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A propeller display is an adapted version of a propeller clock (as seen on the website
of Bob Blick's propeller clock ).
The purpose of this device is to write things (like a clock or a textual message) in thin air!
The device consists of a row of 8 LED's and some other electronics parts mounted on a motor. While this motor is
running, the LED's are switched on and off on specified intervals.
Because it takes a while before an image projected on a humen eye fades out, we can play a mindtrick by writing a whole circle of
text before your eye notices it's gone...
Note that all images below are clickable for a hi-res picture.
The heart of a propeller display is a good motor. I tried a few motors before I found the best motor to
create the propeller display.
The motor I used was stipped out of an old VCR. I think it was used to rewind the tape, as it was just a 5V motor with brushes
that runs at a continuous speed.
Where's a picture of the different parts of the unmodified motor
Starting at the top left and the clockwise we see: the brushes and the magnet glued on the brush mechanism, the anchor and the shaft, a spring and a clip, 2 bearings that hold the
shaft, the placeholder for the bearings and finally the motor packaging, which is now empty.
First, we push the shaft trough the anchor of the motor, so that the larger part of the shaft is now pointing down.
Solder three wires to the terminals on the motor's commutator.
Next, we drill a hole in the bottom plate of the motor (in beween the two brushes, so that the shaft fits into it.
Solder external wires to the brushes if nexessary.
Assemble the bearings into the motor packaging, and glue the bottom plate onto it.
Now, you can put the reversed shaft onto this construction. Because the bearings are separated about 1 cm from each other,
the motor runs smoothly, even though both bearings are on one side of it.
Note that I didn't completely push the shaft the other side, and that I mounted a little screw on the anchor to mount the electronics.
The LED driver we are using is a PIC16F84. A 18 pins , 4Mhz microcontroller.
You need a programmer for this baby. There are a lot of versions of these kinds of programmers. I implemented the programmer
on this webpage to get the job done.
The LED hardware scheme is basically the same as used in Blick's design.
No need to copy it here. Just follow the link, implement the thing, and come back here...
When both are finished, you should have something that looks a little like this:
After finishing (!) your electronics, find out where to drill a hole in the testboard so that it is approximately in balance,
because remember that this construction will be rotating at speeds around 2000 to 3000 RPM.
Drill a hole just big enough so that it fits on the shaft of your motor. (That's why we didn't push the shaft the whole way trough the anchor).
Another small hole will allow us to fix the electronics onto the anchor of the motor.
I work on a Linux system. You'll need following packages to get the propeller display running:
And here's the result when you feed 5V DC into this construction:
http://ubob.ponnet.com/ Benjamin was also inspired to create his own version of the
propeller clock. He calls his inception a 'ghost clock'. He also helped me out with some of the electronics. Thanks!!