Four short tests on real filled mailers. They give the sim the numbers it now guesses (film friction on the
caps, how floppy each bag is) and one real result to check it against (the staircase). About 2 hours of testing.
What the sim gets
Each bag's size and weight.
Friction of the bag on the cap surface (test 1).
How stiff each bag is (test 2).
The staircase angle and slide time each bag really has (test 3). The sim predicts these from tests 1 and 2
first, then we compare.
What you need
The print files below, PETG, about 0.6 kg.
5 filled mailers and 1 small box (list below).
A phone (level app, slow-motion video), a kitchen scale, a ruler, painter's tape.
A flat board about 300 × 400 mm and a few books to tilt it.
1 · Print
PETG, no supports. Print the bars and the coupon face down as the files lie, on the same build plate surface as
Joerg's caps (ask him: smooth or textured PEI): the bag slides on that face. The bars are 217 mm long and the gauge
240 mm: lay them along the bed's long side.
File
Qty
What
bar_41.stl
6
a row of 4 caps as Joerg's deck: 41 mm square, 7 mm gaps
rail_10_a, rail_10_b
2 each
side rails for 10°
rail_15_a, rail_15_b
2 each
side rails for 15°
rail_20_a, rail_20_b
2 each
side rails for 20°
coupon.stl
1
flat plate with the cap surface (test 1)
bend_gauge.stl
1
41.5° triangle that hangs on the table edge (test 2)
Also in the repo: docs/print/bagslide/.
2 · The bags
Use what you have that is close to this list. For each bag: weigh it, measure it as it lies (length × width × height), and
measure the contents' length × width (before packing, or feel it through the film).
Bag
Mailer
Contents
≈ kg
B1
poly mailer 10 × 13 in
a folded T-shirt
0.3
B2
poly mailer 14.5 × 19 in
a hoodie, loosely packed
0.7
B3
poly mailer 10 × 13 in
a hardback book
0.8
B4
padded (bubble) mailer 9 × 12 in
a phone case or small box
0.4
B5
poly mailer 6 × 9 in
a pair of socks
0.1
B6
cardboard box ~200 × 150 × 80 mm
~1 kg
1.0
B6 is the check on the rig: the sim already models boxes well, so it should match.
3 · The tests
Test 1 · Friction (5 minutes per bag)
The board stays on the table at the hinge end; raise the
other end with books or your hand. Read the angle from the phone lying on the board.
Coupon taped on the board, the bag on the coupon, the phone (level app) on the board beside it.
Start angle: raise one end slowly, about 1° per second, until the bag starts to slide. Read the angle. 3 times.
Keep-sliding angle: start steeper, give the bag a small nudge, and lower the board a little each time until a
nudged bag stops by itself. Read that angle. 3 times.
Test 2 · Bending (3 minutes per bag)
Poly mailers only: fold the empty film under first. Padded
mailers and the box: as they are.The gauge stands beside the bag (taped to the table), not under
it. Push the bag straight out, lengthwise, until its front edge touches the slanted line.
Poly mailers: fold the empty film under the bag first, so the contents start right at the front edge (otherwise only
the loose film droops and every bag reads about 30 mm). Padded mailers and the box: test as they are.
Bag on the table with its short edge exactly at the table edge. Tape the gauge to the table just beside the bag: hook on
the table top, the slanted edge hanging down outward from the table edge.
Put a piece of tape on the table at the bag's back edge (the start mark).
Push the bag slowly straight out over the edge, lengthwise. Watch from the side, eye level with the gauge.
Stop when the bag's front edge drooping down meets the slanted edge of the gauge. Measure how far the back edge moved
from the start mark, in mm: that is the overhang. 3 times.
If the bag tips off the table before its tip reaches the slant (the book, the box), write "too stiff".
Test 3 · Staircase (the check)
Build it: stand two a rails (the tall ones) and two b rails on their long edges, a then b end to end, so the
steps go down continuously; the second pair parallel to the first. Drop the 6 bars into the pockets: their end hooks set
the spacing. Tape the rails to a flat table (check with the phone level: within 0.5°).
Phone on a stand, side-on, slow-motion video, a ruler in view.
Start at 10°. Lay the bag centred, long side pointing down the slope, its back edge on the top edge of row 0. Let go without pushing.
Write down what it did: slid off the end, stopped (on which row), or didn't move. From the video: the time from letting
go until it tips over the end of row 5.
Note if the film caught on a cap edge or sank into the gaps.
3 times per bag, then 15°, then 20°.
Top view, to scale (a 10 × 13 in
mailer). The bag is wider than the caps: that is fine. It counts as slid off when it tips over the end of row 5.
Side view, to scale
blue: capsbeige: railrise per row = 48 mm × tan(angle)
4 · Record
Loading the results…
Bags
Test 1 · friction
Test 2 · bending
Test 3 · staircase
5 · Summary
Every Add is saved in the repo (docs/pages/data/bagslide/). When you're done, tell Claude: it reads
them, puts tests 1 and 2 into the sim's bag model, predicts test 3, then compares with what you measured.