Converting actual vehicle measurements to SusProg3D

Often, vehicle manufacturers and professional car builders are able to provide coordinates for the various suspension points, usually obtained with a very sophisticated (and expensive) 3D Coordinate Measuring Machine. Usually these dimensions are "ground based".

This tutorial is intended to demonstrate the conversion of Coordinate Measuring Machine (CMM) coordinates to the SusProg coordinates, particularly to obtain the SusProg3D upright coordinates.

The CMM data supplied for this exercise was provided in imperial dimensions, and was in the following format.

The critical requirement, is that the data must provide two data points on the wheel axis. Usually one will be on the wheel centreline, and the other will be on the axle end. These two points will enable all the upright coordinates, wheel alignment (camber and toe), and track to be determined.

You will need SusProg3D, version 4.50j (or later) to get the latest V2U tools.
This tutorial requires a registered copy of SusProg3D. It will not work with the demo version.

Start SusProg3D.

This tutorial will use imperial units, and a custom axis system to match the supplied data.

Hint for Metric users.
After completing the tutorial and saving the data file, reset the units to Metric. Close and reopen SusProg3D, then open the data file. It will automatically convert from imperial to metric, and display all dimensions in mm.

Go to Settings -> Settings -> Units. Select Imperial, then OK.

Just by looking at the supplied data, it can be seen that X is the longitudinal axis, with +ve rearwards; Y is the lateral axis, and Z is the vertical axis, with +ve upwards. It is not obvious whether the lateral axis is +ve left or right, so choose which seems more appropriate. I have chosen +ve LH.

Go to Settings -> Settings -> Axis System.
Change the lateral axis identifier to "Y" and "+ve LH"; the vertical axis identifier to "Z" and "+ve up"; and the longitudinal axis identifier to "X" and "+ve rear". Click OK.

Check that the wheel mounting flange dimension is correctly specified. 
Go to Settings -> Settings -> Wheel mounting flange.
Select Offset, then OK.

Close SusProg, then restart it.

Setup the Vehicle data.

Select the Vehicle tab, then each of the following items in turn.

Config

For the front geometry, choose "Double A-arm". The remainder of the items can be left as-is.

Click OK.

Datum

Our vertical datum is the ground, so add a note to the vertical datum Z "Ground".
Our longitudinal datum is a point in front of the vehicle, probably the front edge of the CMM measuring surface, so add a note "Base plate front edge".

Using the wheel centre X dimensions, change the longitudinal datum to axle centreline (nominal) front dimension to 45.879", and the rear dimension to 155.855". Note that these dimensions will eventually change, but are close starting points.

Click OK.

Ride Height.

This is used to specify and adjust the vehicle ride height. It allows for the chassis ride height (and consequently all the chassis pivot points) to be adjusted in one single step.
For this example, assume that we are measuring ride heights from the chassis top tube.
The front ride height location will be 28.775", 6.060", 71.576" and the static ride height 6.060".
The rear ride height location will be 28.845", 7.219", 136.623" and the static ride height 7.219".

It is important that both front and rear ride height locations and ride heights are specified, as these two points control the calculated position of the chassis mounting points, relative to the ground. In this case, where the ground is also the chassis vertical datum, then the critical dimensions are that the Z dimension and the Static ride height must be identical, and that the two location points are "longitudinally separated".

Click OK.

Mass.

This isn't used for the basic geometry calculations, but some approximate values can be entered.

Assume that the unsprung corner weights are each 100lb and the corner weights are each 660lb.
Set the centre of gravity height to 18.000".

Click Apply. Notice that the total weights and distribution is updated. Click OK.

Front Wheel

The only thing we know, is the approximate rolling radius. Assume the rolling radius is the same as the wheel centre height, 13.633".

The other dimensions are guesses. They are needed to show a reasonable looking tyre in the display.
So assume a 16" rim diameter , an 8" wide rim, a zero offset, a 8" tread width, a 9" tyre section width, a 16" toe reference length (to match the rim diameter), and a 1000lb/in tyre rate.

Make sure that "identical" is ticked. Click OK.

Rear wheel.

There is no need to enter the rear wheel as we are only doing the front suspension.

This has now completed the basic vehicle data. At this point it is probably wise to save the data.

Go to File -> Save As.
Specify an appropriate directory and file name. I have saved it as Tutorial5Basic

At this stage there is no graphic display, other than a small cross in the centre.

Now we can enter the geometry dimensions.

Select the Geometry tab, then each of the items in turn.

Config.

This is where we specify the controlling dimensions.

Specify the instant centre location as "Suspension link chassis mounting points".
This allows us to specify the wishbone chassis mounting points, and calculate the swing axle and roll centre dimensions.

Because we don't know any of the link lengths, specify the wheel location and alignment as "Wheel location and alignment".
This allows us to specify the wheel location (both laterally and longitudinally), which will then calculate the track, wheelbase and wishbone link lengths.

Specify the "wheel location point" as "On ground".

Click OK.

We are designing the front suspension, and will input data for the LH side.
After Config, the next menu item should be [Front]. If it is [Rear] then click it, and change it to [Front].
The next menu item should be [LH]. If it is [RH] then click it, and change it to [LH].
Hint: If the CMM data has one side of the vehicle with +ve lateral dimensions, and the other side with -ve lateral dimensions, then always use the side that corresponds to the +ve dimensions. We chose LH because we decided that the lateral dimensions are +ve LH. If you have the lateral axis +ve RH, then choose RH here.

Wheel.

This has already been done, as part of the Vehicle setup.

Alignment.

Specify the camber, caster and toein all as zero.

Using the wheel centre Y dimension, specify the "half track" as 30.594".

Make sure that "RH identical" is ticked, then click OK.

Upright.

Using the "Upper ball joint" and "Wheel centre" dimensions, calculate the approximate upright dimensions. For the Z and X dimensiions, subtract the "Wheel centre" from the "Upper ball joint"; for the Y dimension, subtract the "Upper ball joint" from the "Wheel centre".
The top wishbone mounting (upper ball joint) dimensions are:
Y = 30.594 - 22.626 = 7.968"
Z = 21.116 - 13.633 = 7.483"
X = 46.572 - 45.879 = 0.693"

Similarly, the bottom wishbone mounting (lower ball joint) dimensions are:
Y = 30.594 - 24.601 = 5.993"
Z = 8.864 - 13.633 = -4.769"
X = 45.404 - 45.879 = -0.475"
Note that the Y dimension is negative, as it is below the axle centerline.

The steering ball joint is not needed for the basic geometry calculations.

Leave the spindle reference point at zero.

Make sure that "RH identical" is ticked, then click OK.

Chassis.

Using the supplied upper and lower A-arm chassis pivots, enter the Y, Z and X dimensions.

The steering rack ball joint is not needed for the basic geometry calculations.

Make sure that "RH identical" is ticked, then click OK.

Calc.

Just click the Calc.
This will do all the static geometry calculations, and update the graphic.

The display should look "reasonable". If the links aren't in the orientation you would expect, then it is probably because you have input a value with the incorrect sign (-ve instead of +ve) or left a value at zero.
Use Display -> Front, then Left.
I have saved it as Tutorial5Step1

Now we have the basic data, and it will calculate, we can look at the data.

We will start with getting the camber and toe settings set correctly.

Obviously the wheel centre isn't in the correct position, so we need to adjust some data.

But what?

First thing. The Y dimension needs to be increased, by moving the wheel outwards. We do this by increasing the "half track".
Go to Geometry -> Alignment and change the half track from 30.594" to 31.350" (30.594 + 0.756)

Next, the Z dimension needs to be increased. We do this by increasing the "tyre rolling radius".
Go to Geometry -> Wheel and change the tyre rolling radius from 13.633" to 13.654" (13.633 + 0.021)

Calc. Now much closer, but still a few thou out.

Go to Geometry -> Wheel and change and increase the "half track" by another 0.001" to 31.351"; and the "wheel centreline on ground to X datum" by 0.006" to 45.885".

Now the both the wheel centre (spindle / wheel cl point) and the axle end point (spindle reference point) agree with the supplied data. (The axle end point is a thou out in height, so this implies the camber is a little out). 

Check the camber calculation (see above) and it should be 3.183 (not 3.18), so change the camber to -3.183 and also increase the half track by another thou to 31.351".

Recalc. Perfect!
Saved as Tutorial5Step3

OK, now we have the basic wheel location and alignment established.

Now we need to get the top and bottom balljoints, and also to allow for caster.

Using the V2U tool, go to the  "Use axle coordinates" tab, and select "Calculate spindle offset".
We need to see if the wheel spindle is offset (in side view) from the line through the top and bottom balljoints.
Use the wheel centre (spindle / wheel cl point) and the axle end point (spindle reference point) as the coordinates for the axle (Hint. Press "Vehicle" to load these values) and use the supplied upper and lower ball joint coordinates.
Make sure the "Calculate spindle offset" button is selected, and then Calc.
The spindle offset is calculated as -0.009", ie the kingpin axis is ahead of the axle spindle.
In other words, the spindle (in side view) is offset 9 thou behind of the line through the top and bottom ball joints.

So now we will use that offset, and assume that both the top and bottom ball joints are equally offset 0.009" ahead of the spindle axis.

Change to "Calculate upright point"
Enter the values (world coordinates) for the upright top ball joint, and then Calc.
This gives Y 7.535", Z 7.970" and X -0.009"

Similarly, using the upright bottom ball joint values, calculate the upright dimensions as Y 6.252", Z -4.429" and X -0.009"

Plug these values into the Upright input.

The difference between the top and bottom ball joints (in world coordinates) is about X 1.168" and Z 12.252" which is about 5.5 degrees.

So we need to specify the alignment caster as 5.5 degrees. Add this to the Alignment, and then Calc.

The initial calculation showed that the top balljoint was OK for Y and Z, but 0.002" out in X. A little more caster required.

After a couple of tries, I settled on a caster of 5.515 degrees.

The calculated dimensions exactly match the supplied data. Saved as Tutorial5Step4

Well, that's enough for this tutorial.

Now we have the upright dimensions, wheel and tyre dimensions, and basic setup alignment.

Now, it is easy to start varying.

What if a smaller tyre is fitted?

What if the camber is changed?

All of this without having to recalculate the world coordinates! And that is the main advantage of having the upright coordinates in their own axis system. The freedom to move and realign.