Assignment 10 – Build The Hardest Part

My objective for the final project is to experiment with the magnetic “LED throwie.” Specifically, I’m trying to create an LED throwie that can be attached to a magnetic surface and that can, some specified time later, detach itself from the magnetic surface, floating itself back down to earth via a gliding motion (maple seed wing, copter wing, or the like.)

The project consists of three main parts. A) finding a mechanism that can create enough motion of a throwie on a magnetic surface to detach that throwie,  B) creating a circuit that can trigger that motion mechanism at a desired time, and C)  finding a floating mechanism that can be placed onto a throwie that lets it glide to safety once detached.

The hardest part of my project is almost certainly (A), finding a way for the magnet to detach itself. I experimented with muscle wire, electromagnets and relays before finally settling on the vibration of a low-powered pager motor as the most promising way to detach the magnet.

In order to properly test whether the magnet can detach itself without outside force, I had to develop the entire circuit that would be triggering the motor movement. This is because with my hand in the way holding the motor leads to the battery, I tended to inadvertently apply enough force to the magnet to influence whether or not it would detach. In this sense, (B), the construction of the circuit had to be done before (A), the mechanical mechanism could really be tested. So I set about planning and building (B). For (B), I decided to use the ATtiny13a microcontroller (a technique I stole from the Throwie Talkie project). I programmed the microcontroller to wait 15 seconds (just enough time for me to place the throwie and get my hand out of the way) before switching a transistor on to turn on the pager motor (which has the magnet glued to the top of it). I can build this circuit with few enough components that the whole thing can be held together by wires, solder and tube shrink wrap. This video shows the whole circuit in action, and in turn the current status of (A), the detachment mechanism:

and here’s the circuit diagram:

Sorry it’s so fuzzy; I’ll recapture the video in macro mode – I just wanted to be able to post my very first successful test. As you can see, the detachment mechanism is pretty promising, even on this flat surface. In my informal tests without this circuit, I found the perfectly horizontal surface like the one being tested on is actually the *hardest* case to test this out on (because none of the side-to-side vibrational force gets supported by gravity, and there’s little torque on the magnet). Even on this surface, the magnet bounces around and does indeed fall off when it hits an edge (not shown in video). That said, the round Walking To The Sky pole won’t have any edges – so it will have to fall off via sheer momentum, not due to the magnetic surface disappearing. My next test is to take this completed circuit to the statue and see how it does there. If it falls off right away, we win – all I have to do is attach my wings and make sure the wings cause it to float down instead of plummet like a brick. If it doesn’t (and it probably won’t), I have a few more tricks up my sleeve:

*I can add distance between the motor and the magnet via padding on top of the motor (to increase the amount of torque put on the magnet)

*I can add tape to the top of the magnet to weaken the strength of the magnet (though doing so makes it harder to place and sort of ruins the illusion somewhat.)

*I can experiment with strings, making the motor “tug” on the device in such a way to cause the magnet to slip.

*I can work with wheeled magnets, causing the magnet to turn and bounce off the pole. (This idea is still fuzzy. Let’s hope it’s not the last one I get down to.)

Needless to say, even with so much of this project narrowed down into a concrete prototype, there’s quite a bit more experimenting and work to go. But I’d say sorting out the mechanism, selecting pager vibration and testing the circuit to prove the concept of pager vibration as a means of motion and detachment represents the hardest part of my project.

Other updates:

*I experimented with floating mechanisms and found a mechanism that worked fairly quickly – not the maple seed that I envisioned, but rather a simple set of copter wings that can be quickly fashioned out of paper. That set of wings can be easily attached by paper or string to whatever final circuit/mechanical mechanism I come up with.

*As I probably mentioned in class, I scaled back slightly from the “throwie” objective. It turns out that neodynium, the rare-earth magnet used in throwies, is insanely strong. So strong, in fact, that it veers towards magnetic surfaces and sticks even when your aim sucks – which is why it’s great for throwies. However, that same insane strength means it’s insanely hard to detach from a magnetic surface with just a coin cell (3V). This left me with two choices – either give up the low power affordance of throwies (by moving from a single coin cell to more power), or give up the “throwie” of throwies (by switching to a weaker magnet that won’t stick when thrown.) I chose the latter, deciding that ease of construction and weight was more important to me than the “throwing” factor. I hope to eventually find a low-power mechanism that works with neodynium outside of MTI, but given how quickly our demos are due, I had to pick my battles wisely.


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