arb_bushing (-20.2, -8, 23),

hpl_arb_middle (-20.2, 0, 23), hpl_droplink_to_arb(-20.2,-8.3,-18.9)

Additional Information:

There are a few points in the Mini-Baja suspensions that are not used directly for the suspension.

The front suspension has drive shaft and subframe mounts. The drive shaft is used in the rear

suspension.

Mini-Baja front suspension

These

hardpoints

are not used

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Mini-Baja rear suspension

These

hardpoints

are not

used

Warning: Remember to change your working directory before you begin this lesson. If you do not,

Adams may not work correctly. Also remember to move everything you wish to keep from the working

directory before you log off. See the Opening Files tutorial for more information.