Monday, February 24, 2014

Dick Kerr WDLR 06

I've pulled the latest round of prints from the 3d printer, and am really pleased with the results.  I might adjust the assembly but I'm really pleased with the detail.  I'm going to add some relief to a couple edges to make things look thinner, and break the insulators away from the radiator.  The last revisions went really well.

Although I'm excited to work on the cab, I realized that I needed to sort the mechanism.  Returning to my previous work, I started by drawing the gearbox, wheels, and motor in both 2d and 3d.  I dropped the motor and gearbox in the model, and experimented with it's position.  I may abandon the flywheel, as it stands it looks like I can get everything into the hood.  Very cool.

One thing that's been bothering me about my previous work was that I only powered one axle.  Although this might work, with such a small loco and such a small motor I wanted more power transmitted to the rail.  This means connecting things with gears.  There's just enough room in the body cavity to offset the motor to one side and connect the two axles with a series of gears.  I started by drawing the Northwest Short Line spur gear because I thought that I might create a system that was integrated with the NWSL gearbox. . . then better sense prevailed.  A big part of the value of the NWSL gearbox is that the worm and associated thrusts are well worked out: messing with this seemed to invite gremlins.  I can always play with an integrated system later.  

The NWSL gears are all metric, the particular gearbox I chose is .03 MOD.  It seemed logical enough to continue with that gear specification.  I should point out that my version of the NWSL gear is close, but I may not be spot on, because I don't know exactly what the pitch of the NWSL gear is.  I made some good assumptions and may have it, but won't know until I test.  Given that my gears will not interact with the NWSL gears it does not matter, however I'd like to know. . . . 

I've been using Gearotic Motion and AutoCad for my mechanism design.  Gearotic will give you the proper axle spacing between two spur gears.  Using that information, it's possible to layout the precise geometry in AutoCad.  As my plan is to cast the chassis in lead shot filled resin, I'm simply including a minor shrinkage factor in the tolerance.

Gearotic allows you to work from the gear specification and the number of teeth to create a .dxf, stl, or gcode.  Although you can make a printable file from Gearotic, I'll probably use Rhino to design molds.  From there I can make rubber molds and cast gears in engineering resin.  Gearotic Motion was developed by Art Fenerty, who also developed Mach3, a corner stone of the Home CNC comunity.  I love the program.

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