Problem with actuator control and step change constraint #2451

ha-nn · 2025-02-24T14:11:32Z

ha-nn
Feb 24, 2025

Intro

Hi!

I am a applied computer science student and I'm new to MuJoCo. I use MuJoCo for a project on reinforcement learning.

My setup

MuJoCo version 3.2.7, Python 3.13, arm64, macOS

My question

I'm currently working on a maze designed to be solved using reinforcement learning (RL). However, I'm facing an issue with actuator control: the board's motors are set up to apply torque, but the applied force isn't proportional to the input. Specifically, only about 0.15 of the control range (which is between -1 and 1) actually produces any noticeable tilt change, small inputs result in disproportionately large changes, while larger inputs hardly have any effect.

I'm looking for a solution that makes the board's response more predictable and consistent, with a uniform mapping from the control input to tilt angle.

Additionally, I was wondering if it is possible to impose a constraint so that the change in tilt from one step to the next is limited to a maximum value.

Minimal model and/or code that explain my question

<mujoco model="labyrinth">
    <worldbody>
        <body name="board" pos="0 0 0">
            <joint name="tilt-x" pos="0 0 0" axis="1 0 0" range="-5 5" damping="10"/>
            <joint name="tilt-y" pos="0 0 0" axis="0 1 0" range="-5 5" damping="10"/>

            <geom name="plate" type="box" size=".5 .5 .01" rgba=".7 .7 .7 1"/>

            <geom name="wall-left" type="box" size=".01 .5 .04" pos="-.49 0 .05" rgba="255 255 255 1"/>
            <geom name="wall-right" type="box" size=".01 .5 .04" pos=".49 0 .05" rgba="255 255 255 1"/>
            <geom name="wall-top" type="box" size=".5 .01 .04" pos="0 -.49 .05" rgba="255 255 255 1"/>
            <geom name="wall-bottom" type="box" size=".5 .01 .04" pos="0 .49 .05" rgba="255 255 255 1"/>

            <geom name="wall-maze-1" type="box" size="0.008 0.08 0.04" pos="-0.20 -0.41 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-2" type="box" size="0.008 0.08 0.04" pos="0.15 -0.28 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-3" type="box" size="0.20 0.008 0.04" pos="-0.30 -0.20 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-4" type="box" size="0.15 0.008 0.04" pos="0.20 -0.20 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-5" type="box" size="0.008 0.108 0.04" pos="-0.25 -0.10 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-6" type="box" size="0.008 0.108 0.04" pos="0.05 -0.10 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-7" type="box" size="0.20 0.008 0.04" pos="-0.05 0.0 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-8" type="box" size="0.12 0.008 0.04" pos="0.38 0.0 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-9" type="box" size="0.008 0.20 0.04" pos="-0.37 0.15 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-10" type="box" size="0.008 0.108 0.04" pos="-0.25 0.10 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-11" type="box" size="0.008 0.12 0.04" pos="-0.10 0.23 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-12" type="box" size="0.008 0.108 0.04" pos="0.10 0.25 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-13" type="box" size="0.20 0.008 0.04" pos="0.30 0.15 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-14" type="box" size="0.008 0.108 0.04" pos="0.25 0.35 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-15" type="box" size="0.07 0.008 0.04" pos="0.32 0.30 0.05" rgba="255 255 255 1"
                  mass="0"/>
            <geom name="wall-maze-16" type="box" size="0.238 0.008 0.04" pos="-0.14 0.35 0.05" rgba="255 255 255 1"
                  mass="0"/>

        </body>

        <body name="ball" pos="-.4 -.4 .04">
            <freejoint name="ball-joint"/>
            <geom name="ball-geom" type="sphere" size=".03" rgba="1 0 0 1" mass=".000001"/>
        </body>

        <camera name="top_view" pos="0 0 1.75" xyaxes="1 0 0 0 1 0"/>
    </worldbody>

    <actuator>
        <motor name="tilt-x-actuator" joint="tilt-x"/>
        <motor name="tilt-y-actuator" joint="tilt-y"/>
    </actuator>
    
</mujoco>

Confirmations

I searched the latest documentation thoroughly before posting.
I searched previous Issues and Discussions, I am certain this has not been raised before.

yuvaltassa · 2025-02-25T13:49:02Z

yuvaltassa
Feb 25, 2025
Maintainer

Did you try a position actuator?

2 replies

ha-nn Feb 28, 2025
Author

I did but I felt like it moved the same, should I add extra options to the position actuator?

yuvaltassa Mar 5, 2025
Maintainer

Well, ya, position actuators have a different parameterization and semantics.

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Problem with actuator control and step change constraint #2451

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ha-nn Feb 24, 2025

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 1 comment · 2 replies

Uh oh!

yuvaltassa Feb 25, 2025 Maintainer

Uh oh!

ha-nn Feb 28, 2025 Author

Uh oh!

yuvaltassa Mar 5, 2025 Maintainer

ha-nn
Feb 24, 2025

Replies: 1 comment 2 replies

yuvaltassa
Feb 25, 2025
Maintainer

ha-nn Feb 28, 2025
Author

yuvaltassa Mar 5, 2025
Maintainer