Build a brassier fly trap
February 26, 2011
I'm working on a steampunk inspired brass animatronic venus fly trap. I will call her Venux. Venux's robot page is posted, but there is more info in this blog.
- Video 1 is the first prototype.
- Video 2 is the second prototype, including the 'hairs', which are just ornamental at this point.
- Video 3 is the improved prototype, with integrated hinge, better 'hairs' and wiring for the contact sensor.
- Video 4 is a quick test of the touch sensor circuit, still in breadboard stage.
- Video 5 is the "completed" project. Only one flower, but functionally and nicely finished.
- Video 6 is my WIREDInsider Maker contest entry.
Code for Venux is posted in the file attachments below the videos at the bottom of the post.
I entered Venux into the WIREDInsider Maker contest this week with Video 6 below.
I encouraged CtC to enter as well, which means my chances of winning are that much lower. His entry is SWEET!
Well, I wasn't planning on making any changes to the fly. However, I was taking apart an old cell phone for the vibrating motor for another project, and I got a surprise. Instead of a cylindrical motor with an offset weight, I found the vibrating motor in this cell phone was a small coin style pancake motor.
I did a quick test, and it integrated very nicely with the fly. So maybe I'll build a new fly or modify the original one so that it not only lights up, it vibrates and buzzes when it touches Venux.
Well, I'm a little bit disappointed. I brought Venux along to the Steampunk Worlds Fair this past weekend. I wanted to register her for the Mad Science contest. I don't know if she would have won, but it would have been fun to compete.
Unfortunately, right before we left for the event, my son had been playing with Venux. He said she stopped working, so I figured the batteries were getting low. I brought spare ones with me, and thought everything would be OK. As I stood in line to present her to the judges, I was replacing the batteries while the contestant in front of me on line held her for me. The power light came on, but she wasn't moving. I tried swapping out different batteries, but nothing worked so I just got off the line.
I finally tested her today. The batteries were fine. Somehow she lost her program. Once I downloaded the code to her again, she worked fine. I wonder what the heck happened.
Oh well. I had a heck of great time at the fair anyway!
Update: 2011-05-16 (also added close up of the firefly)
I have pretty much finished Venux. She only has one flower, and I may add more later. However, she looks good and she works fine.
Better yet, she has an accessory inspired by one of Gareth's creations. Here's an upated picture of Venux with her new lunchmate.
My firefly is a bit different than Gareth's. No polymorph (glowing or otherwise) was used, and it is a regular green LED instead of UV. However, my firefly reacts to Venux. When the fly's conductive metal parts touch the 5V-connected side of the touch sensor on Venux, it completes a circuit to ground and turns on the LED.
I can amuse myself (and hopefully others) by feeding the fly to Venux. The circuit from my previous update below worked great for the touch sensor. The sensor triggers the Arduino's interrupt and causes Venux to close her mouth on her hapless prey.
I also added some randomness in the code for Venux's moves to make her more interesting.
Update: 2011-04-08 (OK, it is technically the next day, but I haven't slept yet.)
I think I have a good start on the touch sensor. Some Googling led me to a conversation on the Arduino forum, which gave me this nice post about a simple touch sensor based on a simple Darlington pair of transistors. Just what I needed.
The two points labled touch contacts are connected to the two thin coated wires. Each wire runs to one set of hairs on the flower. You can see in the fourth video how the circuit works.
The code is in progress, but basically I use interrupt 0 (interface d2) on the Arduino to capture the falling edge provided by the above circuit. I have a little debouce code so the interrupt cannot be triggered again for 200 ms. I might actually increase this to 500 ms, as I'm getting some false triggering.
I'm pleased with my progress so far. One thing I'm not sure how to handle is to scale this up to four flowers. My understanding is that the ATMEGA328 only supports two external interrupts (0 and 1 on interfaces d2 and d3). I'm not sure how I'm going to make that work with four flowers, so if you have any suggestions, let me know.
The original flower design was just too hard for the servo to open and close. I made a double hinge by rolling the brass around a piece of brass rod. This greatly improved things.
You may also be able to make out in the picture above that i have hot glued the 'hairs' to the inside of the flower petals.
There's a very thin wires soldered to each set of hairs. This is coated wire from a cheap pair of airline head phones. The ends of the wire had to be scraped so they would make contact. This way, I can have exposed metal showing on the wires, but no danger of a short. Nothing is conected to the other side of the wires yet.
The 0.02 inch (0.51 mm) brass rod I used for the control cables failed multiple times due to fatigue. The failure point was always where the wires were bent over and passed through the brass sheet of the flowers. I'm trying again with 1/32 inch (0.81mm) brass rod. I'm hoping the larger diameter will bear up to the stress OK. If not, I'll have to try some stranded steel cable or steel guitar wire or something. I hope the larger brass rod does work, because the smallest stainless steel cable I can find is 1/16 inch, and if I use that I'll have to increase the size of the brass tube I use for the stalk a lot in order to fit the two control lines.
More to come as I continue the build.
I've transplanted Venux to a flower pot, which seems quite appropriate. I plan to make four individual 'flowers' on the plant, each controlled by two servos.
Here are some build pictures:
I cut a circle from the bottom of a plastic flower pot base plate. The Dremel ate through this stuff really nicely. I roughed out the cirlce and then cleaned it up a bit at a time. A compass for making a circle would have saved me some time.
The circle fits nicely into this flower pot, which will hold the batteries, servos and electronics.
I traced out the mouting points for the servos, and marked where I needed to drill. The picture above shows the holes drilled and the rubber grommets installed.
I made a paper template for the flower, then traced it out on 0.005 inch brass sheet and cut it out. I marked the holes where the pull cables will mount (one in the center of each side). Then I started making the 'hairs' by bending up some 0.02 inch (0.51 mm) brass rod. The rod doesn't like to be un-bent, so be careful to bend it where you want it. I introduced a slight curvature as I made the hairs, so they would match the curve of the flower. I marked circles on the flower to match the spacing of the hairs.
Here you can see one set of 'hairs' mounted.
Here's the second set of hairs ready to go. Be sure to mark the holes in the flower so that the second set of hairs will be offset from the first, allowing them to close together like in a real venus fly trap.
Bending and soldering everything in place is a bit of an art. Be sure to sand any of the brass surface that you want to solder, or it will not stick to it at all!