Raspberry Pi Laser Cutter (In Progress)

I have begun to build a Raspberry Pi laser cutter!  It uses CD player/radio modules for the X and Y axes, and will hopefully use a DVD writer laser to cut stuff.  I haven't found this yet.  The CD player/radio modules, in my case, have DC motors instead of stepper motors.  DC motors are less precise than stepper motors, so I am not certain of the precision available to this machine.

A Raspberry Pi controls the extremely simple electronics.  Five outputs from the Pi go into a L293D dual H-bridge chip, which controls the motors.  Four otuputs are for the motors, while the fifth goes into the enable pins of the chip to enable the motors.  This output can be controlled with PWM to vary the speed of both motors.  If you attempt to replicate the L293D setup, I recommend Adafruit's great tutorial on using the chip.

I have written some custom Python code to do some basic stuff with the soon-to-be laser cutter, but I will need to do more complex programming to get any good results.  These DC motors are more complicated than stepper motors when it comes to successfully positioning the axes, so this code will have to be creative!

Experiment 14: What's in a Computer Mouse Ball?

So mouse balls, the kind inside computer mice, not real mice (!!!), are very heavy, but what inside them makes them heavy?  To answer that question, I cut one of them open with a box cutter.  Then, I scientifically observed the contents, and came to the conclusion that mouse balls have a steel ball bearing inside them to give them their weight.  I observed that the metal sphere inside the rubber outer coating was 28 grams in weight and was dull silvery in color.

The sphere was magnetic as well.  I then calculated the diameter with a pair of calipers, then halved this to get the radius.  By cubing this, then multiplying it by 4/3pi, I got its volume in cubic centimeters.  Then, by dividing its weight by its volume, I got approximately 7.03 grams/cm^3 as its density.  This seems a little bit light for steel, but the material was magnetic.  Select other elements are magnetic, but most elements with similar densities (~7 g/cm^3) don't make sense for a mouse ball.  Who makes trackballs out of neodymium?  Therefore, without other data, it is reasonable to conlude that it is indeed steel inside a computer mouse ball.