13 votes
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Hand Eye Calibration

After solving the problem, I created a keynote presentation explaining many details about hand eye calibration for those that are interested. Practical code and instructions to calibrate your robot ...
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9 votes

What is the technology used for no-resistance robot arms?

It's called compliance. Gravity compensation by itself is not enough to achieve this, as well it is not mandatory. For example, if reducers with high reduction ratios are used, robot arm will be very ...
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  • 241
9 votes
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How to create a Industrial Robotic arm controller?

Industrial robots (e.g. Kuka, ABB, Fanuc) use a control cabinet which has the following main components: Drive amplifiers (controllers): The drive amplifiers are responsible for the closed loop ...
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  • 6,322
8 votes
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Designing a 5 bar linkage robot: Plot Clock

Both the forward kinematics and inverse kinematics aren't too difficult, but always a little tricky for parallel manipulators like this one. Consider the configuration in this diagram. The forward ...
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  • 1,357
8 votes

Why don't cheap toy robotic arms move smoothly?

The reason the robotic arm that you linked to does not move smoothly is that the commands given to it are not smooth. That type of actuator does not have any internal logic to generate a smooth motion ...
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  • 4,205
8 votes
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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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7 votes
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Is there a way to determine which degrees of freedom are lost in a robot at a singularity position by looking at the jacobian?

Not by merely looking at Jacobian but by looking at the Singular Value Decomposition of the Jacobian, one can see the degrees of freedom that are lost, if lost. Of course it technically somehow turns ...
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7 votes

How high of a gear ratio can a motor have?

Your calculation of about 80 N⋅m torque for lifting 8 kg with a 1 m lever arm is ok; more precisely, the number is 8 kg ⋅ 9.81 m/s² ⋅ 1 m = 78.48 N⋅m. As mentioned in other answers, you will need to ...
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7 votes
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Why do we generally prefer DH parameters over other kinematic representations of robot arms?

I have been doing a lot of reading up on kinematic calibration and here is what I found: From [1]: A kinematic model should meet three basic requirements for kinematic-parameter identification: ...
7 votes
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velocity of the end-effector

In velocity kinematic, you can establish a relationship between the velocity of the end-effector and the joint velocities, $$ \begin{align} x_{2}(t) &= a_{1} \cos\theta_{1}(t) + a_{2} \cos(\...
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7 votes
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Damping vs Friction

A force balance equation is typically written as: $$ m\ddot{x} + b\dot{x} + k{x} = F \\ $$ where $F$ is an applied force, $x$ is position, $\dot{x}$ is velocity (first derivative of position), and $\...
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7 votes
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Harmonic drives in hobby projects

The core reason for choosing harmonic drives is desire for zero backlash. Moreover, regarding mass and size, they become more beneficial for higher gear ratios as their size and mass do not scale for ...
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7 votes
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What are these mechanical parts attached to robot arm structures, seen on larger robots?

The "pump-looking" things are either hydraulic cylinders, or mechanical dampers if the robot is electrically driven. EDIT: I'll accept @50k4's identification as hydraulic springs. In the "what's ...
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  • 4,326
7 votes
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Using brushless motors for very high torque

Your expectations are rather aggressive for a DC motor. First - 40Nm (350in-lbs) is A LOT of torque! Ex: A max rated torque for 1/4-20 bolt is only 75 in-lb (8.5Nm). Second - The mechanical power ...
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6 votes
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inverse kinematics for 6 jointed robots

I would recommend changing the naming convention since it is a bit misleading. In robotics the world Coordinate system (CS) is usually your fixed, absolute coordinate system. Lets call the ...
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  • 6,322
6 votes

Computing the Jacobian Matrix -- chain rule?

Writing the equations by hand and deriving them is certainly the best way to understand what is happening "in the background". Generating the equations and deriving them using a syombolics engine, ...
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6 votes

What are some ways to estimate torque/load on a robotic arm joint

Model Based: Low cost solution is always software: Develop a dynamic model which computes the load on the motors based on the motions (e.g. with Recursive Newton Euler Algorithm or Lagrange-Euler ...
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  • 6,322
6 votes

About official robotics system toolbox Matlab and Peter Corke Robotics toolbox matlab

There are very few problems having both toolboxes installed. The biggest gotcha is the function angdiff() which is provided by both toolboxes but defined differently. If you want to stick with ...
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  • 1,497
6 votes
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Extended Kalman Filter in robotics - Worth it?

The Kalman filter is an optimal linear filter in the presence of Gaussian noise. It is optimal in the sense that it minimizes the mean-squared error. This means that the covariance of the estimated ...
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6 votes
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D(q) Inertia Matrix and the Jacobian Matrix

I think this is a matter of notations. In the given formula for $D(q)$, the matrices $J_{vi}$ and $J_{\omega i}$ are not simply the direct extraction of columns of the Jacobian of the system. $J_i$ ...
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6 votes

What is the advantage having seven degrees of freedom in a robotic arm?

I guess you are talking about robot arms with 7 DoF like the LBR IIwa from Kuka. If you have 6 DoF, a given end-effector pose is only reachable in a single configuration of the robot. If you have ...
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  • 1,335
6 votes
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Why with the pseudo-inverse it is possible to invert the Jacobian matrix even in a singular configuration?

The pseudoinverse gives a “least squared error, minimum-norm” solution: Out of all $\dot{q}$ vectors at your current $q$, the vector $$\dot{q}_{s} = J^{+}(q)\dot{p}_{\text{in}}$$ satisfies two ...
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  • 609
5 votes

jacobian of Abb irb140 robot

Here is the traditional way. I think this is the kinematics of your arm, but am not 100% sure. Here are the DH parameters and transformation matrix: DH Parameters for the anthropomorphic ...
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  • 5,215
5 votes
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Industrial Robotic Arm

2 kgs is not very much, so i would probably consider arms that are slightly less industrial than Kuka, ABB, Fanuc, Denso and the like. However, 1.6m is pretty long and that may be hard to find in non-...
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5 votes
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What type of servos are used in industrial robot arms like Universal Robot UR5?

Universal states that they use brush-less DC motors with harmonic drives on their FAQ here http://cross-automation.com/blog/universal-robots-top-10-faqs Bigger ones like the KUKA KR5 uses AC servo ...
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  • 241
5 votes

Design and construction of universal robotic arm (5kg, 1m)

To answer your questions about the motors/gearing: To lift 5Kg at 1 metre distance - the "shoulder" torque needs to be 500 Kg.cm or about 5000 N.cm. This is far above the torque of most model servos,...
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  • 1,001
5 votes

KUKA Robotics API IDE

If it's your first time, better off try with a simulator to check that your program doesn't break the robot's constraints or security configurations. The most powerful simulator I came across is "V-...
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  • 168
5 votes
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Comparing industrial robot arms

For example, how does price vary with precision, speed, reach and strength? The price vary a lot, from a couple of hundreds of bucks to hundreds of thousands of dollars ( Willow Garage's the one-...
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  • 168
5 votes
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What is the required theory behind building a robotic arm?

There are 2 (or 3, depending on how the planned lifetime of the robot is) thing thats you have to consider. Static load: The motors stall (zero revolution) torques have to be able to hold the weight ...
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5 votes
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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 ...
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