Questions tagged [kinematics]
Kinematics is the branch of mechanics dealing with the motion of points and objects.
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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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1answer
37 views
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
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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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1answer
62 views
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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2answers
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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
37 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
44 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
49 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
53 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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1answer
40 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
30 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
106 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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2answers
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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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3answers
85 views
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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2answers
166 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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1answer
22 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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2answers
27 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
51 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
145 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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0answers
26 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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1answer
46 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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1answer
119 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
59 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
105 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
70 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
224 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
31 views
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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0answers
58 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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2answers
161 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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0answers
122 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
61 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
57 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
39 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
56 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
71 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
188 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
759 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
268 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
384 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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0answers
63 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
1k views
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
424 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
75 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
144 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
220 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
64 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 ...
