Questions tagged [kinematics]
Kinematics is the branch of mechanics dealing with the motion of points and objects.
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How can the inverse kinematics problem be solved?
The forward kinematics of a robot arm can be solved easily. We can represent each joint using Denavit–Hartenberg transformation matrices.
For example, if the $i^{th}$ joint is a linear actuator, it ...
19
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3answers
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Computing the Jacobian matrix for Inverse Kinematics
When computing the Jacobian matrix for solving an Inverse Kinematic analytically, I read from many places that I could use this formula to create each of the columns of a joint in the Jacobian matrix:
...
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Calculate position of differential drive robot
How do you calculate or update the position of a differential drive robot with incremental sensors?
There is one incremental sensor attatched to each of the two differential wheels. Both sensors ...
12
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2answers
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Differences between Ackermann steering and standard bi/tricycles concerning kinematics?
I got the following homework question:
What are the general differences between robots with Ackermann steering and standard bicycles or tricycles concerning the kinematics?
But, I don't see what ...
11
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2answers
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What are the advantages of using the Denavit-Hartenberg representation?
When one wants to model a kinematic chain and in particular define the frames attached to each body, it is common to use the Denavit-Hartenberg parameters.
What are the advantages of this ...
11
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2answers
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Smooth servo movement for a crawling robot
I made a small crawler robot a little while ago that had two legs with two degrees of freedom each, so 4 RC servos total. While I was programming the movement of the legs I noticed that they moved ...
10
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3answers
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With a 6-axis robot, given end-effector position and range of orientations, how to find optimal joint values
Given a six-axis articulated robot arm holding a tool at its end-effector, if I have a desired tool position and tool orientation, there will be exactly 1 solution to the inverse kinematics equation ...
10
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1answer
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How do I convert link parameters and angles (in kinematics) into transformation matrices in programming logic?
I'm doing robotics research as an undergraduate, and I understand the conceptual math for the most part; however, when it comes to actually implementing code to calculate the forward kinematics for my ...
9
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3answers
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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 ...
9
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2answers
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Why do we generally prefer DH parameters over other kinematic representations of robot arms?
I am specifically interested in DH parameters versus other representations in terms of kinematic calibration. The best (clearest) source of information I could find on kinematic calibration is in the ...
9
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3answers
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Forward Kinematics/D-H parameters for perpendicular joint axes
I am trying to compute forward kinematics of the Kuka youBot using DH convention:
http://www.youbot-store.com/youbot-developers/software/simulation/kuka-youbot-kinematics-dynamics-and-3d-model
The ...
8
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1answer
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Hand Eye Calibration Solver [closed]
I have a rig for which I have a pretty good estimate of the static transformation between the camera and a joint based off of the CAD. It has some errors though and I was hoping to fix it by doing a ...
7
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2answers
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How to calculate the right and left speed for a tank-like rover?
I am trying to control the Rover 5 robot using an Android app with a touch-based joystick control in the app UI. I want to calculate the speed of the left and right motors in the rover when joystick ...
7
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2answers
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Solving Inverse Kinematics with Gradient Descent
I am trying to implement my own inverse kinematics solver for a robot arm. My solution is a standard iterative one, where at each step, I compute the Jacobian and the pseudo-inverse Jacobian, then ...
7
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1answer
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How do you calculate the moment of inertia of a Quadcopter?
I'm building a quadcopter for my final year project. I have a set of equations describing attitude and altitude but they involve $I_{xx}$, $I_{yy}$ and $I_{zz}$. None of the papers I have read ...
7
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2answers
284 views
Is there a tool for building and analysing robots (kinematics, control) visually?
I am reading research papers about robotics and many of them follow the same pattern:
some construction is established
kinematical formulas are read from the mechanical structure
the state space is ...
7
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1answer
802 views
Numpy alternatives for linear algebra and kinematics in python?
Are there any decent python numerical package libraries besides numpy for python? Numpy relies on gfortan which itself must be compiled correctly for your platform to avoid hidden/insidious numerical ...
6
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3answers
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Is configuration space same as joint space?
For robotic manipulator like the one on the picture:
are the configuration space and joint space equivalent? I am trying to understand difference between the two...
6
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2answers
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Holonomics Movement vs Holonomics Constraint
I'm reading Mechanics of Robotic Manipulation by Matthew T Mason and I stumbled upon the concept of kinematic constraints. The book mentioned about two types of constraints: holonomic and nonholonomic ...
6
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2answers
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Drone targeting
Imagine a "drone" and a target point on a 2d plane. Assuming the target is stationary, there are eight parameters:
...
6
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1answer
4k views
Can a Jacobian be used to determine required joint angles for end effector velocity/position?
I'm in the early stages of working with a simple robot arm, and learning about the Jacobian and inverse kinematics.
From my understanding, the Jacobian can be used to determine the linear and angular ...
6
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1answer
2k views
How to convert between classic and modified DH parameters?
I currently have a description of my 22 joint robot in "classic" DH parameters. However, I would like the "modified" parameters. Is this conversion as simple as shifting the $a$ and $alpha$ columns ...
6
votes
1answer
230 views
One of the best ways to numerically integrate the velocity?
I need to get position $x$ from integrating velocity $v$. One could use 1st order Euler integration as
$x_{t+1} = x_t + \delta * v_t.$
However, doing so leads to errors proportional to sampling time ...
6
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2answers
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Assigning Frames and Deriving Link Parameters
The textbook I'm using doesn't have the answers to the practice questions, so I'm not sure how I'm doing. Are the following DH parameters correct given the frames I assigned?
The original question is ...
6
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4answers
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Forward and Revers Kinematics For Modified Hanging Plotter
I'm building a modified version of the standard hanging plotter (v-plotter). The basic idea is that you have two cables hanging from stepper motors which form a triangle supporting the pen at the tip. ...
5
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3answers
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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, ...
5
votes
3answers
546 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 ...
5
votes
2answers
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How much accuracy could I get position tracking with a 3-axis accelerometer and gyro sensor, and compass, and how would I do it?
Given a 12' x 12' field (4m x 4m), a reasonably cheap 3-axis gyro sensor and accelerometer, and compass, I plan to design a device capable of tracking its position to sub-centimeter accuracy for a ...
5
votes
3answers
1k views
Computing the Jacobian Matrix — chain rule?
I am learning about robot kinematics and the Jacobian matrix, and I'm trying to understand how to compute the Jacobian matrix given a kinematic chain, such as a robot arm. I understand the theory ...
5
votes
2answers
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Difference between an underactuated system, and a nonholonomic system
What's the difference between an underactuated system, and a nonholonomic system? I have read that "the car is a good example of a nonholonomic vehicle: it has only two controls, but its configuration ...
5
votes
1answer
108 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-...
5
votes
3answers
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Jacobian-based trajectory following
I would like to control my 7 DOF robot arm to move along a Cartesian trajectory in the world frame. I can do this just fine for translation, but I am struggling on how to implement something similar ...
5
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3answers
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2DOF arm with quick movement: Stepper, servo, or DC motor?
To make a two degree of freedom arm capable of speeds needed to play air hockey, how should the arm be controlled? I'm wondering about speed vs accuracy.
The following image is from a project ...
5
votes
2answers
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following a trajectory with LQR controller
We want our wheeled robot to follow a (rather short) trajectory. We wrote an LQR controller, which works well in simulation. However, our robot offers two problems:
1.) The reported state information ...
4
votes
4answers
77 views
How to understand the angular velocity of link i+1?
My question is a basic one about velocity propagation from link to link, that is how to understand the following equation.
$
{^i\omega_{i+1}} = {^i\omega_{i}} + {_{i+1}^{\;\;\;i}{R}} \cdot {\dot{\...
4
votes
2answers
361 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 ...
4
votes
3answers
846 views
Algebraic and geometric in inverse kinematic
I'm just wondering that is there any case that when algebraic way can't solve the problem while the geometric can ? Cause I'm working on a 2DOF robotics arm This one, I know the length of L1 and L2, ...
4
votes
1answer
593 views
inverse kinematics for 6 jointed robots
I am a uncertain about how to compute the right homogeneous transformation matrix to compute an inverse kinematic Q-configuration.
Looking at robot like this
Where at the end of this robot I have ...
4
votes
2answers
803 views
Robot arm reachability of a pose in Cartesian space
Given a set of robot joint angles (i.e. 7DoF) $\textbf{q} = [q_1, ... , q_n]$ one can calculate the resulting end-effector pose (denoted as $\textbf{x}_\text{EEF}$), using the foward kinematic map.
...
4
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1answer
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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-...
4
votes
1answer
183 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 ...
4
votes
1answer
231 views
Velocity Relation for Parallel Robots
In my course of "Advanced Robotics" with "Fundamental of Robotic Mechanical Systems" as the reference book I saw the following equation as the velocity relation for parallel manipulators such as the ...
4
votes
3answers
334 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 ...
4
votes
1answer
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Velocity Model Motion in Matlab (Probabilistic Robotics)
I want to implement the velocity motion model in Matlab. According to Probabilistic Robotics page 124, the model is as following
\begin{align*}
\hat{v} &= v + sample(\alpha_{1} v^{2} + \...
4
votes
2answers
666 views
How to invert D-H parameters
I currently have a working kinematic chain made by a set of ten links in D-H convention (with usual parameters [ $A_i, D_i, \alpha_i, \theta_i$]).
But my task currently requires the inversion of some ...
4
votes
1answer
36 views
Velocity description in Screw Motion Theory
As described in the book Modern Robotics by Frank C. Park the velocity of a reference frame can be described as :
$$V_s = J_s(\theta)\dot{\theta}$$
$$V_b = J_b(\theta)\dot{\theta}$$
However in the ...
4
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1answer
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How to make one robot follow the other in parallel formation
This is quite a basic question. I'm practising robot programming with VRep. I have 2 K3 robots in the scene. One robot follows a predefined path. I want the second robot to move "in parallel" with the ...
4
votes
1answer
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Defining frames for 5DOF robotics arm
For examples if i have this robotic arm:
Example, for the base rotation (5th DOF in the clip at 0:58), we know that the Z axis for that joint will be the same as the Z axis for the base frame{0}, but ...
4
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0answers
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Any free or paid software for graphical drawing of Robotics Kinematic Scheme? [closed]
I have been searching for days looking for a dedicated software for easily draw kinematic diagrams of robotics like this:
I came by this software but it is a bit hard to grasp. Is there any GUI based ...
3
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3answers
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Forward kinematic computing the transformation matrix
I am the moment trying to compute the transformation matrix for robot arm, that is made of 2 joints (serial robot arm), with which I am having some issues. L = 3, L1 = L2 = 2, and q = ($q_1$,$q_2$,$...
