open diff printable spider gears, adjusted bell, and 12mm M2.5 screws

thingiverse

Human: Spider gears made up from an OpenSCAD script can be found at https://www.thingiverse.com/thing:1588376, measurements were taken from photos of the gears and revised after printing tests. Still working on this project, but now these gears do mesh pretty well. However, I don't have bearings to fix the parts yet, so I cannot proceed with revisions. At the moment, consider that these gears will NOT work with 3D printed gears because they are very small and there is too much friction for such tiny parts (at least in PLA) to take the heat buildup. I plan to try printing in Armadillo and CF nylon once my car is up and running. Another option would be 3D printing in metal (Shapeways). UPDATE: My GPM Traxxas metal replacement gears have arrived. After playing around, I was still not satisfied with how they were meshing, as it seemed too tight. While testing outside the housing, they meshed smoothly, but inside the housing not. After much inspection, I realized that the sat gears need 16mm between their outer faces (the housing has 16.25, to account for print tolerance). However, the filleted inner corners of the housing caused them to be displaced towards the center, seemingly taking a total of about 0.7mm between them, causing them to be too close to mesh correctly. Here is the 14A and B side of the open diff, with chamfered inner corners, starting from where the spider sat gears are chamfered themselves (12mm, to give a few tenths of margin). I note that my metal gears are not the Amazon ones, but https://www.gpmracing.com.hk/en/product-detail?id=3973&fid=&cat=. They are a specially hardened version, but I don't know if they may also have a slightly different size from their original. Also: 14C is adjusted to use M2.5 12mm socket head screws, as the slack between a 2mm pin/screw and the hole it passes through in the axle of the metal gear was permitting an estimated 25º (or more with a thinner pin) of free movement of the bell around the axle each time the gear changed direction. The spider axle gear is provided with 2 separate axles (2.5mm hole as original, and 2mm hole as I have a 1.75mm paperclip). When importing in your slicer program, make sure autocentering is off. Then group the axle only and spider gear axle before moving. Otherwise, you will lose the origines between these two parts. Depending on your slicer, you may need to separate surfaces, heal mesh, or whatever, as there will be 2 volumes intersecting together and some slicers don't like that and will print air if not previously indicated. Part 14A was also adjusted, 0.5mm more on the inside, 0.5mm more on the outside, as there was about 1mm play on this side of the diff that prevented correct meshing. Also from the original plans seemed to require 0.5mm more on this bell to correctly align with gearbox housing 03A.