5
votes
Accepted
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 ...
- 263
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 ...
- 4,386
4
votes
Accepted
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 ...
3
votes
Accepted
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 ...
- 16k
3
votes
Accepted
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 ...
- 217
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 ...
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 ...
- 298
2
votes
Accepted
geometric meaning of rotation matrices related to different frames
Using the notation you have given, the intuitive geometric meaning of rotation matrix multiplication is most clear when the subscript of the first matrix is equal to the superscript of the second (i.e....
- 884
2
votes
Finding a point in a new reference frame <modern robotics>
One of the usage of rotation matrices is to represent the orientation of one frame relative to another. If we would like to represent the orientation of frame {$b$} relative to frame {a}, we need $R^...
- 2,453
2
votes
Accepted
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 ...
- 3,995
2
votes
Accepted
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 ...
- 24.7k
2
votes
Accepted
ROS force vector transformation
If you have robot state publisher that publishes transformations between links/joints. You can use tf package to fetch those transformations.
If you want to ...
- 58
1
vote
Accepted
How to calculate error for inverse kinematics?
First, you don't seem to correctly define pose, homogeneous transformation matrices etc.
A 'pose' is defined by a position and an orientation.
Position is typically represented by [x,y,z]' coordinates ...
- 1,414
1
vote
URDF to SDF Frame of Reference Calculation for Base Joint Fixed vs Floating
I think there is an issue with the URDF-to-SDFormat converter in libsdformat's parser_urdf.cc file since it currently ignores ...
- 306
1
vote
Accepted
Definition of Collision Frame and Inertial Frame in PyBullet or Other Simulation Software
My original answer on this confused linkInertialFramePositions with baseInertialFramePosition, so here is a (hopefully ;) ) more ...
- 884
1
vote
geometric meaning of rotation matrices related to different frames
I believe your question regarding the geometric meaning of rotation matrices to different frames I explain on Medium
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 ...
- 21
1
vote
Accepted
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 ...
- 3,995
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 ...
- 535
1
vote
Accepted
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 ...
- 6,652
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 ...
- 208
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 ...
- 5,312
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:
...
- 189
1
vote
Accepted
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 ...
- 705
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 ...
- 31
1
vote
Accepted
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 ...
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 ...
- 4,385
1
vote
Accepted
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 ...
- 16k
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