01Corner, edge, face: three contacts in sequence
Dropped from 1.5 to 3.0 m the case is already turning, so a corner almost always arrives first. Contact area is smallest there, the same momentum lands on a few square millimetres, and the first peak comes out steepest. The body then pivots over that corner: the whole edge line presses down, contact length grows, and the second peak flattens.
The face lands third. That third peak is the flattest of the three and the easiest to miss on video. With the entire base against the floor, acceleration climbs slowly and holds longer. Which order you get is set by release attitude, not by the case. Change the starting angle and the spacing between the three peaks changes with it, which is why attitude belongs in the same record as the waveform.
02A 0.001 to 0.005 s interval decides what you can see
Loggers here sample every 0.001 to 0.005 s. At 0.005 s you get two hundred rows per second, so a peak lasting 0.002 to 0.010 s falls across half a row to two rows. The shape is lost and a single number is left. Tighten to 0.001 s and the same peak occupies a dozen points, enough to separate the rise from the fall.
Finer is not automatically better. Below 0.001 s, with several channels live, storage and transfer become the limit and long records start losing blocks. The usual compromise: run at 0.002 s to find whether a peak exists and where it sits, then re-run that one drop at a tighter interval. Reverse that order and you spend a day repeating drops.
03Eighty to four hundred g only means something with duration
Peak acceleration falls between 80 and 400 g. The figure alone carries little. Three hundred g held for 0.002 s and the same three hundred g held for 0.010 s do different work: the first behaves like a knock, the second like a sustained push, and the second is far better at loosening mounts. Quoting one without the other is quoting half an event.
Peak and duration therefore belong in the same sentence. A record quoting only the peak is missing half its content. Read duration first: at the 0.002 s end, watch how high the peak goes; at the 0.010 s end, watch the area beneath the curve. Area is what the drop actually handed over. Height alone says how sharp the instant was, not how long it lasted.
04First rebound of 50 to 300 mm, two to five bounces
The case does not stop where it lands. First rebound reaches 50 to 300 mm, set by attitude, floor stiffness, and the case's own elasticity. The high rebounds tend to follow corner-first landings where the pivot never finished: energy the structure failed to absorb came back out into the body. Rebound is measured from the lowest point of the base to the top of the first rise, not at a corner.
Bounces run two to five. Groups with more bounces usually show lower single peaks, because the energy was divided into portions. Groups with few bounces and a high first rebound handed most of it back at first contact. Plot the two figures together and you can say where the energy went. Neither number is worth much on its own, and the pair is what you read.
050.8 to 2.5 s to rest, 30 to 250 mm of drift
First contact to full rest takes 0.8 to 2.5 s. That sets how long the high-speed camera must run: at 0.002 s intervals, 2.5 s needs well over a thousand rows, and a short buffer truncates the tail, which is exactly where a second roll would appear. Cut the record short and the bounce count comes out one or two low, which changes the read.
Landing drift is the horizontal gap between first contact and final resting position, 30 to 250 mm. Large drift means the case rolled and never settled square; small drift means it landed clean and put the energy into one corner. Log it on every repeat. If one attitude keeps exceeding 250 mm, the release fixture is due for adjustment.
| Release height | 1.5–3.0 m |
|---|---|
| Sampling interval | 0.001–0.005 s |
| Impact peak acceleration | 80–400 g |
| Peak duration | 0.002–0.010 s |
| First rebound height | 50–300 mm |
| Number of bounces | 2–5 bounces |
| Time to rest | 0.8–2.5 s |
| Landing offset | 30–250 mm |
FAQ
Why call it three contacts?
A case falls at an angle, so a corner lands first with the smallest contact area and the steepest rise; the body then pivots and the edge line presses down; the face arrives last. The gaps are milliseconds apart, invisible to the eye but clear on the trace.
How fine should sampling be?
0.001 to 0.005 s is the working range. At 0.005 s a peak lasting 0.002 to 0.010 s leaves only a few points and loses its shape; 0.001 s separates rise from fall but costs storage on long records. Coarse first to locate, then re-run tight.
Does a higher peak mean worse damage?
Not by itself. Peak and duration have to be read together. A high peak at 0.002 s behaves like a knock; a moderate peak at 0.010 s is a sustained push and loosens mounts more readily. A peak-only record is half a record.
What does landing drift tell you?
How stable the attitude was. Thirty to 250 mm is the usual spread; when one attitude keeps exceeding 250 mm, the case carried rotation into release, and the fixture needs adjusting before any result is read.
