Questions tagged [kinematics]

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

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Angular Velocities of CoM in Global Coordinate

The block diagram of the robot is shown as above. Here, $\phi$ is the angle between $X_v$ and $X_0$ (Yaw angle of the robot), and $\psi$ is the angle between $Z_b$ and $Z_v$ (pitch angle of the robot'...
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How does it get a bizarre term in triangle law of vector equation in a paper

I am reading the paper "Motion control of wheeled mobile robots" at page 5, as we have the equation (34.7), i wonder how it contains $− dc(s)\dot s$ in side. As the triangle law of vector: $\vec{OP}=...
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Does Vehicle Yaw angle measures same at every point on it? If not, how to translate yaw rotation to COG of the vehicle from different point?

I am using an IMU to measure the yaw rotation angle of a car. I need to translate the rotation measured to COG of the vehicle. I can ignore roll and pitch as I am driving it on a flat surface. So, ...
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26 views

Constant Offset matrix

I've been reading about controlling systems via momentum wheels. Such as in Satellites, or fancy inverse pendulums. In a particular paper, the writer tries to explain away an offset and settling of ...
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101 views

question about spatial velocity in the book <modern robotics>

I think the equation(3.73) should be: $\dot p-w_s$x$p=\dot p-\dot p=0$ have no idea how it can be wrong and don't know the difference between infinitely large body and a body just include the fix-...
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49 views

Null space of the Jacobian matrix for a robotic arm

I have doubts on how to find all the joint velocities that don't produce any linear velocity, so are in the Null space, when we are in a singular configuration. For example, suppose we have a 2R ...
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50 views

Libraries to calculate kinematics using Screw Theory

Most kinematics libraries/packages use the conventional transformation matrices (DH parameters). However, I'm looking for something that uses Screw Theory principles to set up the Product of ...
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1answer
48 views

Do I need to use Inverse Kinematics if I have the coordinates of all joints?

So I have the positions of all the joints (x,y,z) of a robot arm. I need to calculate the angles of the joints to feed them to another similar robot arm. I cannot get the angles from the robot I need ...
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Advice for suspension 101 for a small ATV robotic platform [duplicate]

I'm a recent grad from mech. eng. program and going into robotics field. I want to design a suspension for a small ATV robotic platform on 4 wheels that carries max 75 kg load. I might use the wheels ...
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Effective forces on an object for grasping

For example, a robot or a humankind is grasping an object such as a bottle. Which forces are effective on that bottle ? This is my opinion: When we grasp a ...
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22 views

All Joint Angle values not converging to desired set point (I am using Roy Featherstone's Spatial Toolbox)

I need the robot joint angles to become the same as given (desired) joint angles. The kinematics and dynamics (used Spatial Toolbox) are correct and the motor models are realistic too. But out of 3 ...
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Forward Kinematics of non-planar robot using Roy Featherstone's Spatial Toolbox

I have a non-floatbase 3 DOF non-planar robot whose forward kinematics I need to compute using Spatial Toolbox. The code for this purpose is p = fbkin(q) but as my ...
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3 DOF robot torque not converging Robotics Toolbox

I have a Simulink model in which desired torque is [0;0;0] and current torque should converge to zeros too. But I am getting oscillatory torque as output. This is the block diagram of what I am ...
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1answer
22 views

Joint torque sensor vs end-effector force sensor

I am trying to understand the difference between joint torque sensors, and force sensors, in a robot arm. From what I understand, joint torque sensors estimate the torque at each joint, whereas a ...
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Can Swedish wheels be used in two wheeler configuration?

Can we use any of the Swedish 90°/45° Omni or Mecanum wheels in two wheeler configurations?
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What are the differences between trajectory planning, trajectory tracking, path planning, path following and motion planning?

What are the differences between trajectory planning, trajectory tracking, path planning, path following and motion planning? And what are the basic methods they use?
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Task Space Control Parameters for 6-Dof Manipulator

I'm developing a Task Space controller based on speed for a Universal Robot 5. I've already calculated the Jacobian, position and rotation error for the classic control method: The method works fine ...
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Kinematics with Product-of-Exponentials terminology: not forward, not inverse

I'm working on a kinematic estimation algorithm, and am trying to come up with the right terminology. I'm using the Product-of-Exponentials formulation for kinematic chains (and ignoring position ...
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Adjusting the PWM frequency and duty cycle to achieve the desired angular velocity in differential drive robots

I am practicing C++ and intro to robotics using a simple differential drive robot and a raspberry pi. Also following along the GA Tech course on control of mobile robotics. The implementation I am ...
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2answers
71 views

How can Denavit-Hartenberg representation with only 4 variables describe rototranslations with 6 DOF?

I am wondering how the Denavit-Hartenberg representation is able to describe rototranslations with 6 DOF with only 4 parameters? Some context: Denavit-Hartenberg representations can be used to ...
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2answers
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Controllability of a car with a single trailer

I'm studying the kinematic model of a car with a single trailer. This picture shows the system: I started from the following statements: With these constraints, I got the Pfaffian form: And then ...
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214 views

Finding correct RPY for approaching a known point on a plane

I have a robot with 6 DOF that I want to use to grab a hanging sheet at a specific point near its edge. The grip needs to be perpendicular to the edge and co-planar with the point of course. I have ...
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1answer
56 views

How do I calculate the direction robot is facing, pose from velocity and yaw rate?

I have a simple car robot with four wheels moving relatively slowly (5~10 mph). The robot has a velocity magnitude and yaw rate sensor and the sensor samples about every 0.1 seconds. I want to map the ...
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1answer
86 views

3D Inverse Kinematics Jacobian Construction

I am following this article: Overview of Jacobian IK From the link, an example says: O is a pose vector which represents the initial orientation of every joint And following this, it gives an ...
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2answers
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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 ...
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1answer
71 views

3D Inverse Kinematics Jacobian

I am reading up on inverse kinematics and have a few questions I hope could be answered. This example is from a 3-revolute-joint, where $ E $ is the end effector and $ G $ is the goal position of the ...
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49 views

Add control and planning trajectory to double pendulum [closed]

How do I control a double pendulum to get the end effector link to go in the trajectory shaped in a perfect circle? I have the equation of the circle to go in but I don't know how to get the double ...
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1answer
50 views

Why is the endeffector of a delta-robot on the slant?

A delta-robot is a nice design for a robot, because it allows to separate the motor from the moving parts. As a result, large and heavy motors with 800 Watt can be used and at the same time the ...
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3answers
275 views

Finding Mass/Inertia Matrix of a robot

Hi I am trying to model my humanoid robot. The general EoM is $M(q)\ddot{q}+C(q,\dot{q})+G(q)=U$ I know $M(q)$ is Inertia matrix which depends on joint positions $\textbf{q}$. However, I am having ...
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1answer
52 views

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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64 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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312 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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28 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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29 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
70 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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216 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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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
45 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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1answer
56 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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314 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
68 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
163 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
107 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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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
426 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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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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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
69 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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2answers
202 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. ...