Help creating ellipsoidal ramp

[JimStark]

I am trying to draw a 3D ellipsoidal ramp in Vectorworks 2010.

I've drawn the 2D version, and extruded it, creating an ellipsoidal block. I am trying to adjust the one edge down to create the 'ramp' in 3D.

How do I... do that? Should I go back to the 2D version and go in a different method? Have I gone to this point properly, and just do not know how to use the proper 3D tool? I'm still teaching myself this program, and this is a new step for me. I remember creating a curved ramp in the 'teach yourself' program a few years ago, but can't find it now.

Attached are screen grabs, in 2D and right isometric.

Edited January 4, 2013 by JimStark

[Benson Shaw]

Jim, Lots of ways. I like lofts, so here is an approach:

Draw your plan view with 2d linework, say with oval tool and offset it for the inner/outer curves.

Cut them in half. You don't want to work with the entire oval.

Convert each one to NURBS. Ungroup if you did both at once and they made a group.

Duplicate both. Now you have 4 NURBS curves. Two outer & two inner, stacked.

Switch to Front or other side view

Dbl click one of outer the curves, choose the z constraint mode of the reshape tool.

Start moving points to make the curve rise as you wish. Use the back quote key to turn off snaps if necessary. They will only move in z direction, so your plan shape stays as drawn

Repeat for the inner curve.

Make sure all 4 curves have same direction and loft by clicking them in sequence.

If you need separate color/material on the different surfaces, loft in pairs.

HTH

-B

[Benson Shaw]

If the ramp is constant thickness, loft the top surface as above (makes a group of NURBS surfaces)

Apply the Shell tool in 3d tool set. During the Shell operation, shift click each surface in the loft - they higlight as you click them. You don't have to enter the group to work the Shell tool.

B

[JBenghiat]

If you want the deck of your ramp to be the ellipsoidal shape, this object is fairly simple. Either rotate your extrude or set an angled working plane when you draw your 2D curves. Next use the Split Tool, Reshape Tool, or Subtract solids to get you ramp.

If you want your ramp to have the footprint of your shape, then you need to use NURBS curves and the loft tool.

Start with your two elliptical segments. Convert each one into a NURBS curve with the Modify>Convert menu commands.

If you knew the curve of the ramp instead of the footprint, the loft would be more straight forwards. An Extrude Along Path may also work well. Not knowing the curve, the easiest part of the ramp for VW to calculate is actually a side. (I find that mastering solvable lofts takes some trial and error to really understand what VW can calculate),

Start with the end of an elliptical side at the bottom, and place a 3D locus. Next go to the top and draw a vertical NURBS segment the height of the ramp. This may be easier if you first convert the line representing the top of the ramp to a NURBS curve, then elevating to height.

With the Loft tool, select the single rail mode. Choose the curve as the rail, then the locus and vertical line as profile curves. Click the green check in the mode bar. Preview your curve. The part of the curve you click determines its direction for the loft. If you connect opposite ends of the curve, the preview will appear all twisted. You can correct this in the dialog. You should now have one side of the ramp.

Repeat for the other side.

You can now use the extract tool to get the top curves, one curve at a time. There are now a few ways to get the top surface of the ramp. I think the easiest is to select the two side curves and the beginning and end edges and selecting 3D Power Pack>Create surface from curves. You now have a group of curves representing the top of the ramp.

If you need the whole ramp to be solid, you should be able to fairly easily create the end and bottom, then stitch and trim the whole thing together.

-Josh

[Benson Shaw]

Good method for constant rise, no banking of ramp.

Following is comment about Vectorworks, not JBenghiat's described ramp creation:

After the loft with rail, Top/plan view shows that the upright NURBS in the profile leans away from center during the loft. New top edge of loft is not directly over the ground plane shape throughout the curve. Another way to see this is to extract the top edge and compare in top/plan to ground plane path object.

Anyone else see this?

-B

[mjm]

Benson & Joshua- thanks so much, such useful info.

[Benson Shaw]

OK, There is potential for significant displacement in the Loft w/Rail for side of curved ramp. Here is image with dimensions. Top of loft is not directly over the rail. 6" in 25' radius for this one. Rail here is semicircular NURBS curve. Ovals and other curves may have less or more displacement.

I submitted a bug on this.

-B

[Kevin McAllister]

If your ellipse can be drawn with the arc method, you could try using a curved wall for each segment.

KM

[Jonathan Pickup]

Drawing an ellipse

[JBenghiat]

Benson,

I can confirm what you are seeing, and the larger the scale, the greater the offset. I'm not a NURBS expert (any industrial designers care to weigh in?), but I believe what is happening is that even though the base curve is co-planar, the vertices orient in three dimensions. Imagine taking a piece of flexible wire, drawing a stripe at the top, and bending it into an ellipse. The stripe would bow out at the middle. The more your elliptical segment extends towards its end vertices, the greater the bow.

There may be ways to manipulate the rail curve to untwist it, but that is beyond me.

I can think of two fairly quick fixes to ensure straight sides:

- Use the reshape tool to move the top vertices of the loft into place. If you constrain to y (or x if the shape is vertical), the task is fairly fast.

- Use the project tool to project the top curve onto an extrude.

-Josh

[JBenghiat]

OK, one more method. Split the base curve in half.

Draw another vertical at the mid-point (now end points) at half the total height.

Loft in bi-rail mode, selecting the mid verticals and either the locus or end verticals as the rails. The bottom curve is the profile. (Let the loft keep curves.)

You will have two lofts with much less bow. I imagine that if you split the curve into quarters, it would be even more square.

-Josh

[JimStark]

Wow, you guys rock.

Now, all these ramps are built where one side of the ramp touches the ground, and the other on the next level, but would these still work if I wanted the INTERIOR of this ellipse to be one level and the EXTERIOR to be the other? So the incline travels the width as opposed to the length?

(this is in no way a wheelchair ramp of any kind; it's a staging piece for a performance space)

[JimStark]

Ok, using NURBS, I tried something:

I created 2 NURBS polygons, one set at 0" on the Z axis, and the other at 1'4". This gave me the opportunity to snap the interior ellipse of the 1'4"Z ellipse to the 0"Z ellipse. This has me CLOSE to what I'm looking for.

Does this method sound like it could provide any way to punt my plan later?

[Benson Shaw]

Josh - Yes, the NURBS must do a twist as they bend, and your analogy of the stripe is good. I have several ways to eliminate the bow.

Jim - Yes, exactly. Sounds like you are making kind of a skateboard half pipe, only curved in plan. Can you post an image of something similar to what you want? You say you snapped the two. Do you mean you clicked them with the Loft Surface Tool?

Try this:

Make 3 NURBS curves- the two ground plane and the raised one.

Make a simple Loft Surface ( the first mode, not the Rail or Bi-Rail modes).

Choose Ruled and Keep Curves in the dialog.

My setup view has the dialog text missing because screenshot command bug (reported as bug by others). I annotated in red text.

My rendered view is OGL with Edges, hence the mid surface lines. I ungrouped to show that Loft made 2 surfaces.

HTH

-B

[JimStark]

Attached is a copy on a customised right isometric of the ramp I am trying to make. It's bottom plane is at the 0"Z, while it's top height is at 1'4"Z height.

Hopefully, once I get this working properly, I can more accurately measure the planes, and try to figure out exactly HOW to build this.

[Benson Shaw]

Do your own thing, but one could spend many hours modeling the construction details of this and developing cut schedules. But it's probably faster to just lay out points for the plan curves in Vectorworks, estimate the material quantities from the model, draw a generalized cross section, and then build it from that.

Use Duplicate Along Path to create convenient sized radial sections - 48" max wide? Lay out the plan view base on plywood and cut the curves. Stand up the vertical surface (dbl layer of 1/8" or 1/4" fiberboard?) and bow it to the base. Use right angle jigs to keep it upright & bowed. Scribe & cut a few 1x4 "joists" to fit radially from upper edge to inner curve. Scribe in some 1x4 studs if more strength is needed. The slanted skin is built up fiberboard or plywood bowed onto the joists. Stand up the sections to trim the inner edges, or build everything on tables so the skin can overhang before trimming.

Sorry, running on here. Good luck. Post back with your success story.

-B