Wednesday, July 24, 2019

Fusion 360 - Threads Not Exported to STL

There is one thing that I always have problems with, so hopefully by writing this short blog post I'll remember more often. That problem is creating threads properly. Usually I noticed after I have already printed the part. Always remember to choose the "Modeled" check box. I wish I could make this the default.

Also, if you need to remove part of the hole after the threads in the timeline, you'll have thread remnants, so move the threads to be later in the timeline, then "Cut" the hole.

Thursday, July 18, 2019

Very Large Raspberry Pi Cluster - Part VI

At this point I've shown how the all the Pi will be held in place to make a 2U rack, and next is the overall structure but that will have to wait until next week. So for this post I wanted to talk a little about the software and what we're going to run on all these Pi. A lot of data will be processed and sent to the cluster. So here's the high level of the software stack:

  • Each Pi will network boot from a central server running Oracle Linux
  • The boot image will be running Oracle Linux
  • It will be running Kubernetes and Docker
  • There will be a very large video wall run by a Windows server
  • Everything will be written in Java
  • Gluon is helping
What exactly it will do will remain a mystery until you come see it in person. So sign up for Code One and come see it!

Thursday, July 11, 2019

Very Large Raspberry Pi Cluster - Part V

Last week I said I'd talk more about this part. So here is what the main bracket of the Pi holder looks like and the two parts individually.

The print time for the Pi holder is 98 minutes. It's a lot but it's a lot of plastic too. I print 12 of them at time, at 15% infill, with a .8mm print head, no rafts or supports. I can print one rack in 24 hours. You can do the math from there how many days the printers will be running. I spent a few days optimizing the amount of filament and the print speed with the strength needed. It is over engineers and will not break when being shipped. It is easy to assembly and requires very few parts. The reason for the curves is because it prints faster since the print head doesn't have to slow down when it approaches a corner. I was going to make the front two exes that are square round but it only saved 30 seconds print time and looks better being square when fully assembled.

Here are some views of the models from different angles since these are two separate pieces. Here are two views with the two pieces combined. You will notice a square rod coming out of that slot.

That square rod is a piece of aluminum extrusion. Specifically it is 80/20 series 10 that is .5in x 1in x 18in. I had 16.35mm milled off the end and the ends tapped for 10-32 by a local machine shop (GSFAB in Santa Cruz).

So I print 21 of the Pi Holders and two of them end caps (mirror of one another). Bolt an end cap to one end. Add one plastic threaded insert to the top hole, bolt a Pi on (the bottom holes just sort of clip on), slide it on the 80/20, repeat. After 21 Pis, bolt the last end cap and it looks like this:

So, there's a 2U containing 21 Raspberry Pi in a 19in server rack. I've only got 48 more of these to print and assemble.

Wednesday, July 3, 2019

Very Large Raspberry Pi Cluster - Part IV

So I've had a couple weeks here without much of a progress update. A lot of work has gone on. So here's a quick update before the holiday. First some photos. The first one is of the original prototype 3D printed out with some Pi in it.

This is a very nice design. The Pi just snap in place, there's room in the back to get to the micro USB power plug. But there are three problems:

1. I can only print half a 2U, so things had to be designed in such a way that once side is put into place, slid over, the other side goes in and is slid over and bolted, the first one slide over bolted, then the two remaining Pi on the ends are put in. And it requires two people.

2. It takes 50 hours to print one 2U holding 21 Pi.

3. It requires access to the rear of the rack. Without those rear bolts it wouldn't survive shipping.

So back to the drawing board. And here is the new design.

It's difficult to see what's going on here but there are 23 individually 3D printed pieces; one for each Pi and one for each end cap. They connect together by sliding on a piece of series 10 80/20 1"x.5"x10" long that has had about 3/4" milled off and the ends tapped. These are at the machine shop now so I will show some photos when I get them back.

One thing that's really nice about 3D printing is the RepRap; or the ability to rapidly prototype and revision. 3D printing is slow, but it's faster enough to do this. Here are some of my tests.

The one in the middle is close to the final design. You can see that two of the bolt hols of the Pi have a post and the last one has a threaded insert for a bolt.

Next post I will go into these two parts in detail. They have been designed for strength, speed of 3D printing and ease of assembly.