THE DESIGN OF ATI'S OUTRIGGERS

REPORT NO. 030130

AUTOMOTIVE TESTING, INC.Documentation of Automobile Performance

6 Moores Mill RoadPENNINGTON, NEW JERSEY 08534

AMDG

1

THE DESIGN OF ATI'S OUTRIGGERS

INTRODUCTIONThe basic concept of ATI outriggers was established in 1969, and has not changed since. Asingle outrigger is placed on either side of the vehicle, close to the vehicle center of gravity.Forces are fed into widely-separated strongpoints: the frame or rocker panel at the bottom, andthe roof rail at the top. The lower member is a triangular "control arm", and the upper member isa strut. A cushioning or energy-absorption device is incorporated into the strut to reduce impactloading on the roof rail and the impact shock on the driver.

ADVANTAGES AND DISADVANTAGES OF ATI OUTRIGGERSCompared to front-rear outriggers, the side-mounted outriggers are inherently lighter, becausestresses are tension/compression rather than bending. Their pitch and yaw moments of inertiaare much smaller, and their roll moments of inertia are no greater. Front/rear outriggers usuallyrequire removal of the vehicle bumpers, and for some vehicles the bumpers are structuralmembers: their removal reduces torsional rigidity, which may affect vehicle rollover behavior.Installation time is usually much shorter with the side-mounted outriggers. They can be taken toremote test sites as aircraft luggage, and trackside installation takes only 10-15 minutes.Side-mounted outriggers simplify monitoring outrigger loading, and the driver can better "feel"and can visually observe the "down" outrigger on his side. Strike-down is relatively soft, whichprovides pleasant on-outrigger "ride quality". Many years' experience by several researchgroups have shown side-mounted outriggers to be very reliable.

The only real disadvantage of ATI's side-mounted outriggers is driver entrance/exit, whichexperience has shown to be a minor inconvenience.

FIRST VERSION - 1969The first version, in 1969, was built for rollover testing on Corvair, Falcon and Valiant, andsimilar vehicles. Figures 1-4 show the Corvair set-up. The lower triangular frame was acomplete triangle fabricated with aluminum angle, and was attached to the rocker panel withthree four-inch household door hinges, using "Riv-nut" internally-threaded rivets. The roofattachment was by aluminum angles clamped to the drip rail. Bending moments on the roofattachment were carried across the roof to the clamp assembly on the other side. A steelcastered wheel was attached to the outside of the lower frame. The strut was an aluminum tubeincorporating a production rear-suspension shock absorber. The disadvantage that the driverhad to climb through the window for entry/exit was accepted in the name of simplicity, lightness,and strength.

This outrigger was light and a lot stronger than it looks. The heaviest part was the steel casteredwheel, which was soon replaced by a lighter caster with a small (6x2) pneumatic tire. Theassembly was used in a number of rollover tests in the period 1969-1974, in test programs inNew Jersey, Florida and California. One disadvantage in shipping was the welded-togetherlower control arm which was at one point replaced by a bolted-together unit.

2

VAN VERSION - 1980In 1980 a heavier-duty version was fabricated for testing of VW, Chevrolet, and similar-sizevans. The lower triangle was made from steel tubing, joined with a front-wheel bearing cartridgefrom the recently-introduced Chevrolet Citation as a caster (Figure 5). The rocker or frameattachment was through rod end bearings to welded-up brackets. With this design, all directloads are through pin joints, so all significant loads on the lower control arms and struts aretension-compression, for lowest stress.

Because in testing the vehicle sometimes went off the Princeton University runway into grass,the wheel was from a light airplane, in a heavy-duty aluminum frame. This wheel had adisadvantage besides its weight, in that on strike-down it would violently oscillate for 3-4 cycles.For on-runway use, it was replaced by a block of builder's foam (Figure 6). The foam at 2pounds/cubic foot weighed practically nothing, gave a smooth ride, and left a trail marking thetrajectory, but had to be replaced after one or two tip-ups.The strut was a 24-inch stroke hydraulic cylinder, which allowed adjustment by pumping in oil onone side and air on the other. Maximum loading was recorded with a damped pressure gaugecontaining a "telltale" pointer.

This unit was easily knocked down for shipping, but was strong enough to withstand the "majorthree-wheel lift" shown in Figure 7.

NEW DESIGN - 1981Experience with the van version led immediately to a new "standard" outrigger design, as shownin Figures 8 & 9. The two-tube lower control arm was adopted, along with a slider instead of awheel. The strut was retained from the early version, except that an air cylinder replaced theshock absorber. A more robust upper mount was devised, with quick-release overcenterclamps, to simplify driver entry/exit. When the clamp is released, the assembly could be pulledoff, allowing the door to be opened. The lower control tubes were pinned together at the apex ofthe triangle with a threaded shaft containing a spherical bearing (Figure 10), so that onstrikedown the slider became flat against the road. The slider was band-sawed from aninexpensive slab of low-density polyethylene and screwed to a plywood (later aluminum) discwhich was part of the bearing assembly. The slider was found to have a 0.3 coefficient of frictionon blacktop pavement. The polyethylene disc was 3/4 inch thick for vehicles up to about 3500pounds, and 1 inch for vehicles up to 6000 pounds. These thicknesses allowed 15-20 tip-upsbefore replacement.

The inner ends of the lower control arm tubes were fitted with rod end bearings which attachedto the vehicle frame or rocker panels by a variety of methods. As with the van version, stressesin the lower control arm and strut tubes are tension-compression. The only bending loads are inthe over-roof bar, which must take care of offset between a strut and the force into the roof rail.

When a Volkswagen Beetle was measured with and without outriggers in December 1990 at theNHTSA VRTC IMPD facility, the additions due to outriggers were as follows: weight 70 pounds;moments of inertia 49 lbÛftÛsec2 in roll, 12 lbÛftÛsec2 in pitch, and 74 lbÛftÛsec2 in yaw.

3

PRESENT "STANDARD" OUTRIGGERThe present standard outrigger, for use with vehicles up to about 6000 pounds, is virtuallyunchanged since 1981 (Figures 11 & 12). For lightest weight, the tubes were originally cut tosize for each project, and drilled for the end mounts in a simple jig. These were replaced in 1998with telescoping tubes which are adjustable in 1-inch increments, with permanent end fixtures.The telescoping tubes add weight, but save time in set up. Some additional holes have beendrilled in the roof support for reasons now forgotten, and sponge rubber is used in contact withthe roof rails instead of under-carpet material. A load cell is sometimes used in the strut tomeasure outrigger loads. A pressure transducer is used to set the initial air charge which ispreload before deflection starts, and an O-ring on the cylinder shaft indicates maximum cylinderstroke. A pressure transducer may soon replace the load cell.

INERTIA EFFECTSTesting with and without outriggers has indicated that the roll moment of inertia should not addmore than about 10 percent to that of the vehicle itself. For example, use of the ATI standardoutrigger in ATI's Reversed Steer Protocol testing of a Nissan Pathfinder (Reference 1), isshown in Figure 13A through 13D. The outrigger roll moment of inertia was 10 percent of thevehicle's. The outriggers had little effect, including the effect on roll acceleration, where rollinertia is most important. Figures 14A through 14D show a similar test of a Chevrolet Tracker(Reference 2), where the outrigger's roll moment of inertia was 15 percent of the vehicle's. Theeffect on roll acceleration is considerably more pronounced. The conclusion from several suchcomparisons is that the roll inertia should be less than 10 percent of the vehicle's.

NEW LIGHTWEIGHT OUTRIGGERS - 2002The standard ATI outriggers were designed for robustness and ease of assembly, and somecomponents · for example, the rod ends · are several times larger than required for strength.(Specifications show a surprising amount of weight in rod ends and pins). For these reasons, inanticipation of testing for lighter vehicles in the future, a new set of light outriggers wasdesigned. The new design is identical in concept to the standard, as shown in Figures 15 18,but it is scaled down in metal thickness and in things such as rod end sizes and slider design. Asmall pressure transducer replaces the heavier load cell.

APPLICATION RANGES OF STANDARD AND LIGHT OUTRIGGERSStresses on the Standard outriggers should allow testing of vehicles weighing up to at least6000 pounds. The actual limit is geometric: the vehicle may be physically too big for convenientfitting. The light outriggers are intended for vehicles to about 3500 pounds curb weight. Abovethis the inertia of the standard version would be acceptable, and their installation might be moreconvenient. Weights and inertia moments for the "standard" and "light" outriggers are given inthe appendix.

Because of their geometric similarities, it is possible to "mix and match" most light and standardcomponents, when such mixing is convenient.

4

ATTACHMENT OF LOWER CONTROL ARMSA number of lower control arm attachment devices have been used. The first and simplest,which we will call Type 1, was an under-vehicle cross-tube with clevis ends (Figures 19 & 20).The tubes were fastened to the frame or to angles attached to "lower" the frame with heavy-dutymuffler clamps. This provided a light and sturdy attachment, but could only be used if there wassufficient road clearance under the vehicle.

A second version (Type 2) uses machined plates with holes and slots for adjustment, attachedto the frame (Figure 21 & 22). If crossmembers are needed, they are bolted under the plate andstepped if necessary to drop under the driveshaft and exhaust.

A third version (Type 3) uses machined plates which bolt to the frame or to flat-bottomed rockerpanels (Figure 23). If the rocker has an inclined lower surface, a wedge is required (Figure 24).

A "final solution" (Type 4) is shown in Figures 25 & 18. Made from high strength aluminum witha hardened stainless steel pin, it can be fitted to rocker panels with any degree of curvature.While originally designed for the "light outrigger" it is currently used in almost all applicationsand a larger version will be made if needed.

REFERENCES

1. ATI Test Report No. 100300, Reversed Steer Testing, 1993 Nissan Pathfinder,October 3, 2000. Runs at 2:28:44 and 2:40:18.

2. ATI Test Report No. 072401, Reversed Steer Testing, 2001 Chevrolet Tracker,July 24, 2001, Runs at 0:30:18 and 0:55:08.

5

APPENDIX

WEIGHTS FOR STANDARD OUTRIGGERS, IN POUNDSTubing wall thickness = 0.125 inches

Rod-end bearings = 0.75 inch

Item Number Weighteach

Weight

Roof rail clamp assembly 2 7.9 15.8Roof cross tube 1 6.4 6.4Strut, Driver side 1 10.5 10.5Strut, Passenger side 1 8.2 8.2Lower control arm, front 2 6.3 12.6Lower control arm, rear 2 5.3 10.6Slider assembly 2 3.0 6.0Rocker panel bracket, type 3 4 1.3 5.2Rocker bracket wedge 4 0.9 3.63/4 x 2.5 inch pins 6 0.7 4.2

Total 83.1

WEIGHTS FOR LIGHTWEIGHT OUTRIGGERS, IN POUNDSTubing wall thickness = 0.058 inches

Rod-end bearings = 0.5 inch

Item Number Weighteach

Weight

Roof rail clamp assembly, driver side 1 3.84 3.84Roof rail clamp assembly, passenger side 1 2.68 2.68Roof cross tube 1 2.90 2.90Strut, Driver side, with cushion 1 4.78 4.78Strut, Passenger side 1 3.67 3.67Lower control arms, front, with clevis 2 3.35 6.70Lower control arms, rear, with clevis 2 3.19 6.38Slider assembly, with pins 2 1.84 3.68Rocker panel bracket, type 4 4 0.64 2.56Rocker bracket screws & washers 20 0.34

Total 37.53

6

MOMENTS OF INERTIA FOR STANDARD OUTRIGGERS, IN POUND-FT-SEC22001 Tracker: Rocker separation 60 inches; CG 20 inches, rocker/slider 45 inches.

Item Weight k Mk2

Roof rail clamp assembly 15.0 38 4.58Roof cross tube 6.4 42 5.70Strut, Driver side 10.5 48 5.21Strut, Passenger side 8.2 48 4.07Lower control arm, front 12.6 50 6.79Lower control arm, rear 10.6 50 5.72Slider assembly 6.0 73 6.90Rocker panel brackets, type 3 5.2 30 1.01Rocker bracket wedges 3.6 30 0.70Pins, slider 1.4 73 1.60Pins, Rocker 1.4 30 0.27Pins, roof rail 1.4 38 0.44Sum I0 = 1/12 ml2 1.91

Total 83.1 50.06 44.90

Metric units: 38 kg; 61 kg-m2

MOMENTS OF INERTIA FOR LIGHTWEIGHT OUTRIGGERS, IN POUND-FT-SEC22001 Chevrolet Tracker

Item Weight k Mk2

Roof rail clamp assembly, driver side 3.84 38 1.190Roof rail clamp assembly, passenger side 2.68 38 0.835Roof cross tube 2.90 42 1.100Strut, Driver side, with cushion 4.78 48 2.375Strut, Passenger side 3.67 48 1.824Lower control arms, front 6.70 50 3.600Lower control arms, rear 6.38 50 3.440Slider assembly 3.68 73 4.230Rocker panel bracket 2.56 30 0.496Rocker bracket screws & washers 0.34 30 0.066Sum I0 = 1/12 ml2 0.890

Total 37.53 48.5 20.04

Metric units: 17 kg; 27 kg-m2

7

LOWER ATTACHMENT WEIGHTS

TYPE 1Aluminum tube clevis:Tubing used: 2.5 OD x .125 wall

1.1 pounds each

TYPE 2Long plate to frame: 3.2 pounds each

TYPE 3Rocker bracketsRocker wedge s

1.38 pounds each0 .88 pounds each

TYPE 4Assembly 0.64 pounds each

8

TUBING USED IN STANDARD OUTRIGGERS

Outside Diameterinches

Inside Diameterinches

Weightlb/ft

Roof 2.00 1.750 0.866

Strut outerStrut inner

2.252.00

2.0001.750

0.9800.866

Control Arm outerControl Arm inner

2.252.00

2.0001.750

0.9800.866

TUBING USED IN LIGHT OUTRIGGERS

Outside Diameterinches

Inside Diameterinches

Weightlb/ft

Roof 2.000 1.834 0.588

Strut outerStrut inner

2.0001.875

1.8841.759

0.4160.389

Control Arm outerControl Arm inner

1.8751.750

1.7591.634

0.3890.362

NOTE:Standard outriggers inner tubes were lathe-turned to slide inside outer tubes.

9

PURCHASED PARTS

Stainless steel roof overcenter clamp, load rating 2000 pounds: McMaster Carr #51335A68

Light Version slider pivot bearing: McMaster Carr #6111K54Note: These are machined to cut weight. Rated load is 7400 pounds.

Standard Version slider pivot bearing: McMaster Carr #63125K39Note: Rated load: 7700 pounds axial, 52,000 pounds radial. Stainless steel, Teflon lined.

3/4 inch rod ends (Standard Version: McMaster Carr #59915K28Note: Stainless steel, Teflon lined, rated load 7500 pounds

1/2 inch rod ends (Light Version): McMaster Carr #59915K26Note: Stainless steel, Teflon lined, rated load 4700 pounds

Light Version rocker clevis: McMaster Carr #2447K19

Light Version air cylinder: 1.5 inch bore x 3 inch stroke, McMaster Carr #6471K14

Standard Version air cylinder: 2 inch bore x 4 inch stroke, FLAIRLINE Model ODE 2X4,Flairline Inc, Farmington Michigan

Polyethylene slider material: 12x12 inch sheets:3/4 inch thick McMaster Carr #8657K118; 1 inch thick McMaster Carr #8657K119

10

Figure 1: First version outriggers on a Corvair

Figure 2: First version outriggers in action

11

Figure 3: First version upper mount

Figure 4: First version rocker attachment

12

Figure 5: Van version caster assembly

Figure 6: Van version foam slider

13

Figure 7: Van version in „major three-wheel lift‰

14

Figure 8: „New design‰ (1981) – Early standard version

Figure 9: „New design‰ (1981) Upper mount

15

Figure 10: New design slider assembly

16

Figure 11: Present standard upper mount

Figure 12: Present standard slider assembly

17

Figure 13APathfinder With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Spee

d (m

ph)

05

10152025303540455055606570

With Outriggers: Run # 2-15:30Without Outriggers: Run # 2-29:42

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Stee

r Ang

le (d

eg)

-160-140-120-100

-80-60-40-20

020406080

100120140160

18

Figure 13BPathfinder With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Rol

l Rat

e (d

eg/s

ec)

-40-35-30-25-20-15-10

-505

10152025303540

With Outriggers: Run # 2-15:30Without Outriggers: Run # 2-29:42

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Yaw

Rat

e (d

eg/s

ec)

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

19

Figure 13CPathfinder With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Rol

l Acc

eler

atio

n (d

eg/s

ec2 )

-300

-200

-100

0

100

200

300

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Rol

l Ang

le (d

eg)

-15

-10

-5

0

5

10

15

With Outriggers: Run # 2-15:30Without Outriggers: Run # 2-29:42

20

Figure 13DPathfinder With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Late

ral A

ccel

erat

ion

(m/s

2 )

-10

-8

-6

-4

-2

0

2

4

6

8

10

With Outriggers: Run # 2-15:30Without Outriggers: Run # 2-29:42

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Late

ral A

ccel

erat

ion

(m/s

2 )af

ter 0

.5s

runn

ing-

aver

age

filte

r

-10

-8

-6

-4

-2

0

2

4

6

8

10

21

Figure 14ATracker With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Spee

d (m

ph)

05

10152025303540455055606570

With Outriggers: Run # 53:13Without Outriggers: Run # 55:08

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Stee

r Ang

le (d

eg)

-160-140-120-100

-80-60-40-20

020406080

100120140160

22

Figure 14BTracker With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Rol

l Rat

e (d

eg/s

ec)

-40-35-30-25-20-15-10

-505

10152025303540

With Outriggers: Run # 53:13Without Outriggers: Run # 55:08

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Yaw

Rat

e (d

eg/s

ec)

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

23

Figure 14CTracker With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Rol

l Acc

eler

atio

n (d

eg/s

ec2 )

-300

-200

-100

0

100

200

300

400

With Outriggers: Run # 53:13Without Outriggers: Run # 55:08

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Rol

l Ang

le (d

eg)

-15

-10

-5

0

5

10

15

24

Figure 14DTracker With and Without Outriggers

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Late

ral A

ccel

erat

ion

(m/s

2 )

-10

-8

-6

-4

-2

0

2

4

6

8

10

With Outriggers: Run # 53:13Without Outriggers: Run # 55:08

Time (seconds)-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Late

ral A

ccel

erat

ion

(m/s

2 )af

ter 0

.5s

runn

ing-

aver

age

filte

r

-10

-8

-6

-4

-2

0

2

4

6

8

10

25

Figure 15: Light outriggers on a Chevrolet Tracker

Figure 16: Light outrigger upper mount

26

Figure 17: Light outrigger slider assembly

Figure 18: Light outrigger rocker attachment – Type 4

27

Figure 19: Type 1 tube attachment to frame

Figure 20: Type 1 clevis

28

Figure 21: Type 2 attachment to frame, with cross-bar underneath

Figure 22: Type 2 attachment to frame using angle section

29

Figure 23: Type 3 frame or rocker mount

Figure 24: Type 3 attachment to inclined rocker, with wedge

30

Figure 25: Type 4 „hinge‰ attachment for curved rocker panels