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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 ...
TobiasK's user avatar
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5 votes
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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 ...
Brian Lynch's user avatar
  • 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 ...
RLH's user avatar
  • 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 ...
Chuck's user avatar
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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 ...
SteveO's user avatar
  • 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, ...
BarbalatsDilemma's user avatar
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 ...
50k4's user avatar
  • 6,652
3 votes
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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 ...
r-bryan's user avatar
  • 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 ...
Peter Corke's user avatar
  • 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, ...
50k4's user avatar
  • 6,652
2 votes
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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 ...
Ian's user avatar
  • 11k
2 votes
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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 ...
SteveO's user avatar
  • 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 ...
50k4's user avatar
  • 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.
SteveO's user avatar
  • 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 ...
Akshay Kumar's user avatar
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 ...
sempaiscuba's user avatar
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2 votes
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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: <...
jstm's user avatar
  • 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 ...
50k4's user avatar
  • 6,652
2 votes
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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 ...
Petch Puttichai's user avatar
2 votes
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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 ...
jsotola's user avatar
  • 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 ...
50k4's user avatar
  • 6,652
1 vote
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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 ...
xperroni's user avatar
  • 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 ...
xperroni's user avatar
  • 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 ...
abhishek47's user avatar
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 ...
Alex Smith's user avatar
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 ...
50k4's user avatar
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1 vote
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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. ...
IanTheEngineer's user avatar
1 vote
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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, ...
50k4's user avatar
  • 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 ...
hauptmech's user avatar
  • 4,385
1 vote
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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), ...
MechanicalMan's user avatar

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