How do you weigh a balsa bridge accurately?
Use a scale that reads to 0.01 g, weigh as close to contest day as you can, and know what counts toward the mass. How to avoid failing the weigh-in.
Updated · 1 min read
Short answer: use a scale that reads to 0.01 g, weigh the whole bridge the way the contest will, and leave a margin under the limit, since scales differ.
- Pick the right scale. A kitchen scale reading to 1 g can't resolve a 10 g bridge. Use a jewelry or lab scale to 0.01 g.
- Zero the scale with nothing on it, and place the bridge on the middle of the pan.
- Weigh what the contest weighs. Check whether glue, load hooks or loading blocks are included.
- Weigh several times and in different places, and note the spread.
- Weigh again on test day. Glue and moisture change the mass. Estimates suggest balsa properties can change by about 10% across ordinary humidity.
- Keep a margin. If the limit is 20 g, aim for a bit lower. The organizer's scale decides.
Keep a weight log of every piece as you build. It shows where the grams went. See choosing sticks and efficiency.