Stepper motor & Acrylic gear play

Here at SpikenzieLabs, we’re always on the lookout for interesting and fun components.  We got these in a few weeks ago.  It is a small stepper motor and driver board.  They sell together for $7.95.

One of the cool things about this stepper is that it runs at 5v, and the current to drive it is low enough that you can take the 5v right out of the Arduino.  After playing around with one of these little steppers with the usual piece of tape on the spindle, I thought it would be cool to laser cut some gears.  Here is a look at my project. The first step was to draw out a hole in the center of a gear that would accept the spindle.  Careful measuring done with a digital calliper, then designing the hole in my illustration software.  The lines are extra bold just so that they show up more clearly.

The red line is the actual cut line, large black circle is the center of the gear spindle drawn by the gear drawing software.  The smaller circle is there to help make sure everything is ‘center-center’ while moving elements around. A long time ago, I discovered this site: http://woodgears.ca/gear_cutting/template.html There is an interesting gear drawing capability right on the site.  For a mere 26$ dollars, you can buy & download his GearGenerator3 software.

Really awesome, simple and fun to play around with. Using this software, I set some gears up on a particular grid pattern so that the center hubs of the gears fall right on the grid lines, giving me gears that will always find a perfect mesh on a ‘real life’ grid.

Note the green grid lines going through the center of each gear hub. Doesn’t matter if you’re working in metric or imperial, so long as the scale is good, you can create a bunch of different sized gears that will be interchangeable and find a perfect center hub hole.

The idea here is to make a board that I can interchange gears on a whim, and see the different speeds that gears turn in ‘real life’. For inspiration, I flipped through one of my most all time favourite books, 507 mechanical movements. Now available for free online, http://507movements.com Love it!

With the gears created, I exported them as PDF, and then into Adobe Illustrator.  There is a command in illustrator to ‘Simplify’.  This makes laser cutting much simpler.  Strongly recommend using that command on CAD / other output files before cutting.  Here is an example of one of the gears in illustrator.:

Note the fewer line segments that appear on a gear after using the simplify command. (Blue dots).

Above is the main drive gear, with the spindle cut out.  My measuring was very exact.  Took about 5 pounds of force to get the acrylic gear squished onto the spindle.  I think some of the residue from the tape testing is lending a hand keeping it solid.  The blue colored board is actually clear acrylic with blue protective film still in place.

I based the spacing on a .5″ spacing, so any of the gears that I’ve generated can mesh perfectly with any other.  The holes are laser cut at .08″.  This is the perfect size to send a 4-40 tap through.

Note how you can see right through the center hub of the two gears above.  This was the pint that I started to feel really great.

Tapping acrylic is something we first tried years ago on our Povard POV electronics kit.  Since then, we’ve been tapping acrylic at a feverish pace, and have burnt through a few drills.

Here is how we tap.  The tap going through a 1/4″ ring gear.  I have centered some holes at 15 degree increments.  Zipping the drill in, and reversing it out leaves a very solid threading in the acrylic.  Doing it at high speed versus low speed makes no difference.

Creating a stepper motor mount was pretty simple. I need the center of the stepper spindle to be coming through one of the holes in my board.  I lined up the mount holes on the stepper, and cut them through the .5″ spacing hole board.

Notice how you don’t see the mounting brackets of the stepper?  Measured out perfectly they are directly below the holes cut in the acrylic.

Fitting it all together, I slid the main drive gear back in place, and then loaded in the rest of the gears.  Tapping only the holes that I need to use.

Last minute change for the mount..  I realized that I didn’t have the clearance under above the motor mounts to send a nut & bolt through, so I made a pressure fit pinch plate. This way I don’t need to counter-sink the mount holes.  Peeling away the blue protective sheet underneath.

A few other gears created, a push-bar, and here is what I ended up with.

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