Bumper Switch v2 & Limit Switch V5 (3 Wire Sensors)
The Bumper Switch v2 is a single digital switch with a spring-loaded bumper which can be pushed in to change the state of the switch. This switch requires only a light touch to activate and is one of the 3-Wire series of sensors.
The 3-Wire Sensors are compatible with the V5 Robot Brain or the Cortex. Their sensor cable can be extended using a 3-Wire Extension Cable.
In order for the Bumper Switch v2 to be functional with the V5 Brain, the sensor cable needs to be fully inserted into a V5 Brain 3-Wire Port, and the port needs to be configured as Digital In (High) within the 3-Wire Ports menu.
The Bumper Switch v2 is included in the VEX V5 Classroom Starter Kit and can also be purchased as a 2-pack here.
|Bumper Switch v2||V5 3-Wire Port||3-Wire Ports Menu|
How the Bumper Switch v2 Works
The Bumper Switch has three wires connected to it: a black wire- the ground wire, a red wire-not connected, and a white wire - the signal wire. When the switch is pressed, the white wire and the black wires are connected returning an active digital low signal (0) to the Brain. When the bumper on the switch is not pressed, the black wire and the white wire are no longer connected and the circuit is open. This returns a digital high signal (1) to the Brain. This is known as a digital state, that is the state is high (1) or low (0).
The Bumper Switch needs to be paired with a programming language such as the VEXcode V5 Blocks or Text to create a user program in order for the Brain to use this returned state to serve as an event or as sensing for a type of feedback control.
The Bumper Switch is spring loaded so when the force pushing it in is removed, the bumper moves back up to its original position.
Design features of the Bumper Switch v2
The Bumper Switch v2 is a redesigned version of the Bumper Switch which has been included with VEX EDR kits for over a decade. The new design has some useful and improved design features, these include:
- The Bumper Switch housing has two slotted mounting holes (one on each side) for easy mounting to the robot’s structure
- The Bumper Switch’s red bumper button has a screw in the center of it. This screw can be removed and the button removed to reveal a 8-32 mounting insert below. Additional components can be mounted to the Bumper Switch using this threaded insert.
- The housing of the Bumper Switch v2 has a new narrower profile. This allows the sensor to be nested within a piece of 1x2x1 C-Channel.
|Center Screw||8-32 Mounting Insert||Within C-Channel|
Common Uses of the Bumper Switch:
A Bumper Switch is typically used for three different applications: for user input, for detecting the position of a robot structure, or for detecting a physical object.
User Input: Some examples of user input are:
- Pressing a Bumper Switch could start a conveyor belt system (simulating a factory sorting system) to run for 5 seconds and then stop. This is an example of an event. The switch is pushed to start an action.
- A Bumper Switch could serve as a toggle switch. An example of this would be pressing the Bumper Switch to turn on an LED and the LED stays on after the switch is released. Then the next time the switch is pressed it turns the LED off and it stays off after the bumper is released. A toggle requires additional programming because the program needs to keep track of what state the action is in. Is the present action on, or is it off?
- A Bumper Switch could be used as an emergency stop button and when the button is pressed, the robot will stop running its program.
Detecting the position of a robot structure: When detecting the position of a robot structure the Bumper Switch is nearly always being used as a feedback control loop. The program is continually sensing whether the Bumper Switch is being pressed or not. The classic example of this would be for a robot’s arm. If the arm moves down and presses the Bumper Switch, the switch signals the arm’s motor(s) to stop the arm’s downward motion.
Detecting a physical object: Once again, in this case, the Bumper Switch is usually used as feedback control. For example, if the robot presses the Bumper Switch by driving it into a wall, the robot is programmed to reverse, turn, and then start driving forward again. This is the type of action used by a robotic vacuum cleaner.
Fun game: A fun use of the Bumper Switch as a toggle is with a game of Robot Freeze Tag. This game takes place between two teams of robots. During the game, when the Bumper Switch is pushed by an opponent it “freezes” the robot’s drivetrain until a teammate pushes the switch again enabling the drivetrain once again. The game is over when all the teammates on one team are frozen.
Uses of the Bumper Switch on a Competition Robot:
A bumper switch is a very reliable sensor to be used in a competition because it relies on physical contact, unlike proximity sensors which use light, infrared light, or sound which could become distorted. However, a Bumper Switch is also limited by this method of detection.
For instance, in the 2019-2020 game, Tower Takeover, if a Bumper Switch was used to detect a stack of Cubes, the stack could be knocked over in the process of its detection and the Bumper Switch certainly could not identify the color of the Cubes.
Some examples of the uses of Bumper Switches in a competition include:
Program Function Selection: The V5 Brain with its ability to hold 8 different programs can provide many programmed routines. These programs can be selected by the Brain’s Touch Screen prior to the start of a match. However, a Bumper Switch could be used to select functions within a program or adjust variables in the last moment prior to setting the robot on the field without having to remove the Touch Screen’s protective shield.
Fail safe sensor: The V5 Smart Motors have excellent on-board sensors to control the actions of the drivetrain and manipulators of the robot. However, if a robot structure such as an arm might be able to crash into the robot’s Brain, a well placed Bumper Switch as an emergency stop could avert a disaster in the event of another sensor failing.
Game piece and field element detection: Bumper Switches can be used for many different applications during the game. For instance, a Bumper switch could be used to dump game pieces into a goal when the bumper switch comes in contact with the goal.
Two other examples include, a claw could automatically grasp a game piece when the piece presses a Bumper Switch and a conveyor belt could detect if it is full of game pieces when the top game piece pushes on a Bumper Switch.
Field Navigation: Bumper Switches can be placed on the robot chassis to detect when the robot comes in contact with a perimeter wall or an obstacle. Two Bumper Switches can be placed with one on each end of a side of the robot’s chassis. The two switches can be used to have the robot align itself against the perimeter wall by stopping when both are pressed. This action could be used by the robot in the middle of an autonomous routine in order to recalibrate its position before starting the next step of the routine.
In addition to the Bumper Switch v2, the VEX Electronics product line includes another type of touch sensor, the Limit Switch. The Limit Switch setup for the V5 Brain is exactly the same and it operates in nearly an identical manner as the Bumper Switch. The Limit Switch can also be substituted for the Bumper Switch in nearly all the applications above.
The main difference between the two sensors is the Limit Switch has a spring steel arm to activate the switch instead of a bumper button. More about the arm on the switch:
- The Limit Switch arm is orientated with a 90o difference compared to the Bumper Switch button allowing it to be activated from a different angle.
- The arm can be cut shorter or bent into a custom shape to facilitate it being pressed.
- The arm can be slipped behind a protruding screw to keep the arm pressed down. An example using this could be when the switch is held down the robot will run an autonomous routine for the red side of the field and when it is not held down, it will run the blue side autonomous routine.
The Limit Switch can be purchased as a 2-pack here.
|Limit Switch||Activating the Switch|