Saturday, May 13, 2017

Rhino3d Tutorial: Making Treads and Tracks, Part 1

One of the more odious tasks for me, as a digital sculptor, is tank tracks.
I can do them in my sleep, now, but at first, they were no fun.  Plus, they used to crash my more feeble sculpting computers, leading to much frustration.
I still carry some of that residual hate.  Damn you, tank tracks.  ;)

Now, I'm not going to get technical on you.  There are various types of suspensions, wheel and sprocket arrangements, and tread types.  You can research that on your own.  Here's a good start...
Everything Is In The Suspension
Sherman Road Wheels
M1 Abrams Suspension
Leopard 2 Suspension
WW1 Tank Suspensions

As you can see, there's a variety of approaches.  The simplest is the type used on the early British tanks in The Great War, and which has been emulated in WH40K Imperial Guard Designs and some charming Alternate WW1/Martian Invasion games for their steam tanks.

Also, the tank from Indiana Jones and the Last Crusade.  Tread units running all around an armored block. Simple, and no major complications.  Let's do that one first.

I work in Rhino3d, so adapt to your program and work process as necessary.

 First, a trapezoidal line.  A closed curve, actually.
 I fillet the four corners with a nice radius, rounding it out.
This is what I call my Main Reference Line.  Remember that.
 I extrude that closed curve into a shape
 I offset two curves from the main ref. line.  One larger, the other smaller inset.
 Rhino lets me use two closed curves on the same plane to make a hollow shape.
 I do that, making it slightly narrower than my main tread unit body.
 I subtract that large hollow collar from the main shape using a Boolean Difference.  Basically cut one shape out of another.  This creates a shallow trench all round the center of my tread unit.  Individual track links will fit in this trough.
 I chamfer the outside edges, because I'm a fussy git.
 I create the outline of my track link.  Nothing complicated here, but I want to make sure it fits inside the confines of my trough.
I mirror the line, and make it a solid shape via extrusion.
 I chamfer the edges of the blocky tread link.
 I rotate it 90 degrees, and see how it fits.  It fits!
 I then use a command in Rhino3d called Array Along Curve.  I select my link, select my Main Reference Line, and play with things until I have an evenly spaced number of tread links all around the outside of my tread unit.
 I end up with 57 tread links all arrayed around the edge of the unit.
 Rhino handles the orientation automatically.  In the past, on more complicated builds, I have had to manually rotate each tread link around the curved edges.  Nothing is perfect.
 Now, there's a number of gaps between the links, the trough, and the main body of the unit.  I offset the Main Reference Line a wee bit to the interior.
 And extrude a shape that will be a substructure, holding everything together.  The main details are still evident, but when fused, the unit will be one cohesive piece.  This is necessary for casting and printing.  Small voids equal death.  Lack of detail equals death, too.  A balance is struck.
 So, there's our completed tread unit, ready to be fused together.
 The tempation is strong.  Let's make a tank.  First, we copy the tread unit.
 Create another closed curve.  This will be the profile of the tank hull.
 We extrude it into a shape that fits between the tread units.
 A couple cylinders, one for the turret, the other for the barrel, and it's a tank.  Too squat and fat, though.
 I scale the hull along one axis, squishing it without changing other proportions, and move the tread units up against it.

You can put armored skirts over the top of those tread links on top, you can add any variety of rivets and surface panelling to it.  This is just a simple tutorial on making WW1 style tread units.  More advanced stuff later.

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