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Questions tagged [joint]

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

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25 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
20 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
20 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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0answers
41 views

Best way to actuate J5 (wrist) on 6 axis robot arm?

I'm designing a robot arm with an intended payload of ~2 kg and 60 cm reach. I've been working off of the AR2 arm design, which has the typical turret | shoulder | elbow | wrist roll | wrist ...
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1answer
44 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
116 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
47 views

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
471 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: ...
2
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1answer
493 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
372 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
337 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
544 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
137 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
73 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
443 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
139 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
2k 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
40 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
107 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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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
547 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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3answers
80 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
283 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
304 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
218 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
523 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
2k 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
77 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
133 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, ...
2
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1answer
2k 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
488 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
226 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 ...
7
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1answer
3k 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
1k 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
8k 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 ...