Ivan's base is now constructed! Printed and assembled, I am both pleased and shaking my head a bit at the results. Though the parts do fit and will function just fine, there are some issues that require correction. These issues include gear spacing, outer gear wall thickness, outer gear bearing size, sun gear attaching to upper gear bearing plug, outer gear spacing, M3 / M4 screw usage and length, and a real classic: warpage. For example, consider the gears below:

. On the left we have the outer gear, at upper right is the sun gear and to the bottom right is a planet gear in filaflex. Before printing these gears in more expensive Taulman filament I want to get them designed properly. Looking closely at the outer gear's teeth, we see that they are joined on each side by only one trace of PLA. I am using a 0.75mm nozzle for strength, faster print times, and better translucence of the filament. This means that thin details like the backing of these gear teeth can get lost to wall thickness considerations. The other gears look fine to me though I turned the sun gear upside down to show it's shiny smooth side up and replaced the Filaflex planet gear with red transparent ColorFabb PLA/PHA because I ran out of Filaflex. All of the gears will be printed in Taulman's engineered nylon-like low temperature filament (not bridge, the new one, I forget the number on it).

Before this stuff was printed, one of our team members cautioned us on being overly eager to print up something even thought we knew it would have flaws. The notion was it is best to design things right before proceeding. We countered with the point of 3D printing's value in easy iteration. Well, both philosophies kind of turned out right in a way, and here's why.

There were lots of small errors. Because the errors were small, the design does function though it has some play and rattles like a PLA gearbox does. The thing is that we could have caught some of these errors with more design time but probably not all of them. For example consider the central bearing intended to hold the outer gear on the whole assembly.

We all knew the solution that I had designed had some flaw - it just looked wrong and felt wrong somehow. Though an outer bearing was suggested as a solution, that bearing would have had to be 150mm in diameter or at least 100mm with adjusted gear teeth and the only bearings available were the 608ZZ skateboard bearings - too small! Well when I actually held the parts in my hands I had an epiphany of sorts as I suddenly realized that what was needed was a larger central bearing.

So off I go to the online stores looking for a larger bearing for future revisions of Iivan, in fact an assortment of different bearings might be just the ticket. Also just in writing this I realize a temporary solution is to make a new sun gear with the inner bearing post morphed onto the top of it. I had wished I couild strongly glue the free standing hollow post I had in hand to the sun gear last night and only this morning as I write this do I realize that I can just print a new sun gear which only takes 15 or 20 minutes to do (plus design time and sit and think about it time (which for me is the most time of the whole process)).

Ive gone into detail about this design issue because it is one that most on the team were aware of due to our discussions of it and because it clearly illustrates the trade-offs of design perfection versus excessive iteration. Could we have eliminated some errors? Yes. Am I glad I went ahead and printed it? Yes. So it's sort of a win-win in my book. Ka-ching!

Les