Published unlisted
Edited
Dec 24, 2020
core = require('https://cdn.jsdelivr.net/npm/@openhps/core@0.2.0-alpha.7/')
/**
* We create a custom source node that converts a motor PWM signal
* to linear and angular velocity.
**/
class MotorSource extends core.SourceNode {
constructor(source) {
super(source);
this.leftPWM = 0;
this.rightPWM = 0;
this.maxSpeed = 2.0;
}
/**
* Move the robot by controlling the left and right motor PWM
* @param leftPWM Left motor PWM
* @param rightPWM Right motor PWM
**/
move(leftPWM, rightPWM) {
// Make sure that the PWM is between 0 and 100
this.leftPWM = Math.min(100, Math.max(0, leftPWM));
this.rightPWM = Math.min(100, Math.max(0, rightPWM));
// Update the position and push the frame
return this.updatePosition();
}
updatePosition() {
return new Promise((resolve, reject) => {
// Our max linear velocity with one motor is this.maxSpeed meters per second on 100%
const speedLeft = this.maxSpeed * (this.leftPWM / 100.);
const speedRight = this.maxSpeed * (this.rightPWM / 100.);
// We are going to make an inaccurate simulation
// where we manipulate the angular velocity
// based on the left and right motor PWM.
// In this example we do not take the rotation
// axis into account.
const linearVelocity = new core.LinearVelocity(
speedLeft + speedRight,
0,
0
);
const angularVelocity = new core.AngularVelocity(
0,
0,
2 * Math.PI * 0.5 * (speedRight - speedLeft)
);
// Get the stored position and add the linear and angular velocity
this.model
.findDataService(core.DataObject)
.findByUID(this.source.uid)
.then(storedObj => {
const position = storedObj.getPosition();
position.timestamp = core.TimeService.now();
position.linearVelocity = linearVelocity;
position.angularVelocity = angularVelocity;
const frame = new core.DataFrame(storedObj);
frame.createdTimestamp = core.TimeService.now();
frame.source.setPosition(position);
return this.push(frame);
})
.then(() => {
resolve();
})
.catch(ex => {
reject(ex);
});
});
}
onPull() {
// Pull received, load last stored data and push again without changes
return this.model
.findDataService(core.DataObject)
.findByUID(this.source.uid)
.then(storedObj => {
const frame = new core.DataFrame(storedObj);
frame.createdTimestamp = core.TimeService.now();
return this.push(frame);
});
}
}
motorSource = new MotorSource(new core.DataObject("robot"));
model = await core.ModelBuilder.create()
.addService(timeService)
.from(motorSource)
.via(new core.TimedPullNode(250, core.TimeUnit.MILLI))
.via(new core.VelocityProcessingNode())
.via(
new core.CallbackNode(frame => {
// This node prevents the robot from going off-screen
const position = frame.source.getPosition();
position.x = Math.min(20, Math.max(0, position.x));
position.y = Math.min(20, Math.max(0, position.y));
frame.source.setPosition(position);
})
)
.to(
new core.CallbackSinkNode(frame => {
const position = frame.source.getPosition();
const positionPlot = {
x: position.x,
y: position.y
};
// Check if the last position is different
// if not, we do not want to overlay it
if (
JSON.stringify(data[data.length - 1]) !== JSON.stringify(positionPlot)
) {
// Add the new location to the plot
data.push(positionPlot);
if (data.length > 100) {
data.shift();
}
chart.plot(data);
}
})
)
.build()
{
const robot = new core.DataObject("robot");
const position = new core.Absolute2DPosition(10, 10);
position.timestamp = core.TimeService.now();
robot.setPosition(position);
model.push(new core.DataFrame(robot));
}
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