An Introduction to Fling: the 2021-2022 VIQC Hero Bot

Each year, the IQ Hero Bot is designed from the IQ Super Kit to provide teams with a starting point to play the current VEX IQ Challenge game. It is intended for experienced teams to be able to quickly assemble a robot to investigate the game's dynamics. New teams can also use the Hero Bot to learn valuable building skills and have a robot they can customize to compete with early in the season.

The 2021-2022 VEX IQ Challenge Game is Pitching In. View this page for more information on the game and how it is played. This season's Hero Bot to play Pitching In is Fling. You can view Fling’s build instructions for more information.

For game definitions used throughout this article, an overview of the game rules, and scoring, view the Game Manual for Pitching In.

Scoring Capabilites

Fling can score in the following ways:


Scoring a Ball in the High Goal

Using Fling’s Intake and Catapult Arm, Balls can be efficiently scored in the High Goal.


Scoring a Ball in the Low Goal

Balls can be easily pushed into the Low Goal using Fling’s Intake.


Clear the Balls from the Corral

Fling can use the Intake to effectively clear the Balls from the Corral.


Low Hang from a Hanging Bar

Fling is able to use the Catapult Arm to reach up and low hang from a Hanging Bar.

Design Features

Some of Fling's prominent design features are the Intake, its crank-design catapult firing system, and the compound gear ratio used to move the Catapult Arm.

Ball Intake


Fling’s Intake consists of two 40 millimeter (mm) pulleys separated by standoffs, and four rubber bands stretched between the pulleys.

The rubber bands effectively grab onto the Balls as the Intake spins.

The Intake can spin to pull in a Ball, or be reversed to release a Ball.


The power from the Intake’s motor is transferred by using two 10 millimeter (mm) pulleys and a rubber belt.

This provides a smooth transfer of power. If a Ball should get jammed in the Intake, the rubber belt will just slip, preventing any damage.

Crank-Design Catapult Firing System


The firing mechanism for Fling’s Catapult Arm is a very smooth reciprocating device.

It consists of a set of 60 tooth gears and an articulated tensioning arm.

The tensioning arm pivots on a pin attached to the outside edge of the gears. This creates a crank setup as the gears turn.

On the opposite side of the gear from the pivot connection is a Shaft bushing. The bushing will catch the tensioning arm and increase the crank’s length.

As the crank causes the articulated tensioning arm to become shorter, it pulls down the Catapult Arm and increases the tension on the Catapult Arm’s rubber bands.

Once the crank linkage moves past the over center point, the Shaft Bushing loses contact with the crank linkage and releases the tensioning arm, firing the Catapult.

This entire cycle repeats itself as the gears continue to turn. The Bumper Switch is set up to trigger the behavior of stopping the gears from turning, just prior to the Catapult Arm reaching its over center point.

This allows a Ball to be loaded onto the Catapult Arm from the Intake.

Compound Gear Ratio Used to Move the Catapult Arm


Anyone who has ever tried to pick up a broom by holding onto the very end of its handle has experienced rotational torque.

The gear system for the Catapult Arm needs to have enough rotational torque to overcome the tension of the arm’s rubber bands. In addition, the Catapult Arm is used to hang from the Hanging Bar, so it also needs to have enough torque to lift the robot’s weight.

This torque is generated by using a two stage compound gear ratio.


The first part of the compound gear ratio has the 12 tooth driving gear, which is powered by the motor.

The 12 tooth driving gear drives a 36 tooth driven gear.

This 12 tooth gear into a 36 tooth gear provides a 3:1 gear ratio.

The 36 tooth gear rotates at 1/3 the speed of the motor. However, it transfers 3x the rotational torque to its shaft.


The second part of the compound gear ratio has a pair of 12 tooth driving gears. These 12 tooth gears share the same shaft as the 36 tooth gear from the first part of the compound gear ratio.

There are a pair of 36 tooth idler gears between the pair of 12 tooth gears and the pair of 60 tooth gears on the Catapult firing mechanism. Idler gears do not change the gear ratio.

These 12 tooth gears into 60 tooth gears provide a 5:1 gear ratio.

Combining the two gear ratios of 3:1 and 5:1 form a compound gear ratio of 15:1

At nearly 15x the Catapult motor’s rotational torque, this provides Fling with plenty of rotational torque to both fire the Catapult Arm and lift its weight off the Field using the Hanging Bar.

Tips and Tricks for Programming Fling with VEXcode IQ

Configuring Fling's Drivetrain


Follow the steps in this article from the VEX Library for general information on how to configure a 2-motor drivetrain.

To configure Fling’s specific 2-motor drivetrain, select port 1 for the left motor and port 3 for the right motor.


To ensure the settings are adjusted for Fling’s physical dimensions:

  • change the track width from 173 mm to 267 mm.

For more information on track width, view this article from the VEX Library.

Configuring the Catapult Arm and Intake Motors


Follow the steps in this article from the VEX Library for general information on how to configure a motor.

  • To configure Fling’s specific Intake Motor, select port 2.
  • To configure Fling’s specific Catapult Arm Motor, select port 4.

Configuring the Bumper Switch


Follow the steps in this article from the VEX Library for general information on how to configure a Bumper Switch.

To configure Fling’s specific Bumper Switch, select port 5.

Configuring the Controller


The IQ Controller can be configured to drive Fling as well as control the Intake.

Follow the steps in this article from the VEX Library for general information on how to configure a controller.

Note: Fling’s configuration does NOT allow the VEX IQ Brain’s default driver's program to work with the controller.


Any of the button groups on the controller can be used to control Fling’s Intake.

Note: Fling’s Intake must be configured first before configuring the controller.

Using the Catapult Arm Motor with the Controller


Set the CatapultArmMotor stopping to hold. This will keep Fling’s Catapult Arm held in place after hanging.


Choose a controller button to set up Fling’s Catapult Arm to fire.


Choose a controller button to fire the Catapult Arm.

This button will also move the arm down to allow Fling to hang on the Hanging Bar.

For more information on how to code Fling using VEXcode IQ, view these articles from the VEX Library.

Adding IQ Sensors


Fling has been designed to easily add any of the IQ Sensors. The Pitching In game robot rules allow for plenty of customization to your Fling Hero Bot.

For more information on IQ Sensors, view this section of the VEX Library.

You can also view this article on Virtual Fling used in VIQC Virtual Skills to see examples of how sensors can be added to Fling.

For more information, help, and tips, check out the many resources at VEX Professional Development Plus

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