# Questions tagged [stability]

the state or quality of being stable.

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### Cascaded PID controller implementation

For a project I am building and programming my own flight controller. I have seen the implementation of a single loop PID controller. But after doing some more research I've found that a cascading PID ...
35 views

### How to prove the stability of trajectory tracking with PD control using Lyapunov method?

I'm having a problem to prove the stability of PD control in trajectory tracking. Let say we have a system with double integrator dynamics and we what to minimalize the tracking error $\tilde{x}$. ...
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### How to keep a sensor pointed downward

I am using LIDAR to measure a robot's altitude. The robot's orientation relative to the ground is dynamic; i.e. the XY plane tilts relative to the Z axis. I would like the LIDAR to remain pointed ...
1 vote
107 views

### For a quadcopter do i need to place the gyroscope sensor at the center of mass?

I am trying to build a quadcopter and think it is essential to have its center of mass in the middle. Therefore, I am planning on putting the battery in the center. However, this will cause me to ...
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### Inverted pendulum controller

I had an exam yesterday, and I was asked the following question: Why PID controller is necessary for stabilizing the inverted pendulum on a cart, why not we just use PI or PD? Now I've seen some ...
98 views

### For what step disturbance value the system will become unstable?

I am new to control theory and have difficulties about this question R is the input, Td is the disturbance, C is the output Given that G1=K/(s^2+A*s), where K is the gain and A is a parameter greater ...
40 views

### Grasp stability of a robot

I have read some researches and sources about "grasp stability", but I don't understand what it is exactly. If a grasp is stable, does the hand grasp the object perfectly, accurately or strictly? ...
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### Are examples for jerking robotarms available?

I'm trying to find some youtube videos which are showing robot arms with some malfunction in it. The problem is, that the keyword is unclear. Should i search for “unstable”, “tremble”, “jerking” or “...
1 vote
71 views

### Stability of dynamical system via Lyapunov

I have a dynamical system which has the following form: $\dot x=\mathcal F_1(m_1)x+\mathcal F_2(m_2)x$. My objective is to find the parameters $m_1$ and $m_2$ via LMI (linear matrix inequality) using ...
228 views

### stable altitude quadcopter

I'm currently working on a project to generate a stable altitude and automatic control for a quadcopter I'm using arduino as the flight controller Ultrasonic sensor HC-SR04 MPU-6050 However my ...
1 vote
54 views

### how to make a robot stand after it has fallen [closed]

I have seen the methods to make a bipedal robot stand and walk keeping its center of gravity in stable mode, but how can i make the robot stand if it falls in ground? For example right now i'm using ...
208 views

### Comparison of Balance Bot design

I'm planning to build a Balance Bot and I would like to know which design should I go with. There's a vertical design such as the ArduRoller and on the other hand, there's the typical stacked type of ...
653 views

### Why is it so hard to walk?

At least, on two legs. Asimo, one of the best known humanoid robots, is already capable to walk, although it doesn't seem to do this very stable. And it is a recent result. As far I know, the legs ...
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### PID Gains: Drop in control loop rate, need to retune?

Good Day, I am working on an autonomous quadcopter. May I ask if there is a significant difference if my control loop dropped from 500Hz to 460Hz due to added lines of code that would require ...
791 views

### Using Quaternions to feed a quadcopter PID stabilizing controller to avoid Gimbal lock

I am trying to control my F450 dji quadcopter using a PID controller. From my IMU, I am getting the quaternions, then I convert them to Euler's angles, this is causing me to have the Gimbal lock issue....
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### Locking the yaw direction of a laser pointer

I have a laser pointer on a handle grip and I'm trying to keep the laser pointer's yaw direction, which can rotate at around 10deg/s. So I have the laser pointer on a stepper motor and an ...
• 229
875 views

### Quadcopter: X-Y Velocity PID Controller

Good day, Introduction I am currently working on an autonomous quadcopter project. I have currently implemented a cascaded PID controller consisting of two loops. The inner rate loop takes the ...
700 views

### Quadcopter refuses to fly when the Yaw PID component is added

Good day, I would like to ask why is it that when I add the Yaw control to my PID controller for each motor. The quadcopter refuses to take off or maintain its altitude. I am curently using a ...
120 views

### Fixed Wing UAV: Do inherently unstable systems desire to be stable for all cases when a closed loop control is implemented on them?

As we all know fixed wing vehicles are designed to have inherent instability which is what enables all fixed wing vehicles to fly. However does this apply to all cases? Do inherently unstable ...
1k views

### Quadcopter PID Tuning for Altitude Hold/Position Hold along Z axis

Good day, I have just finished tuning the Pitch and Roll PID's. I did this by setting the throttle such that the quad is weightless. I did the tuning of each axes separately. I would just like to ask ...
1 vote
165 views

### Ultrasonic Sensor's Lag (20Hz) effect on PID contol loop rate (150Hz)

Good day, I would like to ask how is it possible to use an ultrasonic sensor for altitude hold in a quadcopter if the sampling rate of the Ultrasonic sensor (HC-SR04) is only 20Hz before incurring any ...
732 views

### Quadcopter PID: Controller is Saturating

Good day, I am currently creating an autonomous quadcopter using a cascading PID controller specifically a P-PID controller using angle as setpoints for the outer loop and angular velocities for the ...
143 views

### Helicopter Stabilization Algorithm

I've hacked a rc helicopter, and I am able to control it by running a program on my computer. I am interested in writing algorithms that will stabilize the helicopter. For instance, the helicopter is ...
2k views

### PID Control: Integral error does not converge to zero

Good day, I had been recently reading up more on PID controllers and stumbled upon something called integral wind up. I am currently working on an autonomous quadcopter concentrating at the moment on ...
779 views

### Quadcopter PID Controller: Derivative on Measurement / Removing the Derivative Kick

Good day, I am currently implementing a single loop PID controller using angle setpoints as inputs. I was trying out a different approach for the D part of the PID controller. What bought this ...
5k views

### Quadcopter PID Control: Is it possible to stabilize a quadcopter considering only angle measurements?

Good day, I am a student currently working on an autonomous quadcopter project, specifically the stabilization part as of now. I am using a tuned propeller system and I also already considered the ...
157 views

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

I am preparing for an exam in neural networks. As an example for self-organizing maps they showed the inverted pendulum problem where you want to keep the pole vertical: Now the part which I don't ...
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### Humanoid balancing

I'm currently working on Humanoid robot. I've solved the Forward & Inverse Kinematic relations of the robot, and they turn out to be fine. Now I want to move onto Walking. I've seen tons of ...
277 views

### Relation between pole placement and marginal stability?

I'm given an assignment in which I have to design a full state feedback controller by pole placement. The state space system is fully controllable and I've been using Matlab/Simulink to determine the ...
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### Quadcopter stability vs (PID error signal lag and sample time)

The question I am asking is that, what is the effect on stability of increasing or decreasing both the sample time and lagging of error signal to PID. Does it helps in stability or degrade it?
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### PID quaternion contoller

I want to control the attitude(roll, pitch, yaw) of a vehicle capable of pitching and rolling. To do this I have created a quaternion PID controller. First I take the current attitude of the vehicle ...
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### Deciding length of quadcopter arms

How quadcopter's arm length affect stability? As per my view I'll have better control on copter with longer arms but with stresses in arms and also it doesn't affect lift capabilities.
209 views

### How do I decide the size of the time steps between sensing and control actuation?

My Background: My experience is in solid mechanics and FEA. So I have zero experience in robotics/controls. Problem Description I'm developing a control strategy to stabilize a complicated 6-...
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1 vote
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### Building parts, and keeping laser alignment steady

I am building a laser gun for pentathlon targets (also doing one). I would like to know how build a part of the gun and if I can count on a steady laser if it is attached to a motor. The question is ...
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141 views

### On-board monocular odometry for quadcopter stabilization

Has anyone done this with EKF/PID on a small microcontroller? Or know of code snippets to help implementing this?
1 vote
63 views

### How can I know which system is easier to control using PID controller?

I have a inverted inertia wheel pendulum. I suppose that if I have a wheel with larger inertia at its top, the system would be more stable. How can I prove or disprove my conjecture?
226 views

### Step Motor and Bevel gear calibration

I am new to robotics. I want to understand how gears state is preserved as the gears turned to same positions repetitively. I have a bevel gear and a step motor connected to one gear. This gear will ...
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10k views

### How to use quaternions to feed a PID quadcopter stabilization loop?

I'm making a quadcopter. I have set up a PID loop to stabilize it to a given Euler angle (pitch and roll). The problem arises when the roll approaches 90 degrees (45 degrees and up). The values don't ...
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### Quadcopter PID tuning

In continuation of the question I asked here: Quadcopter instability with simple takeoff in autonomous mode ...I'd like to ask a few questions about implementing a basic PID for a quadrotor ...
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### KK2.0 Quad Stablility

I'm running a kk2.0 + 4 20A Multistar ESCs + 4 EMax GF 2215-20 motors + 4 Slow Fly Props After about a foot off the ground, the entire quadcopter starts wobbling like crazy (no auto-level). Any ideas?...
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### Guidance for compensating internal forces on closed loop chain

I'm working on a legged robot and generating joint torques. Basically the robot seems to be statically stable to some extend. The robot goes instable if the center of pressure moves to the border of ...
14k views

### How to stabilize a quadcopter

Today was my quadcopter's first "flight". I'm running megapirate on a Crius AIOP v2 with a Turnigy Talon v2 frame. I only touched the throttle stick on my remote, nothing else. When I felt the ...
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### Is it better to have batteries distributed at the rotors or the center of the multicopter?

I've seen 3 approaches to mounting batteries on a multicopter: All the batteries rigidly mounted near the center of the airframe All the batteries in a bag hanging under the center of the airframe ...
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### What frequency does my quadcopter output-sense-calculate-output update loop need to stay stable?

With a 600 mm (2 foot) motor-to-motor quadcopter, what frequency does my output-sense-calculate-output update loop need to stay stable? I'm estimating a total takeoff weight of very roughly 2 pounds (...
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