Modelling a Raspberry Pi Case - From Cardboard

DESIGN MODELLING - WHY EVEN THE PROS DESIGN IN CARDBOARD?

Hi – I’m Jude and I'm a Design Engineer. I've worked on a range of projects for a variety of companies in different countries - and in many cases we use pretty humble materials to make quick models to communicate and test ideas.

Often in the early stages of a creative process, CAD and Rapid Prototyping can take too long (and might be too expensive for mistakes!) so I wanted to share some techniques that although look simple have a lot of subtle tricks.... As with watching a fancy Chef on TV, they often skim over the details that took them years to master - which may explain why when you try it it's never that easy!

The cardboard Raspberry Pi Case example is not meant to be exhaustive or a final model – indeed, it assumes that you should iron-out the main functionality and aesthetics and then progress with confidence into more serious materials/CAD. The number of iterations is up to you - some might be straightforward, while others can take numerous revisions discussing details with users, manufacturers, etc. though conversations are more productive if you can feel and modify how a product works in front of you.

Just as ‘a sketch says a thousand words’, one could extend that to say a physical model says a thousand sketches… but as with both skills, they should be used appropriately and of course they take some time to perfect. I’m still learning a lot, but hope you in enjoy a few tricks I’ve picked up along the way… (An Instructables Guide of all techniques and more is also being made too!)


Note: A video tutorial of of this was initially done here, but I'm keen to see what you think of it in the Instructables format. Please check out both and let me know what you think!

FEATURES OF MY DESIGN

1. Ventilation
Your Raspberry Pi won't get that hot - but it will certainly not help it to run a movie - while fully air sealed. This was also an opportunity to make a design out of this feature, using an unlikely material - cocktail sticks.

2. Light Pipes
This is a very common technique used in design - where for economy you want the lights (LEDs) mounted on a circuit board, but the board is positioned away from the case or user-interface. By taking a piece of clear plastic, one can 'bounce' the light along it (because of refraction) over some distance. Here I will show you how to do this for yourself.

Experiement as you go - you might see things I've missed and want to change them!

Step 1: Sketch Some Ideas for Your Case

Sketching out a few ideas obviously helps refine what you want to design. If like me, you sketching is so-so, you might want to try Sketch-A-Day...

I considered 6 different grill styles for the case - which not only gave ventilation to printed circuit board (PCB) - but also made a feature of the lights (LEDS) on the board.

I then considered a rounded case or a square-edged case. I selected the square one for simplicity at this stage, but as you can see in other tips, it could be easily rounded too.

Step 2: Make Rough Models or Things You Are Unsure About

I wanted to check how the sketches of the grill looked - in rough - before I committed to modelling them fully. I cut out a window for the front case and inserted the sticks a number of orientations.

Keep experimenting until you are happy.

Step 3: Create a Template (net) for the Case

This is rough guide to the template needed to create all 6 sides of the case. A more accurate one is available here. I'd recommend using (digital) calilpers to measure things if possible - an example is given here.

Step 4: Creating an Accurate Cardboard Joint

This is perhaps the crux of this tutorial, as this technique for joining card together neatly and is not that well known. It involves cutting through the top layer of the cardboard, through the corrugated (wavy) part - but stopping just before the lower layer of card. The edge is then removed as shown below, with a ruler. The results are perfectly presentable for any meetings with designers or users. It is shown in more details here.

Step 5: Creating the Grill (with Cocktail Sticks)

Following your design laid out in your template, begin by cutting out the window, then pushing the cocktail sticks through (in-between the ‘wavy’ corrugations of the card). Glue in place with Hot Melt glue.

Step 6: Light Pipes

Now that the grill is made, cut the holes for the light pipes.

Next take some clear plastic sheet (about 2mm thick) and cut into the sizes as shown. This may require some fiddly cutting and snapping with pliers as shown - please check out this video if you have not done this before, here.

As shown in the final picture - check to see that the light is transmitted effectively, by hovering it over the PCB.

Step 7: Awesome Super-Glue Tip

Did you know that Super-Glue is very strong in tension, but relatively weak in shearing? (which is why it is better to 'roll' your fingers apart, rather than 'pulling' them apart)...

Similarly using insulation tape when constructing large assemblies (that are perhaps in tension) is ideal, as the tape can be pulled off easily once everything is glued in place.

Here it is used as a surface to take small amounts off of with a cocktail stick to apply in small quantities to glue the light pipes in. The advantage is that the superglue is not absorbent and prevents it drying quickly (compared to if it were on a scrap of paper).

Step 8: Main Assembly

Now that your have all the pieces cut out and assembled, you should find that applying glue to the ‘L’-shaped part of the cardboard will allow for tidy joints. Take care not to add too much glue or burn yourself.

Step 9: Power-up!

Hopefully when you connect everything up to your case, it should light up - and you see the various buttons shine through the front of the case!

Thanks for taking a look at this Instructable. I hope you enjoyed it and let me know how this compares to the video here.

Thanks,
Jude.