Jim -

Why Cerrobend? Actually, lead shot randomly packed is only 77% as heavy as cast Cerrobend (Wood's metal). The space between round balls must be factored in, although it would be partially filled with epoxy or other less-dense glue.

According to Wikipedia, a random packing of loose balls in a cavity only fills about 63.5% of the volume. The density of lead is greater than Cerrobend, 11.34 g/cm^3 vs 9.4 g/cm^3, but the advantage is lost due to the low packing density.

Grades on the A&O are steep, and we need all the tractive effort we can get.

As for the DB interference, I'm leaning towards making a fixture and milling it out so that the full height above the motor mount is available for electronics. There's a big winter storm heading my way and that might be a good snow day project.

So far I've found FDM 3D printing to be liberating. It lets me imagine new answers to problems that would have been tedious if built-up in styrene or machined on the mill. So far the primary limiters are my imagination and NOOB learning curve with Fusion 360.

The light package mounting block is a variation of an idea I had decades ago for the long hood of an Overland GP30 or 35 (don't remember which.) Back then I got a block of Sculpey modeling clay and packed it in the end of the shell. Then I carved out openings for the various LEDs (all hand-colored blue meanies) and incandescent headlights, also enlarging holes for the various grab irons that poked inside. After sculpting the block was hardened by baking in the kitchen oven.

With the printed blocks I will have to carefully trim the length of brass grab irons so that they don't extend past the inside wall of the shell.

I'm substituting brass detail parts including the handrails, grabs and lift rings since those are delicate and easily broken (the plastic lift rings are far undersize.) The A&O is all about operating sessions, so some innocent but ham-fisted handling of equipment must be anticipated.

All the best,
Bob

Back to the original topic: remotor, and including some benefits.

The effort to install a new, smaller motor in my RC GP9s comes with a benefit to increase headroom inside the shell. This afternoon I milled a TB1935 module to make it narrower, only 1.3." I narrowed it as far as I felt comfortable while holding it in a Sherline vise. It now slips easily in a new RC GP9 shell. So far so good. There are a couple of pinhole leaks in the enclosure, due to voids during injection molding, but not enough to significantly influence bass response. It does, however, now equalize changes in barometric pressure.

Soon a difficulty became apparent. The dynamic brake blister is narrower inside than the shell itself. Rut roh!

Plan A: The DB part has not been assembled, so there are two slots for the exhaust stacks that could be used to hold it in a fixture for milling. That wouldn't be too difficult but the result would be a part that loses the alignment "lip" and reduces the amount of gluing surface. A strong joint is desired because most operators will pick up the finished locomotive by the DB blisters when re-raining after an "oopsie." Stuff happens.

Plan B: After careful measurement I discovered that I had about 0.2" of clearance between the bottom of the speaker and the top of the new motor mount. Originally I planned to center the driver in the DB fan opening, with the passive radiator situated towards the back of the long hood. That wouldn't work since it would interfere with the rear drive tower. However, it can be flipped around 180 and still leave some room for wires.

Either way, I still plan for the primary weight to be Cerrobend poured into the bottom of the OEM fuel tank maybe with the fuel tank taped to the bottom of a pot filled with cold water. The new brass frame also helps.

Looks great Craig. The mothership will welcome #405 with open arms.

Glad to hear that, Craig! It is very encouraging for the Portescap remotors. Did you tune any motor parameters in the decoder or just run with the defaults?

And kudos for spending a few hours to show me around Fusion 360. That helped a LOT. I still find myself staring at the screen with a dumb look on my face thinking "there should be an easy way to do this..." It is a steep learning curve, and my designs are neither elegant nor optimal, but at least they are functional.

I just couldn't help myself.

Once the GP9 motor mount was done, I turned my focus to P&D F3s. These will be receiving Tang Band T1-2025SC speakers mounted vertically. They have an unusual tripod mount and require space underneath the bottom passive radiator for the bass to get out. The extension to the two tripod mounts near the cab is a bit flimsy. A little bit of Elmer's school rubber cement will keep it from buzzing.

Here's the CAD. I left gaps on either side of the motor to allow heat to escape. That shouldn't be much of a problem since the coreless motor produces 1.7 times the torque per Amp compared to the Pittman 8414.



The first installation. The 4 holes on the side bars are for mounting an HO Loksound 5 decoder and a small circuit board on a slab of styrene.



Most of the sound escapes the shell through the dynamic brake intake side grills and roof exhaust grills, along with the radiator fans.