Building the Wheels

The plans show that the wheels comprise a V-pulley (with one of the flanges removed) sandwiched against two or three layers of plywood cut in the shape of the wheel.  The sandwich is held together with bolts that go through the plywood pieces and a hole in the V-pulley spokes.

My V-Pulley has perpendicular reinforcing ribs along the spokes; drilling a hole through the spokes would weaken the spokes.  So I need to modify the plans to preserve the structural integrity of the pulleys.

Pieces for the pilot wheels
Pieces for the pilot wheels

My solution is to cut wedge-shaped pieces that I can fit between the spokes on the back side, and have the bolts go through the wedges on one side and the wheel plywood on the other.  There also are some other design alterations I had to make to accommodate my pulleys.  But I think they will work out Ok.

The plans also call for a “live” axle for the drive wheels.  By “live” axle, I’m referring to one axle that’s attached to both drive wheels so that both drive wheels turn together.  This would be a simpler solution, as I could have just one gear sprocket on the axle and have it turn both wheels.  This is the way the real steam engines are built.

One of the problems with this approach is that, when the engine goes around a curve, the outer wheel spins a little bit faster than the inner wheel.  If both wheels are fixed to the axle, then one of the wheels will have to slip on the track.  This will cause the outer wheel to have a tendency to try to climb the rail and derail the engine.

Pieces for the drive wheels
Pieces for the drive wheels

My solution is to take advantage of the computer controller I’m going to build and have the computer turn the outer wheel faster than the inner wheel.  If I can do the arithmetic correctly, then I should be able to program the motor controller to make the wheels turn so that that is no slippage.  I’m also thinking that another advantage to this approach might be that, if I can turn the outer wheel faster than the inner wheel on a curve, then in theory I might be able to have a track curve with an even smaller radius.  Turning the outer wheel faster should force the engine to try to turn with the curvature of the track.

So I’ll need to build the wheels and axles so that all six wheels can spin freely on the axle, and add a drive sprocket to each of the rear wheels.

Click on each image to get a description of its construction: