Phase 4 of 5 · Test

Test

Testing to failure is how you find out where your mass should go.

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Test

Home test rig

Practice on a rig that matches the competition apparatus. If your home wall is off by a centimeter, your test results are off too.

To see the real setup before you build yours, watch the 2027 Boomilever Event Supervisor Guide (video, opens YouTube in a new tab) (video).

PartSpecificationRule
Testing wallRigid board at least 40 cm wide × 30 cm high (¾" plywood works), smooth and plumb. Mount it so it can't flex.6.b.i
Bolt holeNo larger than 0.266" diameter, about 5.0 cm below the top edge, centered side to side. Mark its horizontal and vertical centerlines on the face.6.b.ii
Contact linesHorizontal lines 10, 15, and 20 cm below the bolt center. Vertical lines 4.0 cm left and right of the bolt center.6.b.iii, iv
Mounting bolt¼-20 × 60 mm connector bolt (17 mm head), hex nut and flat washer on each side of the wall. Set 3.0 ± 0.1 cm between the bolt head and the wall face.6.b.v
Loading block5 × 5 cm square, about 2 cm thick, center hole for a ¼" eyebolt (1" eye, max 3" long) held by a wing nut.6.c.i, ii
Chain, S-hooks, bucketChain and S-hook from the eyebolt to a 5-gallon bucket. Whole loading assembly no more than 1,500 g. Hang it with about 2" of clearance above the floor.6.c.iii to v, 4.c.ii
SandClean, dry play sand. Our gravity-fed hopper with a gate valve lets you pour smoothly without shock-loading the structure.6.d
Stabilizing sticksTwo ½" dowels about 18" long with a spring doorstop screwed into one end. You may steady the bucket only with the tips. Never lift or push it.6.e, 4.c.iv
Scales and timerStructure scale to 0.01 g. Load scale to 1 g (range to at least 16 kg). Timer set to 6 minutes.6.f to h
Safety. Wear eye protection. Keep feet and hands out from under the bucket. Balsa fails suddenly and can throw splinters.
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Test

Test protocol

Run every test the same way so you can compare one build to the next.

  1. Weigh and inspect

    Weigh the structure to 0.01 g. Look for cracked joints, glue globs, and twisted sections. Photograph it from the side and the top.

    Record mass

  2. Write your prediction

    Before loading, write down how much you think it will hold and where you think it will break. This is practice for the estimated-load tiebreaker, and it trains your engineering intuition.

    Record prediction

  3. Mount and measure

    Hang it on the bolt. Check the reach (chain centerline 40 to 45 cm from the wall), centering (within 2.5 cm), wall contact (inside the 4 cm lines, above the 15 or 20 cm line), and that the loading block's bottom is above the bolt line.

    Record reach and contact depth

  4. Start filming

    Use a phone in slow-motion mode, from the side, with the whole structure in frame. A second phone from above helps. Failure happens in a fraction of a second; the video shows where it started.

  5. Load smoothly

    Pour sand at a steady rate. Watch for bowing, twisting, or creaking, and call out what you see. Stop at failure or when you reach your target.

  6. Weigh the load

    Weigh the bucket, sand, and loading assembly together (remove any broken pieces first). That total is the load supported.

    Record load held

  7. Collect the evidence

    Find where the break started using the video, then look at the pieces. Label and bag them with the build number. Use the next sheet to diagnose the failure.

    Record failure mode
Test copies, not the original. Build at least two of each design. Test one to failure to learn its limit. A structure that already held a big load may have hidden damage, so don't count on it in competition.
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Test

What broke? Learn from the failure

A broken boomilever is data. The part that failed first tells you where you need more strength, and every part that didn't fail is a place you might remove mass. Pick what you saw:

Then write it in your build and test log.

Keep going