5
votes
Accepted
What to do when position control with trajectories is interrupted?
If you have no possibility to detect the obstacle apriori (e.g. with cameras, vicinity sensors...) If you already hit an obstacle and your position error increases, you can only detect the problem by ...
- 1,657
5
votes
Accepted
What is torque bandwidth in actuated joints and how does it affect the control systems?
The torque bandwidth is typically referring to the maximum frequency of motion at which the actuator can provide that torque. So your actuator can provide a peak torque of 100 Nm, as in it can hold up ...
- 1,377
3
votes
Velocity description in Screw Motion Theory
The body velocity $V_{b}$ is the velocity of the frame with respect to the world, as seen from the frame's perspective. Its rotational component $\omega_{b}$ contains the rotation rates around the ...
- 619
3
votes
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Gazebo joint->SetForce() call applies forces to the whole model. How to circumvent that?
As you mentioned in your update,
One of the possibilities is to simply add mass to the chassis
This works because, at some point, you need a reaction force. An applied force (or torque) at any ...
- 16k
3
votes
What to do when position control with trajectories is interrupted?
In 1981 Raibert and Craig wrote a paper Hybrid Position/Force Control of Manipulators which was published in the June 1981 issue of Journal of Dynamic Systems, Measurement, and Control. It was ...
- 4,386
3
votes
Can we simulate a actuator with a very strong torque with a PID controller
What you're asking for cannot be accomplished with a PID controller. As I understand your question, you want to be able to choose PID gains that would always produce a "good" trajectory, ...
- 218
3
votes
What is the meaning of joint space and configuration space and task space?
All "spaces" are used to define the current state of the robot, but with differences. The state of the robot is a point (also known as a configuration or pose) in a space. Please note that ...
- 6,652
3
votes
Accepted
Why aren't more bipedal (or even quadruped) robots made with joints/articulations similar with those found on atmospheric deep dive suits?
Why aren't they, you ask? Typically, it would be a worse design.
Atmospheric deep dive suits, and, for that matter, space suits, are designed to maintain constant internal volume. Otherwise the ...
- 1,271
2
votes
How can the inverse kinematics problem be solved?
There are two broad approaches:
analytic solutions, given an end-effector pose, directly compute the joint coordinates. In general the solution is not unique, so you can compute a set of possible ...
- 1,692
2
votes
Joint Space Singularities
Assuming it is a robot with a serial structure:
You will always be able to move every joint of the robot in any pose.
However the singularitites still exist, and you can end up in a singular pose, ...
- 6,652
2
votes
Accepted
Lateral load on a servo motor
The second design will put more stress on the servos over time, so there are indeed real structural reasons for the design.
However, it also looks like the second design is more of a prototype ...
- 11k
2
votes
Accepted
Reference request: Path accuracy algorithm in the joint angle space
The forward kinematics of the manipulator will correctly identify the larger displacements of the end effector for small rotations of the proximal joints, as opposed to the smaller displacements of ...
- 4,386
2
votes
how to find maximum force of a robot joint
As I understand, you do not actually need the force, you just want that your simulation to behave somewhat realistically.
Instead of complicating everything with dynamics, I suggest you remain at ...
- 6,652
2
votes
How can I attach an arm to a double-flat drive stepper motor?
You can use a D or Double D shaped shaft collar/coupler. Or obtain a Double D shaped punch, depending on the design of the piece you are attaching to the shaft.
- 4,386
2
votes
What are the differences between wheel and manipulator joint encoders?
Encoders used in wheels and manipulator joints are essentially the same. It is the post-processing pipeline that changes their usage and significance. These encoders basically sense the rotational ...
- 671
2
votes
What is the rectangular-shaped joint in this diagram?
That diagram appears to be taken from the paper Design and development of a Mechanism of Robotic Arm for Lifting (Part 5), by M.H.Ismail et al - which is available to download as a pdf file from ...
- 1,054
2
votes
Accepted
Spherical (Ball) Joint in Robot Model not Working in Gazebo
Answer:
The issue is that <origin>, <mass>, and <inertia> tags must be nested inside a <inertial> element for each of the links, instead of being nested in the <link> tag.
correct:
<...
- 141
2
votes
How to calculate effort/torque values of a joint
The wrench characterizes the forces and torques acting on the respective linkages. Part of this is motor torque, the other forces and torques are loading the mechanical structure (and motors down the ...
- 6,652
2
votes
Accepted
State of the art trajectory for fine precision robots
For very high-precision applications such as finishing, milling by CNC machines, jerk-bounded trajectories (that is, trajectories comprising polynomials of degree 3 of higher) are often used. If you ...
- 1,829
2
votes
Accepted
How does this end effector work?
The actuator has two raceways cut into it.
One is a screw thread, and engages with a rotary screw nut that is turned by a motor. Turning the nut moves the actuator linearly.
The other is a spline ...
- 518
2
votes
How do I decide the minimum number of link lengths and joints my manipulator must have from the configuration space?
If you should consider not just points, but poses (position and orientations). If you can write these as a table, where the columns are the coordinates
...
- 6,652
1
vote
Accepted
My robot keeps getting saved as one cylinder leaving out the bottom cube
I suppose that what you're seeing when you add your robot model to the world is something like this:
That is, only the top part of the robot is visible. The problem is not that the bottom part isn't ...
- 1,353
1
vote
What is the purpose of an empty link without any child elements?
In this particular case, it's probably used as a projection of the robot's root link on the floor. This is often useful for motion planning or SLAM, where the robot's pose is read (or set) as the ...
- 1,353
1
vote
IMU based joint angle measurement
"roll value of the second IMU also increases whenever the first axis rotates" — yep, that's how it always is. For the second joint, obtain the difference in the roll angles from both the IMUs. You're ...
- 323
1
vote
Making a motor controlled joint passive
Depending on the motor type, you may be able to freewheel the motor. With a brushed DC motor this could be achieved with most commercial H-bridges, controlled with fast current decay.
Flyback diodes ...
1
vote
How to determine the direction of X-Axis in Denavit Hartenberg process? [Sketch inside]
The DH method is ambigous. There are multiple solutions which are correct and leat to the same TCP pose.
Try to make a minumum amount of changes in the coordinate systems with the transition. If you ...
- 6,652
1
vote
Accepted
Adding a floating joint to a sphere in urdf
The joint type you've added to the URDF is fixed rather than the desired floating. ...
1
vote
Accepted
Parallel axis theorem to determine the moment of inertia
If the distance between the axes is zero, then there is no change in the inertia for that specific axis.
You can verify your calculations with a CAD software. Most of them (Solid Works, Inventor, ...
- 6,652
1
vote
Can we simulate a actuator with a very strong torque with a PID controller
Industrial robot controllers (and most "real" robot arm controllers) will have a feedforward term to remove the effect of gravity. Often called gravity compensation. You noticed how necessary this is ...
- 4,385
1
vote
Accepted
How modular arm joints work
Like Andy said, a Harmonic drive seems to be the most likely answer. But your final question is very vague. The other option is that it is a direct-drive system (with a clutch to protect the motor), ...
- 378
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