Introduction: Long-Range RFID-Controlled Dry Cleaner Conveyor
This guide will take you through the electronics-side of how we made our large-scale robotic artwork, "Replantment." It connects two, independent, decades-old, dry cleaner conveyors to cutting edge Long-Range Simultaneous RFID arduino and motion controllers. It covers the basics of controlling big motors and lights with electrical relays (switches), and using Sparkfun's new Long-Range RFID controller. Hopefully by seeing how we made our large, interactive artwork, this how-to will help you with your projects!
Along the way we will share lots of tips about sourcing strange items, making your electronics safer, hacking big machines, and how to help keep interactive artworks from bricking on you in a gallery setting!
**Psst -If you are in the NYC area, you can even go check out this project for free at the Pratt Manhattan gallery until Feb 17!**
The other half of this year-long art project is about rapidly creating silicone and polyurethane molds in the field and replicating natural plant forms collected from all over the world as glowing, UV sensitive leaves. For details on how we made the leaves, check out our other How-To article:
If you want to learn more (especially on the philosophical / artistic side) about this artwork, and many more that were part of Madeline Schwartzman's "See Yourself E(x)ist" exhibition, you can see the manual here:
Step 1: Sourcing Conveyors
Dry Cleaner conveyors are one of those things that until you start thinking about it, you may not realize there are huge entire industries built around these. When you start researching it, it is fascinating and there are great corporate videos about all the minutae and design considerations you probably didn't think about, like if the products need to be able to tilt, go up inclines, make slower turns, and so forth.
Finding a conveyor system within a very small price range can be super tricky though. We considered several options.
Build Your Own
For our artwork we needed about 2, 4 meter conveyors. One way to do this would be to manually build one from scratch. You can find lego-like parts to make your own fully customized conveyor at mcmaster- https://www.mcmaster.com/#overhead-conveyors/=1aqw...
This would have potentially worked for us, but when we ran the numbers, it looks like it was going to be at least $3,000-$4,000 USD to get a minimally sized conveyor we wanted
Two big companies in the US selling new conveyor systems are
This is a great option if you have the money because the people at the companies are super helpful, and can help you find something you precisely need. Unfortunately I don't think we were able to get a quote for anything under $12,000 USD
Ebay and craigslist are decent sources to look into for finding used conveyors. Down side is that shipping is REALLY expensive for something this heavy, so you will want to look locally. Another downside is that you might not be able to be too sure of the condition or quality or if all the parts are there in what you find.
These conveyors really hold their value since they are built to pretty much run for 100 years, so that means they are still kind of expensive used. We saw prices for basic 10 foot conveyor systems ranging from $3,000 USD (for a pile of components from craigslist) to $9,000 USD for quite good looking used systems.
Maddy really worked her magic with the find that led to our conveyors. She saw a dry cleaning business that had been closed for 12 years, peeked inside and noticed they still had conveyors in there. She hunted down the owner, and inquired about them. They tested them, and he offered a price of just $200 per conveyor for us to take them away! We hired some extra handy folks to help us de-install them, clean them up, and transport back to the gallery! Overall buying, de-installing, installing, and transporting the machines cost us $1700. Not bad at all!
What a great find! We called the people at Railex about our model of conveyor to see if we should pre-preemptively order extra parts for these conveyors (which have been around since the 70's I think), and he actively discouraged us, and said they would run forever, just put some 3 in 1 oil on them!
Step 2: Installing Conveyors
Getting them up to the second floor of the gallery was a bit tricky, but once there we managed to install them without too much difficulty. Our machines come from the Railex coporation, and appear to be system 722 single plane garment conveyors model C 200. http://railexcorp.com/products/garment-conveyors/
They have 204 hanging positions, are about 3 meters long, and have 18'-5" of total hanging length.
- These things are really heavy and powerful! Make sure you have adequate room for people to move safetly around them before locking them into position!
- Make sure they are mounted securely to the walls and/or ceiling
- Lay down lots of heavy blankets under heavy equipment to not screw up the floors
Step 3: Hacking the Conveyor
Controlling them is not too difficult! They already have remotes. The conveyors each come with 1 motor power supply cable and two foot pedals that can each tell the machine to go forward or backwards.
(note when working in a strange place like a jungle or a gallery, I recommend making a PIFpack like Plusea's , mine helped me a ton! http://instructables.com.mevn.net/id/PIFpack-SERIOUS/ )
Unscrewing the foot pedal reveals that inside are just two electrical switches. When the button of one switch is pressed, it just makes a connection that tells the machine to go one way, and when the other button is pressed it sends a different signal to go the other way.
So to control them with an arduino is quite easy! We just need to replace those two switches with an electrically controlled switch (or a relay). Since we want to control them to go forward or backwards, we want two relays (one for each button switch inside the foot pedal). Luckily there are nice 2-channel relays available everywhere: https://www.amazon.com/SainSmart-8-Channel-Duemila...
I think people get scared of relays because they tend to be used with high-voltage AC current, but they are super simple! While the machine is entirely disconnected from any power sources, all we have to do is
- snip the two wires going to the button in the foot pedal,
- connect these two wires to the two screw terminals of the relay
- connect the other button in the foot pedals's two wires to the two terminals of the other relay
- on the other side of the relay are 4 ports labeled GND, VCC, in1, in2. connect the GND and VCC to the corresponding parts on the arduino
- connect in1, and in2 to ports 5 and 6 on your arduino
- connect your arduino and load this diagnostic code
This is basic code to go through output ports on the arduino and turn them on and off. Connect your relays to any ports 5-13 to test and see if they are working.
If they are working the little red lights on the relays should turn on and off. That's great! Now if you are ready for the real test, look and make sure there are no loose wires, and your relays are insulated from anything metal. Plug in the power to your conveyor, and it should turn on for a second, move one way, stop, and go the other way for a bit as the arduino code runs! Hooray! You have a robot conveyor! you can now adjust the code to make it do whatever you want!
**By the way, there are generally two types of relays you can buy:
- Regular- These Electro-mechanical relays physically use a little magnet to make a connection just like any button or light switch. You can hear a little "click" when they turn on. They are cheap! But they can break down easier.
- Solid-state - Solid State relays use some kind of magic to open-or-close the circuit without any moving parts (so they don't make a click sound). In theory this makes them more reliable over many duty cycles. They tend to be a lot more expensive, but we bought them since our artwork has to run reliably for as long as possible!
Step 4: Lighting Design
We had to do lots of experimenting with different types of glow powders and different types of lighting.
For the best "pop" highlighting the fine details of your leaves, you want a really low wavelength (below 400nm, like 390nm). This reduces the amount of white light that get shined out by the light, and makes the light source to be not as distracting. The lights we found worked best were these:
Some of the glow powders we used were these:
When hanging the leaves you also need to find material that does not fluoresce. Some types of netting were too weak, or glowed brightly (even though under normal light they were clear). Some zip ties, and some hot glues fluoresce too, so watch out if you don't want those aspects to suddenly gain lots of attention. The net we used was from:
Step 5: Relay Controlled Power Switch
Your goal here is to take a power strip that already has on-off switches, and replace those switches with digitally controlled switches.
What you need to do is:
- Open the power strip (find a european or asian one that has individual switches for each plug port)
- Tin some heavy gauge wire with solder
- Use some flux and tin up some nice patches on the two metal areas that the switch on a certain port normally connect
- Connect heavy duty wire to the metal areas
- Drill some holes on the side for the wires to come out
- Use hot glue to add strain relief to the wire and secure them on
- Connect ends of wire leads to your relays
- Mount everything on a heavy duty non-conductive surface
- Mount all of that inside an enclosure so moving parts don't rip electronics out of place and cause a short or worse.
This is the part where you are working with big voltages that can get out of control and cause property and human damage.
Super awesome Synth badass of Bastl Instruments, Peter Edwards, gave some extra good safety tips to check if you are putting your own relay-controlled strips together. I followed his advice and made my strips much more robust and safe! You should too! Thanks Peter!
"Not to be a bummer but if people need a photo tutorial to mod a power strip, they shouldn't do it. For real. But if they DO then here are some musts....
1. The relays must be better insulated.
It should at the very least be screwed to a wooden board...but really it should be housed.
2. The black wires you're using must be twisted and tinned. This ensures there are no loose strands of wire sticking off that could short against something.
3. There should be some kind of strain relief so if the wire is pulled it won't yank on the guts of the power strip. A knot in the wire before it goes through the hole could do the trick.
4. The conductors in the power strip must also be tinned. this will ensure that the wires solidly bond to the surface when you solder them.
5. Not to mention you should probably be using flux. This helps the condition the oxidised and dirty conductor surfaces so they accept the solder. The whole idea is that you want clean, solid solder connections and don't want cold solder joints, which can create intermittent contacts as the weak solder connection shakes around. This can cause sparks or can break off and short against other contacts.
6,7&8. An art space I work with in NY burned up recently(ish) because of a faulty power strip. I've lost expensive electronics that have come in contact with high voltage."
Step 6: Bonus! Long-Range RFID Control
When we got the conveyors, they also gave us thousands of dry-cleaner slips, and this beautiful device to organize them. How cool would it be if we could use the actual slips to command the machine around?
Turns out there is some brand new consumer-level RFID technology that can read cheap, unique RFID tags from 4 meters away, and also read up to 100 at a time! A system from Sparkfun costs about $300 (reader and antenna) https://github.com/sparkfun/SparkFun_Simultaneous_...
You can get the tags for about 10-50 cents each, and they stick right on the dry cleaner tags. Thus you have a simple, magical feeling way of controlling the machine!
They have some straightforward examples at sparkfun for how to use these, which we adapted to control our machines. The machines don't actually have any sensors that let them know what position they are in, BUT we can count the amount of time they are on and in which direction to approximate (using dead reckoning) about what leaves are on display in the front of the conveyor! Getting this fidelity really nailed down well is for a later iteration of the project.
For the labels, we just fed them through a simple inkjet printer and listed details such as their location we collected them!
RFID-Arduino-Another Arduino (I2C messaging between arduinos and RFID)
Here's some example code you can adapt that can READ an ID on one Arduino Uno connected with the Arduino sheild, which then sends this message over I2C to a second arduino which can read it and then perform actions. You can customize the actions however you want!
To connect arduinos via I2C you need
- MAKE SURE THEY ARE RUNNING OFF THE SAME DIGITAL VOLTAGE SUPPLY. For instance they are both powered by the same computer, or the exact same USB hub. Note, this is not SIMILAR voltage supplies, it has to be the exact same, or else they won't have the same ground reference voltage, and won't be able to communicate.
- Connect pins A4 and A5 from one arduino to the other (or pins 20 and 21 on an arduino Mega)
- Then use this code to send messages between them! Easier in some ways than you would think!
Master's Code (with the RFID reader shield connected by i2c to slave)
Slave's code (bare Arduino connected by I2C to other arduino):
Step 7: Transport and Organize
We collected the leaves from all over the world, so one of the hardest parts was getting them to one place. This required several suitcases on multiple trips, dropping them off on planes and trains and swapping on different journeys around the world.
Step 8: Hanging Leaves
Test your machine, make sure it's running great! Then add your curtains, and attach all the leaves how you want them!
We drilled two small holes and passed very thin zip ties through the leaves to connect them with the curtains.
Step 9: Finishing Touches / Fix-It Manual
Interactive art is really tricky! Paintings don't disappear entirely if they get a smudge, or you use slightly wrong colors, but interactive artworks can break down or suffer code failures!
To prevent against this you should design with the "escalator principle" from the beginning ("if it breaks it at least becomes stairs"- mitch hedberg). So scaffold your interactions from your ideal situation to viable alternatives.
For instance our project holds several tiers of interaction when one fails or doesn't work it goes to lower levels:
- RFID control of conveyors to position leaves
- RFID triggers conveyors to move around
- PIR motion detector triggers conveyors to move around
- Conveyors move around patterns based on an arduino
- Conveyors move around based on on a simple timer
- Conveyors sit and light up and look pretty
Before leaving an interactive artwork in a gallery, make sure to leave instruction manuals and guides for how to fix common problems that may come up! This will help prevent your giant artwork from becoming a giant paperweight in the middle of the gallery for the months it is on display! It can also help you help the gallery debug their system!