30 votes
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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 ...
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11 votes

How do the PID parameters (Kp, Ki, and Kd) affect the heading of a differential driving robot when they are increased individually?

Proportional term: this controls how quickly to turn the steering when the heading is not at the set value. A low P will lead to sluggish steering, reacting only slowly to set heading changes. It may ...
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  • 1,021
10 votes
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How to program a three wheel Omni?

The math involved for controlling a holonomic robot is really not too bad. It is basically just high-school trigonometry and knowing how to set up the problem. First, lets start with the joystick. ...
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  • 5,215
10 votes
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Holonomics Movement vs Holonomics Constraint

You can look at degrees of freedom as if they were the number of variables that you need to use to describe your system. So, for a robot moving in a 2D plane, its state would be represented by: $$ s=\...
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  • 214
7 votes

Do I need to use separate function in PID algorithm to make the bot go LEFT or RIGHT?

No, but you do need to calculate the P/I/D terms correctly. You have: I = I + previous_I; followed by: previous_I = I; ...
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6 votes

Robot never goes straight

Since the open-closed loop issue is already mentioned, I will give a comment to the "I once tried to run a dc-motor without a load". Yes you might damage your motor with this but you can also damage ...
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  • 1,647
6 votes

Is there any robot stability control equation that describes the relation between velocity of the robot and its orientation?

That's not obvious. If I'm in a tank, going 0.5 km/h, I don't need to slow down at all. If I'm in a bobsled going 100km/h and the track banks, I don't need to slow down at all. When you steer, you ...
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5 votes

What is the technical name when robot wheels are aligned to perform spot turn?

Looks like wikipedia calls it Active Four-Wheel Steering. Although, what you're talking about is the left and right side steering opposite of each, whereas Active Four-Wheel Steering in automobile ...
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  • 306
5 votes
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Programming language?

The short answer is, frustratingly, "it depends". Nearly every established language can be used to program one robot platform or another. In my short career as a roboticist I have already used Python,...
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  • 1,266
5 votes
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L293D won't turn motor backwards

The motor driver chip you state you are using, the L293D, is a "quadruple half H driver." This means that, instead of two full H circuits capable of driving a motor forward and reverse, you have four ...
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5 votes

How has the Mars Exploration Rover (MER) has been working for 11 years if it was designed for 90 Sol?

There are 2 main reasons why the MER is still operating long after it's 90 Sol planned lifetime. The first is political, strategic, and can be summarized as 'Under promise, over deliver'. When a PI (...
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  • 4,235
4 votes
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Kinematics of a 4 wheeled differential drive robots

This is an old question but I see it repeated without a real answer. Sticking with a kinematic model only, here's what I would do: The linear velocity of the robot is $\upsilon$ and the angular ...
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4 votes
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What is the technical name when robot wheels are aligned to perform spot turn?

I'm not aware of any technical name for the alignment of the wheels except -- literally -- "steering". Spot turns in theory are no different than any other turn. You simply align the axis of each ...
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4 votes
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12V compressor and air pressure control

Whether a single 3-way, 2-position pneumatic valve (typically with a work port, an input port, and an exhaust port ‒ see page 3 of nationalpneumatic.com's pdf about valves) will suffice depends on ...
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4 votes
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Sensors' field of view in car driving

How fast are you driving the car and are you allowing slip during turning? From this powerpoint, the turning radius is given by: $$ R = \frac{L}{\delta} $$ where $R$ is the turning radius, $L$ is ...
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4 votes

Choosing the state vector for an EKF

In general, I try to obey the following two rules when selecting states: Only use the states necessary for control, and Choose states to be measurable properties, whenever possible. For example, on ...
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4 votes
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Meaning of symbol, 'curly N' in the equation of Linear Gaussian system dynamics

They are modeling the probability as a normal distribution with the given mean and variance.
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  • 4,326
3 votes

Particle filter weight function

A little background. You need to weight each particle by the liklihood of the particle being correct. The probability the particle is correct is given by the probability that it is correct given the ...
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3 votes

How do I determine the heading of a six wheeled robot?

Where your robot will go will depend on where the axes of the wheels intersect. If all the axes are identical, it can turn around any point on the axes, or go straight, perpendicular to the axes. If ...
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3 votes
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Cascading PID DC Motor Position & Velocity Controllers

I have done this myself, controlling the exact position of a brushless DC motor as its velocity ramps up and down. And I did it using a position controller only. Sounds obvious, but it worked ...
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  • 6,337
3 votes
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Reverse lift mechanism

I assume that your 2 channels control forward/backward and left/right. But even if the 2 channels control forward/backward in each wheel (differential-drive style), it should still be possible to do ...
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  • 10.8k
3 votes

What is the technical name when robot wheels are aligned to perform spot turn?

Differential drive Left and right wheels drive clockwise and anticlockwise, at same speed, for robot to rotate with reference to central point between wheels You may want to let front and back pairs ...
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  • 419
3 votes

What is the easiest and efficient way to detect human in close range distance and make the robot follow it?

Following a human can be relatively easy, but it depends on your requirements and your sensors on how easy this is. If you use ROS there are some available packages: people_tracker which uses a ...
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  • 260
3 votes

Is there a way to use a stress-ball-like device as acceleration control interface

Barometers are cheap, easy to use, and very sensitive. They can be placed inside a sealed rubber ball and detect changes in pressure. See for example these sensors: www.takktile.com. (The makers of ...
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  • 5,215
3 votes
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How to find kinematics of differential drive caster robot?

Kinematics of mobile robots For the figure on the left: I = Inertial frame; R = Robot frame; S = Steering frame; W = Wheel frame; $\beta$ = Steering angle; For the figure on the right: L = ...
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3 votes

Multi-Rate Sensor Fusion using EKF

Part 1. Use one or the other. Often odometery is used instead of kinematics or dynamics for prediction, at least in my work. Part 2. This is handled by the construction of the measurement equation ...
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3 votes

Plotting location using wheel encoder data

A few things: I took a look at your data set. Did you make sure you used the time column correctly? The first entry is "1429481388546050050" without the decimal. To make it in seconds, it should be ...
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  • 950
3 votes

Self balancing robot control system strategies

I can recommend an alternative which has worked for me quite well. I derived the dynamical model of a inverted pendulum, then linearised it around the stable operating point. With this simplified ...
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  • 71
3 votes
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TWIP robot - DC gearmotor speed/Encoders

:EDIT: Let me put some numbers on this. Let's say you want to get from any angle to vertical in half a second. Say for now (more on this unrealistic scenario later) that you want to get from "...
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3 votes
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How to increase the traction of tyres/wheels

Two seemingly contradictory approaches come to mind. One is to increase the friction between the wheels and the track. You can do this by coating the tires with a soft material, such as a gasket or ...
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