If the Axle Group is steered, then it is probably uses the Ackerman steering principle, whereby each wheel turns a different angle, consistent with travelling along concentric arcs. Trailers can have drawbar front axles. Rear axles for most vehicles are fixed; those that steer must be linked to either the front axle (if there is one) or the front coupling.
The Guided selection means that the axle is guided by rails or curbs.
For wheel types, the difference between the various tired wheels will only be apparent when animating the vehicle in 3D.
Axles Identical means that all the axles have the same basic dimensions. If you select this, the values for all axles will be set to same as the currently displayed axle (not necessarily axle 1) and the axles will be set to evenly spaced at the current Uniform Spacingvalue. Multiple tabs will be reduced to a single tab with text similar to Axle 1 to 3 (Identical).
Select 2nd Steer if this axle group turns, but the turn angle is linked to the turn angle of another axle group or coupling. A rear axle group is automatically linked to the front axle group, if one exists, or the front coupling articulation angle, if not. A front axle group is similarly automatically linked to either the rear axle group or coupling. A unit cannot have both front and rear axle groups linked. The primary axle group cannot have linked steering, and neither can a fixed axle group. When you select 2nd Steer, you can enter details of the steering linkage ratios.
Select Uniform Spacing if all the axles in the group are the same distance apart, and enter a value in the field. Identical axles are deemed to be evenly spaced.
Select Wheel Angle Limited To if you know the maximum angle that any wheel in the group can turn, and enter the angle in the field provided. Note that if the axle group is of the Ackerman type all wheels will turn by different amounts; in this case you should enter the greatest angle of any wheel in the group.
If you are defining a drawbar axle group, enter the Drawbar Length. Note that the coupling (if any) at the end of the drawbar must be specified on the Couplings tab. Also for a drawbar, enter the Maximum Articulation Angle which is the angle between the drawbar and the unit to which it is permanently attached.
If you are defining a nosewheel, bogie or drawbar axle group, you must specify the Axle Group Pivot Offset. This is the distance in front of axle 1 on front axle groups and the distance behind axle 1 on rear axle groups.
On units with tired wheels, the outer face wheel track is measured over the outer faces of the outermost tyres on an axle. It is most important that this value is correct if you are specifying steering turn angle by curb-to-curb turning circle radius. Note that on Pendel axles, this dimension is measured to the outer faces of each sub-axle.
On units with rail wheels, the rail gauge is measured between the faces of the wheels in contact with the inner faces of the rails.
Certain vehicles can have axles lifted from road contact when unloaded. Select Retracted to specify an axle of this type. Note that you cannot define all axles in a group as retracted, so by definition you cannot change this setting if the group only consists of one axle or if all axles are identical. The only exception to this rule is the primary steered axles of a tractor used as a trailer which may be retracted.
Bogies Per Row and Bogie Spacing apply only to Pendel axles, and each tab represents a row of bogies. Bogies Per Row is the number of bogies in each row across the width of the unit. Bogie Spacing is the distance between the pivot points of each bogie. You can specify irregular spacings by entering values as "1.5,2.1,1.5". In this case the first spacing is the distance between the outermost bogie and the adjacent bogie, the second value is the distance between the next two bogies and so on. The last value is assumed to apply to any remaining bogie spacings. The row of bogies is assumed to be symmetrical so you only need to specify spacings for the bogies on one side.
Axles Per Bogie, Bogie Axle Spacing, and Bogie Pivot Offset apply to Tandem bogies which have multiple pivots along the centerline of the unit. Each tab represents a bogie. Axles Per Bogie is the number of axles in a single bogie. Bogie axles are all identical and Bogie Axle Spacing is the distance between any two. Bogie Pivot Offset is the distance from the natural centre of the bogie to the actual pivot position. This is zero by default.
If the axles are not equally spaced, select Offset From Previous Axle, and enter a value in the field. Note that axle 1 has no offset.
On non-turning axle groups such as fixed and undercarriage, you can select Self-Steered to allow selected wheels to rotate freely about their vertical axis, much like the wheels of a shopping cart, on the Ackerman principle. This will affect the Autodesk Vehicle Tracking calculation of effective axle offset on multi-axle groups. Select the directions in which the self-steering applies.
It is widely assumed that self-steered axles have no effect on the position of the effective axle, but if you consider that they have some effect, you may wish to specify the effect of the axle compared to a fixed axle with the same wheels by specifying a Self-Steered Friction factor. A zero friction factor means the self-steered axle has no effect on the effective axle position. A value of 100% means the self-steered axle has the same effect as a fixed axle. In addition, the wheel angle will be adjusted by the same friction factor.
On axle groups that include Ackerman steered wheels you can select Fixed to prevent selected wheels from turning. Select the directions in which the axle is fixed.
Total Wheels Per Axle or subaxle can be any positive value, odd or even. If you specify an odd value the odd wheel will be drawn at the centre irrespective of the wheel placement specified in the next field.
Wheel placement defines how the wheels are positioned along the axle. It can be set to At Ends of Axle, Evenly Spaced, or Specified Spacing. If you select Specified Spacing, you must provide the Wheel Spacing, the distance between centres of the wheels. The default is twice the wheel width.
If you are defining an Ackerman axle with wheels located at the ends of the axles, then you have the option to set a Stub Axle Length, which is the distance from the centre of the wheel group to the pivot at the opposite end of the stub axle.
On units with tired wheels the Tire Diameter is measured to the tread surface for units with tires. Note that this does not affect path prediction where all axles are identical, but may affect the calculated effective axle offset when the track width of each axle in a group varies, and therefore affect the resultant path.
On units with rail wheels the Wheel Diameter is measured to the surface in contact with the rail, and the Wheel Width is measured to the outer faces of the wheel. Default values are provided, but if you know the actual value, then overwrite the default.
On units with tired wheels, the Tire Width is measured at the contact point. Note that this does not affect path prediction where all axles are identical, but may affect the calculated effective axle offset when the track widths of each axle in a group varies and therefore affect the resultant path.
Click the New button to add an axle after the last one currently defined. For example, if you have 3 axles defined the new axle will be axle 4. The new axle will be initialized with the same values as the current axle.
Click the Insert button to insert an axle at the current location. For example, if you are displaying axle 2 of 3, the inserted axle will be numbered 2. The inserted axle will be initialized with the same values as the current axle.
Click the Remove button to remove the currently displayed axle from the group. Note that you cannot remove axle 1, instead you must clear the Front Axles or Rear Axles selection on the Unit tab to remove the axle group completely.