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5 votes
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Confusion in fixing DH frames

The updated image solves the problem. You did not consider the end-effector coordinate frame earlier. Also, the crosses (going into) in the diagrams should be replaced by dots(coming out), because the ...
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4 votes
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Quadcopter frame design

A frame in that configuration or any other witch holds the props in a square without being unbalanced would work, the reason that most people do it with cross bars is because the FC batteries and ESCs ...
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  • 1,909
4 votes

Confusion in fixing DH frames

Add a coordinate system that matches the previous coordinate system exactly. The last rotary joint will be the parameter for the next-to-last coordinate system, and the link length will be the ...
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  • 4,336
3 votes
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Not understanting the result of a relative transformation

Wow, this is a spectacularly detailed question, so thanks for that, welcome to Robotics, and I'm sorry you're having trouble with this. The trouble that you're having is that you're inverting the ...
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3 votes
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How to rotate a rotation quaternion in the body frame to a rotation quaternion in the world frame?

As pointed out in my earlier comment, this is actually simpler than you may think. Remember, $qs$ and $qr$ are fundamentally different, where the former represents orientation (in reference to the ...
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  • 217
3 votes
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Confusion about order of homogeneous transform multiplication

The mistake is in the second matrix $T_B$ in the last column this column means that you want to transfer the Frame by -2 in it's X direction and by -2 in it's Y direction which in your case is like ...
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3 votes

Quadcopter frame design

To answer your questions directly, the X-shape is not the only design that will work. There are many variations of frame design around a number of rotors that can range from 3 to (in some cases) 8. ...
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  • 10.9k
3 votes

Can you identify the construction material/system used in the pic?

The original T-slot frame system, was developed in the 80's by item GmbH and was quickly developed into the MB Building Kit System, hence I've always known it as item bar. Since then though, there ...
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  • 4,123
3 votes
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How to use the Homogeneous transformation matrix?

A homogeneous transformation matrix $H$ is often used as a matrix to perform transformations from one frame to another frame, expressed in the former frame. The translation vector thus includes [x,y(,...
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3 votes

How to calculate Euler Angles from gyroscope output?

Using the Gyroscope First thing to note is that the gyroscope is reporting angular rates with respect to the sensor. So if the sensor is rotating with some rate, the data it's outputting will be in ...
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3 votes

How to calculate Euler Angles from gyroscope output?

First you need to integrate the output from the gyro to get the actual X, Y and Z angles. angleX = gyroAngleX + gyroInputX angleY = gyroAngleY + gyroInputY ...
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3 votes

How to calculate Euler Angles from gyroscope output?

Look into a complementary filter. It isn't the correct way to go out this but it will give you usable data for attitudes around level. It's also worth mentioning that you will not be able to track yaw....
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  • 1,825
2 votes

Simple vector problem, Weight vector components & sine and cosine of rotation?

You've written your equations as if the weight vector you drew was positive, but then used a negative weight vector in your calculation. If you flipped $W$ around in your drawing you'd get $$ \begin{...
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  • 2,689
2 votes

Assigning parameters in perpendicular axes: D-H is a must

Here are the step that are in my course for using D-H convention: Step 1 Define the z axis of every joint Step 2 Define the origin frame R0 (O0, x0, y0, z0) Step 3 For i in [1, n] (n=number of ...
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  • 166
2 votes
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How to prove expression for relative pose in one frame given relative pose in another frame

Consider the graph below: Starting from the point $2k+1$, we can count the transformations anticlockwise, ending up again at the same point; hence, the aggregate transformation shall be the identity ...
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1 vote
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URDF for a real robot

For a real robot, do I need a URDF as well? It is not necessary to create a URDF for a real robot, but it's highly recommended. Many of the tools are designed to leverage it. For example the ...
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  • 1,174
1 vote

Relative rotation and a new reference frame as the rotation of the first object

I've found the solution. Instead of using intrinsic matrix to angle conversions such as: $yaw = atan2(R_{n_{1}\leftarrow n_{2}}(2,1),R_{n_{1}\leftarrow n_{2}}(1,1))$ $pitch = asin(−R_{n_{1}\leftarrow ...
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  • 21
1 vote
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IMU Change of reference frame

The IMU senses deviations from gravity within the inertial frame. Essentially, IMU measures the specific force $f_b$ given in the base frame as: $$ f_b = R^{bn}(a_{ii}^n-g^n), $$ where $g^n$ is the ...
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1 vote

How to make two frames relative to each other

So it seems like what you want to perform is camera-lidar extrinsic calibration. Seems like you have the translations figured out but not the rotation? You can use one of the already available ...
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1 vote
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Doubt about axis\angle representation

Depending on which matrix you convert to an axis angle representation. If you do it successively, you end up with 3 axis with 3 angles in 3 different frames ($R_0$, $R_1$ and $R_2$). It is trivial ...
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  • 6,447
1 vote

Shifting through Z axis for Calculating Kinematics?

If I understand your question correctly you are asking about what rules there are for assigning coordinate frame axes compatible with DH parameters? There are definitely rules when assigning ...
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1 vote

How to determine the rotation matrix and translation vector of a fixed LiDAR from the sensor frame to an aircraft's vehicle frame?

It sounds to me like you have a system with an unknown parameter that you want to estimate. That is the purview of parameter estimation literature. If this parameter to be estimated is not changing ...
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1 vote

Forward Kinematics Frame Simulation in MATLAB

suppose you calculate the positions of your joints $p_i, i=1\ldots6$ using your homogeneous matrices. The best solution in my experience is to plot the initial configuration e.g. like this: ...
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  • 189
1 vote
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Build (Assembly kits?) the frame of a robot

I mentor several FTC (First Tech Challenge) Robotics Teams. These teams build medium size robots (about 50cm cube starting size). For this size, there are four Building Systems that are the most ...
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1 vote

Problem with Coordinate Transformation

Turns out I was transforming before interpolating the data, and my interpolation function assumed that the two streams of data were taken at the same time stamps. A simple mistake. So I was comparing ...
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  • 31
1 vote
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Assigning parameters in perpendicular axes: D-H is a must

I found this video helpful when learning about the DH method. DH is all about describing the differences between coordinate systems using rotation and translation about/along the X and Z components ...
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1 vote

Assigning parameters in perpendicular axes: D-H is a must

Each parameter is for a simple transform such that when all 4 are combined you go from one frame to the next. It can be helpful to understand each of the 4 simple transforms, and you should do that if ...
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  • 4,245
1 vote
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Gyro measurement to absolute angles

Your first step works because it is implied that your frames are "aligned", meaning that: $$ \theta_{X_0} = 0 \\ \theta_{Y_0} = 0 \\ \theta_{Z_0} = 0 \\ $$ In general (as with any integration!), you ...
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  • 14.9k
1 vote
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composition of rotation matrices

I'm not sure what you mean by: $R_A^C$ must for a 2x2 matrix be defined as $[xa \cdot xb , xa \cdot xb ; ya \cdot yb , ya \cdot yb]$ because I don't know where you are getting the names or ...
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  • 14.9k

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