I've always wanted to make one of these POV globes. But the effort with all the soldering of LEDs,wires etc. has deterred me because i'm a lazy person :-) There has to be an easier way ! In this instructable i will show you how to build a POV globe with less electronic parts than other projects. The reason is the use of the adressable LED strips APA 102. This stripes don't need any driver electronic and can be directly connected with only 2 wires to a microcontroller. The state of the LEDs is ( and has to be ) VERY fast changable. To get a stable image the SPI clockrate is about 10 Mhz and could be even higher. For further information about the LEDs look here.
Another advantage is the use of normal bmp files that are stored on a microSD card.
Let's go !
Here is a list of the main parts you'll need. For the LED ring i use my 3D printer, you can also use a slice of a PVC pipe (diameter 150-180mm).The bearing brackets are also printed, but can be made of a wood piece for example. For the basic frame i use some old metal profiles, feel free to use other metal profiles, wood, plastic or whatever. Be sure that the frame is torsionally rigid and a bit weighty.
For the drive shaft:
brass sleeve 10mm, length 100mm
Flexible Shaft Coupler 5mm to 8mm (those who where use for Nema 17)
for powering the LED ring over the shaft:
2 pcs. ball bearing 6300 (10x35x11) full metal
bearing brackets, see STL files or make from wood with a 35mm whole saw
Brushless Motor with 5mm shaft
ESC for brushless motor,possibly with fan
Alternatively you can use a combination of a brushed motor/esc with enough torque.
The motor described above has enough torque but never reach his max current of 50 Ampere. My supply measure less than 4 Ampere. So there is no use for a 50 Ampere ESC. I put a heatsink with fan on my 18Ampere ESC and it works fine.
For accurate "firing" the ESC i use an
another option is a
We need 12V for the motor and 5V for the LED ring.
The Parallax Propeller Microcontroller:
Don't be afraid of this microcontroller, it is a powerful 8-core mcu with 80Mhz and is just as easy to program/flash as an arduino !
Another (my) choice is the P8XBlade2 from cluso, the microSD reader is already on board !
For programming the arduino and propeller you also need a USB to TTL adapter board like this one
Here you see the housing. Make it from any material that is sturdy enough. In the end you need some kind of a cubic cage with approximately 100mm edge length where you can mount the motor and the ring/ bearings. The cube is mounted on a solid wood plate with distance bolts. A hole for the motor was drilled into the plate.
I choose a threaded rod with a length of 250mm. The length of the brass sleeves are about 30 and 50mm depending on the size of the cage and the shaft coupler. The upper (and longer) sleeve has to be isolated from the rod because it forms the positive pole for the ring supply. This is done by insulating tape and plastic washers. The sleeve will not fit on the rod with the tape until you increase the inner diameter from 8.0mm to 8.5 - 9.0 mm by drilling/milling. The other sleeve including the rod forms the negative pole.
Now it's time for the bearings. I choose bigger ones than the standard bearings because of better conductivity. Place the bearing in the holder and position the plate on top of it. The small hole at the side is for the cable. Don't forget the shaft and the washer between the bearings/sleeves.
I 3d-printed the holders, have a look at the stl/zip file.
Have a look at the schematic how the motor electronic has to be connected.
If you have never program an arduino look at instructables :-) The two buttons are for motor speed. If you switch on the power supply the ESC gets a value of 500µS. Press one of the buttons to switch on the motor. The sketch took the value "StartPos = 625". Later, if you've found the right speed this value has to be changed. By using the left or right button you decrease/increase the speed, press both buttons at the same time for 2 sec. and the motor will stop.
Be sure that the motor/globe rotates counterclockwise, like the real earth :-)
Here comes the core ! Printed with my 3d printer but as i said above there are also other options. To save weight i have many holes place in the frame. Now cut two strips off, each with 32 LEDs. Better count off several times before using the scissor :-)
Placing the strips is a littly bit tricky. You have two strips/columns that generates odd and even lines. The odd lines are at one side of the ring, the even lines are at the opposite. Mark LED number 16 at each strip (respectively line number 32 and 33) and fix it at the frame like showing at the pictures. One led fits exactly between two opposing LEDs. So you have two place the second strip with an offset !!!
After that you can fix the PCB/PCBs, i made small slots in the bracings so the PCBs can easily attached.
Before you mount the ring on the shaft, you must balance it. Use a thin stick to balance and screws or nuts as counterweight.
In this schematic you see how the MCU board is cabled to the other parts at/in the ring. I also attach a photo of the hall sensor and the magnet. The schematic use an older and bigger fritzing MCU-board because i don't find fritzing templates of newer/current Propeller Boards. Feel free to ask your questions for the board you'll choose/get.
This is the binary that can easily transfer to the prop-board. Here is a link to one of my previous Instructables that also use the propeller microcontroller and show you a HOW TO.
Ok, first we only copy the test picture to the sd card.
Next time you start the motor you'll get the right speed.
The next step is no longer necessary with the new software, from a speed of 38 to 44 rps the odd and even lines are "locked" correctly.
(Use the up/down buttons for fine tuning if necessary.)
Now you can "fill" the card with your other pictures.
Have fun !!!!!!
You want to use your own pictures ? No problem, i show you:
the best brightness correction for images is to use gamma correction with a factor of 0.45
save as BMP with 24bit color and no RLE
after saving the size of the file has to be 23094 byte !
Any other size won't work.
If you want, store several images at the sd card. They are shown one by one each after one rotation.
Now it's up to you to create a better Death Star than mine !
Some things I noticed:
(January 13, 2017), added the ring.stl in step 6