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Questions tagged [kinematics]

Kinematics is the branch of mechanics dealing with the motion of points and objects.

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Are underactuated robots easier to program?

The first examples for passive dynamics were introduced by Ted McGeer in the early 1990s. The main principle of so called underactuated robotics is, that not all joints in the system can be controlled ...
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52 views

underactuated robot problem

Lets say the robot has 4Dof and the operator gives (x,y,z,roll,pitch,yaw ) as control input( rank(J) < dim(task) ). Now the robot is overwhelmed and will probably show some jerky movement. But can ...
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State Space model for bouncing ball

In lecture 5.5 Bouncing ball, slide 26, Coursera's Control of Mobile Robot course, how are the state space equations formed in "Equations of motion in-between bounces"? Why is [0 -g] added? And how ...
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101 views

How do I find the inverse kinematics of a 5-DOF manipulator having the following DH parameters?

alpha = [ -90, 0, 0, 90, 0] a = [ 0, 400, 200, 0, 0] d = [63.5, 0, 0, 90, 100] I am trying to calculate the joint angles but I am stuck ...
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20 views

Maximum value of norm of mass matrix M

How do I compute the maximum values for ||M(q)|| and ||M_dot(q)||, the induced 2-norms, where M(q) is the mass matrix from the standard dynamical model of a robotic manipulator. I have the numerical ...
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24 views

Vertically moving robot

I want to build a 4WD robot that can travel vertically by pushing against opposite rails. The wheels push against the rails and generate friction, the robot moves upwards as the wheels rotate. This is ...
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1answer
42 views

Wrong forward-kinematic after calculating from DH-parameters

I'm working on an exercise about DH-parameters for my robotics course in university and I ran into a problem, because my solution is different from the one given by my professor. I calculated the DH-...
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2answers
110 views

Struggling to understand Jacobian Inverse Kinematics

I'm trying to find a method to control a moveo 5dof arm. My goal is to calculate the right angle to turn for each stepper motor to reach a desired point in real environment. I've spent time looking at ...
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22 views

how to normalize PWM if the value exceeds the maximum speed limit

I have implemented inverse kinematics for nonholonomic mobile wheeled robots, and the RPM range of the motor that I used is -50 to 50, while for PWM is from 1300 to 1700. But in certain cases, the RPM ...
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1answer
41 views

How do I compute the translation and rotation velocities of a robot

I am stuck at computing the translation and rotation of a robot moving onto an ellipse given by: $$ p(t) =(m) + \cos(t)∗a + \sin(t)*b $$ where m = center of ellipse and the two axes a (horizontal) ...
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43 views

Can somebody explain how these forward kinematics matrix equations were formulaed?

Here's the link to the entire answer: Designing a 5 bar linkage robot: Plot Clock
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77 views

Using pre multiply or post multipy for rotational matrix to get a new homogenous transformation matrix?

I am confused about how do I multiply the rotational matrix in this case. I know that both T1 and T2 needs to be multiplied by a rotational matrix but I don't know how to multiply the rotational ...
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1answer
57 views

Why using screws instead of homogeneous transforms in kinematics and dynamics?

Can anyone give a justification for using screws (twists, wrenches) instead of the traditional approach (rotation matrices, homogeneous transforms)? Even if screws are more compact, the situation gets ...
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1answer
85 views

Finding Joint speeds for each joint of a 6DOF arm (UR10) using the Inverse Jacobian

Background: I have access to a UR-10, 6DOF robotic arm through my school (I'm very new to robotics). I know the desired set of linear speeds that I want in the x,y, z-direction in terms of the end ...
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1answer
51 views

Creating linear end effector motion using joint speeds: Converting tool speed to joint speeds

Background Information: I'm new to robotics and my school currently has access to a 6DOF Universal Robot (UR-10). I'm programming it using its scripting language URscript and the arm has these two ...
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32 views

Help to get Jacobian of triangular platform - from center point to apices

I'm creating a simulation of the parallel robot similar to this construction: Without getting into details - the robot is "closed" with the triangular platform, apices of which are positioned in the ...
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80 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
23 views

Motorised Stage for laser

The problem I want to be able to move the direction a laser is pointing. This means I need to have motorised rotation of the laser head in the x direction and in the y direction. I am unsure of the ...
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3answers
151 views

What is the best SE3 library for python?

I am currently googling on this topic but I would like to hear your opinion. What is the best self-contained SE3 library that offers interconversion between quaternion, rotation vector, ...
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0answers
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Algorithm for orientation (pan/tilt) towards a moving point

Main Question: note: The code in this question is pseudo-code, I'm using Python, but my pseudo-code is a mix of Python and C++. I have a camera on the top of my robot's "head" which has pan and tilt ...
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41 views

Orientation problem between Gripper and Object ??

I am working on a pick and place project using ROS & MoveIt!, I wrote my own pick and place functions which generate grasp poses according to the pose of the object and then automatically picks. (...
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2answers
63 views

Help to get robot jacobian from system of implicit equations

I have system of two equations that describes position of robot end-effector ($X_C, Y_C, Z_C$), in accordance to prismatic joints position ($S_A, S_B$): $S^2_A - \sqrt3(S_A + S_B)X_C = S^2_B + (S_A - ...
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118 views

Denavit-Hartenberg Exam Question

I am having a bit of trouble with the pictured question: I am able to do part a and b, however c is proving very difficult. My lecturer never really explained much beyond what is asked in a and b. ...
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Inquiry about Velocity Propagation (theory)

I interpret the saying "linear velocity is associated with a point and angular velocity is associated with a body" as a reference to the fact that when assigning a frame to a body and the body is ...
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142 views

How to find jacobian using kdl that matches with bullet physics jacobian

I am trying to calculate jacobian with kdl (pykdl) and bullet physics (pybullet). With bullet physics I can only find Jacobian of whole robot, but I want to find Jacobian for a kinematic chain. So I ...
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0answers
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Dimensions of an X Quadcopter frame

I'm writing a paper on the calculations required to design of an X frame Quad copter for any particular load.There isn't a lot of material available to guide me through what actually needs to be ...
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103 views

Treatment of euler angles in quadcopter control

In most implementations of quadcopter control systems I've seen, each axis of the quadcopter is controlled independently. For example, to control the rate in the roll axis, the desired output is ...
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1answer
53 views

Screw based Jacobian

I am working on kinematics of 5-DOF robot. I already derived geometric Jacobian for position and orientation control. But for singularity analysis, I require a simplified jacobian. And that can be ...
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1answer
53 views

State space model

I want to design a LQR controller for my two wheeled mobile robot. While designing the controller, I need to find gain, K for the LQR which this required the state space model of wheeled mobile robot. ...
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1answer
37 views

Metrics for rigid body motions in SE(3)

As SE(3) does not have any bi-invariant metric, what are the available pseudo metrics for comparing two homogeneous matrices for rigid body motions ? In other words, how to compare two dual ...
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1answer
53 views

What is an “actuation state”

The paper A Feedforward Control Approach to the Local Navigation Problem for Autonomous Vehicles by Alonzo Kelly uses the term actuation space. Feedforward solves the historically significant ...
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1answer
67 views

Jacobian of kinematic IMU Model

I have the following problem: given two Input Vectors $x = \begin{pmatrix}x\\y\\z\\v_x\\v_y\\v_z\\q_1\\q_2\\q_3\\q_4\end{pmatrix}$, $u = \begin{pmatrix}a_x\\a_y\\a_z\\w_x\\w_y\\w_z\end{pmatrix}$ time $...
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1answer
160 views

What is difference between 2 wheels and 4 wheels and tracked differential mobile base kinematics?

In generally I know that no difference between 2WD and 4WD mobile base control kinematics equations. but is there really difference between two wheels differential mobile base and tracked/...
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1answer
611 views

calculating differential drive robot ICC position

I don't understand how to calculate the ICC position with the given coordinates. I somehow just have to use basic trigonometry but I just can't find a way to calculate the ICC position based on the ...
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1answer
232 views

State prediction of vehicle with Ackermann steering geometry using Kalman-Filter

I am trying to have a Kalman-Filter (or Extended-KF) give me positions for a small remotely controlled vehicle with an Ackermann steering geometry (moving on a plane surface). The control commands I ...
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1answer
332 views

Inverse Kinematics 5DOF - general approach - Wrong solution MATLAB

Can anyone name a good source for a general approach (cookbook-like) for the inverse kinematics regarding a 5-DOF? The paper by De Xu et al. is aiming for a general approach, but it doesn't work for ...
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53 views

From a linear force actuator that spans multiple links and joints to the equivalent motor torque

I am programming/using a rigid body joint-space dynamics solver for robots in which I want to implement linear force actuators between links with their equivalent torque sources that are 'spanned' by ...
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2answers
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Understanding the Robot Jacobian

Although I have an understanding of what Jacobians are in general and how to calculate Jacobians, I fail to understand how the idea of Jacobian came for use in kinematics and why they are used for ...
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2answers
383 views

Quadrotor Dynamics: Calculating angular velocity of quadrotor

I am trying to simulate and implement the controller of the paper Geometric Tracking Control of a Quadrotor UAV on SE(3). To do this I need to first implement the dynamics of the quadrotor. According ...
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1answer
66 views

Urdf as a way to model dynamics?

Since urdf format serves the purpose of kinematic model but also extends for dynamical properties such as mass,moment of inertia and centre of masses, can it be considered a viable dynamical model of ...
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2answers
131 views

Inverse Kinematics problem formulation (optimization)

Note:Q is a diagonal posituve semi-definite matrix Why is the IK formulation like that? It looks like it's trying to find the optimum dq/dt that will minimize the magnitude dq/dt. How is that giving ...
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1answer
201 views

Significance of link length ratio in serial manipulator

I am formulating a problem to optimize link lengths of 3R serial manipulator shown below : I do not assume any explicit relationship between the link lengths, but in one of the papers (http://www....
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1answer
63 views

Expressing a global point in different frames

I am trying to express a vector defined in global coordinates in different frames using homogeneous transformation matrices. There are in total 3 frames. Frame 1 lies in the origin and is fixed to ...
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2answers
357 views

Using jacobian of arm robot to calculate transformation matrices?

I have been given a Jacobian for a 3 revolute joint robot. I need to obtain the origins of each of the joint. Origins of the joints can be obtained once I get $T^0_1$, $T^0_2$, $T^0_3$ and $T^0_4$. ...
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2answers
315 views

How to check reachability of manipulator to a point?

I have written a MATLAB code for inverse kinematics of 3R robotic arm, which returns value of joint angles for given link lengths and end effector position and orientation. But if location of point is ...
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1answer
186 views

Optimization of link lengths for 3R serial manipulator

I am trying to formulate an optimization problem for determining link lengths of 3R manipulator shown in picture below, Following are the constraints, Robot arm should be reachable at point x = 100, ...
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1answer
48 views

How can serial manipulator have unique condition number for given end effector position?

I am reading about Condition Number which is considered as measure of manipulability of robotic arm, it is defined as $$ k = \parallel J \parallel \parallel J^{-1} \parallel $$ Where, $$ \parallel J \...
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3answers
157 views

DH Parameters with offset base

I'm looking at a pan tilt (RR) system. I want to define the kinematics between a world frame and the end effector. Every example I've seen looks at the world frame as being at the first joint (the ...
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112 views

Beginners guide to Inverse Kinematics for biped robots? [closed]

I'm building a LynxMotion Scout biped and believe that IK are the best way to develop an effective gait. I'm a mechanical design engineer - I currently have minimal skills / experience with ...
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3answers
286 views

Confusion in fixing DH frames

I am analyzing a concept of a surgical robot with 4 revolute joints and one sliding joint. I am not able to fix the coordinate frame for last prismatic joint. Following are the schematics of robot and ...