project description : automated shading system for tillandsia
Tillandsia is really easy to take care of. These plants need minimal water, they don't require dirt and therefore don't require repotting... they just don't like direct sunlight. So, we fixed that part.
Using recycled light bulbs seemed to fit perfectly with the theme of "follow the light". It was also much cheaper than buying special pre-made terrariums (and more eco friendly!) In addition, the small enclosure provided a good 'greenhouse' in a way- when watered, it tends to get pretty humid within the light bulb, which tillandsia loves! These bulbs that our plants are kept in are half painted. This is to provide a side that the direct sunlight won't go through completely. We used two light sensors: one on the front, clear side, and one on the opaque, white back. The light sensor in the front continually tests for whether or not there is direct sunlight- and when there is, it will command the bulb to turn and hand over the command for sensor two (there's a wait for the duration of the turn to prevent antagonistic commands within that turn). From there, sensor two will test to see whether or not the direct sunlight has gone away- and when it has, the bulbs will turn back. The turning mechanism is a simple gear rack attached to a motor. This motor is set to 'pulse' in two ways: using the shaft encoders, the motor will turn 180 degrees in response to direct sunlight, and then back 180 degrees when the direct sunlight has gone away.
We did run into quite a bit of trouble while creating all of this though (as indicated by our joyous cries at the fact that our project actually worked when showing it to people).
Among the things that we changed from the initial conception of our device was most notably the turning mechanism - originally we favored a pulley system over a rack and pinion system. But the rubber bands slipped a lot due to just the weight of our light bulbs, and getting the rubber bands on just right was hard enough... luckily, we were inspired by Lynn to replace our pulley system with simple gear train! Other than that, a lot of aspects of our device stayed pretty close to our initial prototype, with just some small changes in dimensions/design of the box-frame. Unfortunately, our program was very finnicky up to the day that we presented. Luckily it worked... We're still not sure what went wrong there. Depending on the day/configuration, the motor would not turn a complete 180, or would go above 180 - this changed from day to day, even without the plants being attached. We would have to change the power/distance/gains a few times before getting it to work again. Oddly, it favored the same inputs for gain/distance/power every time- but we had to change it, run it a few times, and then change it back for it to work... In addition, we tried multiple ways to try and slow down the speed of the turn, but unfortunately, NXT would not let us do that. The only way to slow down the NXT motor is to turn down the power - unfortunately, lower power = no movement for our system, since there was a lot of weight/torque/friction involved. But we got a lot of laughs and gasps of adoration at the sudden turn that our bulbs took, so I guess that's a plus. To be honest, we never really noticed how silly it looked. We were more frustrated by it I suppose...
Overall, there are many improvements that could be made if given more time. Things we were considering during this process were creating the box-frame out of wood for a better aesthetic; delrin just seemed like a sturdier fix. We were also considering making the gear/axle/bushings ourselves for better over all integration- with the legos + delrin in our prototype, there was a lot of torquing and in balance because the bushings wouldn't sit flat on the gear shelf. We also considered putting the entire thing on an actual curtain rod, since this is what our actual design called for... but PVC pipe is much cheaper. With our current design, the PVC pipe can easily be removed and the entire motor box/display can be put onto a curtain rod anyway.
The white "shielding" paint of our bulbs also has an undesired effect- you can't actually see the plants from the inside of the window ! However, acrylic paint was the best and cheapest option we had on our hands at the time (aka FREE and already on hand), and it demonstrated the point well enough. Ideally, we would perhaps coat it with a thin layer of spraypaint (more clear) or even perhaps tint it with tinted window paint (for cars? or sunglasses?).
Aesthetics aside, there is still one pretty big issue that we'd definitely like to fix given time. The turn of the bulbs is still slightly too fast for our liking. This can be easily fixed with a gear train to slow it down- the reason that we didn't do this is because we already had our gear support shelf printed out. An alternative solution would be to drive the system with a different motor that applied the same amount of power but turned at a slower rate. Either of these changes would make for a steadier motion, which would allow us to replace the (ANNOYING) piano wire with twine or hemp... for better aesthetics. (I'm a sucker for good looks I guess.)
Other add ons to our project would be perhaps a small solar panel array on the shelving box to power the entire system, which would make it very sustainable and much easier to go battery/cord free! In addition, we'd probably want to add a different controlling mechanism for deciding when to turn- instead of bang/bang control (aka, if it goes above a certain value, then turn), perhaps we'd have it check over a period of time to see what the change was like- if it was a cloudy, windy but sunny day, it wouldn't necessarily turn at a brief flash of bright sunlight. Another possible mechanism would be to add a temperature sensor and integrate those two things together.
Regardless of all the things we could have done, I'm very satisfied with my project. I feel accomplished, but it's great to know that there are so many possible ways of making this project even better. It was tiring and painful and frustrating, but the end product is something that I'm very proud of - and was very proud to show off during the exhibition!
All smiles!
- Julia Um, Cabrina Kang, Julie Barron
