24 Oct

plantbox project 1: the train

I had an idea a year or two ago of a small train that travels along a track that leads along a wall of plants, each enclosed completely in a box so that water could not get in. This way the plants would not get overwatered. The train would then water the plants to their individually needs.

I had envisaged a sort of water-carrying trailer. The main carriage would couple onto some exposed wires in the track coming from a box it was passing, and use that to detect moisture in the soil of the box. Depending on that, the trailer might then tip its load into a hole in the side of the box, and the train would then return to its depot for a recharge and for a reload of water.

Yesterday I had an easier idea. A small aquaduct would travel along the top of the boxes, which would keep a container on each box topped-up with water. When the train detected dry soil, it would tip the containers over. The containers would be counterbalanced so that when empty, they go back up to the top of the box to refill, and in the top position, they would stay where they are unless physically pushed over-balance. This is a much simpler arrangement, I think, as the train is then just two motors and some electronics. One motor to drive the thing forwards/backwards, and the other motor to swing a hammer.

I’ve designed the basic shape of the thing to test out how the movement would work and to decide how to fit the electronics and battery. After 3D printing it with my Anet A8, the motors fit very snugly. The front wheels (with the square axle holes) fit perfectly over the motor axles, and the back wheels (round axles) are almost perfect – a little drilling needed to expand the axle holes slightly.

I think the way I’ll attach the electronics is to add some catches on the back part of the fuselage (where the round axle wheels are) so that a little 3D printed box of electronics can be snapped into place over it. This way if I change the design in future, I don’t need to reprint everything.

The boxes that the plants go into will be completely enclosed in transparent plastic, protecting from the environment and acting as a mini greenhouse. The boxes will all have small water containers which are counterbalanced so that that can be tipped over to empty, and then when they right themselves, they start filling up again. I have not decided yet on the mechanism of refilling. Maybe a ballcock mechanism that is automatically lowered into the water container when it is in position?

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