Friday, 20 May 2011

Do Cartwheels, Feed People

Rotational Hydroponics. It's an idea that's been around mostly unknown for the last decade, and has the potential to revolutionise* the way we grow food.
*Pun intended.
MS-Paint Art by me. :P
Essentially, by rotating plants plants around a source of light, you can manipulate the way they grow by the combination of heliotropism and geotropism.

Hydroponic and other soilless food production methods are already important for our society's sustainability, as you can increase the crop yield per acre of plants as many times as you want by growing them closely together indoors and stacking them up in many layers. More importantly, this has the added benefit that crop yields are far more reliable than traditional agriculture, as the growing areas can be sealed from pests and their growing climate controlled to a high degree, and as a closed system there is no runoff fertiliser or pesticide to poison our waterways.
Proposed Vertical Farms - Wikimedia Commons
This means that we can produce clean local food for humanity in skyscrapers, with easily automated maintenance and picking, while repairing the massive damage that our destructive monoculture field farming has already done to nature.
Provided a pipeline of water from coastal desalination, or the likes of the Great Manmade River in Libya that was doing so well until a couple of rogue nations recently considered haphazardly firing Depleted Uranium munitions there, it would be entirely possible to grow food hydroponically in the middle of the sahara desert, with the huge power generated by solar panels there, and where their partial shade stops the soil from being baked in the sun, start Greening the Desert like the Permaculture Research Institute have already proven they can do.

But enough of that contemplation. A main advantage that seems to be added by this particular method is the speed of plant growth. Apparently by constantly rotating the plants about once every 30-45 minutes, the plant is constantly fighting against gravity and righting itself towards the light, as this stimulus is on the edge of the reaction time of about 10-12 minutes observed in plants. By causing the growth-promoting auxins that the plant generates in tropism to be repeatedly and evenly distributed on both sides of the plant, this causes the plant to grow strong and fast.
I'd like to do my own experiments to confirm this, since I'm relying on commercial info.

So far, a few small-to-medium firms in the USA and Canada have been touting their own solutions to this concept, variously named the OmegaGarden, RotoGro and B-Pod. The first company seem to have received the most press so far, and they did a case study with one of their systems, the 'Carousel', in which basil was grown in a few 8ft long cylinders, under a total 6 KiloWatts of lighting from CFL's, and produced 900lbs of basil leaf in 4 weeks, at a cost of 3.7kWh/lb, or about £0.20/kg here, assuming £0.12/kWh for electricity. I don't know about you, but the cheapest I've seen Basil going for recently on this island was £14.50/kg for bags of dried leaf, due to the huge cost of importing the stuff from sunnier climes. We're talking about fresh herbs here, which are much more expensive on the open market.
A delicious sea of green - case study.
Wonderful, but I have two big problems with these systems for starters; first of all they don't sell them in Eurasia, and secondly they are very expensive even without international shipping on such bulky parts.

So, I've been talking to people for months about the idea of producing a modular version of this system that could be produced cheaply using CNC tools in such a way that it could be flat packed and easily assembled wherever desired. A few weeks ago I got to throwing conceptual ideas around with another creative fella called Jay, who admins the new site, and came up with the idea that it would actually be more convenient to put plants into a rotating cylinder as a series of narrow rings that could be attached together, rather than loading beams holding the plants onto a cylinder of pre-determined length.
The main advantages of such a design are that it's much easier to keep the cylinder's center of gravity in the middle, and the user can easily define the size of their unit by however many rings they want to put on.

So very recently after finishing my course and getting my reprap together, I set to designing such a system. At first I was looking at making segments out of 2 main parts that would bolt together, with one flat side opposite another with slim beams sticking up from it. I soon realised that not only was such a design horrible to print, but it would could end up using hundreds of bolts just to keep each ring together. Eventually a spark of inspiration at 2am led to this:

Brown Rockwool Cube faded for a better view.

The biggest problem before had seemed to be deciding on a drivetrain for the system, and whether there would be some complicated mechanism of belts or chains going on in order to achieve the right speed of rotation. That was, of course, until I found that someone had thrown out a broken halogen heater after the last winter, and with my usual determination for salvage, I found what was wrong with it, and noticed a wonderfully useful part within.
They break. What else do you expect from something corporate-made priced at £10?
The machine had broken ultimately because a shaft on which the heater was rotating at the base came loose, and the wires going into the base through that shaft were tugged and stripped bare against its edge. I decided not to repair it since it wouldn't have been safe again for long anyway. The brilliant part that I pulled out was this low-speed synchronous motor:

Danger, danger! High voltage!
The benefits of this of course, are that the very low rotational speed makes it perfect for simplifying the design, and I can hook it up to the same mains power as the lighting when I finish building my first system. I tested it already and it seems to put out some decent torque at that low speed.

With some more design work I have this together so far:
Universal motor mounting on the top-right of the base, difficult to see here.

Next I'm going to design a mount for the lights, and a tray to hold nutrient solution. Other developments to consider are, how many rings can the motor handle at full growth, and can tightly packed pebbles serve as a re-usable hydroponic medium in this setting, or would they end up bruising the roots?

You can keep track of my current design development for this project here on Thingiverse.


  1. This was a great post, puns and all - but the best part? The MS-Paint art. Fantastic! ;)

  2. Wonderful post and blog. I noticed your comment reply to mine at and the sneaky detective that I am, found your blog and this post.

    I'm very much interested in rotational hydroponics for improving hydroponic yields. The problems I saw was with the lack of scientific data supporting orbitropism as the Omega Garden guy likes to call it. After contacting him, he does admit that published research hasn't been done yet which really needs to be in place to get this growing method better known and utilised.

    So I suggested this to my sister who was looking for a topic to research for her Hons dissertation in biology. And she thought it was a great idea and so built a scaled done version and made a comparison between plants (lettuce) grown rotationally (tested at various rpm) compared to non-rotational with all other variables such as nutrients, light intensity, distance to light etc. all controlled for as best as possible. The end result was statistically significant additional root and stem dry mass for the rotational plants but no significant difference in leaf dry mass. Unfortunately due to limits on time the plants weren't able to grow to maturity so the leaves were very small - but with more root and stem mass for the rotational plants you would expect faster growth later on as they would have more access to nutrients leading to bigger leaves and more energy for faster growth etc.

    She's yet to publish it and she's now doing a PhD on a totally different topic so the trail has ended a little. But I am planning on designing my own version to do my own testing (and eating of course). It won't be published as I'm not affiliated with any university but with complete transparency over the methodology and video documentation all posted online it will at least provide more data.

    Unfortunately I won't be able to start for another 6 months or so until I can get some spare funds and time together.

    So this is really a 'brother in arms' message with some thoughts for possible collaboration.


    Justin (just9700 aht yahoo doht com)

  3. Justin that's all kinds of awesome. I'm glad to hear your sister took up researching orbitropism; sadly at the uni I went to the course structure was quite rigid about what we could do for our final-year project. I would have loved to have taken on any of the projects that I've barely started in the last year as my FYP, since I would have had far more resources at my disposal there and things would probably go a lot quicker.
    Oh well, anyway from the sounds of your sister's findings, it may be worthwhile for us to research how well a root crop can do in a rotary hydroponic system. That might require some adaptation in growing medium however, such as something spongy other than rockwool (for food safety) that could expand to make room for thick roots. Perhaps something like onions, radishes, baby carrots or even ginger could be grown that way.

    In the next couple of months I'm aiming to get my conceptual design of a cowled wind turbine to be more at the stage of design completion that the rotary hydroponic system is currently at, which will probably happen once my mad rush to plant seeds in spring dies down a bit. Once I get that figured out, I think I'll see whether I want to prototype energy or food production first, probably depending on what materials I have to hand and whether there has been any oil scare here by that time.
    I'm not sure whether it would be wise to try a kickstarter/indiegogo campaign to fund prototyping such a piece of open hardware. I loathe all the people who send out silly wasteful trinkets like keyrings, CD's, etc. as rewards to people donating a bit. I'd probably want to send little pot-plants to people. :3
    Please don't ever stop being curious.