Techniques

Connecting/Disconnecting Groups

We designed Crossbeams stiff to create a strong joint. Crossbeams' stiffness requires you to connect groups of pieces in One Direction. When distances get large, you may violate this slightly, but don't force it.

Bad Connection Two Directions

Wrong
Connecting/Disconnecting Two Directions

Good Connection One Direction

Right
Connecting/Disconnecting One Direction

Trusses

Trusses require joints with 45° legs. Crossbeams joints have 90° legs. To create trusses in Crossbeams, you must separate the othogonal struts from the angular struts by a small distance in two dimensions or three dimensions.

2D Truss Separation

Two Dimensions

3D Truss Separation

Three Dimensions

Three-Dimensional Angles

Crossbeams' angles extend in two dimensions. However, many real-world models have three-dimensional angles. We use two techniques to model three-dimensional angles. Our Eiffel Tower kits serve as good examples.

First, filling the three-dimensional angle up to the corners helps viewers imagine the three-dimensional angle. We use this technique in the 355-piece Eiffel Tower.

3D Angles Method 1

Angles to Corners

Second, rotating the model 45° and making angles look like straights creates three-dimensional angles. We use this technique in the 684-piece Eiffel Tower. This technique works best where all angles are three-dimensional, because some two-dimensional angles are now difficult to reproduce.

3D Angles Method 2

Angles like Straights

Gears and Frames

This simple geared system binds when you spin the handle and brace the opposite side.

Gears Binding

Gears Bind

The shafts double as frame struts. (Shafts are rotating beams, while struts are fixed beams.) When you spin the handle down and brace the opposite side, you apply downward force on one side while the other side remains fixed. The system is unsure whether to apply the force as rotational motion to the shaft or torsion to the frame. The less play in the bearings, the better chance it will choose rotational motion. However, even with excellent bearings, this system reduces power and increases wear.

Instead, we put the same system in a frame. It spins great, even under heavy load.

Gears Not Binding

Gears Spin

Make sure you have good frames around your geared systems. Try mentally removing shafts from your geared system. If the system remains rigidly together after removing shafts, you have a good frame.

Overcoming Rotational Size Limitations

There's no limit to the size of Crossbeams models, provided everything remains rigid. However, motion forces size limitations, because the shaft in our rotating joints is 7.6mm in diameter. Large loads placed on a rotating shaft cause bending.

Here, we're trying to rotate the upper cylinder relative to the lower cylinder. The large cylinder size, small shaft diameter, long shaft length, and large potential deflection angle make the rotation wobbly.

Wobbly Rotating Cylinder

Deflection angle can be reduced by embedding the shaft in the fixed side and securing it to a second rotating joint.

Shaft Embedded in Fixed Side

A shorter shaft reduces the torque placed on the rotating joint, further reducing wobble.

Shorter Shaft

For rotating systems that can handle slight bumping between the two sides, the systems can be placed at a minimal distance with an axle_s stiffened with a gear between the two.

Fixture for Tight Rotating Rotation

Now, the cylinders themselves limit the wobble and deflection angle. We use this technique in our Tyrannosaurus Rex hips.

Tight Cylinders Limit Wobble