rbs

RBSManager

A Swift library for connecting to ROS using ROSBridge and Websockets

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RBSManager

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A Swift-native library for handling the WebSocket connection to a Robot Operating System (ROS) master running ROSBridge. Control your robots with a mobile phone.

It is largely a drop-in replacement to my earlier Objective-C library, RBManager. Fun fact, the extra S stands for Swift.

RBSManager provides a wrapper for the different ROS functionality calls:

Dependencies

RBSManager uses the following Github components, installed with the CocoaPod:

  • Starscream -- a Swift native Websocket library
  • ObjectMapper -- a tool to translate JSON data into Swift objects (used by the ROS message system)

Thank you to their developers!

Acknowledgements

Additionally here are some of the users that have contributed code or message definitions. Thank you to them too!

Example

To run the example project, clone the repo, and run pod install from the Example directory first. The example project connects to the Turtlesim node and provides the following operations:

  • demonstrate a subscriber to display X, Y and Theta state of the turtle
  • rotate a turtle icon to show how the theta value changes
  • control a turtle using left, right, up, down buttons to demonstrate publishing a message
  • reset the turtlesim using a service call demonstration
  • accept dynamic host values
  • configure the background using a custom modal colour picker and set parameter service calls
  • teleport a turtle with an alert view and service calls using a message object
  • click multiple directions simultaneously (easier on a device) to properly steer the turtle around

Requirements

  • iOS 10+
  • Swift 3+
  • ROS master running a ROSBridge server
  • A valid Apple developer account if you want to test on an actual device

Installation

RBSManager is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'RBSManager'

Usage

As mentioned the library itself behaves very similar to RBManager. It contains a singleton object so that only instance of the manager is needed -- RBSManager.sharedManager()

Delegate

The manager will post events to the following methods at various points:

func manager(_ manager: RBSManager, didDisconnect error: Error?)
func managerDidConnect(_ manager: RBSManager)
func manager(_ manager: RBSManager, threwError error: Error)

The error objects will either be forwarded from the socket itself or be related to manager functionality. The error description will include info about what went wrong.

All delegate calls are done on the main UI thread. Processing and JSON handling are done on a background thread to avoid locking the interface.

Messages

Messages are the core ROS component and RBSManager implements the Mappable protocol to handle them. There are currently a small number of messages included in the library and more will be added in the future (I had to select which ones I felt were most important). Custom messages can be added as long as they inherit from RBSMessage and properly follow the Mappable protocol.

Messages should generally have foundation object types like Float64 and String but can also handle nested RBSMessage types. The catch is that nested objects need additional setup to handle the init methods in place. View the TwistMessage type to see how that works.

The way that Swift works meant some compromises with the overall message system (mostly relating to object types and casting) so I hope to review it and improve over time.

Subscribers

Create a new subscriber by calling the following method on the manager:

func addSubscriber(topic: String, messageClass: RBSMessage.Type, response: @escaping ((_ message: RBSMessage) -> (Void))) -> RBSSubscriber
  • topic -- the ROS node to subscribe to
  • messageClass -- the type declaration of the message to receive (eg. use TwistMessage.self)
  • response -- a callback to receive the message

Example:

let turtleSubscriber = turtleManager?.addSubscriber(topic: "/turtle1/pose", messageClass: PoseMessage.self, response: { (message) -> (Void) in
    // update the view with message data
    self.updateWithMessage(message as! PoseMessage)
})

As a change from the delegate pattern of RBManager , the callback structure maintains a more Swift-like process and better allows multiple subscribers on the same topic. The subscriber object also exposes most options available to ROS, like queue length and throttle rate.

A subscriber will auto subscribe when the manager connects but you can connect/disconnect manually by calling .subscribe() or .unsubscribe() respectively.

Publishers

Create a new publisher by calling the following method on the manager:

func addPublisher(topic: String, messageType: String, messageClass: RBSMessage.Type) -> RBSPublisher
  • topic -- the ROS node to publish to
  • messageType -- the type of message ROS is expecting (eg. geometry_msgs/Twist)
  • messageClass -- the class type that you will be sending (eg. TwistMessage.self)

Example

let turtlePublisher = turtleManager?.addPublisher(topic: "/turtle1/cmd_vel", messageType: "geometry_msgs/Twist", messageClass: TwistMessage.self)

Create a new message object separately and publish it by passing the message object to .publish(_ message: RBSMessage)

A publisher is advertised when the manager connects but you can manually change it's state by calling .advertise() or .unadvertise()

Service calls

Service calls are made to perform an operation on ROS, with or without parameters and a response value. Create a new service call by using the following method on the manager:

func makeServiceCall(service: String) -> RBSServiceCall
  • service -- the ROS topic/node to make the request with

Example

let serviceCall = turtleManager?.makeServiceCall(service: "/reset")

The service call can be triggered by calling .send(_ response: ((_ response: RBSResponse) -> (Void))?). That optional response callback can receive the service call response and return an RBSResponse of data.

Version 0.4 moves to the RBSResponse data type, which includes additional context about the request. Use response.values to look for the data returned by the call.

Example

serviceCall?.send({ (response) -> (Void) in
    if let values = response.values as? [String:Any], let value = values["value"] as? String {
        self.number = Float64(value)
    }
})

To pass data to the service call itself, assign data to one of: dataArgument (dictionary), messageArgument (an RBSMessage object) or arrayArgument (array)

Parameters

The manager can also handle setting and getting ROS parameters by generating a service call object with preformatted properties.

func getParam(name: String) -> RBSServiceCall
func setParam(name: String, value: Any) -> RBSServiceCall

Use the regular send callback to receive data.

Design considerations

Multiple subscribers

While building a custom robot controller, I investigated the best way to subscribe to the same topic multiple times. While subscribers allow IDs to be assigned, the return values do not respect these. In practice this means that if two subscribers have different refresh rates, they will both receive the message at the fastest rate specified.

To get around this it is recommended that you use the iOS notification pattern to distribute messages based on your requirements. A single DataModel type object can subscribe to each unique topic and share the messages with the individual controllers.

Tools

Custom message generator

As a convenience, I've included a Python script to generate Swift message files. It isn't perfect, but will do most of the work necessary for the messages to compile. It is located in the Tools folder.

python ./custom_messages.py [class name] [variables...n]

where

  • [class name] = the name of the file/class (should include Message for consistency)
  • [variables...n] = variable name and Swift type, separated by colon

Example:

python ./custom_messages.py ExampleMessage stringData:String floatData:Float intData:Int

Roadmap

This library changes a lot of things from my previous work and will definitely be in progress for some time. Please take that caveat into account when building a project and reach out to me if there is a feature you think the library is missing.

  • populate all standard ROS message types
  • convert all Dictionary based parameter handling to custom objects using JSON mapping

Actionlib

The rosbridge project does not mention any support for the actionlib components. The protocol is listed here. If this is functionality you're looking for, I suggest connecting with that team.

Author

wesgood, w [at] wesg [dot] ca, @wesgood

Mobile software developer, mechatronics engineer, robot enthusiast.

License

RBSManager is available under the MIT license. See the LICENSE file for more info.

TL;DR; Please do lots of cool things with my library, but share them with me so I can see what it's being used for. Even better, include a link or acknowledgement of the library in your project.

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