Friday, July 20, 2018

Tenshodo Brass SD24 rebuild

Tenshodo SD24 Total Rebuild and Repower


I've been working on this old brass Tenshodo SD24 for a couple of years on and off.  My goal is to make it a decent running locomotive.

I selected a high torque rare earth magnet motor with a 2mm shaft.  This motor runs around $6 each.  These types of motors are far superior to anything else out there.  They are very good on the low end, but at 24v, you never reach the top end so the locomotive may seem a bit slow.  If you run trains at low speeds, this is the type of motor you want.  The torque is very high, much more than you are probably used to.

I made the motor mount on the 3D printer just the right height so the motor shaft is aligned with the drive shaft on the gear tower.

Here's where the problem is located:  these locomotives used a 2mm rubber hose to connect their 2.3mm shafts to the old open frame motor.  I could save this hose and with a drop of glue make it work probably ok.  The hose takes away just a bit of freedom of sideways movement, and that little bit almost certainly adds up to frequent derailments on most track, unless you have huge radius and large turnouts.

Let's table the hose for now and move to more serious problems.

The motor shaft connects to a hose that connects to a drive shaft that connects to a bakelite gear on a gear tower that connects to another bakelite gear that connects to another bakelite gear that connects to a worm gear on a shaft connected to another worm gear connected to another drive shaft that connects to 2 more worms.  Each worm connects to an axle.  That's 3 bakelites, 4 worms, 5 total shafts.

The trouble starts with mating a bakelite gear to a metal worm.  Once worn a little, lots of binding will happen.

No I'm going to replace anything with another drive system.  In this shop, things get fixed, so let's figure out how to solve the problem.

Getting new hose is easy, but perhaps we can make couplings.  Gears are riveted on, but not impossible to replace and we have plenty of those around.

Fabricating a new gear tower is totally possible using aluminum and may be the way to go, plus I really want to make something like that anyways.....

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