How do you leave clearance for a car or pass-through block?

Short answer: draw the opening full size from the rules, add a small margin, keep glue and cross-pieces out of it, and put the bracing above it or outside it.

What the rules may require

Some contests require a toy car, a small block or a rod to pass along or through the bridge, with a stated width, height and sometimes position. Others require an opening at the load point for a hook or an eyebolt. Read exactly how the opening is measured and what passes through.

How to design for it

1. Draw the opening on your plan at full size, with the real object next to it.
2. Add a small margin, a millimetre or two, because glue and build errors eat clearance.
3. Keep it clear all along. Check for glue bumps, pins and cross-members.
4. Brace above or outside it. In a through truss, top bracing must clear the vehicle's height.
5. Test with the real object or a cardboard copy at several stages of the build.

Common mistakes

• Measuring the opening from the wrong edge.
• Gussets or cross-pieces that stick into the space.
• A deck that has warped upward.

See designing around the loading block, deck or through truss and reading your rulebook.