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You can build an animated, real-time solar system in OpenCode by having its agent write a Three.js scene. The coding agent and the AI model are separate things with separate costs. OpenCode is the tool you work in. The model it calls comes from a provider account or a local model that you configure, and whether that model costs you anything depends on that provider’s current terms. The sources behind this guide do not establish a current free quota for any named provider, so treat “free” as a description of one particular setup, not a promise that every OpenCode model is free.
Separate the coding agent from the model cost
OpenCode describes itself as “an open source AI coding agent” in its official introduction. That same introduction says you need API keys for the providers you choose to use. The models documentation describes support for 75+ LLM providers and local models, a figure the page gives without a date.
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In practice there are three ways a model can reach OpenCode. Each has different prerequisites and different cost rules.
| Route | What you need before you start | Who sets the access and billing rules |
|---|---|---|
| External provider account (your own API key) | An account with the provider and an API key entered into OpenCode | The provider. Its free allowance, rate limits and billing are set in its own terms, which can change. Not established by the sources cited here. |
| OpenCode Console (optional) | An OpenCode Console account | OpenCode. Its Console documentation describes per-request usage charged against pay-as-you-go credits. This is one paid path, not a requirement. |
| Local model | A model running on your own machine, configured in OpenCode | Your hardware and the model’s license. The sources cited here do not state hardware requirements or quality levels. |
If the goal is a build that costs nothing, the decision is about which route you can verify today, not about OpenCode itself.
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Choose and record your model
The model list changes, and OpenCode says its recommended list is non-exhaustive and may not be current. Use the live picker rather than any article’s list, including this one.
- Read the models page to understand how providers and identifiers are named in configuration.
- Start OpenCode in your project folder and run
/modelsto see which models your current configuration exposes. - Select one model and write down four things: the provider, the exact model identifier, the date you checked, and the access route from the table above.
- Read that provider’s own free-tier, rate-limit and account terms before you rely on them. Those terms, not OpenCode, decide whether a request is free.
Recording the date matters. A model that is free this month may not be next month, and a tutorial that names a model without a date is already out of date.
Set up the project
The build needs only a browser and a small Three.js project. Three.js is a browser-oriented 3D library. Its fundamentals guide describes it as a way to make 3D content for web pages, covering scenes, lights, shadows, materials, textures and 3D math. It does not supply astronomical data, so every position and speed in the scene is a value you choose.
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- 【Space Enlightenment】The Solar System Model Kit allows kids to color and build their own solar system model, providing kids a more intuitive understanding of the planet in the solar system. With a Solar System Instruction, which introduces kids to the relevant details of the solar system, sparking their curiosity and desire to explore astronomy and science!
- 【High Quality】The solar system science kit for kids 3-5 is made of durable polystyrene foam with a smooth surface that's easy to color, and includes 12 acrylic paints, which are safe and odorless. Kids can use their imagination to create the planets of the school solar system project!
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- 【Wide Application】The Solar System Kit is perfect for themes and activities about the solar system and planets. It’s great for enhancing classroom learning about the solar system and also makes a fun family activity.
- Install OpenCode by following the steps in the official introduction, then add your provider key as that page describes.
- Create an empty project folder and install Three.js from npm with
npm install three. - Serve the folder through a bundler or development server, so that the import of the OrbitControls addon described below resolves in the browser.
- Open the project in OpenCode and begin the scene work from the prompt below.
A starting prompt for OpenCode
Give the agent a bounded task with a clear structure. This prompt asks for a scene graph and interaction, not a claim about orbital accuracy:
Create index.html and main.js for a Three.js scene.
Use a Sun at the origin, an Earth that orbits the Sun,
and a Moon that orbits the Earth. Parent the Moon's orbit
object to the Earth so its motion is in Earth's local space.
Add OrbitControls with damping enabled. Animate with
elapsed time. Label the speeds as illustrative values.Review the output before running it. Check the hierarchy yourself, because a plausible-looking scene can still attach the Moon to the wrong object.
Model the solar system as a scene graph
The key idea is parenting. The Three.js scene graph guide uses this exact example and states it directly: “The Earth orbits the Sun. The Moon orbits the Earth.” When a parent rotates, its children move with it, so the Moon’s motion can be written relative to the Earth rather than to the Sun.
Rank #3
- Solar system model kit: package comes with 12 pieces foam balls, 2 pieces foam rings, 15 pieces bamboo sticks, 15 pieces toothpick flags, 12 color pigments, 2 pieces painting brushes, 1 pieces paint tray palette. Now securely shipped in a sturdy cardboard box to guarantee all pieces arrive undamaged and ready for your project.
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- Easy to assemble: You can identify the different planets by writing the planet's name on a blank toothpick flag and inserting it into a foam ball. No glue required, they can be easily assembled using bamboo skewers, create your planetary model to understand how our solar system is arranged.
- Fun learning tool: You and your kids had a great time painting and putting this together and learnt a lot about the planets in the process. It was a decent lesson representing the Solar system for a young child. Perfect for handmade craft, DIY decoration, school project, science projects and more.
Why the hierarchy matters
If you add the Moon directly to the scene and give it a position far from the Sun, you have to calculate its path around the Sun yourself. Parenting does that work. Rotate the Earth’s orbit object and the Earth and Moon move together; rotate the Moon’s orbit object and only the Moon circles the Earth.
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import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';
const renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);
const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(60, window.innerWidth / window.innerHeight, 0.1, 1000);
camera.position.set(0, 20, 40);
const sun = new THREE.Mesh(
new THREE.SphereGeometry(3, 32, 32),
new THREE.MeshBasicMaterial({ color: 0xffcc33 })
);
scene.add(sun);
// Earth's orbit object sits at the Sun's centre
const earthOrbit = new THREE.Object3D();
scene.add(earthOrbit);
const earth = new THREE.Mesh(
new THREE.SphereGeometry(1, 32, 32),
new THREE.MeshStandardMaterial({ color: 0x3377ff })
);
earth.position.x = 10;
earthOrbit.add(earth);
// Moon's orbit object is a child of Earth, so it moves with Earth
const moonOrbit = new THREE.Object3D();
earth.add(moonOrbit);
const moon = new THREE.Mesh(
new THREE.SphereGeometry(0.3, 16, 16),
new THREE.MeshStandardMaterial({ color: 0xcccccc })
);
moon.position.x = 2;
moonOrbit.add(moon);
scene.add(new THREE.PointLight(0xffffff, 2, 0, 0));
scene.add(new THREE.AmbientLight(0x404040));
const controls = new OrbitControls(camera, renderer.domElement);
controls.enableDamping = true;
const clock = new THREE.Clock();
function animate() {
requestAnimationFrame(animate);
const t = clock.getElapsedTime();
earthOrbit.rotation.y = t * 0.5;
moonOrbit.rotation.y = t * 2.0;
controls.update();
renderer.render(scene, camera);
}
animate();The numbers (orbit radii, rotation rates, sizes) are arbitrary and chosen for legibility. They are not measured values, and the scene does not model gravity.
Add camera controls and the animation loop
OrbitControls is an addon, so import it explicitly as shown above. The OrbitControls documentation says the addon supports camera orbiting, dollying (zooming) and panning. When damping or automatic rotation is enabled, controls.update() must run every frame. If you add auto-rotation, pass elapsed time in seconds so the speed does not depend on the display’s frame rate.
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What “real-time” means in this build
In this scene, real-time means the objects keep moving as frames render, and the camera responds as you drag. It does not mean the Earth and Moon are where they really are today. To show actual positions, you would need an external source of orbital data and a documented model for applying it, and this build includes neither. Label the animation as illustrative if you publish it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshooting
| Symptom | Likely cause | What to check |
|---|---|---|
| Blank page with a module error in the browser console | The Three.js import path does not resolve | Confirm npm install three ran and that your bundler or server serves the project folder |
| OrbitControls is undefined or not found | The addon was not imported from its explicit path | Use three/addons/controls/OrbitControls.js as in the code above |
| Camera ignores mouse drag after enabling damping | No controls.update() call in the loop |
Confirm the call sits inside animate() on every frame |
| Moon circles the Sun instead of the Earth | The Moon’s orbit object was added to the scene, not to Earth | Check that moonOrbit is a child of earth |
| OpenCode shows no usable model | No provider key is configured, or the chosen model is not in your catalog | Run /models again and confirm the provider in the models documentation matches your account |
Reproducing the build
Keep the project to three parts: the scene graph, the controls, and the loop. Record the model and date you used, so a reader can tell whether the setup still works. If a provider changes its free terms, the rest of the code does not need to change, because the graphics work does not depend on which model wrote it.
Further reading on Three.js fundamentals is available in the free online tutorial series Discover three.js.
Best Value
- Science Kits for Kids 8-12: Complete model solar system for kids includes wood set, puzzle, and fun fact cards. This two part DIY solar system kit allows kids to build a cool model, paint, and learn about the major 9 planets. Designed for 8 & up.
- Science Fairs & More: Bring the planets to life with our Nine Planets kit. Makes the perfect realistic solar system model for elementary school science fairs & more. Proudly display in a bedroom, science fair, or classroom. For girls and & boys.
- Planetary Enlightenment: Foster a love for learning with our solar system project, an engaging educational science kit that makes complex concepts easy to understand and enjoyable for young minds. Includes fact cards for quick and accurate solar system information.
- Planetary Delight: Unleash creativity and curiosity with our solar system project kit . Children will delight in their exploration of the universe while having fun accomplishing this all in one kit. We offer the perfect science kits for kids age 8-12.
- Craft & Learn: Everything you need to build the wood model, paint the major planets, and build the puzzle. Includes The Sun, Mercury, Earth, Jupiter, Uranus, Venus, Mars, Saturn, and Neptune. Includes paint and brushes. Build the model in approximately 1-2 hours.
Also note the wider trade-off: an agent writes faster than you can verify a hierarchy, so check the parenting and the animation math yourself before you trust the scene.
Frequently Asked Questions
Does using OpenCode mean my AI usage is free?
No. OpenCode’s introduction says you need API keys for the providers you choose, and its Console documentation describes pay-as-you-go credits for one optional route. Whether a given model costs anything depends on that provider or local setup and its current terms.
Does the solar system in this build show where the planets really are?
No. The build uses a scene graph with arbitrary speeds and sizes. Showing actual positions would require an external orbital data source and a documented model for applying it.
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