Questions tagged [joint]

The point of contact between elements of a robot with the parts that surround and support it

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Why aren't more bipedal (or even quadruped) robots made with joints/articulations similar with those found on atmospheric deep dive suits?

The sole reason I'm making this question is due to the fact that such joints/articulations would allow the electric motors to continuously move while the walking motion is performed, instead of the ...
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What is the meaning of joint space and configuration space and task space?

I'm reading an article about teleoperation systems and it talks about three spaces that include joint space, configuration space and task space frames. I do not know what these are, can you explain?
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How to translate a joint configuration

I'm currently working on a basic implementation of the RRT algorithm to control my 6DOF robotic arm. But how can I reduce the node to be in the radius of the nearest node of my graph without using the ...
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In MuJoCo I have a model with one hinge joint made of two meshes that I can't get to actuate

The joint just opens 180 degrees and shakes in place a little. What am I doing wrong that would make this egg slicer open and close smoothly? ...
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DH Parameters of a 2 DOF RP Robot

How can I determine the DH parameters of the robot shown in the figure ? As i know, the z axis should show the rotation axis for rotary joints and direction of extension for prismatic joints, so the ...
2 votes
1 answer
63 views

Estimating distance between joint positions

I was wondering if there is any good way to estimate the difference between two joint states of a robotic arm. Currently I am using something like this: $\sqrt{\sum_i^N{(JStateA[i]-JStateB[i])^2}}$. ...
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I would like to add a prismatic joint to the Z axis of the 6th joint of Urdf

I have a urdf file,urdf of UR5 robot and added a prismatic joint to the end of 6th joint of the robot with the "prismatic_joint" tag (By copying other joints and links) ...
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87 views

Joint space trajectory script unclear

I have a script provided by The MathWorks Inc. that makes a robot end-effector follow both a task space and a joint space trajectory through several waypoints. These trajectories are then plotted in ...
4 votes
1 answer
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Why are serial manipulators almost always made of single dof joints?

I am currently taking my first robotics class and I found it curious that all serial manipulators have single dof joints. Why not use joints with more dof and reduce the number of components? Will ...
1 vote
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51 views

Why do some humanoid robots use a slanted yaw joint on the hip?

In this image, we see LHipYawPitch, as well as a dedicated LHipPitch. Why would they combine the yaw and pitch in the upper joint instead of making a dedicated yaw joint? I understand that this makes ...
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1 answer
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How to calculate displacement of the end effector by the yaw, pitch, and roll in the spherical joint?

For planar robots, we can calculate how small changes in the angle of each joint corresponds to the displacement of the end effector, by constructing a jacobian consisting of cross products between ...
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What are joint angles of Kinova Jaco in home position?

I want to work with Kinova Jaco with spherical wrist in CoppeliaSim, because currently I do not have access to a physical manipulator. The model there is in reset configuration (arm fully extended and ...
2 votes
1 answer
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How do I decide the minimum number of link lengths and joints my manipulator must have from the configuration space?

I have a configuration space in 3D where my manipulator must reach certain points. Taking into account all the factors how do I decide the mininum number of links and joints my arm must have?
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what are shoulder ball and socket joints called? (i am trying to design and build a hydraulic assistance mech suit)

I'm having problems finding the right sort of joint for my shoulder connection. It is a flat surface on the side of the mech body and I need to create a joint with maximum movement rotating: up, down ...
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1 answer
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My robot keeps getting saved as one cylinder leaving out the bottom cube

I created a robot in the model editor that is made up of a cube and a cylinder with a revolute joint between them but after saving it and inserting another instance into the world, I only get the ...
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1 answer
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What is the purpose of an empty link without any child elements?

I was looking at a model xacro [urdf] file in a ROS tutorial when I saw: ...
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1 answer
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Velocity description in Screw Motion Theory

As described in the book Modern Robotics by Frank C. Park the velocity of a reference frame can be described as : $$V_s = J_s(\theta)\dot{\theta}$$ $$V_b = J_b(\theta)\dot{\theta}$$ However in the ...
1 vote
1 answer
158 views

How does this end effector work?

I've seen this linear actuator end effector on a few industrial SCARA 'bots but I am having trouble visualizing how it works internally: It looks like a type of lead screw, but the nut must spin ...
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3 votes
2 answers
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How to compute associated (partial) Jacobian matrix for each joint of a serial manipulator?

Given DH parameters of a serial manipulator, the forward kinematics gives me T0n = T01*T12*T23*...*Tn-1n , n is the DOF of manipulator. I can calculate the Jacobian matrix J for the end-effector by ...
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2 votes
1 answer
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IMU based joint angle measurement

Let us assume we have a two 2-DoF robot. Both axes rotate around x. And the goal is to measure the joint angle values with the roll value from IMUs attached on each link. However, the problem is that ...
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Robot arm with steppers - speed

I am using a 5 axis Robot arm (Robolink robot from Igus) to perform some 3D printing routines. By now I am trying to use them and have him have some good position (and speed) control. The robot is ...
3 votes
2 answers
124 views

Making a motor controlled joint passive

Anyone know of a good (and economical) way to make a motor controlled arm become a passive link on trigger? That is, the joint can be active (motor controlled) or passive (rotate freely). The tip of ...
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2 answers
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How to determine the direction of X-Axis in Denavit Hartenberg process? [Sketch inside]

The rules of assigning axes for DH parameters are (as I know them): 1- Z: in the direction of the axis of rotation/translation of revolute/prismatic joints. 2- X: perpendicular to the previous Z axis ...
2 votes
1 answer
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How can I attach an arm to a double-flat drive stepper motor?

This is my first robotics experience, outside of one class 10 years ago. I've been Googling this question for about an hour but I can't find an answer! I'm using a ROHS Step Motor 28BYJ-48 (with an ...
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1 answer
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What are the differences between wheel and manipulator joint encoders?

As far as I understand the joint encoders output the angle and the wheel encoders output speed. Is that accurate? In either case, how do the differences affect the kinematic calculations, as in path ...
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What is the rectangular-shaped joint in this diagram?

What is the rectangular-shaped joint under the M1? What does it do, and what is its DOF?
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2 votes
1 answer
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Spherical (Ball) Joint in Robot Model not Working in Gazebo

I'm having trouble including a spherical/ball joint in my robot model. I have tried using the 'ball' joint type defined by sdf (http://sdformat.org/spec?ver=1.6&elem=joint#joint_type) but the urdf ...
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1 vote
1 answer
597 views

How to calculate effort/torque values of a joint

I have a robotic arm with 6 DOF. For each joint, I get get the Joint Wrench, which is composed by the force and torque of the parent and child links of the joints. In other works, for joint 1 I can ...
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1 answer
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State of the art trajectory for fine precision robots

Which kind of trajectory would one use for a fine precision robot? I know trapezoidal and cubic trajectories, but errors get very high when stopping at every configuration and when speeding up to ...
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2 answers
301 views

Inferring joint orientation on multi-joint arm

Not a robotics question in the strictest sense, I guess, but related closely enough, I hope: I have an arm-like articulated two(-plus-one)-joint appliance that I want to use as a 3D input device. It ...
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2 votes
1 answer
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cable-controlled flexion and extension

I'm new, please be gentle :-) I'd like to control the position of a single-axis joint using one cable for flexion and another for extension. In many of the anthropomorphic designs I've seen each of ...
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1 answer
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Adding a floating joint to a sphere in urdf

I am trying to create a sphere that I can control through pybullet. I have a basic urdf specification that looks like this: ...
2 votes
1 answer
2k views

Gazebo joint->SetForce() call applies forces to the whole model. How to circumvent that?

The following code applies a force to the joint in an update method call. The problem is that the force seems to dissipate / is applied consecutively to other parts of the model, specifically the ...
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1 answer
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Parallel axis theorem to determine the moment of inertia

I need to use the parallel axis theorem to determine the moment of inertia of each robotic arm link referred to the joints of the 3 DOF manipulator. The moments of each link's centre of mass are: The ...
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3 answers
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how to find maximum force of a robot joint

I want to know if there is any equation that calculates the maximum force of a robot joint. The force that we should not exceed. For example in human leg, if we apply a big external force to the knee,...
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3 votes
3 answers
814 views

Can we simulate a actuator with a very strong torque with a PID controller

I use gazebo to simulate a robot arm. To control its joints, I use PID controllers. As you might know, PID are sometimes pretty hard to tune and this is the case for a robotic arm. To avoid any tuning,...
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4 votes
1 answer
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Lateral load on a servo motor

Looking at pictures of existing designs for quadropod robots, the servos in the legs seem to usually be mounted inside the chassis, with a second attachment at back of the servo as well, such as this: ...
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3 votes
1 answer
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Reference request: Path accuracy algorithm in the joint angle space

I am currently reviewing a path accuracy algorithm. The measured data are points in the 7 dimensional joint space (the robot under test is a 7 axes Robot, but this is not of importance for the ...
1 vote
1 answer
789 views

How modular arm joints work [closed]

Hello I'm trying to figure out how modular arm joints are designed and what kind of bearings/shafts are used for a modular-type robotic arm. Take "UR arm" for example. I believe those 'T-shaped pipes' ...
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8 votes
2 answers
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What to do when position control with trajectories is interrupted?

What are strategies used when trajectories, which are applied to a robotic joint, are interrupted? Say a robotic arm hits an obstacle, the controller just keeps applying the trajectory. Then at the ...
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2 votes
1 answer
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Gazebo: moving joint with model plugin

This is my first week with Gazebo. The tutorials are clear (except for my dearth of C++ knowledge) but now that I'm working to move out on my own things are getting cloudy. I made a model comprising ...
1 vote
2 answers
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Are joint state vectors limited? [closed]

Are joint-state vectors $q$, which define the position and orientation of a set of joints, limited somehow? I know they are used for the rotation part of the transformation matrix => therefore I ...
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1 answer
223 views

Joint Space Singularities [closed]

I would like to clarify my self on singularity configurations. If I am moving the robot in joint space only one joint at a time, can I come to a singular configuration? If so how? Thanks
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3 DOF Inverse Kinematics Implementation: What's wrong with my code?

I am currently trying to implement an Inverse Kinematics solver for Baxter's arm using only 3 pitch DOF (that is why the yGoal value is redundant, that is the axis of revolution). I for the most part ...
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1 answer
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What is torque bandwidth in actuated joints and how does it affect the control systems?

The rest of my student team and I are in the process of redesigning an exoskeleton and building it based on an existing one. From the papers that we have been reading there are some references to low, ...
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5 votes
4 answers
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Determine what the rotation axis is given a rotation matrix

How do I find out around which axis the coordinate system has to rotate, if the rotation matrix is given? $ {^{a}R_{b} } $ = $ \left(\begin{matrix} 0 & 1 & 0 \\ -1 & 0 & 0 \\ 0 & ...
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1 vote
2 answers
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Stewart platform as robotic wrist joint

I'm planning the design of a wrist for a humanoid robot. I would like to choose a design that is sturdy while allowing for dexterity comparable to a human wrist. One option that was presented to me ...
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9 votes
2 answers
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Adding an Actuator or Force to a (Featherstone) Articulated Rigid Body Model

I'm working on a project where I need to model a system that is essentially comprised of a series of ball-and-socket joints attached to a base, which is attached in turn to a prismatic joint (rail). ...
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5 votes
3 answers
293 views

What is the technology used for no-resistance robot arms?

I saw a high end robot arm once that I could move and bend it to any form I wanted with no resistance, as if the robot arm didn't have any weight. I'd like to know more about them. What is this class ...
1 vote
2 answers
1k views

joint positions of a robot

I would likte to find the joints positions using joint angles, link lengths etc. How can I define the position of the each joint using DH parameters?