Merging modern software development with electrons and metal
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Sometimes Paper Is Better Than Tech

If you’re one of the elite few who has followed my blog for a while, you know that I like quality pens, pencils, and paper, as well as technology such as 3D Mechanical CAD.

I’ve been working on the electrical portion of a new machine, and this week I started on the layout.  We normally let our tech do the final layout since he does the actual wiring, but I need to make sure everything will fit, and with his help, want to get as close as possible to the final arrangement.  (Ideally, I want to work with our mechanical engineer and tech to get all the DIN rail and component holes placed correctly, because it’s a lot better when these holes are made by the sheet metal shop.)

I thought about trying to use 3D MCAD, but decided instead to cut sheets of vellum to match the panel size, and print life size profiles of the various components.  (I used vellum because I can easily tape and re-tape the cutouts to it).

This approach works well because:

  • I don’t have to create 3D models.  Some manufacturers do not supply 3D models.  Using 2D prints, I can use a PDF (by using Print View and scaling the output – thanks Adobe!), a 2D file such as DXF or DWG, or 3D (by scaling the print or creating a projection).
  • It’s much quicker to move the component prints around.
  • And, to be honest, I like the tactile touch of moving the paper cut-outs around and that everything is life size, not downsized on a smaller computer monitor.

Doing a full 3D model does have some advantages; working in 2D, I have to make sure I accommodate how deep the components are.  But even in 3D, you have to add extra space for hard to model items like cables.

March 28, 2015   1 Comment

End Effector Notes: STL, VRML, and Colors

I’ve been having major problems importing my end effector into Denso WINCAPS III and maintaining my desired colors.

WINCAPS III can only import Direct-3D (*.X) or VRML Ver 2 (*.WRL) files.  On the other hand, most MCAD software won’t export VRML files.

I used DesignSpark Mechanical (DSM) to create my design.  DSM can export 5 3-D file formats: STL, OBJ, 3D PDF, SKP (Sketchup), and XAML.   I was frustrated trying to set the colors I wanted in DSM; help (including blogs and forums) is still very limited, and I couldn’t figure out how to change the color of imported STEP files.  I was able to get to this:

DesignSpark Colored End Effector

DesignSpark Colored End Effector

Since I choose to export to STL, the next step was to convert from STL to VRML using meshconv, but when I imported the resulting VRML file into WINCAPS III I got this:

Initial Result in WINCAPS III

Initial Result in WINCAPS III

Yuck!  All my color is gone, and my part is white hot and glowing purple.  I’m pretty sure part of the problem is that the WINCAPS simulator has a bright light, which as far as I can tell can’t be adjusted; when the part is rotated, the bright spots change.  But the major problem, which took me a while to figure out, is that STL files normally do not retain any color information.  After all, it’s not needed by most 3D printers, and STL was invented for 3D printers.

I did a little more research on the DSM export formats.  I am using two conversion tools, meshconv (a command line converter) and MeshLab (which includes a viewer and much more).  Of the 5 DSM 3D export formats, meshconv and MeshLab are only able to import STL and OBJ.  While OBJ may be able to contain color information, it wasn’t retained when I tested exporting from DSM to OBJ and then importing in meshconv or MeshLab.

I tried using SketchUp.  I was able to color the parts with a bit of effort (see below for an example), and export to VRML using a add-on, but WINCAPS III didn’t like the resulting VRML file.

End Effector In SketchUp

End Effector In SketchUp

So I ended up using MeshLab: I exported from DSM to a STL file, imported the STL file into MeshLab, colored using MeshLab (pretty easy), exported from MeshLab to VRML, and finally imported the VRML file into WINCAPS III.  The colors in WINCAPS are pretty different from MeshLab’s colors, but they’re much better than my first attempt.

End Effector in MeshLab

End Effector in MeshLab

The Final Result

The Final Result

March 25, 2014   No Comments

Eagle 3D PCBs with Alibre: Assembling the Model Part II

Before starting to put all the pieces together, spend some time planning.   Things to think about include:

  • What is your naming convention?  A good naming convention for parts and assemblies really helps you remember what is what.  Which is a more useful name for a connector model, Part_21 or AMP 5499206-IDC-26?
  • How are you going to assemble the part?  Are you going to use any sub-assemblies?  Good use of sub-assemblies makes assembling the model easier and more logical.
  • Do you have all your part models?  I like to have all my models ready before assembly, but you could start with what you have, and download or create as you go.
  • Do you need to modify any manufacturer provided models?  For example, your part might be slightly different from the closest manufacturer model, or you may need to modify the part (e.g. by adding reference geometry) so you can easily add constraints.
    • I’ve come across both these cases, and will discuss them more in the future.
  • Are you going to directly import your manufacturer models into your assembly, or convert them into Alibre parts first?  Alibre Design 2011 can directly import STEP, SAT, and IGES parts into assemblies.
    • IIRC, previous Alibre versions couldn’t directly import into assemblies, which is why my current designs convert all imported parts into Alibre parts.

Here are my tips on adding constraints:

  • Come up with a naming convention for constraints: J1_Align_Pin1 provides much more information than align22.
  • Position the parts so you can see all the features you plan on using to mate the parts together.  I really like using the triad tool, with minimum motion mode off.
  • I’ve had much better results using the manual constraints dialog than trying to use quick constraints.  Sometime I’ll give quick constraints a try again.
  • I’ve found it’s always necessary to move and zoom all around, and every time I use the icons, my constraints dialog goes away, so shortcuts are the way to go:
    • Pan: press and hold middle mouse button, then move mouse pointer
    • Rotate: position the mouse pointer where you want to rotate, then press and hold right and left mouse buttons, then move mouse pointer.
    • Zoom in: press Page Up
    • Zoom out: press Page Down
  • Be careful where you click; it’s easy to select a feature you don’t want.
  • I like anchoring one part (for example, the PCB) so I know which part will be moving when I add constraints
  • Check the defaults.  Often, the mate constraint will show the current distance between parts, so I have to change it to zero.
  • Use your PCB layout as a guide.  OK, if I could get Alibre to handle the silkscreen layer this wouldn’t be necessary, but it’s handy when I have a PCB full of holes and no silkscreen information on the PCB model.

January 13, 2011   2 Comments

Eagle 3D PCBs with Alibre: Assembling the Model Part I

The final step in creating a 3D PCB model is to assemble all the pieces together.  Normally Alibre assemblies are created by constraining the parts.

A constraint limits how two parts can be located relative to each other.  Three constraints fully constrain a part.  For example, think of mating a through hole connector with 10 pins in one row to a PCB.  You could add three constraints like this:

  1. Use an Align constraint to align the axis of the connector’s pin 1 with the PCB hole for pin 1.  Now the connector is limited to two degrees of freedom: it can move close and farther from the PCB and it can rotate 360 degrees  around the pin-1/hole-1 axis.
  2. Use another Align constraint to align the axis of the connector’s pin 10 with the PCB hole for pin 10.  Now the connector cannot rotate: it can only move close or father from the PCB.
  3. Finally, use a Mate constraint with a zero offset to mate the bottom of the connector with the top of the PCB.  Now the connector cannot move at all; it is attached the the PCB just like you had perfectly soldered a perfect connector to a perfect PCB (pins centered in the holes, connector just touching the PCB, etc).

That sounds pretty easy, right?  Well, the reality is often different.  Extruding a PCB is straightforward.  Mating parts together is not; there are many possible ways of mating the parts together, and the best approach depends on the specific parts and PCB.  I think MCAD assemblies are complex enough that an expert could write a book just about assemblies (and I’m definitely not an expert).

I haven’t found a lot of practical information on Alibre assemblies.  My findings so far:

  • You should definitely read the Alibre Design User Guide chapter on assemblies.  It covers what’s available, including about 20 pages on constraints, but is brief and descriptive.  It does not give any examples or practical advance.
  • Based on the table of contents, the Learn 3D CAD book also only covers constraints briefly (about 20 pages), but still looks like it’s worth the price, since it has a real world example, and advice on overall design (top down vs bottom up).  I’m planning on getting the PDF version when the 2011 update is available.  Note 10/5/2011:  the Learn3DCAD website is no longer active, so this is no longer an option.
  • The Alibre forums look useful if you have a specific question, but aren’t a tutorial.  Also, if you’re on maintenance, there’s always tech support for specific questions.
  • I’m not sure how useful Alibre’s paid training materials (DVD, exercise book, online seminars) since they don’t provide detailed information on the contents.  I suspect they wouldn’t cover some of the problems I’ve had.

Next up in this series: some specific tips from my experience.

January 11, 2011   No Comments