Gate 1 → Gate 2: waiting for a block on gate 1 followed by gate 2
#
gate
event
t (s)
blocked dt (s)
v = w/dt (m/s)
since prev. block dp (s)
T = 2·dp (s)
Runs
No runs yet — press Record (or the hub's button).
Hub
Hz
SPS
readings
× 5 ms
LSB
mm/s
mN
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Console
Calibrate the force sensor
reading —
1Tare — take everything off the hook, let it settle, then press Tare.
not done yet
2Known mass — hang a mass you trust (a 100 g slotted mass is ideal), let it settle, press Calibrate.
= 0.981 N (g = 9.81 m/s²)
not done yet
3Check — hang a different mass and compare.
expect 1.962 N · reading —
Tare and calibration are stored on the hub; redo the tare whenever the cart is turned over or the hook bar is swapped. The hub averages 16 readings (0.2 s) for each step — keep the mass still.
Download runs
Tick the runs to include. Each row has t, x, v, the acceleration calculated from v–t, θ, ω, α, F and both gate states.
How to use
Connect. Switch the hub on (blue LED blinking), press Connect Bluetooth and pick PickleHub-xxxx. Or plug the USB-C in and use Connect USB (desktop Chrome/Edge). The LED goes solid when connected.
No hub yet? Press Demo (no hub): a simulated cart bounces between two springs on the rail, past both photogates, and everything below works exactly as it does with a real hub — record, fit, export.
Record a run. Press Record (or the hub's BOOT button): the hub zeroes x and t, frames stream into a new run; press again to stop. Runs stack in the list with their own colours; tick the eye to overlay them, click a run to select it for stats and CSV.
Read the graphs. Hover for values at a time; drag across a chart to select a range — the table shows Δ, mean and a least-squares slope for every visible run and quantity (slope of v–t is a, slope of x–t is v̄), and the fitted line is drawn on the chart. Click once to clear.
Pick points. Switch the tool to Pick points and click any chart: the nearest data point of the nearest run is marked and numbered. Consecutive points on the same run and chart are joined, with their Δt, Δ value and slope. Two points on the v chart give the calculated acceleration a = (v₂ − v₁)/(t₂ − t₁), shown with the numbers substituted. The a chart is the same idea done for every frame (slope of v–t over ±80 ms).
Download several runs.export runs… in the Runs panel downloads any set of runs as one stacked CSV, one side-by-side CSV, or one file per run.
Gates. Each beam edge arrives with its blocked time dt and the time since the previous block dp. Set the flag width for v = w/dt (cart flag blade 20 mm; a marble is 16 mm), the gate spacing for the two-gate speed (launcher bar 50 mm). A pendulum through one gate: T = 2·dp.
Force. Tare with the hook empty, then Calibrate with a known mass. Both are saved on the hub.
Wavy v or a while the wheel turns? The ripple is locked to the rotation, so it is the magnet, not noise: tick θ and turn the wheel slowly by hand through one full turn — it should be a straight ramp of 6.28 rad. A wave on the ramp means the magnet is off the chip's centre (the Ø4 magnet's sweet spot is ±0.25 mm) or too far away; a trace that goes backwards part-way means an axially magnetised magnet (a diametric one grabs a steel pin on its curved rim at two opposite points). AGC (Hub panel) should sit around 30–100; near 128 the chip's gain is maxed — bring the magnet closer.
Protocol and commands: firmware/README.md. Web Bluetooth needs Chrome or Edge; on Linux enable chrome://flags/#enable-experimental-web-platform-features.