Loads | Wobbl

Flag

--load "200 N down @ top"

Pass --load as many times as you need, and Wobbl adds the loads together. Each one is written the same way, in this order.

Syntax

MAGNITUDE UNIT  DIRECTION  [bearing]  [at X,Y,Z]  @ FACES  [rigid]

Kinds of load

Wobbl tells the kinds apart by the unit, by whether there is a point, and by the word bearing.

Kind	Example	What it means
force	`200 N down @ top`	the total force, spread evenly over the faces by area
force along the normal	`20 N normal @ face 4`	pushes into each face along its own normal, and a negative value pulls out
force into holes	`300 N -x @ hole d=6.6`	the force spread evenly over the hole faces, with the peak where it meets the hole edge reported separately
bearing load	`300 N -x bearing @ hole d=6.6`	a bolt or pin pressing on the side of the hole the force points to, shared equally by the holes picked
pressure	`0.2 MPa @ top`	pushes into the faces, and a negative value pulls
gravity	`3 g down`	the part’s own weight times the factor, with no faces needed
remote force	`2000 N -0.87,0,-0.5 at 0,-30,66 @ holes d=6.6`	a force at a point off the part, carried by the faces
moment	`0.8 N*m +z at 210,0,25 @ top and within 14 of 210,0,25`	a torque about an axis through the point

Gravity needs no faces and points down unless you say otherwise. The g means gravity only when there is no @, because with faces the same letter reads as grams of force. A moment needs an axis, and when you leave out the point it turns about the center of its faces.

Bolts and pins in holes

A bolt or a pin that pulls on a part presses on one side of its hole, and the far side carries nothing. Write bearing after the direction, or at the very end after the faces, and Wobbl puts the force on the loaded half of each hole with a cosine distribution that peaks where the bolt pushes hardest. When you pick several holes they share the force equally, and the result lists this in its assumptions.

Flags

--load "300 N -x bearing @ hole d=6.6"--load "1.2 kN -y @ holes d=8 bearing"

Without bearing the same string spreads the force evenly over the whole hole, all the way around, which suits a flange or a press fit better than a single bolt. A bearing load needs hole faces and a force unit, so Wobbl refuses it with a pressure, a moment, gravity or a point off the part.

Directions

A direction is one of +x -x +y -y +z -z, a word, or a vector like 0,0.7,-0.7 that does not need to be unit length. The words follow the usual view where z is up and the front of the part faces minus y.

Word	Direction
`up`, `down`	`+z`, `-z`
`right`, `left`	`+x`, `-x`
`back`, `forward`	`+y`
`front`, `backward`	`-y`
`normal`	into each face along its normal (forces only)

Loads that act off the part

A remote force or a moment acts at a point that is not on the part, like a belt pull at a pulley or the torque of a motor on its flange. It reaches the part through the faces after the @, and there are two ways it can get there.

By default the load is distributing, which means the exact force and moment are spread over the faces without making them any stiffer, the way an RBE3 element does. That is close to a bolt group sharing a load or a flexible part pressing on the faces. Add rigid at the end and the faces are tied to the point as one rigid body instead, through a CalculiX *RIGID BODY, which suits a stiff motor flange or a clamp. Several rigid loads on the same faces merge into one attachment, which is how the drone arm example puts both thrust and torque on its motor pad.

Flags

--load "25 N up at 150,0,15 @ top and within 15 of 150,0,15 rigid" \--load "0.5 N*m +z at 150,0,15 @ top and within 15 of 150,0,15 rigid"

Either way, Wobbl also solves the other idealization and reports how far apart the two are, and the confidence drops when the verdict depends on the choice.

Units

Any common unit works. Forces take N, kN, lbf, kip and kgf, pressures take MPa, kPa, Pa, GPa, psi, ksi and bar, moments take N*m, N*mm, in-lb and ft-lb, and gravity takes g or m/s2. A load in imperial units makes the whole result print in psi and inches, with the metric values next to them. Units has the full list.