Floating and Spinning Earth Globe
Introduction: Floating and Spinning Earth Globe
The objectives of this project were (1) to make an object float, by means of magnetic levitation and controlled by an Arduino Nano and (2) documenting the whole process allowing other people to build one on their own.
There were some requirements, too. First, I wanted an object of a certain size and weight, floating in a very stable way (no jitter, no oscillations,...). Additionally, safety was a concern (the main magnet has a 24 Volt and 25 Watts rating, producing quite some heat).
And last but not least: the end result had to be 'nice', earning its place in my living room !
I finally came up with an 11 cm (4.3") magnetically levitated earth globe, not only floating but rotating at a fixed pace as well, illuminated by two digitally controlled led strips and nicely fitted inside a wooden lantern.
The movie below explains it better than a thousand words ... check it out !
Supplies
This is a list of the most important components I used
* a wooden lantern (of course). Internal dimensions: 180 x 180 x 300 mm minimum
* wooden laths and planks
* spacers, nuts and bolts
* plexiglass 3 mm (you will have to cut it yourself)
* heatsink 1.85°C/W, 100 x 88 x 35mm
* electromagnet ITS-MS-7040-24VDC: this is a fairly strong electromagnet weighing 800 grams, and rated at 1200 Newton holding force, 24 V DC, 24 Watt
* 3D printed 'globe rotation hall sensor assembly' (link to STL file provided in this instructable)
* 3D printed spider to hold the six rotation coils (link to STL file provided in this instructable)
* Empty plastic spools to create coils
* Block Enamel-coated copper wire 0.28 mm
* Adafruit RGB ledstrip APA102 60 led 1 meter
* Honeywell hall effect position sensor SS495AAnalog Devices
* temperature sensor TMP36Neodymium magnet circular 10 mm height 5 mm
* Neodymium magnet cube 20 x 20 x 20 mm
* DC to DC (step down) convertor Velleman VMA404
* Arduino Nano R3PCB designed with Autodesk Fusion 360 (Schematic and Gerber files attached to this instructable)
* a lot of electrical components (PCB BOM attached to this instructable)
* Wall power supply 24 Volt 36 Watt DC plug 2.1 x 5.5x 11 mm
Software, tools and online services
* Autodesk Fusion 360: PCB design. Autodesk has a free version of their software, and it's working great
* Seeed studio Fusion PCB manufacturing. You will need to upload the Gerber files (zip file attached) when placing your order. PCB will be delivered, ready for assembly.
* Highly recommended: oscilloscope, e.g. 120
Tektronix TBS1052B
* 3D printer
* soldering station
* The usual tools like tweezers, pliers, multimeter ...
Step 1: Understanding Magnetic Levitation
One way to achieve magnetic levitation is to position an electromagnet above an object—in this case, an earth globe—which contains a very strong magnet. By constantly measuring the vertical position of the object, we can vary the magnetic force exerted by the electromagnet on the object's magnet to keep the object in place.
This happens much in the same way as driving a car on the highway. By constantly measuring whether the car drifts to the left or to the right, the driver can stay in his/her lane by applying small corrections only. This mechanism is called a "control system" or "feedback system."
This magnetic levitation control system is not a "linear" system at all. For instance, the relationship between current applied to the electromagnet and force exerted (on the globe's magnet) is quadratic. Moreover, this force varies with the distance between electromagnet and magnet—which seems logical. But this relationship also is quadratic! That means that the "parameters" (we'll talk about that in a moment) used to keep the globe's position stable are critical.
Any change to the globe's weight, the magnet, the electromagnet or the position of the sensor will probably result in a highly unstable globe, and you will have a hard time finding the correct parameters (which will be trial and error, I'm afraid) to obtain stable operation again. Indeed, this non-linearity also makes it difficult to apply mathematical methods to calculate these parameters.
Step 2: Globe Lifting Control System: How Does It Work ?
So, how does it work? 234