Hot answers tagged

30 votes
Accepted

Robot never goes straight

I'm posting this as an answer because it is the answer. You can't. As @BendingUnit22 mentions, you are attempting "open loop" control. Noise and variations will mean that your robot will never ...
user avatar
  • 14.7k
17 votes
Accepted

ROS: Best practices?

Very short answer: 2 Sensors Regarding whether reading from sensors all in one node or each separately, you should ask yourself this question: Are the sensors meaningless without the other? This ...
user avatar
  • 3,210
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 ...
user avatar
  • 4,098
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 ...
user avatar
  • 14.7k
13 votes

What's the difference between feedback and feedforward control?

In the simple models and block diagrams of control systems you will find in basic textbooks, they will show you a single diagram with a feedback section which uses measurements of the target parameter ...
user avatar
  • 4,235
11 votes
Accepted

Quadcopter PID Algorithm

The glaring issue I see at the moment is that you are forcing polarity on the I and D terms. In general, you are using a lot of sign checks, sign assignments, and conditional programming. None of that ...
user avatar
  • 14.7k
11 votes
Accepted

Control VS artificial intelligence?

In robotics, it all boils down to making the hardware(in essence, the actuator) perform the desired action. The basics of control systems tell us that the transfer function decides the relationship ...
user avatar
10 votes
Accepted

How can we use the accelerometer for altitude estimation?

The barometer carried on the pixhawk has an altitude resolution of 10 cm. If that isn't enough, you could write a kalman filter that uses the accelerometer data in the prediction step and the ...
user avatar
  • 1,825
10 votes
Accepted

How to create a Industrial Robotic arm controller?

Industrial robots (e.g. Kuka, ABB, Fanuc) use a control cabinet which has the following main components: Drive amplifiers (controllers): The drive amplifiers are responsible for the closed loop ...
user avatar
  • 6,437
10 votes
Accepted

What is the terminology used to describe control without measurement?

In control theory, we refer to this as "open-loop control", which emphasizes the lack of a feedback loop. The wikipedia article has several examples of open-loop control.
user avatar
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, ...
user avatar
  • 10.8k
9 votes
Accepted

How to tune the PID parameters using Fuzzy Logic?

The paper Controlling of Quadrotor UAV Using a Fuzzy System for Tuning the PID Gains in Hovering Mode by E. Abbasi, M. J. Mahjoob explains how to tune PID gains with fuzzy logic. You can find many ...
user avatar
  • 1,104
9 votes

What is the technology used for no-resistance robot arms?

It's called compliance. Gravity compensation by itself is not enough to achieve this, as well it is not mandatory. For example, if reducers with high reduction ratios are used, robot arm will be very ...
user avatar
  • 241
9 votes
Accepted

Multiple control loops with overlapping effects

Typically with a multiple input, multiple output (MIMO) system, a control engineer uses a state feedback controller. This style of controller leverages a state-space model of the system and generally ...
user avatar
  • 14.7k
9 votes
Accepted

How do I determine the required encoder resolution for a control system?

First I would question your math that got you to the 12b sensor. If you have a $dy$ of 1 mm over an arm that is $r = 1$ m long, then $\sin(\theta) = dy/r \rightarrow \theta = \mbox{asin}(dy/r)$. If ...
user avatar
  • 14.7k
9 votes
Accepted

How to approach any advanced control problem in robotics

Models. If you want to get good at control engineering, get good at modeling. If you want to impress a controls professor, get good at modeling. Models are how you're going to do 90 percent of your ...
user avatar
  • 14.7k
8 votes

What is $\alpha \sin(\theta) + \beta \frac{d \theta}{d t}$ in the inverted pendulum problem?

The function $f$ comes from the equation of motion for the inverted pendulum problem (inverted pendulum alone, not including the motion of the wheeled platform). If you consider your figure but ignore ...
user avatar
  • 1,357
8 votes

Using genetic algorithm for tuning controllers

Genetic algorithms are a machine learning technique to remove the need for a user to 'fine tune' a system, and instead allow a computer to figure out how to tune the system. The benefits of this ...
user avatar
  • 81
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 ...
user avatar
  • 375
8 votes
Accepted

Impedance Control vs Position Control

In classical position control, the feedback controller only cares about the position error and is tuned to minimize it. This is done by using very high gains, i.e. if there is even a small position ...
user avatar
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 ...
user avatar
7 votes
Accepted

Is the geometric inverse problem's solution "continuous" for a redundant robot?

I don't know if there is a formal proof to this, but in general, no the set of all possible joint configurations that correspond to a particular end-effector pose is not continuous. I think of the ...
user avatar
  • 5,215
7 votes

What is the learning (control) algorithm inside Cubli?

You should start by reading their academic papers: M. Muehlebach, G. Mohanarajah, and R. D'Andrea, Nonlinear Analysis and Control of a Reaction Wheel-based 3D Inverted Pendulum, in Proc. Conference ...
user avatar
  • 5,215
7 votes

Explanation of Quadcopter Dynamics, Components and Control

A couple things, the first is that the controller does not really care what the "real" values are. Everything is relative, if the controller sees that it is sinking it will increase the thrust until ...
user avatar
  • 1,909
7 votes
Accepted

PID control: zero out integral on error sign change?

Generally, in a well-tuned PID, most of the job is done by the P term, which is responsible for driving PV to SP. Then, D and I serve as corrections: the D term regulates the profile as of how we ...
user avatar
7 votes

Control VS artificial intelligence?

I think, it is easier to explain these areas in terms of guidance, navigation and control layers for an autonomous robot. Let's stay an autonomous robot is commanded to reach a desired goal position ...
user avatar
  • 357
7 votes

Motion Planning vs. Control

There is a saying in software engineering which states that your company structure is reflected in your software architecture (I cannot recall the exact phrase). This is true for a robot control ...
user avatar
  • 6,437
7 votes
Accepted

Cartesian Velocity Control between Two 3D Poses

You essentially want to find the time derivative of a linear interpolation between two rotations. The easiest way to obtain this would probably to convert the rotation matrix between the two ...
user avatar
  • 931
6 votes

Why does a ID controller not exist?

You almost never see ID controllers because they generally don't do anything useful. Here is what they can do: 1) The D part will respond to changes in the system. It will try to correct and move the ...
user avatar
  • 2,689

Only top scored, non community-wiki answers of a minimum length are eligible