Set up an AGV

An AGV moves as one vehicle: you command a speed forward, sideways and around, and the AGV module in Motorcortex works out what every wheel has to do. For that it needs the vehicle type and where each wheel sits. Its parameters are under root/AGVControl/, and the values you set are stored in control/control.xml.

Choose the vehicle type

The type is set in config.json, in the AGVControl block. The AGV module only starts when Enable is true and the application has axes:

"AGVControl": {
  "Enable": true,
  "MobilePlatformType": "differential"
}

Set AxesControl/NumberOfAxes to the number of axes the type needs, plus the axes of an arm if the AGV carries one:

The module also accepts tricycle and flappybot; they are not covered here.

Describe the wheels

All positions are in m, in the vehicle frame: x points forward, y to the left, and a positive rotation turns the vehicle counter-clockwise, seen from above. Click a type to jump to its parameters.

Differential

Two driven wheels on one line, and casters that follow. The parameters are under root/AGVControl/mechanism/:

The distance between the wheels is wheel01/positionY minus wheel02/positionY. A differential AGV cannot move sideways: a sideways speed is ignored.

Mecanum

Four mecanum wheels. The order is fixed: wheel01 front right, wheel02 rear right, wheel03 rear left, wheel04 front left. For each wheel, under root/AGVControl/mechanism/wheelNN/:

Only the distance of each wheel from the centre, |positionX| + |positionY|, affects the wheel speeds.

Omni-steered

Four wheels that each drive and steer. For each wheel, under root/AGVControl/mechanism/steeredWheelNN/:

A steering angle of 0 means the wheel rolls straight forward, along x; a positive angle turns it counter-clockwise. The module has no steering offset: make sure each steering axis reads 0 when its wheel points forward, with the axis’s position transformation.

Link the wheels to the axes

The AGV module works in wheel speeds, in rad/s. Link its outputs to the axes, and the actual values back:

The links go in a link file, to root/AxesControl/axesVelocitiesInput for the drive wheels, with the Index of the first axis. For an omni-steered AGV the steering angles go to root/AxesControl/axesPositionsInput, after the drive wheels.

Then set up each wheel axis:

• Drive mode: run the drive wheels in CSV, 9 in root/DriveLogic/driveMode. See Drive logic.
• Direction: a positive wheel speed must drive the vehicle forward on both sides. On a differential AGV the motors on the two sides usually face each other, so one side needs a negative gainNum in its position and velocity transformations.
• Units: the transformations must give rad and rad/s at the wheel, after the gearbox.

Limit the speed

The limits are under root/AGVControl/, in m/s and rad/s:

Drive it

The vehicle takes its speed as a twist of six values: forward, sideways and up in m/s, then the rotation about x, y and z in rad/s. Only forward, sideways and the rotation about z, the sixth value, are used. There are three inputs, and targetVelocityConfigSelector/configurationIndex picks the one in use:

The input must keep updating: when it stops for longer than hostInSignalTimeout, the vehicle stops.

Check the odometry

The module works out where the vehicle is from the wheel speeds alone: there is no other localisation.

resetActualPose sets actualPose back to actualPoseRef.

1. In simulation, drive forward and check that actualPose grows in x.
2. Turn left and check that the heading grows.
3. On the real vehicle, drive a measured distance and compare it with actualPose. A difference that grows with distance means a wrong wheel diameter; a wrong heading after a straight run means the two sides differ.