# Spiro World

**Prerequisite:*** FreeFall*

**Levels:** *Challenge, Practice*

To pass the Spiro challenge, you will have to pilot your spuCraft through a circular maze and you’ll have to do so smooooothly. You will have to create input scripts that coordinate the four thrusters. It is a job for polar coordinates.

The Spiro challenge has many different parts that you must put together to get the full working whole.

#### List of Links

- Reference Sheets
- Video: Intro to Spiro
- Video: Thruster Inputs
- Video: Polar Thruster Inputs (Assignment, Part A)
- Video: Checking Polar Thruster Inputs (Assignment, Part A)
- Video: Derivatives of Polar Coordinates (Assignment, Part B)
- Video: Riding the Ring (Assignment, Part C)
- Video: SpuCraft Alignment and Automatic Micro Control
- Video: Crossing the Bridge (Assignment, Part D)
- Video: Crossing the Origin (Assignment, Part E)
- Help! I can’t figure out…

#### Reference Sheets

Here are the reference sheets from the SpuPilot. Click to enlarge.

#### Video: Intro to Spiro.

Here’s a video which outlines the goals of the Spiro challenge.

#### Video: Thruster Inputs

In the Spiro challenge, you will need to coordinate the four thrusters of the spuCraft. To get started, we discuss how the program the default scripts. We will use this as a springboard to generating more complicated scripts.

#### Video: Polar Thruster Inputs (Assignment, Part A)

The video outlines how to write thruster scripts so that forces are applied in directions of the polar basis vectors. After watching this you should be able to complete Part A of the Spiro assignment.

#### Video: Checking Polar Thruster Inputs (Assignment, Part A)

If you have your polar thruster scripts working correctly, it should look like that presented in this video.

#### Video: Derivatives of Polar Coordinates (Assignment, Part B)

In order to calculate acceleration in polar coordinates, you are going to need time derivatives of the radius and the angle. In this video, we work through the chain of chain rules that need to be calculated in order to express the derivatives in terms of quantities given.

#### Video: Riding the Ring (Assignment, Part C)

The video poses a mini-challenge. Figure out how to modify the radial force function in the SpuPilot so that the craft essentially pilots itself around the outer ring. In particular, the script should provide the correct amount of inward force so that the craft can travel around the ring, keeping the derivative of r constant. Therefore, if the time derivative of r starts off at zero, it will remain zero and the spuCraft will travel around the circle at constant radius.

#### Video: SpuCraft Alignment and Automatic Micro Control

Before you start thinking about how you are going to cross the bridge, you might want to check out this video. It gives you some tips about how to stay in the center of the outer ring and how to get perfectly aligned with the bridge.

#### Video: Crossing the Bridge (Assignment, Part D)

In order to cross the bridge effortless, you are going to have to perform a little more analysis. This video walks you through that analysis and uncovers one more problem that needs to be solved.

#### Video: Crossing the Origin (Assignment, Part E)

At the origin, your equation for the time derivative of theta breaks down. This causes your automatic thrust strategies to go haywire as the spuCraft crosses the origin.

#### Help! I can’t figure out…

Can’t figure something out? Here are some posts aimed at getting you back on track.

- Equations aren’t working? Did you check units?
- Do I need the variable Omega?

Do you have other help topics you want to see? Ask on Piazza.