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

spider gears made up from openscad script https://www.thingiverse.com/thing:1588376, measurements taken from photos of gears, and revised after printing tests

still working on this, but now these gears do mesh pretty well now, but I do not yet have the bearings to be able to fix the parts, and so cannot proceed to revise further – at the moment consider that this will NOT work with 3D printed gears, as are very small and there is too much friction for such tiny parts (at least in PLA) to take the heat buildup – I will try printing in armadillo and CF nylon once car is up and running 😉

UPDATE: my GPM traxxas metal replacement gears arrived.. after playing around, I still was not satisfied with how they where meshing, just still seemed all too tight.. while testing outside the housing they mesh smoothly, but in the housing not.. after much inspection, I realise that the sat gears need 16mm between their outer faces (the housing has 16.25, to take into account print tolerance) BUT 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 now too close to mesh correctly – for the moment, during tests, here is the 14A 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). Once tested some more will also upload 14B with chamfered inner corners 😉

PD I do note that the metal gears I have 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 do not know if they may also have a very slightly different size from their original that they replace

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 thru 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, causing a delay and a “knock” as the gear came back against the pin each time.

IMPORTANT: spider axle gear is provided with 2 separate axles (2.5mm hole as original, and 2mm hole as I have a 1.75mm paperclip) – IMPORTANT: on 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 2 parts – also, 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 inside, 0.5mm more on outside, as there was about 1mm play on this side of the diff that prevented correct meshing, and also from the original plans seemed to requiere 0.5mm more on this bell to correctly align with gearbox housing 03A

https://www.reddit.com/r/EngineeringNS/comments/g1dat8/tarmo4almostdonebutihaveastrange_issue/fnn874e/