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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17k views

Position Control vs Velocity Control vs Torque Control

Please can somebody explain to me the difference between Position Control, Velocity Control, and Torque Control? Specifically, I am thinking in terms of a robot arm. I understand that position control ...
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3answers
23k 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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2answers
420 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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1answer
594 views

Building a balancing robot with differential drive

I've already built a two wheeled balancing robot using some continuous rotation servos and an accelerometer/gyroscope. I upgraded the servos to some geared DC motors with 8-bit encoders with the goal ...
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4answers
1k views

Optimal location of the center of mass for an inverted pendulum

I'm building an inverted pendulum to be controlled by DC motors, but I've run across a conundrum. Personal life experience tells me that it's better to have a lower center of mass to maintain balance....
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2answers
279 views

“Time-varying” and “nonautonomous” dynamical systems and their Lyapunov analysis

It is possible to distinguish the properties "time-varying" and "nonautonomous" in dynamical systems regarding Lyapunov stability analysis? Does it make a difference if the system depends explicitly ...
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3answers
539 views

Proportional controller error doesn't approach zero

I'm reading this pdf. The dynamic equation of one arm is provided which is $$ l \ddot{\theta} + d \dot{\theta} + mgL sin(\theta) = \tau $$ where $\theta$ : joint variable. $\tau$ : joint torque ...
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6answers
577 views

Effectiveness of a Mobile Robot In Relation To Mass

Do mobile and/or autonomous robots become more or less effective the bigger they get? For example, a bigger robot has bigger batteries, and thus bigger motors, whereas a smaller robot has the exact ...
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2answers
1k views

What does SE mean in robotics literature?

I've come across the abbreviation SE several times recently. I know it has to do with the pose of the robot, and the degrees of freedom. Most recently I found it on page 8 of this paper: D. Kragic ...
5
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1answer
72 views

Cartesian Impedance control Damping Design (Double Diagonalization)

In the literature, it is often seen that for a system: \begin{align} \Lambda \ddot{e} + D_d \dot{e} + K_d e = F_{ext} \end{align} A dynamic damping matrix is required for a robot to take ...
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4answers
2k views

Dynamic torque simulation for a 6 DOF robotic arm

I am working on a 6 DOF robotic arm(industrial manipulator). I have the basic structural specs (dimensions, weights etc) for the links and joints with me. Basically, I want to simulate both static ...
5
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1answer
221 views

Calculating required torques for a given trajectory using Lagrange-Euler

I have a 2DOF robot with 2 revolute joints, as shown in the diagram below. I'm trying to calculate (using MATLAB) the torque required to move it but my answers don't match up with what I'm expecting. ...
5
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1answer
105 views

Conventional Land Vehicle Dynamic Models for GPS/INS augmentation

I am looking to augment a GPS/INS solution with a conventional land vehicle (car-like) model. That is, front-wheel steered, rear wheels passive on an axle. I don't have access to odometry or wheel ...
4
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1answer
2k views

Why do series elastic actuators have more accurate and stable force control?

The other day, somebody was telling me about a robot in their lab, and they mentioned that it has "series elastic" actuators. But after doing a bit of Googling, I'm still not sure as to what this ...
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3answers
2k views

What is the difference between screw and wrench in rigid body motion?

A screw is defined by a six dimensional vector of forces and torques. It can represent any spatial movement of a rigid body (as written here). But I don't get the following distinction between screw ...
4
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2answers
938 views

What is the bicycle model for a dynamic robot?

I was asked this in a phone interview for a robotics job. Googling has not really helped. I assume it is some sort of state prediction model that can be used in a Kalman filter. Can anyone give me a ...
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4answers
6k views

how to implement tracking problem with PID controller

I'm trying to implement the tracking problem for this example using PID controller. The dynamic equation is $$ I \ddot{\theta} + d \dot{\theta} + mgL \sin(\theta) = u $$ where $\theta$ : joint ...
4
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1answer
103 views

Why do we need coriolis and centrifugal forces when it comes to the dynamics of a robotic arm?

So we all know (and love) the typical dynamic equation of a robotic arm: $$ M(q) \ddot{q}+C(q,\dot{q})\dot{q}+G(q)=\tau $$ Where M is the mass matrix, G is gravity and C is Coriolis and Centrifugal ...
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1answer
83 views

robotic arm DOF

I'm working on an assignment and was wondering aobut the degrees of freedom this system has. The generalized coordinates are: $\underline{q}:$ \begin{bmatrix} x \\ \theta_{1} \\ \theta_{2} \\ \end{...
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2answers
194 views

Biped State Space Implementation

Currently I working on a humanoid robot using inverted pendulum model and use LQR for walking stabilizer. Input u is Torque, State x is angle and angular velocity and y output is angle. I got the ...
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2answers
715 views

Where to make changes for simulation project Bullet/Gazebo/ROS/Orocos

I am starting to develop robotics project which involves simulation (and maybe real world programs) of soft-body dynamics (for food processing) and clothes/garment handling (for textile industry or ...
4
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1answer
79 views

3-DOF Robot Dynamics error in Robotics Toolbox

I am trying to compute dynamics of 3 DOF robot using Robotics Toolbox by executing this code: robot.accel(q, zeros(1,3), zeros(1,3)) But I am getting this error: ...
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2answers
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How do quadcopters turn left and right?

In this picture, a sketch of a quadcopter is displayed with rotor's direction of motion. The magnitude of the rotational velocity is depicted by the thickness of the lines (thicker lines are higher ...
3
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1answer
277 views

Can a state matrix have a row of zeros?

While formulating a state matrix of a system, say a system of a typical cruise controller, \begin{equation} \begin{bmatrix} \dot{v} \end{bmatrix} = \begin{bmatrix} -\frac{b}{m} \end{bmatrix} \begin{...
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2answers
91 views

Should the therotical parameters match the physical setup constraints when modeling a robot?

I'm working on modeling and simulation of robotic arm, after I obtained the mathematical model of the robot, I used that to implement some control techniques, to control the motion of the robot. The ...
3
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2answers
4k views

How to implement PID control for robotic arm?

I'm wondering that, PID control is a linear control technique and the robot manipulator is a nonlinear system, so how it is possible to apply PID control, in this case. I found a paper named: PID ...
3
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1answer
145 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 ...
3
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1answer
140 views

Understanding Impedance Control

I have a question regarding impedance control for a robotic manipulator. Given that we have a task space trajectory: $\ddot{x}$, $\dot{x}$ and $x$ And the dynamics model of the robot: $$\tau = M(q)\...
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2answers
113 views

When and when not to use the Inertia tensor in Kinetic energy computing?

I'm trying to obtain the dynamic model of a 3D robot (academic problem), I have obtained the D-H table, the transformation matrix for each pair of links and the total transformation matrix. Now I'm ...
3
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2answers
281 views

Do walking robots use accelerometers?

My understanding of walking robots (e.g. https://www.youtube.com/watch?v=xJlkBBdyBYI) is that they use a gyroscope to determine the current orientation of the robot, or each joint of the robot. This ...
3
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1answer
157 views

Reachable Position with endeffector robotic arm

I have a 7 DOF robotic Arm. All the 7 Joints are rotational and have upper and lower joint angle limits. Now assume my end effector has a certain Pose $x = [X, Y, Z, a, b, c]$. My Question now is ...
3
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1answer
594 views

Guessing the K matrix gain for the Optimal Control LQR?

I'm are going to create a LQR to control a system. The problem is to choose the Q and R weighting matrices for the cost function. The Q and R matrices are going to minimize the cost function so the ...
3
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1answer
1k views

Mass Matrix in Lagrange equation

I want to find the equations of motion of an RRRR robot.I have studied about it a bit but I am having some confusion. Here, in one of the lectures I found online, it describes an Inertia matrix of a ...
3
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1answer
258 views

Dynamic tracking precision of UR5/10

I am willing to use a universal robot arm (UR10) in a path following mode. i.e. I have a desired trajectory for the robot's effector and I would like the effector to follow it as close as possible. ...
3
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0answers
366 views

Holonomic constraint forces using Lagrange multipliers

Consider a multibody robotic system with Lagrangian $ L = \dot{q}^{T}M\dot{q} + V $ and equations of motion of the form $$M(q)\ddot{q}+C(q,\dot{q})\dot{q}+A^{T}(q)\lambda+N(q)=0 $$ where $N=\frac{\...
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2answers
1k views

Damping vs Friction

I am using a physics simulator to simulate a robot arm. For a revolute joint in the arm, there are two parameters which need to be specified: damping, and friction. If a torque is applied to the joint,...
2
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3answers
1k 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 ...
2
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2answers
1k views

What's the diffrence between $H_2$ and $H_\infty$ controll?

There a two controllers named $H_2$ and $H_\infty$. Can someone explain if: They have have guaranteed stability margins? Do they have a Kalman filter? Are they for both SISO and MIMO systems? Can I ...
2
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1answer
64 views

Confusion about Jacobians stemming from class notes

So I thought I understood well enough what a Jacobian was (in the context of an $n$-DOF robot) -- a function that takes a vector of n joint positions and returns an $n \times n$ matrix that can be ...
2
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1answer
2k views

D(q) Inertia Matrix and the Jacobian Matrix

There is something I need to verify. Say we have the following RPR robot manipulator. The DH table yields 3 rotational matrices: \begin{equation} R^0_1, R^0_2, R^0_3 \end{equation} Using these ...
2
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3answers
948 views

Compensating for Yaw in Lateral Quadcopter Movement

I'm trying to make a quadcopter move laterally at a certain angle. I've been able to find the proper roll and pitch angles for this (that work with a yaw of 0°); how would I adjust these values to ...
2
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1answer
30 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} ...
2
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2answers
435 views

Understanding the kinetic energy expressions for a 1 link vs 2 link robot arm

I'm studying these lecture notes on dynamic models of robot arm links, slides 33-36, where two examples are given for the kinetic energies for a single link and two link robot arm. In the single ...
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2answers
404 views

Combining centres of mass and Inertia tensors

I'm trying to build the dynamic model of a 6DOF robot, and the company that has built it, kindly provides a document having the masses, centres of mass, principal axes of inertia and principal moments ...
2
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1answer
513 views

Dynamic model of a robot lifted by a balloon (Multibody system)

I'm having a hard time trying to understand how to obtain the dynamic model for a system similar to the image. The balloon is a simple helium balloon, however the box is actually an aerial ...
2
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1answer
90 views

Free-floating sphere dynamics using Roy Featherstone's spatial_v2 toolbox

I am using Roy Featherstone's spatial_v2 to model a mobile robot. I encountered a problem so I went back to modeling a free-floating sphere to familiarize myself with the library and the algorithms. ...
2
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1answer
109 views

When are non-diagonal matrices advantageous for linear quadratic regulators?

When setting up an optimal control problem using a linear quadratic regulator, one often chooses semi-definite matrices Q and R such that the objective function J has the form $$J=\int_{t_0}^{t_f}(...
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1answer
509 views

Euler-Lagrange Dynamic model

I'm working on a masters thesis and need to calculate Mass inertia matrix ($M$), Coriolis/Centrifugal matrix ($C$), and the gravity matrix ($G$) in the equation $M\ddot{\theta} + C\theta + G = \tau$ (...
2
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1answer
690 views

Linear State Space of a 6DOF robot

I'm new to the field of robotics, so this is a pretty basic question: I'm assigned with the task of constructing a linear state space model of a 6DOF robotic arm that moves in 3D space. I believe the ...
2
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1answer
317 views

Dynamics of a robot manipulator with a force acting on the end-effector

I have this exercise The dynamic model is $B(q)\ddot{q}+S(q,\dot{q})\dot{q}=\tau+\tau_k$ Where $B(q)$ is the inertia matrix, $S(q,\dot{q})\dot{q}$ are the centrifugal and Coriolis terms, $\tau$ is ...