Build-a-Bird: Day #3—2/8/2011

 Day #3 was a very productive day—it could even have been called ‘gear-tastic!'  Thanks to a gear plug-in Amon downloaded onto our computer, we were finally able to make a gear with a full set of teeth!

Our pride and joy

We might have cheered quite loudly when this gear finally appeared on our screen, but even with the plug-in, it took us quite a long time (about three quarters of class) to make it correctly.  We had to deal with some constraints because we were using the plug-in, such as not being able to choose the overall diameter of the gear, having to select the size of the center hole from a dropdown menu, and not being able to alter our gear once it had been created.  The last condition meant that we had to start over countless times, and as usual use quite a bit of trial and error, but in the end we were very pleased with our result.

It was easy to select the size of the center hole (1/4 inch), as well as the number of teeth (20), but since we had no say in the gear’s diameter, it was a little bit difficult for us to make the entire gear the size we wanted it to be.

For example:

Our first gear

 Looks great, right?  That’s what we thought, but then we realized that there was no hole in the middle of the gear.  We thought that was strange, since we had specifically made the size of the center hole ¼ inch.  We leaned in closer to the screen, and as we squinted we realized—the hole was in fact there, it was just the size of a pin prick.  At first, we thought that we had incorrectly sized the hole, but a check told us that its size was indeed ¼ inch.  We quickly realized this brought the overall size of our gear to something HUGE, definitely much larger than the 6.5 inch limit.

We returned to our gear plug-in menu, and tried to figure out what might allow us to change the gear’s overall diameter.  One—diametral pitch— caught our eye because we didn’t know what it meant.  A quick Google search brought us hope—it turned out the diametral pitch determined the number of teeth per inch of the gear's diameter.  Its default had been a value of .5, meaning our gear could only have one tooth for every two inches of diameter.  With twenty teeth, no wonder we had created such a giant gear.  We were curious to find out what the opposite end of the diametral pitch spectrum looked like, and changed the value to the plug-in’s maximum: 200.

This time, instead of bus wheel-sized gear, we ended up with a gear roughly the same length as a grain of rice.  The ¼ inch hole looked gigantic.  We tried again, this time with a much more conservative diametral pitch of 10, and to our delight produced a correctly sized gear.

One more close-up

We looked at our Lego model to try to determine what we should next build with SolidWorks, and decided to start with the piece we deemed ‘the little red rotater.’  After a demo from Lyn, we decided we could drill a loose-fit hole for piano wire in the side of the piece, thereby eliminating the problem we would have had of needing cut holes in two different planes with a 2-D printer.

Sketch

SolidWorks part

We went on to sketch the base, wanting to decide every dimension in advance in order to make it easier to create on SolidWorks.  In his demo, Lyn had also showed us the variety of possible ways to attach parts to each other, and we quickly decided the best way to attach pieces to our base would be to cut small holes in the base that would correspond with protrusions on the pieces we wanted to attach.  It was very interesting to note the huge effect that a size difference of one hundredth of an inch could have on the way two pieces fit together (tight fit vs. loose fit vs. much too big or small).

Base sketch