Blind Mice Part 1
exploring 3D graphics using VVVV.
One of the things you quickly learn when working in 3D is that doing
anything with a 2D mouse is a pain. Particularly I found I was spending
a lot of time shuffling the camera position which involves a tricky
combination of keystrokes and mouse movements. I wanted to
get a camera control that would allow me to fly the camera smoothly in
Looking for "3D Mice" in Google found a variety of more-or-less ugly
and expensive commercial options, but also this
project linked off Slashdot.
Humm I thought, how hard could that be to copy.
basic principle of Three Blind Mice is to run three threads round three
rollers from old mechanical mice. By using the mouse reports to
calculate the length of the extended thread this allows the position
where all the threads join to be calculated. First job was to interface
the mice to a PC. I am using old Microsoft Itellimice. The "z" axis on
these mice which measures the position of the wheel is very low
resolution and not suitable for this application. So, you need two mice
to get the three axis of measurement required.
It turns out that Windows makes it rather hard to extract input from
individual mice if you have several connected to your PC. It is also
rather tricky to override the normal mouse behaviour of moving the
Windows cursor. Therefore rather than connect the mice directly to a PC
I decided to interface the mice to an AVR microcontroller. The AVR then
has a serial interface to the host PC.
mouse interface is a bit of pain to work with, but with a bit
of effort I was able to get things connected.
the electronics working I chose to use a box file as the fame for
installing the mechanics. I like the idea of hiding this rather odd
project inside this ordinary piece of stationary. I cut the mice to
just keep enough of the PCB mounting and roller mecanism to meet my
needs. For the third axis I introduced a third mouse with only acts as
a mechanical frame and as a "remote" optical shaft-encoder for one of
the two actually interfaced to the AVR.
The original design uses simple weights to tension the cords. I wanted
something more compact and portable. I decided to use spring-loaded
retracting security badge clips. This photo shows one of the mice and
the tensioning device (in fact this is the third-access without any
active electronics). The cord is wrapped around the black horizontal
roller and through a hole drilled in the plastic tab above the roller.
As you can see HOT GLUE is an essential construction component on this
For the software I decided to run the calculations to get the mouse
position on the AVR. This means that the results don't need further
processing (except for scaling) on the host PC.
At this point a project I had thought might take a week at the
beginning had taken more like a month. Still I had a 3D mouse and it
actually works pretty well. The main problem is that that the data from
the mice does drift leading to innaccurate absolute lenths for the
location cords. As long as you don't make too sudden movements you can
use it for several minutes without having to reset the reference point.
I wrote a couple of little applications in VVVV to show off the mouse
both as a camera positioning tool and also as a 3D drawing tool. The
problem with camera positioning though is that you have no orientation
data for the mouse. You basically can look at a fixed point from
different angles, but not change where you are looking. In the back of
my mind I came up with a solution to fix this limitation, and I knew
that I couldn't rest until the job was done properly. So, with a heavy
heart I embarked on part 2 of the Three Blind Mice project.
Blind Mice Part 2
aim of part 2 was to add orientation sensing to the original design.
These days you can get a lot of chip-based solutions to sense
orientation (except around the vertical axis). However I had an idea
which was more in line with the spirit of the original design.
opto-mechanical mouse has two horizontal rollers at right angles to
measure the ball's motion. My idea was to remove the ball and add
off-centre weights to the rollers so that gravity makes the rollers
always want to orient in one position. A bit of experimentation
convinced me that this idea could give good enough results to be
useful. On the photo you can see the two small nuts I fixed to the
the first stage of Part 2 I interfaced a third mouse to the AVR and
doctored it as described to sense the orientation of the mouse against
the horizontal plane. Amazingly it works really quite well!
last challenge therefore was to sense orientation around the vertical
axis. To do this I mounted a shaft through the middle of the mouse and
connected it to a shaft-encoder. This shaft encoder was connected to
the spare on one of the original mice in part 1.
you can set some reference for the vertical axis in the mouse you can
use this arrangement to get the mouse's orientation in all three
should add at this point that the maths to translate from the mouse
data to its orientation is mind bending. 3D rotation about arbitrary
axis is not a pretty subject.
So, here we are at the end of the project. A full six axis 3D
controller built from old computer mice. Eat your heart out Nintendo
and Sony. This is the future.
software (running in background on the photo) allows the 3D mouse to
control the camera view on a scene. You can pan around the scene any
way and observe it from all angles. The 3D
mouse is a little odd to start with, but once you get used to it then
it actually becomes quite natural.
Open the full screenshot from the thumbnail on the right. In the top
left window is a red box which shows the position and orientation of
the mouse. In the bottom left window you see a scene viewed from the
point of view of the mouse. The right hand side is a VVVV patch to
create these views.
is a project I am glad to be done with now. Much more hard work then I
ever thought to start with, but I do love the fact that finally I got
the results I wanted and only used scrap components.
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