1/16 Scale FrankenDiff

[ddmckee54]

Pictures, I think I've got pictures - if I can just decode how to insert them.


If this works, you should be able to see the Frankendiff Mk-I. Well that seems to have worked. This was the 1st version of the diff, and it looks OK - just kinda mmeeehhhh.

Enter the Frankendiff Mk-II.

This is the current version, and it looks more like the Kong diff which will be in the next image.



I initially called this my Wall of Shame, but it's more a collage than a wall. On the left side from bottom to top you have:
1 - The MK-I front diff housing. If you look closely you can see that I have recessed pockets for the screw heads, more on this later.
2 - The Mk-I rear diff housing. It's ALMOST identical to the front half, except the mounting screws go into blind holes.
3 - This is the final version of the Mk-I diff. Everything fits, and it WOULD have worked - it just looks like something you could build out of a box of Tinker-toys.
4 - At the head of this column is the Kong axle, the thing that started this journey into madness. It's a nice axle, and at $A40-$50 USD fairly cheap. But it's unobtainium as a center axle.

Just to the left of the Kong axle is the back-side of the Frankendiff MK-II. I took the rear cover off so you could see that I also re-designed the ring-gear/diff pocket for the Mk-II. The Mk-I housing would allow a noticeable gap to show at the top and bottom of the center section. The Mk-I's rectangular diff pocket didn't give me any place to correct that gap. The Mk-II's diff pocket gave me room to stash 2 more screws under the pinion housing, closing up those gaps.

What are the differences between the Mk-I and the Mk-II! A LOT, but with the exception of the 2 extra screws in the center section all the changes were just to make it look better. I slimmed the diff halves by a total of 2 mm, then added pads on the outer ends like the Kong diff has. That meant I had to redesign the pinion housing and the rear cover to compensate for the 1 mm change on each side. I also got rid of the recessed pockets, nothing like a full-sized mockup to show where you need to make better choices.

The bottom row on the right side is the pinion housing iterations, these were:
1 - The oldest version - the bearing pocket ID's were too small. I also had recessed pockets for the screw heads. It looked good on the screen - real-life, too thin.
2 - The next version - the bearing pocket ID's were too big.(Round off error, my fault. Also got rid of the recessed pockets.)
3 - The next to the last version - the outer bearing pocket fit just fine, the inner one not so much. 3D printers just REFUSE to properly print something when it starts in mid-air. The latest version is still screwed onto the Mk-II diff.

The next row on the right side is the rear cover iterations, left to right:
1 - The oldest version - just didn't look right, it needed something.
2 - The next version - I added a boss. Why's it need a boss? For the drain plug silly! (Didn't print well, that starting to print in mid-air thing again.)
3 - The last version - including the drain plug.

In the upper RH corner is my latest descent into madness - hubs, wheels, tires, and unseen but holding up the wheel is the front axle that will be donating its' spindles/knuckles. The doo-dad that looks like a brake drum is the 1st iteration of the front hub, as usual the bearing pockets were too small. I overcompensated on the next version, but it was close enough that I could shim it with a piece of tape to put everything together. It looks good- and it would work. But the effort needed to get the 3 parts lined up to start that dinky little M2 screw was enough to convince me to make the wheel and hub 1 part - with a separate cover to hide the M4 Nylock nut.

The tire you see is the Lesu 1/16 scale "narrow" tire. I ordered a set of both the "narrow" and the "wide", to see how they looked - since the specs on them are sketchy at best. There's only a 1-2 mm difference in width between the two sets, not enough to justify the extra $5 per pair of tires. In addition to the minimal difference in width, they need different wheel profiles. The "narrow" tire needs a 39 mm OD on both sides for the wheel profile. The "wide" tire needs 39 mm on one side, and 40 mm on the other side - go figure.

Don