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. 

DIY Panniers

I love panniers. I just don’t like spending $100+ for a pair of ’em. When Jamie showed up at Starbucks with a DIY pannier on his bike, I knew I had to do some research. Here’s what I found:

Looks like I’ll be making more than one of these. :-)

HVAC Debug Update: I’m Making Progress

Determined to debug my HVAC problems, I created a list of steps to follow. I planned to verify the presence of power and control signals at the furnace control circuit and the condenser.1

Not feeling comfortable about my knowledge of how my HVAC is wired, I searched and found Thermostat Wire Color Codes and a thermostat wiring schematic.2

First, I verified the 24V transformer’s primary is getting line voltage.3 Then, checking the secondary, I found no voltage. I tried again. I pulled it out of the furnace and tried again. Still no dice. I guess I could have just measured the impedance across the secondary and discovered the transformer was bad4 and needed replaced.

Unfortunately, by the time I discovered this, the local appliance parts and electrical supply stores were closed for the week. Home Depot and Lowe’s were still open but neither has a matching transformer. Looks like it will be next week before our HVAC is working.5

I’m concerned: if I replace the transformer, is something else wrong that will kill the new one? Or did the transformer just die of old age? I guess I’ll find out.

Fortunately, the weather is getting cooler.6

  1. Essentially, this is rule #1 of debugging: is it plugged in? 
  2. Ya gotta love the Transonics wiki’s disclaimer/warning/license: “The following information may have errors; It is not permissible to be read by anyone who has ever met a lawyer. Use is confined to Engineers with more than 370 course hours of electronic engineering for theoretical studies.” I’m still trying to figure out how this applies to me
  3. Yes, this means the breaker was ON and the furnace cover was off. If you’re thinking of using my post as a guide to debug your HVAC system, you should read the preceding footnote. 
  4. It was shorted. 
  5. Does this help? ;-) 
  6. But I don’t have forever; the heat doesn’t work either. 

Hot Weather Means the AC Dies

Our HVAC stopped working in the hottest week of the summer (so far…). Rather than call an HVAC tech, I’m trying to fix it myself.1

Symptoms: no fans start running even though thermostat is correctly set (and for that matter, fan set to “on”).

Checks so far:

  1. Breakers
  2. Thermostat batteries
  3. Short yellow to red and wait two minutes
  4. Interrupter by condensor
  5. Look for fuses in furnace control circuit and interrupter (there were none)

At this point, I think it’s time to verify voltages and signals, starting with the transformer and furnace control circuit, then moving outside to the condensor.

Wish me luck!

1After all, what could go wrong? ;-)