Spin Rig V0.1: Simulating Gravity with a Sock and a Phone

V0.1: Spin Rig Driven by Sebastian

Our very first gravity experiment.

The goal?

Simulate and measure 1.5 G of artificial gravity using just a sock, a phone, and a human arm (my arm).

Goal

Generate 1.5 G (~14.715 m/s²)
Measure it using the Phyphox app
Hit target RPM by hand while tracking live data

Materials

Human (Sebastian)
Sock (to hold the phone)
String (0.5 meters / 1.64042 feet)
iPhone 12 Pro
App: Phyphox – Centripetal Acceleration mode
YouTube: 31 BPM Metronome (@DrumsetFundamentals)

The Thinking Behind It

To simulate gravity through rotation, we use:

$$ a = r \cdot \omega^2 $$

Where:

$ a $ is acceleration (meters/second²)
$ r $ is radius (meters)
$ \omega $ is angular velocity (radians/second)

For our 1.5 G target:

$$ a = 1.5g = 14.715 , \text{m/s}^2 $$

First Radius Assumption: 0.5m

Using $ r = 0.5 \text{ meters} $:

$$ \omega^2 = \frac{14.715}{0.5} = 29.43 \quad \Rightarrow \quad \omega = 5.425 , \text{rad/s} $$

Convert to RPM:

$$ \text{RPM} = \frac{\omega}{2\pi} \times 60 \approx 52 , \text{RPM} $$

Gravity Targets at 0.5m Radius

We can look at a table of what the RPM would be for various G-Forces given our 0.5 meter radius:

G-Force	Acceleration (m/s²)	Angular Velocity (rad/s)	RPM
1.00 G	9.810	4.429	42.3
1.25 G	12.263	4.952	47.3
1.50 G	14.715	5.425	51.8
1.75 G	17.168	5.860	56.0
2.00 G	19.620	6.264	59.8

So we did a practice run at 52 RPM using a metronome that counted 52 BPM.

🤔 Realized Mid-Test: Our Actual Radius Was Bigger

Because I, Sebastian, was holding the string, the radius was actually larger!

Revised radius:

Arm (center of chest to fist): 0.85m
String: 0.5m
Sock slack: 0.1m

$$ r = 0.85 + 0.5 + 0.1 = 1.45 \text{ meters} $$

Revised Rotations Per Minute Spin Target for 1.5 G

Still seeking the same acceleration for 1.5 G’s:

$$ a = 14.715 , \text{m/s}^2 $$

We re-calculate the math:

$$ \omega^2 = \frac{14.715}{1.45} = 10.15 \quad \Rightarrow \quad \omega = 3.1856 , \text{rad/s} $$

Convert to RPM:

$$ \text{RPM} = \frac{\omega}{2\pi} \times 60 = \frac{3.1856}{6.2834} \times 60 \approx 30.4 , \text{RPM} $$

With the new radius, we get approximately 30.4 rotations per minute or around 31 RPM.

Final target: ~31 RPM

In Action

Spin Rig in Action

What We Observed

Using Phyphox’s Centripetal Acceleration mode:

Acceleration peaked ~14–15 m/s²
Angular velocity hovered around 3.2 rad/s
✅ Confirmed: We hit ~1.5G manually for several moments!

Spin Rig in Action

What We Learned

We can manually simulate fractional gravity with simple tools
Radius matters more than we initially estimated
Phyphox + metronome is a solid DIY setup
Future versions need smoother spin stability + structure

What’s Next

Move to motorized + Arduino-driven rig (V0.2)
Add fixed-length arms for consistent radius
Begin simulating gravity profiles (e.g., Moon → Mars → Earth)

Reflections

This might seem like a small experiment, but it’s the foundation.
It’s how we’ll go from backyard physics to orbital testbeds.

At Spark Gravity, we believe anyone should be able to run gravity experiments, not just ISS astronauts.

This is the first spin of many.