Greenhouse 2
Grid Hardware
Published: 2020-05-23

This is the development diary for Greenhouse 2, the second iteration of my homebrew micro-rack.

2020-05-01 – Introduction

The original Greenhouse was a success, but several lessons were learned from it.

  • Use of mITX boards minimized footprint, but drove up cost and reduced choice
  • Over/under PSU design minimized horizontal footprint, but led to increased vertical spacing and more complex mounting
  • Minimizing horizontal footprint wasn’t worth it
  • Fully open design probably didn’t cool as effectively; pushing air where you want it isn’t as effective as forcing it to be pulled through where you need it
  • Even moderately complex cutting and shaping of metal is a nightmare without proper tooling and space

And so the next iteration will be changed in several fundamental ways.

  • Use of mATX, or possibly full ATX boards
  • Side-by-side mobo/PSU mounting
  • Solid wood sidewalls, rather than open metal framework
  • “Wall” of 140mm fans at the back of each system tray
    • Fans attached to tray, not chassis
    • Possibly with small diverter walls on the trays to guide airflow
  • Plan for 1 GPU per tray, instead of expecting zero
  • Reduce vertical unit spacing, with a goal of 6 or 8U rather than 4
  • Reduce complex shapes. Try to only use 90 degree/perpendicular cuts. Use a dremel to cut where possible

It will be some time before any actual work gets under way. The goal is to have the new rack ready when Ryzen 4 CPUs come to market – probably half a year from now. In the meanwhile, I plan to re-use the cardboard tray mocking technique from Greenhouse 1 to plan the basic layout and such.

2020-05-23 – Trays, etc.

There are three things I want on the tray:

  • mATX mobo: 9.6"sq
  • ATX PSU: 6” x 3.5”
  • 140mm fans: 5.5"sq

Mobo + PSU, rounded up, is 14” width (fan height and PSU width are close enough that I think it makes sense to mount PSU on its side). Add an inch for padding and that’s 15” – only enough for 2 140mm fans, with 4 inches of open space.

Bump tray width up to 17” and that allows 3 fans, with just enough space (1/2”) for power/ethernet cable routing. This obviates the need for a diverter wall on the tray; it’s just wall-to-wall airflow.

Won’t be able to detach power/eth until the tray is partially/mostly pulled. Screw in a 1/2”-1” strip right under the tray rails, at the back, as a cable guide. Maybe glue a tiny bump right under the rightmost fan, to keep cables to the side of the fans.

Put 3 of the same strip across the bottom of the chassis for stability and rigidity. Top will be an extra tray, screwed in place, so that the top machine tray will have channeled airflow.

Tray rails will be L-channel, as in Greenhouse 1.

Remainder of chassis (including trays) probably made from this shelving. At 97” length, that’s 5 trays per shelf, with a foot left over.

Each tray will be mounted slightly less than 7” apart: 42” minimum sidewall length/height. One extra inch on top/bottom is 44”, but let’s round up to 4’ just to ensure there’s enough space.

  • Shelf 1
    • 5 trays (17 * 5 = 85”)
    • 12 inches spare
  • Shelf 2
    • 2 trays (6th machine tray, plus top cover) (17 * 2 = 34”)
    • 63” remaining
    • 1 sidewall (48”)
    • 15” spare
  • Shelf 3
    • 1 sidewall (48”)
    • 49” spare

That shelving is 11.25” wide, so each tray rail would be 11” long. Slotted angle comes in lengths by the foot, so I need 12 feet of it, which is three of these.

Also, this time I’m not working things by hand. I’ll be picking up a Dremel Saw-Max to handle the finishing cuts of both wood and metal.

  • 3x MDF shelf @ 20: $60
  • 3x steel angle @ 15: $45
  • 1x Dremel saw: $100

Total cost: $205

(Plus <= $10 of spacers, bolts, screws, nuts, and washers.)