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 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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1answer
79 views
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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1answer
26 views
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 ...
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1answer
40 views
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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40 views
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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1answer
47 views
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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1answer
25 views
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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1answer
46 views
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 ...
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1answer
77 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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2answers
167 views
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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1answer
80 views
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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1answer
92 views
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 ...
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2answers
94 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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2answers
917 views
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 ...
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1answer
578 views
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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1answer
61 views
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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1answer
103 views
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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1answer
566 views
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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1answer
408 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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1answer
64 views
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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1answer
252 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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1answer
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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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1answer
1k views
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:
...
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1answer
1k 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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1answer
872 views
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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3answers
664 views
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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3answers
735 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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1answer
223 views
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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1answer
92 views
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 ...
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1answer
730 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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2answers
193 views
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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1answer
3k views
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 ...
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2answers
51 views
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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1answer
214 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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1answer
1k views
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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1answer
993 views
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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4answers
329 views
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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2answers
333 views
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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2answers
459 views
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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3answers
263 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 ...
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2answers
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?
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3answers
3k views
DH Matrix to homogeneous transformation matrix for each joint
Given a DH matrix for a set of joints, how would you convert the data into homogeneous transformation matrices for each joint? I've looked online, but can't find a good tutorial.
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1answer
86 views
Joint angle correction using LM
I have a camera mounted on a rotational joint. I need to calibrate the extrinsics of this camera. I can fix the camera at an estimated angle (facing the ceiling). Then I want to get the real angle.
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1answer
138 views
What type of mechanism is this?
Held and rotated by the knurled ends, one in each hand, the silver spokes rise and fall in order for the assembly to rotate. What is it, some companies' salesmen show tool? Found in an old building, ...
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1answer
3k views
Denavit–Hartenberg parameters of a robot with spherical wrist
What are valid values for the Denavit-Hartenberg parameters $d$ and $a$ (sometimes called $r$) of the last 3 links of a robot with spherical wrist?
From this reference, "A spherical joint can be ...
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1answer
676 views
What do we call a coupling with infinite range of rotation
In most situations, range of motion is limited by the fact that we need to carry power or information past a joint. So, past a certain point there are either cables in the way, or the cables would ...
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2answers
254 views
What is the name of this mechanical linkage?
I am trying to find a joint like these for a robot I'm building. It is often called a swivel joint or a universal joint, but with a modified spider. I can't find one anywhere and would prefer not to ...
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1answer
4k views
Building Robotic arm joint
I am very new to robotic design and I need to determine what parts I will need to assemble an arm joint. The joint will contain one timing belt pulley which a remote motor will be turning, a forearm ...
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3answers
2k views
restricting range of motion with complex constraints
I am looking for a way to restrict a robot's range of motion, using complex constraints such as not tearing of a cable attached to the robot.
Take an articulated 6-axis robot arm as shown below, with ...
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3answers
12k views
How can the inverse kinematics problem be solved?
The forward kinematics of a robot arm can be solved easily. We can represent each joint using Denavit–Hartenberg transformation matrices.
For example, if the $i^{th}$ joint is a linear actuator, it ...
