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MoveIt Task constructor - Merge example

asked 2020-03-18 05:31:04 -0500

Madcreator gravatar image

Hi,

I am learning how to use MoveIt task constructor and as there is few examples and documentation about it, I am having a hard time to create a merge task : move both arms of a PR2 robot at the same time (ie: lower them of about 10 cm at the same time).

void planTest(Task &t) {

t.loadRobotModel();

auto cartesian = std::make_shared<solvers::CartesianPath>();
cartesian->setProperty("jump_threshold", 0.0);

Stage* current_state = nullptr;
auto initial = std::make_unique<stages::CurrentState>("current state");
current_state = initial.get();
t.add(std::move(initial));

// planner used for connect
auto pipeline = std::make_shared<solvers::PipelinePlanner>();
pipeline->setPlannerId("RRTConnectkConfigDefault");

auto merger = std::make_unique<Merger>();

{
        auto stage = std::make_unique<stages::MoveRelative>("lower object left", cartesian);
        stage->properties().set("marker_ns", "lower_object");
        stage->properties().set("link", "l_gripper_tool_frame");
        stage->properties().set("group","left_arm");
        stage->setMinMaxDistance(.03, .13);
        // Set downward direction
        geometry_msgs::Vector3Stamped vec;
        vec.header.frame_id = "base_footprint";
        vec.vector.z = -1.0;
        stage->setDirection(vec);

      merger->insert(std::move(stage));
}


{
        auto stage = std::make_unique<stages::MoveRelative>("lower object right", cartesian);
        stage->properties().set("marker_ns", "lower_object");
        stage->properties().set("link", "r_gripper_tool_frame");
        stage->properties().set("group","right_arm");
        stage->setMinMaxDistance(.03, .13);
        // Set downward direction
        geometry_msgs::Vector3Stamped vec;
        vec.header.frame_id = "base_footprint";
        vec.vector.z = -1.0;
        stage->setDirection(vec);

      merger->insert(std::move(stage));
}


t.add(std::move(merger));
}

The error returned when running is :

Error initializing stages: current state: required interface is not satisfied merger: start interface of 'lower object left' (↑) doesn't match mine (?) merger: start interface of 'lower object right' (↑) doesn't match mine (?) merger: no child provides expected push interface

I don't really manage to understand the "interface" mechanism of MoveIt task constructor and there isn't much information on internet...

I managed to understand and use "Alternatives" and normal task workflow by trial and error but merger seems to be trickier and no examples are available for now.

thanks for your help.

Regards,

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@Madcreator: if @v4hn's answer answered your question, please accept the answer by clicking the checkmark left of the answer. It will turn green.

We don't close questions here on ROS Answers if they are actually answered.

gvdhoorn gravatar image gvdhoorn  ( 2020-04-10 04:22:00 -0500 )edit

Oups ok, made the modification :) Thank you for the advice !

Madcreator gravatar image Madcreator  ( 2020-04-10 07:18:16 -0500 )edit

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answered 2020-03-18 10:46:21 -0500

v4hn gravatar image

You actually hit a bug in the inference of logical information flow. If you replace the Merger in your example by Fallback or Alternative, you will see the same error.

To work around it for the moment, you can restrict the direction of computation by hand for both MoveRelative stages via stage->restrictDirection(PropagatingEitherWay::FORWARD), but I'll work on a fix now, as your code should be valid.

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With this pull-request merged, there should be no need for the workaround I describe here anymore.

v4hn gravatar image v4hn  ( 2020-04-14 08:55:00 -0500 )edit

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Asked: 2020-03-18 05:31:04 -0500

Seen: 450 times

Last updated: Mar 18 '20