15 January 2016 / Last updated: 27 Jan 2017

Good, Better, Beast - Week 4

Execution time:

Let’s Get Physical…

Ahoy. We promised to venture beyond the comforts of CAD this week and commit to something real. Well, our word is our bond…
We went through two rounds of prototyping, where we improved the structural strength of the tile, fine-tuned the fits of interlocking components, and generally honed the details.

Prototype #1

proto-type 1
This guy demonstrated nice ease-of-assembly, but had more flex than we wanted and the fits were a tad loose. The swivelling legs worked great and the detent latch felt pretty good, though the interference was a bit loose.
We took some notes from Dan Emery, who posts some very useful lasercutting design guides. Of course, there’s a wealth of good guidance out there. If you’re keen to design for lasercutting to any level of detail, I strongly recommend that you read up before starting out. You’ll avoid some common pitfalls, and end up with a far better design more quickly.

Prototype #2

proto-type 2
Same idea as #1, but we beefed up the top and bottom panels to improve stiffness and strength, and also removed the weight-saving cutouts. Laser cutting beams have width, which results in the finished part edges having a small offset relative to the cutting path. To improve the tightness of the fits, we offset all edge by 0.05 mm to compensate for the laser width of ~0.15. We might increase that for tighter fits, but that’s more fine-tuning. An even more effective solution is to use nodes, as Dan Emery describes here and here, though this approach is a bit more labour intensive as you have to create new features, rather than simply offsetting an edge.

Prototype #3

Having learned a few lessons from #1 and #2, we’’ve bit the bullet and committed to a design and production run of 6 units (ok, so it’s not a huge commitment). The part arrived last night and we’re looking forward to starting assembly of these babies next week (or maybe this weekend if we’re keen).

Fun with Nipples

The design of the BeastTile hinged joints provided a nice opportunity for some ingenuity. First we discovered lighting nipple (M10x1mm threaded hollow tube, AKA ‘all-thread’), which allows us to pass rods through the hinge axles for added rigidity. Further we were led to an array of related products used in the manufacture of lighting fixtures.
After some playing, we arrived at this nifty system...
We laser cut and tap the thumbnut (which lets us customise, so we’re not limited by what’s out there). The thumb nut is to clamp the leg in position on the left, and holds the hinge together when two tiles are connected. We could use standard nuts, but this design provides better grip for finger-tightening so no tools are needed in the field.
The black component (known as a ‘cord grip’) screws onto the standard M10 threaded nipple, and has a grub screw to clamp the rod. We’ve been able to get a lot of functionality into a single feature, and it’s all thanks to nipples.
Before we finish up, below is the final design of the power hub. We ditched the second DC jack (it was a nice-to-have for daisy-chaining) to make room for a nice illuminated rocker switch from RS components. The switch enables us to switch power the all the devices on a tile, without affecting power to the network switch (which has a built-in power switch). The DC jack is a high-current unit, from Switchcraft and is rated up to 11 A, though you pay a premium. Common jacks are usually only rated up to 5 A, but we’re trying to maintain the 2.4 A capacity on each USB socket, so we needed at least 8 A at 12 V (2.4 A @ 5 V x 8 ports = 98 W = 8 A @ 12 V). This is just in case we want to run lots of power-hungry devices… Future-proof!
power bank
Very good. See you next week for an update on the first production build. Here’s a carry case concept to say goodbye.
carrying case
If you have questions or just want to say hi, you can find us on gitter.
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by Team balenaThe global group of product builders that brings you balena

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