“Tripod” update

I spent a little more time last night polishing my take on the Slopes tripod. In the process, I noticed there’s still more work to do. I expect this prototype will not be my last. My concerns are:

  1. I haven’t accounted for tolerances. Maybe I’ll need to make the openings 0.5 mm larger.1 With OpenSCAD, this would be relatively easy to do increasing the size of three objects by 0.5 mm on two dimensions each. With 123D Design, and the diagonal cuts on this design, I’ll have to do 0.25 mm tweaks on fourteen surfaces.
  2. The Slopes tripod has at least one relief cutout adjacent the shutter release. I’m going to inspect and measure Jamison’s GoPro camera and to see whether this effort is necessary.

I think the Slopes tripod is a great idea. I’m planning on getting a ReplayXD Prime X camera, even though its image quality is a little lower than the GoPro’s because the Prime X is much lower profile. I think I’m going to try making a low-profile tripod for a cylindrical action camera.

  1. It’s time to get some calipers so I can accurately measure the printed article to compare with the design. Right now, even though I’ve printed two (and waiting for the third) footstops, I don’t know whether printed articles are oversized, undersized, or what. 

Low-profile “Tripod” for GoPro cameras

Designing stuff with OpenSCAD can be frustrating. Not having the native ability to create fillets on edges, the workaround I’ve discovered1 is tedious and slow:

  1. Create a primitive object that is smaller than the desired object by the radius of the fillet.
  2. Use the minkowski() function to apply a sphere having the radius of the desired fillet to the primitive, effectively applying a fillet to every edge of the primitive. Warning: minkowski() is slow.
  3. Use the difference() function to remove fillets (and excess size) from those edges that don’t need fillets.

This is the process I’ve used designing my footstops so far.

There are free CAD programs that make fillets easy; one is Autodesk 123D Design. I had tried using it a little in the past, but it has its own difficulties.2 Regardless, I decided it was time to try something new.

The Slopes “tripod” for GoPro-sized action cameras is a nice project to duplicate. This comparison shows the result. I’ll print it next week.

I have a lot to learn. :-)

  1. I believe there are fillet libraries I could use, too. 
  2. It’s much harder to be precise. Repetitive tasks (such as the grooves on my footstops) can’t be programmed; each one must be created individually. 

3D printing solid parts

This last Monday evening, I went to the Hillsboro Public Library 3D Print Lab to get one of my longboard footstop designs 3D printed. I was concerned my design wouldn’t meet their requirements because I had done nothing to minimize the amount of plastic it would need.

In preparation for the lab, I had downloaded and experimented with Meshmixer, a program for modifying .stl files. Meshmixer can automatically hollow out objects but I didn’t know whether the resulting object could actually be printed. After all, 3D printers can’t print on air; there must be a supporting structure. So I showed up at the lab with my original unmodified .stl file.

At the lab, I learned a few things:

  1. The program that drives the 3D printer is smart enough to create a temporary supporting lattice underneath an otherwise unsupported portion of a printed object. For example, if you want to print a sphere, the program would automatically generate the portion of a cylinder beneath the sphere as a support base. The program generates a weaker connection between the support base and the desired 3D sphere so the base can be removed from the sphere with some effort.
  2. Not all unsupported portions need a support lattice. Objects can expand out at up to 45 degrees before a temporary support structure is needed under the cantilevered portion.
  3. The program is smart enough to automatically hollow out solid objects, defining a minimum wall thickness and then filling the interior with a lattice to support the object’s top surface. The picture at the top of this post shows coarse and fine lattices.

In short, the program that drives the 3D printer is smart enough to solve these problems automatically. Cool!

Longboard Footstop in OpenSCAD

My local library, the Hillsboro public library, has 3D printing open labs — every Monday evening for a couple of hours, the library accepts .stl files on thumb drives and prints them for free over the next week. This is such a cool resource, it seems irresponsible not to take advantage of it.

For my first project, I decided to design a longboard footstop.1 Earlier this week, I started researching 3D CAD software and settled on OpenSCAD.2 OpenSCAD is different from most 3D CAD software in that you program a part instead of manipulating objects on a screen. For example, this is how I defined the tab of the footstop:

union() {
tab_s = tab_length - tab_width/2;
tab_r = tab_width/2 - stop_chamfer;
tab_h = 2*(tab_height - stop_chamfer);
translate([-tab_s/2, 0, 0]) cube([tab_s, 2*tab_r, tab_h], center=true);
translate([-tab_s, 0, 0]) cylinder(r=tab_r, h=tab_h, center=true);

Designing the footstop, some of OpenSCAD’s other limitations became obvious: fillets and chamfers are not easily defined, especially along curved intersections of primitives.3

This is my third iteration of the footstop and I think it’s good enough to print next week so Jamison can try it out. I suspect I still have a lot to learn when it comes to getting a design ready to print. For example, how important is it that this footstop be hollow? If it needs to be hollow, what’s a reasonable wall thickness? I experimented with MeshMixer a bit, but expect I’ll need to wait until Monday.

I wonder what I should design next. I think I’d like to try some sort of GoPro mount.

  1. If imitation is indeed flattery, RipTide and PSD Designs should feel complimented. ;-) 
  2. Pronounced open ess cad
  3. I’m gathering resources that address this issue. 

A No. 1 Day!

I was No. 1 at the blood drive this morning.1 :-)

  1. Yeah, there’s even fine print for this simple statement. I was fourth to give blood. The three ahead of me went straight into the medical information booths without having to wait. Still, I arrived before the volunteer who signs donors in, hands out the medical information booklets, and gives the queue numbers. 

How to ask an expert the right questions

“What questions should I be asking you?”

Sooner or later, most of us will need the advice of an expert.1 When we do, we won’t always know what questions to ask. That’s because knowing the right questions is part of what makes an expert an expert. Fortunately, there is a simple question you can ask:

“What questions should I be asking you?”

This question fundamentally changes the relationship. The expert, instead of merely answering your questions, is now responsible for ensuring you get answers to the right questions.

When you ask this question, you’ll see a visible change in the expert. The expert will stop, think, and then answer a question you didn’t know to ask. Moreover, this question will be one the expert, in her expert opinion, thinks you should have asked.

That’s magic!

  1. Image credit: “The Deanna Troi Is In” by JD Hancock. Used under a Creative Commons license.