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Impedance Control vs Position Control

In classical position control, the feedback controller only cares about the position error and is tuned to minimize it. This is done by using very high gains, i.e. if there is even a small position ...
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5 votes
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Is there a rule of thumb for actuator torque overhead?

When selecting an actuator, you need to consider not just the force but also the power. Power = force x speed The faster you need to lift the lever, the more power you'll need. Companies like Maxon ...
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5 votes

Jacobian of a 6DOF arm

Write the forward kinematic equations $$\vec(x) = F\vec(\theta)$$ Taking the partial derivatives of each $\vec (x)$ term with respect to each joint variable $\vec(\theta)$ will give you $J$.
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4 votes

What is the torque/force required to rotate the base of a robot arm?

You need enough torque to overcome friction, and to accelerate the load. If you know the friction torque ($\tau_f$), and the mass moment of inertia along the motor axis ($I$), then the minimum motor ...
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  • 375
4 votes

Impedance Control vs Position Control

You can view impedance control as having more control over the force resulting at the end effector, than in position control. In position control, the goal is to get to the reference position no ...
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3 votes
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Force-torque sensor reading when a robot is stationary

The answer is $\vec{G}$! and also any $\vec{\tau}$ torque caused by it, if the axis connecting the geometrical center of the sensor (assuming it measures torques relative to its geometrical center) to ...
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3 votes
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Understanding Impedance Control

Yes, it is the same, $F$ should be the same as $F_{ext}$. And $F$ comes from a sensor or an estimation, in general from a force sensor. The diagram seems correct and you may have $F$ and $F_{ext}$ ...
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  • 477
3 votes
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Why do we need coriolis and centrifugal forces when it comes to the dynamics of a robotic arm?

But my understanding is that all calculations happen relative to the base frame This is incorrect. Take a look at this two-link arm manipulator. The point ($x_2,y_2$) is obviously expressed in a ...
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3 votes

Is there a rule of thumb for actuator torque overhead?

I always add 100-120% overhead (normally this just means the next bigger unit than exactly what I need) but also this comes with experience, a motor that can just barely lift your load will do so very ...
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3 votes
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Verifying motor selection calculations

I think your Pmotor calculation is correct. The reason for the difference with the CIRC link is in the P=F*v equation they are referring to the linear velocity. Your conversion is converting the ...
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  • 181
3 votes

What are the best ways to transmit force through air efficiently?

Attach a metal square-shaped frame to the first robot, fill the edges with magnets, take your second robot (should have non actuated free moving wheels, like the ones on chairs) and fill it with ...
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3 votes

What are the best ways to transmit force through air efficiently?

There are very limited options for effectively transmitting force across a distance, other than with projectiles of some kind which won't achieve your goals or be allowed under the rules. Based on ...
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3 votes

How to limit large acceleration and jerk from PID controller?

As a general remark, a PID controller can be designed to take into account only constraints occurring at the commanded variable - the end-effector velocity in your case - through the so-called ...
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3 votes
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Will this have more or less lifting strength

Every action has an equal and opposite reaction. Each motor/joint in a linear chain of actuators (snake) needs to be capable of supplying the appropriate reaction forces. This mean that, if you have ...
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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 ...
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  • 6,437
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 ...
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2 votes

Quadrotor dynamics: How is torque created

Each motor generates torque to spin it's fan. As the fan turns, the quadrotor will experience the same torque on the frame, only in the opposite direction. This is similar to a helicopter - the tail ...
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  • 121
2 votes
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Can I measure torque from this motor by only measuring the current?

Can I use current sensing to measure the torque on a wormgear drive? Nope as the worm-gear is not back-driveable by construction. what would be the best path forward? Using an FT sensor mounted at ...
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2 votes
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From a linear force actuator that spans multiple links and joints to the equivalent motor torque

Yes, it is the Jacobian transpose. The Shadmehr site you cited has been reorganized. The "Forces and torques" chapter is linked to by the lab's publication page. The F&T chapter has the ...
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  • 1,136
2 votes

IMU gravity sensing

That is partly possible if you fuse linear acceleration and angular velocity. Estimate the gravity direction from IMU when the robot is stationary. Now you know the gravity direction. Once your ...
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  • 1,375
2 votes

Force sensors output when inclined

This is me trying again with the help of @Chuck's answer. So in the general case, the torque equilibrium equation about A is $\vec{r}_{A \rightarrow COM} \times \vec{W} + \vec{r}_{A \rightarrow B} \...
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1 vote
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Calculate Torques & Forces From Jacobian Matrix

Your computations of the transformation matrices are incorrect. DH transformation matrices are computed as a multiplication of four matrices: rotate about z by $\theta$, translate along z by $d$, ...
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1 vote

Center of Mass of a Box

Let's consider the rectangle to be in a vertical plane, all one single rigid part. The bottom edge is the one resting on the table. Since you specified quasistatic, we only care about the first ...
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1 vote
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Quadrotor dynamics: How is torque created

You're right that each spinning prop creates both a force and a torque. The force is created opposite the direction of the flowing air; each action has an equal and opposite reaction. The same way you ...
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  • 424
1 vote

When not to use pseudoinverse?

Short answer: you can use it. Long answer: Depend on your case, but I have seen many papers where they use the pseudoinverse of the non-square Jacobian matrix. The rectangular Jacobian matrix opens ...
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  • 477
1 vote
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Compute vector of attraction plus repulsion forces in a 2D force field mapping

In the simplest case where targets and obstacles are just points in your space, it's not that difficult to come up with good representations of attractive and repulsive forces. For the sake of ...
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1 vote

Force controller with feedback issues

You can try the following. Set an admittance you want as $ F_e = m_d \ddot q + c_d \dot q$ then, you can solve for $q$ as the velocity reference $q_r = \frac{F_e - m_d \ddot q_r}{c_d}$ and ...
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  • 477
1 vote

Jacobian of a 6DOF arm

By taking the time derivative of the forward kinematics equation, you get a Jacobian equation, as @steveo said in his answer. What is interesting is that by using some properties of rotation matrices, ...
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1 vote

DJI E310 Thrust Coefficient

I found a new paper titled "Quadrotor Parameters Identification and Control System Design" (https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7910684) by the same authors published on the ...
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1 vote

What is the torque/force required to rotate the base of a robot arm?

If you only use Newton's second law, you'll get pretty close in your analysis. $\sum F = m a$ $\sum M = I \alpha$ Using only the first equation and the idea that a torque is a force at a distance ($...
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