I have a kit for a raised bed that I just haven’t gotten around to putting together yet. The raised bed I have is this one (or very like it… may or may not be the same manufacturer, but same specs): http://tinyurl.com/8x8squarebed . This bed is square instead of rectangular, with a little more total square footage (~5.9 m^2 rather than 4.5 m^2).
The dimensions are different than the “standard” Farmbot, but would this raised bed work with the Farmbot? If so, how complex would the modifications to the existing (or, at least, coming in February) kit be in order to make it work? Would the existing bed be strong enough (or would it be relatively easy to brace it to be strong enough)?
I am also building a FarmBot on a larger footprint, however I did not widen mine because the main bar that goes on the gantry was only available in a 1.5 m extrusion. I also find 1.5m to be a convenient width because it’s easier to access the plants in the center of the bed without having to walk on it, compacting the soil.
I’m curious how you will overcome this limitation. There is probably another supplier or you can special order, or even weld multiple extrusions together.
FuturistPlayground You have missed something critical and fatal and it explains why aluminium extrusions stop at 1.5m and why welding is out.
Linear Thermal Expansion maths as you can do here. Lets go 0 to 40 C with expand rate .0.000023 (m/moC) and 1.5 meters. Cool as it warmed up it only lengthened by 1 mm.
Now 0 to 40C is presuming for no reason the metal will not get heated up more. Then you have to remember this is optimistic this is presuming the aluminium is not coated black. Worst case is the metal could get to what a roof of the dark car was record at being 93.4 degrees. So lets now do 0-100C.
1.5 would be 3.9 mm length change. 5mm is where mountings might start creeping with each expand and contract but that is not the worst of it.
Turns out aluminium oxide coating expands at .0.000008 (m/moC)yes slower than pure. Welcome to the next nightmare too much length it is going to crack the coating on the aluminium over and over again structurally wreaking itself.
Something that catches people is most aircraft that are aluminium are made of sheets no bigger than 4 foot x 8 foot.or 1.2 x 2.4 metres. Not that we cannot make sheets bigger than that is normally not a wise idea.
“XL” device measuring 3m wide, 6m long was prototyped. https://farmbot.io/2016/01/03/launching-with-one-or-two-devices/ As you will see here it was running into thermal expansion nightmares and it was worked out fairly substantial redesigns will be required. 2.4m will be right on the range of question mark.
Being able to swap the main gantry bar with steel and protect it from rusting some how would get around thermal expansion problem and get to 2.4-3m widths without major issues from heat.
Sorry Ledgehanger as you can see by the launching one device instead of two sorting out the issues at bigger widths is not simple. I would not say that someone will not work it out but guessing when is hard.
Thank you for the detailed and well thought out reply. Based on that, I probably need to consider building a bed from scratch.