How to fly across an ocean


This post is cross-posted from the White Star Balloon Blog

Flying across the ocean is no small feat.  It takes the concerted efforts of dozens of people, working hard at lots of difficult problems, from modeling balloon volume and flight dynamics, to planning interactions with air traffic control.  The diagram above gives a little bit of an idea of the effort involved in getting across the ocean.  Any single block represents tens to many hundreds of man-hours worth of effort.

Components in Purple represent things which will actually be flying across the ocean.  This hardware and software must perform flawlessly at all times.

Components with a red heptagon represent significant software efforts.

The red square shows the components which lie on amazon EC2, spread across three instances, with a total cost of $100 a month (during flight season) to maintain.

Pink commands are sent using PubNub, a service without whose generosity our public page would not be possible.

All of these systems are in the critical path, and a failure of any single flight system will compromise science data.  Fortunately, we always have positive control of our craft, thanks to a dead-man cutdown, which operates entirely autonomously, and a 9602 modem which will respond with rough location coordinates even if all other flight systems have failed.  Our ground systems all have hot-backups, and can all be operated from anywhere on the Internet, so these systems are as redundant as they can be.


Creating SVG files for solder paste stencil stencils from KiCad


Eventually, hand soldering surface mount components becomes a pain, especially if you’re doing small manufacturing runs. It’s much easier to work with solder paste and a hotplate.  Joints are higher quality, and you can manufacture more boards at once.  If it was good enough to get Sparkfun started, it’s certainly good enough for us! Working with solder paste does require a stencil, though.  The stencil contains precisely sized holes which allow solder paste to be precision applied to the metal pads on your PCB.  There are many companies which will provide cheap and high quality stencils, but if you have access to a laser cutter, there’s no reason you can’t do this yourself.

There are a lot of guides out there for creating SVG stencils from Eagle, so I’ll be covering KiCad in this tutorial.  Additionally, the laser cutter I have access to at the LVL1 Hackerspace is a Full Spectrum laser which can cut directly from Inkscape, so I’ll be basing this tutorial on Inkscape.

Step 1

Generate gerbers from your completely routed KiCad PCB project.  There are a lot of good guides out there for getting to this point in KiCad.

and a collection of resources here:

Step 2

Open your PCB in a program like Gerbv.  Any gerber viewer capable of outputting to SVG is alright for this, but I like gerbv the best.  You’ll want to open the solder paste layer, which KiCad names by default to something like “pcbFileName-SoldP_Front.gtp”.

Export to SVG, put the file anywhere you like. In Linux, you have to manually add the SVG file extension.

Step 3

Open the file in Inkscape.

Ungroup the objects by right-clicking on a pad or line and selecting “Ungroup.”

Open the “Fill and Stroke” menu.

Clear the “Fill”.

Turn on “Stroke” and set it to a color that your laser cutter likes.

Our full spectrum laser will try to cut the inside and the outside of the stroke if it’s too thick.  .1mm is thin enough that our laser cutter software will only cut the outside of the stroke.

Step 4

Before proceeding, you can delete the board outline, since it’s unnecessary.

Select all the objects, and open the “Transform” menu under “Object.”  Under the “Scale” tab, MAKE SURE that “Apply to each object seperately” is CHECKED.  This maintains the centroids of all your pads.  You’ll have to play around a little bit to get this value just right. Decreasing the size of the features is necessary due to the thickness of the stencil material.  The thicker the material, the more you’ll need to reduce the size of each feature.  For overhead transparency plastic, 90% is just about right.

Now you’ve got a finished stencil SVG, suitable for lasering.  In a future post, I’ll show off how to soldering using paste and a hotplate.