# Tag Info

11

In controls this is known as disturbance rejection. In order to sustain your motion in the presence of high winds you need the controller to be as responsive as possible, and an accelerometer would help. A fast loop rate will also help. You also have to deal with the nonlinearities of thrust, drag, weight, and lift. Depending on the design of your ...

10

Typically, a coordinate frame is placed at the robot center. The x-axis points forward, the y-axis points left, and the z-axis points up. Then, we measure angles with respect to the x-axis. So, a 90 degree angle would mean along the y-axis, as shown, So, "12" corresponds to 0 yaw, or straight forward. "9" corresponds to 90 degree yaw, or along the y-axis....

9

Generally the main factor in positioning sensors is the actual beam width of the sensors themselves. It's usually the case that the longer range the sensor is, the narrower the beam width. So firstly you need to work out the range you are aiming to sense at and pick some sensors that work at that range. Then you've got to decide on how wide an angle span ...

9

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: $$s=\begin{bmatrix} x \\ y \\ \theta \\ \end{bmatrix}$$ For a robot moving in a 2D plane to be holonomic, it must have the ability to change any state ...

8

To expand on thisismyrobot's answer, beam width is indeed important. However, there are a number of other factors, such as the reflectivity of the environment (acoustic "brightness"), transmission frequency, etc. Although it is from 1988, Obstacle Avoidance with Ultrasonic Sensors covers the challenges well - the physics of echo-ranging appear to have ...

6

Re-implementing your solution, I get this: Angle Between Vectors First, you want the angle between points $A$ and $B$ -- not specifically the unit vector. (via Fx Programming): $\theta = math.atan2(B_{x}-A_{x}, B_{y}-A_{y})$ Vehicle Yaw Angle Next (and I suspect this is your problem), you need to subtract the vehicle's yaw angle $\psi$ from your ...

6

Hi and welcome to the wide, ambiguous, sometimes confusing world of research. But seriously, looking at 20 years of papers will sometimes produce these confusions. Let's look at what's going on. In the first reference, what they are saying is: An INS/Gyro is nice, but has an error in it. That error changes (drifts) over time. Therefore, the error in the ...

6

I implemented something like this in College: https://github.com/Auburn-Automow/au_automow_common/tree/master/automow_planning Basically we just passed the vertices of the boustrophedon path as goals to move_base. Here's a video of a bag file being played back: https://www.youtube.com/watch?v=R7nLgYquECg Here's the class paper we did for the planner: ...

5

Generally, for indoor flight, commercial quadcopters do not measure position. Instead, they measure the change in position so as to prevent the quadrotor from moving when it should not. So while accelerometers are not great for maintaining an estimate of the quadrotors position they can be used to stabilize the system, i.e. to determine what commands needed ...

5

Increasing the sampling frequency of the sensor doesn't improve it's accuracy or precision. That is a feature of the sensor which you usually cannot change. If you try to estimate your position by integrating accelerations alone, you definitely will accumulate error over time, because every sensor is noisy. If you want to use the accelerometers to determine ...

5

I'll assume you're talking about a 3D vector here. Can you just generalize normalize() like that? Is it that common (i've never seen it so if it is, then news to me). Otherwise, obvious compass wrap issues apply to each of the X and Y components. Why not call them roll and/or pitch and/or yaw? (mixing 3D and 2D nomenclature confuses the question). My 2D ...

5

I did a little step-by-step tutorial with images, but if my other answer regarding aligning frames didn't work well for you, or the definition of "Front Plane" or "Top Plane" is confusing in Solidworks (spoiler: it is), then consider making your own axes. From the assembly tab, go to reference geometry -> axis, then select the assembly planes to make an ...

5

The most important point is the scale. If you do monocular SLAM, your map will only be accurate up to scale so that you e.g. cannot compute the length of the travelled path in meters. The scale between your map and the world is not even constant over time so that if you come back to your starting point, it's going to be difficult to match the beginning and ...

4

You can use the INS / GPS as updates to the output of your first EKF. This is, in fact, not chaining, but simply conditioning the estimate based on the added information from the INS / GPS. Suppose we have the following functions: $x_{t+1|t}$, $P_{t+1|t}$ = EKF_PREDICT($x_t$, $P_t$, $u_t$), for inputs as state $x$, covariance $P$, and control inputs (...

4

Think in terms of your control loop speed. A typical fast control loop speed is 1kHz. Some robots use a faster rate, some slower. Usually your control loop speed is higher than you really need it to be. So each control frame lasts for 1000us. Within this control frame you need to: Sample your sensors Perform the control calculations Send the new outputs to ...

4

You need to do a bit of Calculus. First a note about your input parameters: Actually acceleration depends on Force and mass. You don't specify what units your max. thrust is in so let's assume your max. thrust is your acceleration. We can do the same thing with your max. torque then and assume that it is also your acceleration (angular) and forget about ...

4

Cartesians Robot use sensors. All robot need sensors. Sometime they are external (camera looking at the robot), sometime they are on the robot (IMU). Basically what you're asking is : How can an animal without any way to sense the world move from an exact point to another ? Well, it can't. Why do you wish not to use sensors ? There are very cheap ones ...

4

You have to know your initial heading, let's call it $\theta_0$. So you start at some position, $p_{start}$, and you're trying to get to some end position, $p_{end}$. Assume starting position and ending positions are given by: $$p_{start} = <x_0 , y_0> \\ p_{end} = <x_1 , y_1> \\$$ Those positions are absolute, but you are trying to get from ...

4

Apparently a magnetometer is useless in indoor environments like man made buildings. I cite from this paper Multi-Magnetometer Based Perturbation Mitigation for Indoor Orientation Estimation Nevertheless, the success of these sensors for orientation estimation is conditioned by their capacity to sense Earth’s magnetic field in environments full of ...

4

Precise vehicle location is not a very useful piece of data in autonomous driving so I would not expect to see many products focusing on it. Path planning and following for cars is a solved problem. If you have a static environment where nothing changes, any good position sensing will let you control a vehicle to follow a path. However, there are very few ...

4

If you are able to sense obstacles with a sensor pattern that is circular (eg laser scanner, contact sensors on a circular body, etc), and you can rotate the robot pose without translation, then you can satisfy the assumptions of the Bug algorithm. If you use a point model for your robot in the map, then you grow the obstacles by the radius of your robot. ...

4

It is usually a combination of 2 different pieces software. Generally a higher level software which implements most of your autonomy, advanced navigation algorithms, and a lower level software which deals with interfacing the motors, a simple state estimator, and accepts waypoint commands. Most common is ROS for the higher level software, and a PX4 for lower ...

3

Is ... GPS data ... fused with the accelerometer data? Yes, many aircraft use sensor-fusion techniques so both GPS data and accelerometer data effect the estimated X, Y, Z position. Often they use a Kalman filter to do the data fusion. ( kalman-filter; Why do I need a Kalman filter? ) Measuring X,Y,Z accurately for each photo is important for assembling ...

3

amcl receives the integrated odometry information over the tf topic between base_link and odom and then computes the correction between the odom frame and the map frame as the odometry accumulates drift. Frames are defined in REP 105

3

Okay, so most(if not all) transational drift robots or meltys use an acceleorometer to indicate the heading of the robot. What this acceleorometer does is calculates the rate of rotation based on G-forces around a given radius. The data that is accumulated from the accelerometer is then used to light up an LED once per rotation - giving and indication of the ...

3

The solution is actually not quite linear. There are at least two cases: 1) The fastest solution does not require maximum turning at all times. 2) The fastest solution does require maximum turning at all times. For an example of 1), consider the goal is straight ahead of the drone. For an example of 2), consider the goal is very close, but straight behind ...

3

This representative sample of what's out there may give you some idea of what's out there at various price points: Unfortunately, you're talking several thousand dollars for an outdoor unit with 10's to 100's of meter range (as of March 2015). The chart is from a blog article I wrote on the topic. Google used a \$70-80K unit on their original vehicles. The ...

3

First you need to understand the math, then you need to know how to program it. So let's begin with the math. This is high school material, so I go through it quickly. The math Any two points you take on a circle make a line (of course). The line bisector of that line passes through the center of the circle. If you have two of such line bisectors that are ...

3

Here are a few ideas: Buy 0.050" spacing prototyping board. For example, here are some possible boards that could work on Digi-Key. Use a PCB prototyping service and fabricate the board you're looking for; this would have the advantage that you could add other circuits to the panel that you may need for your project. Remove the boards from the wheel modules ...

3

Your intuition is mostly correct. Returning to where you started and re-observing landmarks you mapped earlier is called closing the loop in the SLAM literature. As you mentioned, your uncertainty will grow as the errors accumulate before you return to the start, if you don't have an absolute sensor. An absolute sensor is one that directly measures your ...

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