BIM Flower

Making a field of flower-like shapes appears to be a challenge with Revit, but is a good exercise of how to make adaptive components and insert them into a pattern-based panel.
The first step is to plan the model. My approach is to make triangular petal object using the Generic Model Adaptive family template. This will be loaded and placed in a Pattern-based panel with a hexagon type, using mirrored pairs of petals This looks like a cloverleaf. This will be added to a divided surface defined using a Mass object. Good practice is to start simple and add complexity. Eventually I want the petal pairs to fold gently upward.

Petal

You must create an armature for constructing the shape of the petal. Think of this as scaffolding for construction. In the film industry, this is known as “rigging”.

 Upon opening the Generic Model Adaptive, create a triangle of adaptive points. It does not matter where one draws the triangle, but it usually helps to draw it approximately the size that you anticipate using in the final.

Trace a chain of reference lines connecting the points to make a triangle. Create a random set of point objects, and then use Pick New Host to place them on the reference lines.

Construct additional reference lines and host additional points on them to enable locations for the control points of the curve that will make the petal.

You can test your rigging by selecting a reference point on a line and changing the “Normalized Curve Parameter” value. This is a number between 0 and 1 that locates a point on a curve (or straight) line as a linear proportion along the length of the curve. The reference lines should move and change without breaking or separating from an endpoint. 

Draw spline curves with control points on the reference points that you created. You can move the curves around by changing the Normalized Curve Parameter of the reference points.

The shape can be drawn all on the default workplane. When it is inserted, all points are going to be in the same plane.

I have not been particularly rigorous with controlling the curves in my model. I suspect that there are cases that will cause the spline curves to cross each other, which would create a chain that cannot be made into an extrusion. Also, I have not controlled it to try to make sure that the form is smooth. My shape has some abrupt changes, sometimes. However, if you anticipate the size and shape of the final instances of the flower, you can probably avoid failures.

Select all of the curves to determine a closed chain and extrude it. I locked the top and bottom profile of the extrusion so that I don’t accidentally modify it into a blend. This also gives positive and negative offset values. Make the extrusion the thickness of the stock that you will use to manufacture the panels. I set it for 1/2”. It would probably be best to set it to .25” positive and .25” negative so that it is centered on the insertion point, but I did not.

Cloverleaf

Next, make the pattern-based panel. Set the dimensions to be close to those you expect to use in the final. Change it to a Hexagon.

Draw crossing lines to construct the center of the hexagon.

 Load your petal into the panel, and place a petal with the first of the placement points at the center and the next two at the edge. I designed my petal to have a straight edge between the first and second points, allowing me to place petals in the hexagon in pairs that join along the straight “fold” edge. Place the first petal in clockwise order, the second in counterclockwise order, and so on. (This is why I should have extruded it both positive and negative. In my model the petals don’t line up perfectly because one in each pair extrudes up and the other extrudes down.)

Flex the model by using a 3D view to drag the hexagon vertices up and down. The petals should deform to move up and down with each vertex independent.

Surface

 Next, make a mass surface for arraying the petals. Open a New Mass.

 CTRL click on the center plane to make additional vertical planes.

 Click on a vertical plane to make it the active drawing surface and draw a spline. Draw splines on each vertical plane. It is best to use the same number of control points for each spline (although usually one or two more control points doesn’t matter.)

 Make the blended sweep by ctrl clicking all four splines and choose the Create Form icon.

 Click the surface of the mass to select it. Choose the Divide Surface icon. With the divided surface, choose the Hexagon pattern in the Properties panel Type Selector. I changed the spacing of the divided surface lines to be a fixed grid approximately the size of my final design.

 Switch views back to the cloverleaf panel. You can select the grid and then use the button for Reset Points to Grid to move all of the flexed control points back to the grid.

 Load it into your mass.

  In the mass, use the type selector of the divided surface to choose your cloverleaf panel, wait a few moments, and the pattern is created on the surface. It may fail for some of the panels when the angles are too extreme. I suspect that mine failed for two panels that created a self-intersecting curve that could not be extruded. I could either make the mass surface a little more gentle or I could refine the design of the panel so that it is more robust. I simply ignored the error by clicking on Delete type.

Folding

 The next step is to go back to the cloverleaf to make the petal pairs curl up at the edges. The concept is to place reference points on the adaptive control points and then move them up vertically. They must move vertically in relation to the adaptive points and not the level workplane. This means the reference points must be hosted by the adaptive point.

 Using the 3D view, place a reference point anywhere. Use the Pick New Host to select the adaptive point that controls the corner of the petal. Hover over the placed reference point and Tab until you can select the reference point.

 In its Properties panel, it has an Offset property. Change the value in this property and the point should move vertically away from the adaptive point. You can flex the model by spinning the 3D view and changing the Offset to see the point move. You can then select the instance of a petal to highlight it in blue. The insertion points are then indicated. You can hover over an insertion point and tab until you can select it. Move it up to snap to the offset reference point. The petal should be “bent” upward.

 (In this screen capture, I had deleted the petal, expecting to place it again with a snap to the offset reference point. This is not a necessary step because you can drag the insertion point of the already inserted petal to the new location hosted by the reference point.)

Reload the model into the mass to test the offset point.
If everything looks fine, go back to the cloverleaf family. Add five more reference points in the same way. I arranged the reference points so that there are two over the first adaptive point, two over the third adaptive point, and two over the fifth adaptive point. These will be the edges of the petals, while the spines of the petals go through the second, fourth, and sixth points.

 Make Parameters for the three offsets of the three petal pairs. This is useful for controlling the petal pairs so that both edges go up the same amount. I put in default values of 4”, 6”, and 8”.

 Associate the appropriate offset parameter with the six reference points. You should be able to control their vertical displacement by changing the parameters.

  Move the petal insertion points to snap to the appropriate reference points. Flex the model by changing the parameter values and see the petals fold up and down.

 Reload into the mass surface. Again, there could be problems with one or all of the cloverleafs. Try changing the size of the divided surface grid to see if it will build at some size. Usually it will build at a size close to the size of the hexagon grid in the cloverleaf.

Changing the fold dimension

 Because we used parameters to control the offset, there is one additional feature to exercise. If you click the divided grid, you can then select an individual cloverleaf. In its Properties panel, the offset parameters appear. You can fold the petal pairs upward by changing these values. In this way, you can make even more complexity in your form.

Breaking it

 While everything looks great in my model, a few more trials show that the cloverleaf is not robust -- it will break under some circumstances. If the pattern is less than 1’7” it will not work. My guess is that the curves become self-intersecting and cannot be extruded.

However, since I am able to make the design that I wanted, I will ignore the brittleness of the model. 

Helix

A helix is actually a very simple shape for parametric modeling. Think of it as a segment of a shell that is rotated and translated (offset) with each increment. You can make one in Autodesk Revit very easily.

Create a family with a generic model. You can make an extruded box drawn in an elevation view. I drew a reference line to define an angle through the family center. Rotate the box to align with the reference line. Create a parameter for the angle. Make sure that its type is "angle". Draw a angular dimension on the reference line and associate it with the angle parameter. Create an index and a angle_increment. Create a formula for calcuating the angle of rotation from the index and angle increment. That's all there is to the family. (I have added some extra parameters in anticipation of changing the radius of the helix and the size of the patch.)


In a project file, you can insert the helix facet. Insert 20 or 30 copies. Change the index of each copy and it will spin around the axis to the right location.

Simple parametric family in Revit

One of the coolest things about Autodesk Revit is the ability to make shapes that are governed by formulas. This is the essence of algorithmic design, and while several other tools on the market are more flexible and powerful than Revit in this regard, there are interesting things one can do in Revit's BIM environment.

There are several concepts that one must grasp. First, a new Revit family should be drawn using reference planes and references lines. It is easier to impose constraints on the reference planes than it is on the model lines and model geometry (model lines tend to lock to reference planes and points by default and it can be unpredictable or unwanted.) Use dimensions to establish the essential geoemtric relationships of your family, such as lengths and angles. Second, the Revit family must have named parameters. You associate these named parameters with the dimensions and angles in your geometry and model. Third, there must be an "index" value that triggers the formula. Typically you will type in the index value and then the formula will calculate the geometry parameter. Finally, you must enter a formula using the index (or indices) that will calculate a geometric relationship.





Once a family has been created in this way, you can insert multiple instances of it into your project and then set different values for the index. The geometry will alter for each instance based on the formula.

Below you will see the same project file after changing the formula in the beam family.






Here it is with the cosine determining the angle of the beam. (I am sure that I have not done this in the simplest way, but I added the extra calculated parameters just to convert the units of the parameters so that the formula would not complain about "inconsistent units". Apparently the cos function requires that the input value must be in degrees. Input value in integer or number does not work.)

Making cut paths using Revit

We have been cutting wood with our CNC router for several years, both in two axis applications and three axis. However, we have rarely cut other materials and I suspect few people realize that we can cut almost anything. I decided to do a project with aluminum to show off the capability of cutting other materials. Besides, anything you make out of aluminum will look beautiful. The project is to design a canopy over a train station platform that would be 240 feet long. Build a model of the structure at ½” = 1’. The models will be ten feet long which is an awkward size to move around. Consequently, the models must be manufactured in two 5 foot sections. Aluminum cost us about $215 per sheet of 3/16” thick by 4’ by 8’. It is not cheap but it is not prohibitively expensive either. I used grant funds to buy a sheet for each of my students, and some for me too. Cutting aluminum is just like cutting MDF or plywood except the particular settings for revolutions per minute and linear feet of movement are different. Chuck called his suppliers and other experts and also experimented to find good settings. Slow is good, plus we used a blower to air cool the bit and push the shavings away. One of the problems that we encountered was that the bit lifted the aluminum sheet off the bed and then mangled it. We designed the locations of drill holes in AutoCAD so that we could screw the sheet firmly to the sacrifice board without damaging the pieces of the model. Just like cutting MDF or even laser cutting, I needed to create a cut path sheet in AutoCAD to load into MasterCAM for running the CNC router. The AutoCAD drawing needs to be the accurate size of the model (120’ in the design should be 5’ in the model) and all lines need to be polylines (PLINES). It is helpful to have a 4’x8’ rectangle drawn to represent the sheet of stock material. My process involved making the model in Revit. I created sections through the model at the location of every part profile that I would need. I then used a sheet template to create a new 4’x8’ sheet and laid out all of the parts on the sheet carefully to avoid wasting material. There are numerous steps to convert the Revit sheet to the DWG file, but it is really pretty easy. The sheet can then be exported to a DWG file. The file will then open in AutoCAD 2010 as a Paper Space sheet. This peculiar command will save a Paper Space DWG into a new Model Space flle. Each part exists as a BLOCK, so it must be EXPLODEd. The first time through, the EXPLODE command produces SPLINES, ARCS, LINES and other objects. The PEDIT command will convert a SPLINE into a PLINE. I recommend converting all SPLINE segments into PLINES and then using PEDIT Join to recreate closed loops. If you join a spline into a PLINE then the spline will not become a proper curve. So convert the spline to a pline first and then join it. I used the OFFSET command to create new paths to cut holes in the largest elements to make them lighter and more elegant. The DWG drawing was then saved as a DXF 2004 file because that is what MasterCAM wants to import. It imported without errors and Kyle rotated it in MasterCAM to the orientation that the router expects. He set the tool cut depth, linear speed and revolution speed and designated the order to cut the profiles. When designating the order, it made sense to first cut all of the holes so that we could put screws in each hole, and then pick parts in a proximate pattern to avoid moving the head needlessly. Cutting at first produced rough and rather nasty edges, but after adjusting the cut settings and adequately securing the stock the cuts came out beautifully. Here are the parts laid on tables awaiting assembly. The scrap is also beautiful and reminiscent of a dressmaker’s remnants. It is all pretty easy and straightforward. I am dying to see 110 feet of aluminum canopy models lined up outside Langford Architecture Center!

More form making with Revit

Here are some of the sketches that I have produced with Revit to model a train station canopy. The basic idea is to make a swept blend form that has two profiles parallel to the track and a path perpendicular to the track. The form can then be chopped into various sectional ribs and purlins that create the primary and secondary strucure of the canopy. One conceptual trick is to use the offset command on the profiles P1 and P2 to make several profiles and eventually several concentric shells. One shell will eventually be the purlins, one shell will be the beams, and perhaps a final shell will become columns. If you edit the basic founding curve then you have to recreate all of the subsidiary profiles. That is not difficult, but it seems like there should be an easier way. Once the form has been created and tweaked and shaped, you need to cut it up to make the structural mmbers. I built a new family of void boxes that can subtract away the bays leaving just the structural members. The family is parameterized to include bay spacing, a bay depth, and a structural thickness. It also has a parameter that works with the array object to repeat the bays. One instance of this bay family cuts the purlin shell into individual purlins. Another instance cuts the beam shell into beams. A third instance cuts the column form into columns for each bay. I am not really satisfied with the columns. I cannot figure out a way to shape the columns so that they are responsive to the roof form above them. Of course, one could just use form making tools on each column individually. I have posted a bunch of screen dumps that might serve as inspiration.