Lightweight Hydroponic Tower

Last year I developed a planter system for the patio table that could take 2-inch net cups and I was planning on converting it to hydroponics (with better fitting joints and a water feeding cap. Several things dawned on me, not least of which was that I don't get 360 degrees of sun, and turning a tabletop planter is ok, but a hydroponics tower is less good. Also, each piece took a lot of time and filament, so less than ideal. Then earlier this year I noticed someone had perfected things and they were all over the toobs. So a new thing hit me, with new criteria:

• A simpler design
  • No cross bracing internally to stuff up clearances
  • ✓ A narrower diameter means a more stable unit, even in PETG
• Must be printable on the mini
  • total X or Y dimension must not exceed 90mm (4 parts per print on a mini)
  • ✓ 86mm for a tube. 
  • ✓ Caps have stick out bits that need rotating, but still fit in this footprint
  • ✓ All the planter parts can be printer 4 to a bed as well
• Must use less filament
  • Ideally less than 50g per tube part
  • ✓ About 33g of PETG per tube part (tube cap and planter accessories are a lot less)
• Must print quicker
  • less than 12 hours per 4 piece print
  • ✓ 10 hours 50 minutes in PETG with 3 perimeters and 5% infill

Design things for conversation

I did think of using downspouts (both the round and square) but I don't have anything to cut that properly, so I went this route.

The geometry will drip water from the plan above onto the grow cube below, once it's run down the sides and found the top cube. Lips around the holes limit water spilling out, and caps will cover the holes that are not being used.

Due to the size, the walls are thinner so use a dark and opaque filament or you'll have algae eating your nutrients. PLA and PETG are both generally food-safe but check with your supplier (Prusa's line is safe with the exception of the army green I think - don't quote me), PETG will hold up to heat better but goes softer. I've not had a problem with PLA for my planters in a year (in the south of the UK).

Reuse and all that. My reservoir is also supported by my Kratky/DWC bits, and there is a reservoir return support for that 76mm hole.

Downsides

There are 2 things I'd like to address one day. 

• The net pots don't stack inside each other. Due to the horrid geometry, this is currently baffling me.
• a simple lock in the twist mechanism. I did consider a divot to lock the lugs in place with friction, but with tolerances being what they are, this was not easy. I may design a piece that fits into the gap in the receiver.

My diameter choice

In order to get the dimension part right, I couldn't use the 2-inch net-cups I have because they either stick out a lot (at 45 degrees to the side of the pipe) or fall out a lot (if flat against the side). So I designed a square net-cup to hold the 1.5 inch (36mm) grow cubes I have. Although, for cost-saving, buy a Grodan slab (or equivalent) and cut up the 36x36x40mm cubes yourself with a bread knife.

My height choice

I wondered about the height to print things and settled on 110mm for 1 main reason: The net-pot sticks out in about the middle and looked nice. If you use the different offset tubes, you get a decent separation side to side, and then the 220mm height which is more than most plants you'd grow in a system like this (herbs and leafy greens for example). Just using the 30-degree offsets you get about 50mm of side to side stem separation and about 105mm vertically.

Extension pieces are also provided. 

• A 55mm one to give you nearly 6" planting
• A 110mm one for no reason other than it fits with the other tube parts
• A 175mm one to max out the Mini print height
• a 205mm one to max out the Mk3 print height

For the reservoir return tube, I wanted to have an option that ran the water into the water to reduce the waterfall noise. Neighbours and grow-tents in mind so the same heights from 110mm up are also present.

Your cup offset choice

The 30 degree (plus and minus) give a good plant separation for most herbs, and they mostly face front so if you don't have the greatest sun option these are great. If you do have a good sky full of sun, then the 60 degree (plus and minus) will give a much wider (50% more) separation.

Your cup-cap choice

Do you leave your net cups in when they are not being used? Well, there are 2 different hole covers. The planter cap is used when there is no cup, and the cup cover will slide inside the cup. The reasoning here is that the cups don't stack so will be a mission to store them, so store them in the tower and hope you don't have root invasion.

Printer tuned tolerance padding

As usual, things that slide together have tolerances based on your printer set-up. While my Mk3s are XY dang-near spot on, they still drift a bit when doing circles, especially with PETG. Therefore, a good fit for me to slide the pieces together well with PLA in these models is 0.15 (0.05 in square mode). My Minis are reasonably similar for PLA (loose at 0.15 a smidge tighter, and 0.2 a little loose rather than the usual 0.1 in square mode) but printing PETG on my Mini needs the 0.35 set of parts. This padding value only refers to the receiver/female part of the tube. In testing across my 4 printers, the cups and blanking places all fit in the holes as they have fixed clearance) and the male parts of the tubes have no padding on them and they seem to print out identically regardless of the machine I used.

TIP: Let your parts cool to the ambient temperature they will be in before committing to a tolerance and printing everything. I found the parts continue to cool after they come off the print bed and what was flipping tight to start with, and ok at "around" room temp, became quite loose in the garden.

Extras you will need

Most of the stuff you will need is regular hydroponics stuff. Basically, this is a form of Nutrient Film Technique (NFT).

• A reservoir with a hole cut in the top for the return (a 3-inch hole works well) and a smaller hole to feed the water tube out). Size is up to you. I use this 35l tote which supports 2 towers easily: https://smile.amazon.co.uk/dp/B001O3IE6E
• With the tote above, you can use a lot of the parts of my Kratky/DWC stuff to make holes prettier and add a water gauge. Added the reservoir return support here for that purpose and a 76mm hole in the tote lid.
• A water pump. The specific one depends on your head height. Any pond pump will work as long it can pump the water the required height from the top of your reservoir to the top of your towers.
• Water delivery tubing. Irrigation tubing is fine for me. The thick stuff routes water and the thinner tube for the take-offs and feeds into the top of the towers.
• Optionally an air pump, tubing and stones to aerate the water, but the water falling back will do most of that heavy lifting, and since you are doing NFT, the roots will grow air-roots in the space in the tower.
• Taps, elbows, joints etc for your plumbing.
• Something to hang your towers off. I use a clothes rail but anything sturdy will do.
• Something to hang your tower with. I use 3mm paracord, but the holes support up to 6mm cord.
• 36x36x40mm (1.5 inch apparently) grow cubes. I use these ones: https://smile.amazon.co.uk/dp/B00PK99H1Y Or go for the Grodan 1m slab and bread knife option for a gazillionth the price.
• Fresh water and nutrients.