16
votes
Position Control vs Velocity Control vs Torque Control
I'm going to take a slightly different tack to Chuck.
What is Torque Control?
For me, Torque Control is about performing a move with an explicitly defined torque, rather considering torque just the ...
- 4,088
15
votes
Position Control vs Velocity Control vs Torque Control
Torque is analogous to force for rotating systems, in that:
$$
F = m a \\
\tau = I \alpha \\
$$
Where $\alpha$ is angular acceleration and $I$ is moment of inertia. $m$ and $a$ are mass and linear ...
- 14.6k
13
votes
What's the difference between a holonomic and a nonholonomic system?
For a nonholonomic system, you can at best determine a differential relationship between state and inputs. You cannot determine a closed-form geometric relationship. This means that the history of ...
- 4,326
10
votes
Optimal location of the center of mass for an inverted pendulum
The two views are not contradictory; they apply to two different situations, which you are treating as a single one.
Your personal experience about having a low center of mass applies to situations ...
- 10.8k
9
votes
Accepted
Proportional controller error doesn't approach zero
If you're only using proportional force, then at some point it will be balanced by the force of gravity -- your error will converge on that balance, not zero.
To compensate for the mass of the arm, ...
- 10.8k
8
votes
Accepted
How do quadcopters turn left and right?
This is video is from an Edx course on Autonomous Quadcopters...It is 10 minutes and goes over the "Flying Principle" of quadrotors.
But basically what you are missing is the reactions. The famous ...
- 328
8
votes
Accepted
Can a state matrix have a row of zeros?
Yes, a state matrix with zero rows and/or columns makes sense and is viable. It typically signify pure integrators in the system. In the example you give,
$$
\dot{v} = -\frac{b}{m} v +\frac{1}{m} u
...
- 375
7
votes
Proportional controller error doesn't approach zero
I would like to use P (proportional) controller for now.
Just a proportional controller will never make your error stay at 0. Your system is not damped and a proportional controller acts like an ...
- 342
7
votes
Accepted
Damping vs Friction
A force balance equation is typically written as:
$$
m\ddot{x} + b\dot{x} + k{x} = F \\
$$
where $F$ is an applied force, $x$ is position, $\dot{x}$ is velocity (first derivative of position), and $\...
- 14.6k
7
votes
Accepted
What does SE mean in robotics literature?
In that context, SE means "Special Euclidean" group, e.g. SE(3)* which is shorthand for "the special Euclidean group of rigid body displacements in three-dimensions".
*Planning ...
- 1,009
6
votes
What's the difference between a holonomic and a nonholonomic system?
A holonomic constraint is a constraint on configuration: it says there are places you cannot go. That is a reduction in freedoms. That’s (usually) bad.
A nonholonomic constraint is a constraint on ...
- 516
6
votes
Accepted
D(q) Inertia Matrix and the Jacobian Matrix
I think this is a matter of notations.
In the given formula for $D(q)$, the matrices $J_{vi}$ and $J_{\omega i}$ are not simply the direct extraction of columns of the Jacobian of the system.
$J_i$ ...
- 1,789
5
votes
Accepted
Why do series elastic actuators have more accurate and stable force control?
Series elastic actuators tend to have more stable force control because the spring filters out the high-frequency motion of the mechanism. A low frequency in the system dynamics means that you can use ...
- 4,205
5
votes
Mathematical modelling of system dynamic on matlab
the Simulink diagram is straightforward. It is a matter of connecting blocks. For the differential equations provided in your post, the simulink is
For $u_1$ and $u_2$, I've chosen the unit step. ...
- 2,310
5
votes
What's the diffrence between $H_2$ and $H_\infty$ control?
In short answer:
yes
Kalman filter is a special case of an $H_2$ observer
Yes
Yes ... LQG is just Kalman filter + LQR controller, which are both special cases of $H_2$
Depends on the use case. $H_2$ ...
- 2,679
5
votes
Accepted
Confusion about Jacobians stemming from class notes
Short answer
Robot Dynamics and Control by Spong et al. (especially Chapter 5) can definitely help you on this matter.
Long answer
First of all, you are partially correct about a Jacobian. It is ...
- 1,789
5
votes
Can workspace of a manipulator change after considering its dynamics?
The workspace of a manipulator is strictly determined by its kinematics. Since kinematics only consider the geometry of motion, without regard to forces and torques needed to accomplish tasks, you ...
- 4,326
5
votes
Accepted
Cartesian Impedance control Damping Design (Double Diagonalization)
A hint towards what the answer is given in the paper. Namely, one can use the generalized eigenvalue decomposition, which in this case can be formulated as finding eigenvalues $\lambda \in \mathbb{R}$ ...
- 921
4
votes
What is the difference between screw and wrench in rigid body motion?
I will try to make it as simple as possible. Imagine you have a SCREW, when you WRENCH it, it TWIST forward or backward.
From your wiki link
The components of the screw define the Plücker ...
- 43
4
votes
Why I'm getting very long terms in the inertia matrix (or dynamics model) of the robot using matlab script?
You can use the 'simplify' command , e.g : a=simplify(A*B) .This command is calculating some trigonometric functions thus making your expression shorter .
- 41
4
votes
Proportional controller error doesn't approach zero
Controllers type
A more mathematical approach to the error.
Suppose you have a close loop system like above. The equation is:
$\hspace{2.5em}$ $Y(s) = \frac{G(s)C(s)}{1+G(s)C(s)} R(s)$
The error ...
- 143
4
votes
Damping vs Friction
Friction would be your standard "sliding friction", and exerts a force opposing the motion, proportional to the load (or the normal-force of the load, when talking about your classic sliding), but ...
- 321
4
votes
Position Control vs Velocity Control vs Torque Control
I think Mark Booth's answer was best. Talked about the applicational differences between the modes, without getting into theory or detracting from the original question.
If I can expand a little ...
- 41
4
votes
Dynamic torque simulation for a 6 DOF robotic arm
The dynamics of robotic arms are fairly complex, especially when there are more than three joints to consider. The problem is that the movement of each joint moves all the links beyond it, which can ...
- 218
4
votes
What does SE mean in robotics literature?
It is a mathematical concept call the "Special Euclidean" group. Roughly, it is a combination of a rotation and translation. You'll also frequently see SO3, which is the special orthogonal group which ...
- 2,679
4
votes
"modern contact dynamics" - Why are spring-damper contact models not being used anymore for dynamic simulations in robotics?
The author appears to be writting in a self promotional style, where the details listed about other work are simplified or ignored so that their claim, that their approach is better, can be ...
- 4,205
4
votes
Accepted
Why using screws instead of homogeneous transforms in kinematics and dynamics?
About why screw axes:
According to Kevin Lynch in his video of Twists, "just like the time-derivative of a rotation matrix is not equivalent to the angular velocity, the time-derivative of a ...
- 146
4
votes
Why we want to write all linear system into form of first order differential equations?
I will use Mr. Richard Feynman's quote to answer your first question:
Finally, we make some remarks on why linear systems are so important.
The answer is simple: because we can solve them!
Yes. ...
- 2,310
4
votes
Accepted
Finding Mass/Inertia Matrix of a robot
The inverse dynamics of a robot is given by the relationship
$\tau = D^{-1}(q, \dot{q}, \ddot{q})$
where $\tau \in \mathbb{R}^N$ is a vector of the required torque per joint and $q \in \mathbb{R}^N$...
- 1,522
4
votes
Accepted
Velocity-Control of a manipulator without a dynamic model
Your intuition is partially correct in the sense that you ought to go with position control implemented via velocity commands resorting to a kinematic (not dynamic) model of the manipulator.
This can ...
- 3,490
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