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Questions tagged [dynamics]

Dynamics is a branch of applied mathematics (specifically classical mechanics) concerned with the study of forces and torques and their effect on motion, as opposed to kinematics, which studies the motion of objects without reference to its causes.

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Gazebo does not calculate dynamics when joint_trajectory_controller with position command_interface is used

I was wondering why Gazebo does not calculate dynamics (velocity, acceleration, effort) when JointTrajectoryController is used with ...
0 votes
1 answer
213 views

what is difference between twist and classical velocity

In ch 8.2.1 Classical Formulation in the book Modern Robotics by Frank C. Park I know some remarks about this formula.The origin of coordinate system is coincidence with the mass center of the rigid ...
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1 answer
58 views

Lynch, Park derivation of the dynamic equations of motion

In Park and Lynch's "Modern Robotics" textbook (Section 8.2.1), they give the following derivation for the velocity and acceleration of a point $p_i$ with respect to a fixed body frame $\{b\}...
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Designing the kinematics and Dynamics of a spherical joint as 3 revolute Joint

I am working on a project where I am trying to mimic human like motion and for that I am designing a 7 DOF arm with the spherical joint in shoulder as 3R joints and 2R joints for elbow and 2R joint ...
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0 answers
34 views

How does joint torque varies wrt joint velocities in Recursive Newton Euler algorithm?

I'm currently working on solving the inverse dynamics of a 6-axis articulated robot, similar to the UR5, using the recursive Newton-Euler algorithm. I'm very confused with the results I'm getting, as ...
0 votes
1 answer
57 views

Define system forward dynamics with sympy

I would like to model the dynamics of a robot via the usual discretized system of equations $$ x_{k+1} = f(x_k, u_k) \qquad x\in\mathbb{R}^{n_x}, \quad f:\mathbb{R}^{n_x}\times\mathbb{R}^{n_u} \to \...
1 vote
0 answers
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Issues with Torque Distribution in State-dependent Differential Riccati Equation (SDRE) Controller for 4W SSMR Trajectory Tracking

I am currently working on implementing a State-dependent Differential Riccati Equation Controller (SDRE) to track the trajectory of a 4-wheel skid steer mobile robot (SSMR), where torque serves as the ...
0 votes
2 answers
122 views

Dynamic model of a robotic arm

I have a question regarding the dynamic model of a robotic manipulator. It is commonly written as follows: $$ \tau = M(q)\ddot{q} + C(q,\dot{q})\dot{q} + G(q) + J^\intercal F_{ext} $$ From what I have ...
1 vote
1 answer
425 views

Peter Corke Robotics Matlab Toolbox the problem of inverse dynamics in the Franka Emika Panda model

I have the following question about the Franka Emika Panda dynamic model. In case I perform the solution of the inverse dynamics problem using Robotics Toolbox (Peter Corke) I get different results ...
10 votes
4 answers
40k views

What's the difference between a holonomic and a nonholonomic system?

I was wondering if a 1D point mass (a mass which can only move on a line, accelerated by an external time-varying force, see Wikipedia - Double integrator) is a holonomic or a nonholonomic system? Why?...
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11 views

Hexacopter Simulation

I am doing a project to simulate a hexacopter with the mathematical model and its dynamics with PID. I've got the theoretical knowledge but am stuck on simulation. Would any of you happen to have any ...
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0 answers
28 views

Help with clarifying UR10e center of mass

I'm doing an assignment related to the Universal Robot UR10e robot for a robotics class. I have to use the center of mass of each link to solve the problem. I found the information on the link below (...
1 vote
1 answer
240 views

Robot model explodes in Gazebo

I am currently working on developing a model of a robot that moves in space (gravity=0) in the Gazebo simulator. The robot is based on a body with one continuous joint and two revolute joints. Jount1 ...
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0 answers
32 views

What is the preferred approach to derive the kinematics/dynamics of a floating base 3-link robot?

I would like to derive the kinematics and dynamics of a floating planar robot with two leg links and a hip link while the robot is in free-fall (i.e. no ground contact at the "feet"). This ...
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0 answers
75 views

Relationship between Lie Algebra (Murray, Lynch) and spatial vector (Featherstone) approaches

I am curious about the relationship between the Lie algebra/group approach to robot kinematics given by Murray (et al.) in "An Introduction to Mathematical Robotic Manipulation" and Lynch (...
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35 views

Screw theory for kinematics/dynamics of mechanisms

Is screw theory commonly used for general kinematics/dynamics of mechanisms (not just robotics)? I'd be interested in anything that covers the types of mechanisms you would find in a typical ...
0 votes
1 answer
47 views

Controlling motion of single link

This seems like it should have been a well studied problem, but I can't find any solution. We want to define what a motor must be commanded to do to move a single link with mass $m$ and length $l$ $...
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0 answers
77 views

What are the gain and bias parameters used to control actuators?

When I read the Mujoco official document, the following paragraph raises my confusion: Different settings of the gain and bias parameters can be used to model direct force control as well as position ...
1 vote
2 answers
2k views

Moment of Inertia of a Dumbbell

hope you are all doing well. I am taking a course at Coursera about Robotics and in one of the quizes, I had some problem with a particular question. I passed the quiz (4/5 correct answers), however I ...
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0 answers
25 views

Understanding Virtual Velocities in Delta Robot Dynamics Modeling

I want to model the dynamics of a delta robot, and I came across this article. It utilizes the Newton-Euler method with virtual work to derive the equations. There's a section called Simulation ...
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0 answers
37 views

Rolling friction of a swedish type omni wheel dependent on the direction of movement

I'm trying to find, as well as derive, the equation for rolling friction of a swedish type omni wheel (not mecanum) that depends on the angle at which the wheel is oriented to the direction of ...
0 votes
0 answers
82 views

How do you get the force acting from the first robot link on the second robot link knowing the forces and moments in the base of the robot?

Inverse dynamics (ID) is the concern of finding the required joint forces from a specification of the joint positions, velocities, and accelerations. In the figure bloew, the ID problem would be the ...
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1 answer
57 views

How to compute the force applied to point P given the torque registered by the sensor?

I have the following set up: I want to understand how to compute the force that is being applied to the F_knife point given the Force/Torque registered by the sensor at T_Sensor. The position vector ...
0 votes
1 answer
64 views

How to reduce the turbulence of a robotic arm, when it's end effector touches a surface?

I am working on a project related to tele-robotic ultrasound where I have to tele-operate a virtual UR5 robotic arm with a end-effector(a thin rod) through a haptic device in PyBullet. When I make the ...
1 vote
1 answer
138 views

Gazebo joint velocities do not agree with joint displacement

In a simulation that I am running, which is described below, the angular velocities that I get from the joint_states topic, do not give me the angular displacement I calculate from the joints angular ...
2 votes
2 answers
181 views

kinetic and potential energy of 3 DOF robot having 2 cylindrical links

Assume two uniform cylindrical links robot has 3 DOF as shown in the figure. Where link one has 1 dof that is rotation on its main axis. The second link has 2 DOF yaw and pitch movements. I can ...
1 vote
1 answer
41 views

what does free or forced torque mean in robot arm dynamics?

I'm trying to understand the dynamics (torque , velocity, etc ) of how a simple 2 DoF robotic arm rotates. I am using the RoboAnalyzer simulator 1 . It has a Inverse Dynamics setting of "Free&...
0 votes
2 answers
118 views

Is the angular velocity vector the derivative of a time-varying quantity?

On page 111 (section 4.6) of Robot Modeling and Control (Second Edition) by Spong, Hutchinson and Viyasagar, the authors define a "body velocity" vector $\xi$ of the end-effector as follows: ...
1 vote
0 answers
101 views

PD control with gravity compensation

Given the robot dynamics of the form $$M(\theta)\ddot{\theta}+C(\theta, \dot{\theta})\dot{\theta}+G(\theta)=u$$ where the notations have the standard meaning ($M$ is the inertia matrix, $C$ is ...
3 votes
1 answer
627 views

Calculation of IMU offset for Placement of Inertial measurement unit away from centre of mass

I am working on a 6DOF IMU that contains a 3-axis accelerometer and a 3-axis gyroscope. I am building a project to plot the position and orientation of a vehicle/dirt bike in a 3d plane. However, the ...
1 vote
1 answer
310 views

4 wheeled differential wheeled (skid-steer) robot steering problem

My question is about a square shaped differential wheeled robot, I built, that has a hub-motor (BLDC motor) attached to each corner, i.e., the wheels on the same side, either left or right, have the ...
1 vote
1 answer
1k views

Center of gravity offset for accelerometer and gyroscope readings

I am working on a 6DOF IMU that contains a 3 Axis Accelerometer and a 3 Axis Gyroscope. I am building a project to plot the position and orientation of the turret/cabin in a crane in 3D space. The IMU ...
1 vote
1 answer
110 views

Determine the maximum joint velocities for a PTP-Movement

Assuming an industrial robot performs a PTP movement with a speed of 100% for each joint, it often happens that the joints never reach 100% of speed because the torque limits of the actuators are ...
1 vote
5 answers
488 views

Why we want to write all linear system into form of first order differential equations?

It seems to be taken granted that when we deal with some control system, the first thing we want to do is to linearize the system and put it in form of first order differential equations like $\dot x =...
1 vote
0 answers
145 views

How to interpret and apply results from Inverse Dynamics

I am applying Recursive Newton Euler Inverse Dynamics to a simple two link model. If I apply the result torques and forces using PhysX or Bullet Physics I get unexpected results. The model spins and ...
0 votes
2 answers
151 views

"modern contact dynamics" - Why are spring-damper contact models not being used anymore for dynamic simulations in robotics?

While researching different physics engines for dynamic simulations in robotics I found the following statement on the MoJoCo documentation website: Physics engines have traditionally separated in ...
0 votes
1 answer
188 views

Newton-Euler Inverse Dynamics by Screw

I paste this algorithm from textbook Modern Robotics P294 in chapter 8: This is coordinate invariance of Newton-Euler equations. In the textbook, they use the ...
1 vote
1 answer
101 views

Bullet vs SimMechanics: Inverse Dynamics and sensed forces/torques

This question may be a little broad, but I could not find any other information. How accurate are the inverse dynamics functions in SimMechanics compared to Bullet? How accurate are the sensed/...
3 votes
1 answer
202 views

Can inverse dynamics control be regarded as a function?

I know that inverse kinematics ($p \rightarrow q$, p: desired pose of the end-effector, q: joint angles) is not a function because there might be multiple joint angle vectors q that result in the same ...
1 vote
2 answers
226 views

Estimating angular velocity from position

If you have two position estimates $P_{t_1}$ and $P_{t_2}$ and times $t_1$ and $t_2$ how do you extract the average angular velocity from them? The linear velocity is a simple difference but how do ...
2 votes
1 answer
314 views

Finding error in euler angle from quaternion

I'm currently working on creating a ROS controller package for franka arm, which I choose to implement a feedback linearization controller that works as following: Assume we have a planned trajectory $...
3 votes
1 answer
96 views

Articulated Body Algorithm with gear ratio

I am reading up on the proposed articulated body algorithm by Featherstone, which goes like: Pass 1: \begin{equation} \nu_0 = 0\\ \nu_i = {^i}X_{\lambda(i)}\nu_{\lambda(i)}+s_i\dot{q}_i\\ c_i = \nu_i \...
0 votes
1 answer
102 views

3-links Robot Dynamic PD Computed Torque Control

I am designing the PD control of 3-links robot using Simulink. I can't figure out what to do in the 'Robot' block to get the acceleration d_qq back to calculate the error. What is happening in this '...
2 votes
1 answer
46 views

In Dynamic Motion Primitives, why we need to approximate f if f_target is given?

I seem to misunderstand something crucial regarding finding the force vector in the process of DMPs: The way I understand it, I should come up with a dataset of trajectories $\{y_i\}_{i=1}^n$, and ...
0 votes
1 answer
53 views

Body angle of a centre-articulated robot

Wondering if anyone can help me out with this one, or point me in the right direction. I am working on a centre-articulated robot, which is steered via a push-pull chain drive. The chain drive is ...
0 votes
1 answer
109 views

Why in forward bending knee orientation in quadruped legged robot require less torque in knee joint?

I'm trying to find answer in terms of physics explanation, why knee joint torque requirement is less in the forward bending leg orientation of a quadruped legged robot. I'm referring this article, in ...
0 votes
2 answers
69 views

Force sensors output when inclined

So here is the context: I am working on a motorcycle simulator. It consists of a motorcycle frame mounted on different actuators (see picture on the left). In particular, the two actuators at the ...
1 vote
1 answer
180 views

How to solve this basic dynamics/inverse kinematics problem

Suppose I have a 6-DOF robot arm with revolute joints whose tooltip is at some position $\bf{r_0}$ and I want to move it through some trajectory ${\bf r}(t)$. For simplicity, assume there are just 2 ...
1 vote
0 answers
512 views

Computation of centrifugal and Coriolis matrix

So I have a seesaw-cart electromechanical system which I want to control. It has 2-DOF (the angle of the seesaw $\varphi$ and the cart position $s$). I used the Euler-Lagrange method to get my ...
2 votes
2 answers
124 views

Why applied joint torque will affect another joint?

I want to ask a very simple question. For the robot dynamics Newton-Euler algorithm, suppose there is a two-link planar robot, we can write the simple dynamic equation form as $M(\theta)\ddot{\theta} ...