Hardpoints and frames¶

Every point of a model is given globally at t = 0, where it is used. When several elements share a point (the outer ball joint of a control arm, the spring's lower mount), name it once under points and use the name:

points:
  uca_outer: [0.0, 0.68, 0.52]
  lca_outer: [0.0, 0.72, 0.13]
  spring_bottom: {from: lca_outer, offset: [0.0, -0.10, 0.05]}
joints:
  upper_ball: {type: spherical, body1: carrier, body2: uca, location: uca_outer}
forces:
  spring: {type: spring_damper, body1: lca, point1: spring_bottom, point2: spring_top, stiffness: 60000}

A name stands for the numbers in every point field: location (joints, bushings), point, point1, point2 (forces, measures, sensors) and position (bodies). Move the point and everything that uses it moves along.

Points¶

form
`[x, y, z]`	global at t = 0; numbers or formulas: `[0.15, 0.40, =z_uca]`
`{mirror: name}`	the point mirrored at the x-z plane (`y` negated): the other side of a vehicle
`{from: name, offset: [dx, dy, dz]}`	another point moved by an offset
`{in: body or frame, local: [x, y, z]}`	in the frame of a body or of a named frame (below)

Points defined by others may come in any order; a loop is an error.

Points in a body¶

A part drawn in its own coordinates – a wheel carrier from CAD, a subframe, a seat in the cabin – is easiest described there. in: takes a body or a frame:

frames:
  carrier_cad: {origin: [0.0, 0.71, 0.32], z: [0, 0, 1], x: [1, 0, 0]}   # the part's CAD origin
points:
  tie_outer: {in: carrier_cad, local: [-0.12, -0.01, -0.07]}
  caliper: {in: carrier_cad, local: [0.05, 0.02, 0.12]}
  head: {in: chassis, local: [0.4, 0.35, 0.6]}     # from the chassis' center of mass

In a frame: the coordinates are along its axes from its origin. Give a part a frame for its own origin and axes (as in CAD) and every point of the part in it; move or turn the frame and the part's points go along.
In a body: the body frame, i.e. its center of mass and its principal axes of inertia, at t = 0. With the default orientation [1, 0, 0, 0] these are the global axes, so local is the offset from the center of mass; with a turned body they turn with it.
A body's position and orientation may themselves be a point and a frame. A point in a body that places the body is a loop and reported as such.

Like everything else the result is a point at t = 0; the body carries it from there.

Frames¶

A frame has an origin and an orientation. Its name stands for the orientation in every orientation field (joints, bushings, torsion springs, sensors, measures, bodies) and for its origin in a point field:

frames:
  lca_axis: {origin: lca_front, z: [lca_rear, lca_front]}    # z from one point to another
  wheel_axis: {origin: wheel_center, z: [0, 1, 0]}           # z along a direction
  sensor_frame: {origin: head, orientation: [1, 0, 0, 0]}    # Euler parameters
joints:
  lca_pivot: {type: revolute, body1: lca, location: lca_axis, orientation: lca_axis}

key
`in`	a body or frame: `origin`, `orientation` and `[x, y, z]` directions are in its frame (point names stay global)
`origin`	a point name or `[x, y, z]`. Default `[0, 0, 0]`
`z`	the direction of the z axis (the axis of a revolute or cylindrical joint, a prismatic joint's direction): `[x, y, z]` or two point names `[from, to]`
`x`	where the x axis points, made normal to z: `[x, y, z]` or two point names. Default the global x axis (y if z is along x)
`orientation`	Euler parameters instead of `z` and `x`

Tuning hardpoints¶

A hardpoint is a number like any other: in the viewer, tick hardpoints under View, click one, and tune its coordinates; the joints, springs and frames that use it follow. A formula in a point ([0.15, 0.40, =z_uca]) makes it a parameter with a slider, a fan (≋) and a root locus (⌁) – a design study of the geometry.

The inspector of a hardpoint lists what uses it. Points and frames nothing uses are reported by the checks (points and frames not used).

Example¶

freedyn2 examples double_wishbone: a double-wishbone front suspension on a rig, built from hardpoints, with a tire spring on a road with a bump.

All keys¶

key	value
`id`	id
`in`	string	A body or frame: origin, orientation and [x, y, z] directions are then in its frame (a body: center of mass, principal axes at t = 0); point names stay global.
`origin`	[x, y, z] or a point name	Origin. Default [0, 0, 0].
`orientation`	list of 4	Euler parameters, global. Default [1, 0, 0, 0], or from z (and x).
`z`	see text	Direction of the z axis: [x, y, z] or two point names [from, to].
`x`	see text	Direction the x axis points to (made normal to z): [x, y, z] or two point names. Default the global x axis (y if z is along x).