Hot answers tagged

10

Typically, a coordinate frame is placed at the robot center. The x-axis points forward, the y-axis points left, and the z-axis points up. Then, we measure angles with respect to the x-axis. So, a 90 degree angle would mean along the y-axis, as shown, So, "12" corresponds to 0 yaw, or straight forward. "9" corresponds to 90 degree yaw, or along the y-axis....


10

Addressing the shoulder joint, which is rather more complicated than elbows and knees... After this one, the other joints become far simpler to visualize or engineer. Here is how the ball and socket shoulder joint could work: Freedom of movement: Approximately 60 degrees end to end, all around. Less than for humans, but it can be tweaked to around 80 ...


9

Let's look at how a quadrotor flies, then apply that to a trirotor. Let's assume that we want to remain in a stationary hover position. To do that, you need to balance all the forces: thrust from the propellers vs. gravity, and the torques of each motor. Each motor produces both thrust and torque according to the equations: $$ T = K_T\rho n^2 D^4 $$ $$ Q = ...


8

You're trying to implement more PIDs than you have degrees of freedom. In a quadcopter, you have only 4: $(Z, \phi, \theta, \psi)$ i.e. (Altitude, Roll, Pitch, and Yaw). via (http://www.draganfly.com/uav-helicopter/draganflyer-x4/features/stability.php) Interestingly, from a PID perspective you definitely do have desired values for $\phi$ and $\theta$: ...


8

Yes, a state matrix with zero rows and/or columns makes sense and is viable. It typically signify pure integrators in the system. In the example you give, $$ \dot{v} = -\frac{b}{m} v +\frac{1}{m} u $$ where $v$ is the speed, $u$ is the externally applied force, and $bv$ is some viscous damping force. Now if the viscous damping coefficient is zero (no ...


7

If your goal is to experiment, then use the cheapest option possible -- it will give you the freedom to make more mistakes. Carbon fiber would be great if your design is in a fairly final state, but are you 100% assured that you correctly determined all the thicknesses, mounting holes, wiring guides, etc? Are you good enough working with carbon fiber to ...


7

As others have said in comments, a screw is probably your best bet. It's mechanically pretty simple to set up, and could be made to look fairly tidy, which is always nice in a home. But the main problem, as always is going to be doing this on the cheap. The cost of the parts soon adds up. Even if your motors are only $15, you still need to buy the lead ...


7

Your mechanism will depend on the type of dispenser you want. Like if its gravity feed or not. I will assume it is, so I make this sketch to give you some idea: The hole size will depend on how many candy you want to dispense at each stroke. (Of course its related to the candy size). The electro-mechanical actuator can be a crankshaft one, a solenoid, a ...


7

The principle lying underneath the sphero robot's design and locomotion is shifting of the centre of mass of the ball and making it unstable which makes the ball roll [1,3,4,5,6]. A controlled and calculated shifting of the centre of mass to the appropriate position can achieve desired trajectories of the ball. Apart from the above said principle, a few ...


6

In short, what you are trying to do is well beyond the capabilities of top robotics research labs. That said, here is a short list of general areas you need to look into: Robotic arm dynamics (to swing the racket) Vision processing to track the shuttle Shuttle dynamics to predict shuttle path (this is not well studying so you would most likely have to ...


6

Given that an homogeneous transformation $T \in SE\left(3\right)$ can be expressed as $$ T= \left( \begin{matrix} \mathbf{R} & \mathbf{p} \\ 0 & 1\end{matrix} \right), $$ where $\mathbf{R} \in \mathbb{R}^{3 \times 3}$ is symmetric and $\mathbf{p} \in \mathbb{R}^{3 \times 1}$, then we seek for the inverse $T^{-1}$, such that: $$ T^{-1}=\left( \begin{...


5

You seem to have 2 separate (but related) problems you are trying to solve at once. Let's break down your conundrum into smaller pieces: How do I communicate commands from a slow system (30Hz) to a fast controller (200Hz), and how do I communicate data being received at 200Hz back to my 30Hz thinktank? How do I control what is happening at 200Hz, when I can ...


5

I would say any application where a large number of communications nodes are required (sensors or actuators) would benefit from being implemented as a system bus (in contrast to point to point links such as UART or Ethernet), due to wiring complexity, determinism and modularity. Any control system requires a high degree of determinism, which high bandwidth ...


5

Robotics is a relatively new field of study. Besides technological problems, there are psychological and even moral issues that need to be resolved. Some examples of these non-technological issues include familiarity with and fear of robots, trusting robots and robot rights. Other issues have to do with popularity. You may be interested in reading this ...


5

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 a weight of 100 N held at a torque arm of 1 m. If you want to swing that weight back and forth you could do it at up to 4 Hz, but no faster without damaging or ...


4

I'm not sure what in the linked question about development tools makes you think that they are not mature. It is true that most of them are proprietary and not open source. But I thought that the tools were quite mature even back when that question was asked three years ago. Today Xilinx, Altera, and Lattice all have freely available development environments ...


4

You need to do a bit of Calculus. First a note about your input parameters: Actually acceleration depends on Force and mass. You don't specify what units your max. thrust is in so let's assume your max. thrust is your acceleration. We can do the same thing with your max. torque then and assume that it is also your acceleration (angular) and forget about ...


4

Defining the state of the quadcopter as $\bf{x} = \left[ \begin{matrix} \mathbf{p} & \mathbf{v} & \mathbf{r} & \mathbf{w} \end{matrix} \right]^T$ where $\mathbf{p}$, $\mathbf{v}$, $\mathbf{r}$, and $\mathbf{w}$ are the position, velocity, angular position, and angular velocity of the quadcopter respectively. A simplified transition model for a ...


4

There are two good search terms that come to mind. The first one is a "candy machine mechansim", or "dispenser mechanism" (e.g. http://www.woodworkingformeremortals.com/2012/10/make-candy-dispenser.html). There are several models of off-the-shelf pet food dispensers and cereal dispensers that use this method. The second term would be a screw conveyor (a.k....


4

A variety of techniques are used for propeller shaft sealing. One of the most common is a "packing gland" or "stuffing box", as in illustration below from a dieselduck.info web page which has details of using such seals. Also see boatus.com, which describes how much leakage to allow, and when to repack. Two or three drops of leakage per minute is ...


4

A frame in that configuration or any other witch holds the props in a square without being unbalanced would work, the reason that most people do it with cross bars is because the FC batteries and ESCs must go somewhere. For your proposed solution you would have to balance all of that equipment around the ring running power and control lines all around ...


4

I think this is a great question. The two basic options are make it yourself or have someone else make it. EDIT: check the bottom for a third option... Make it yourself To make it yourself you need to choose a material and manufacturing process for the part, then acquire the material and skills needed. (Usually people select a process they know how to do ...


4

It really depends on the objects you are sorting, and the flexibility you're looking for as the system is maintained over the years. Using physical methods to sort is very reliable. Many times you can align the parts, such as by using curves, chutes, vibration, and parts feeding mechanisms. Look up vibratory bowl feeders and cap feeders for examples. ...


3

Erik, your wish is my command: "High torque pancake stepper motor" comes to mind. Can you develop one, and a couple of extra's? :) Seriously, you're looking at a combination of technologies and disciplines. Precision positioning of a "High torque pancake stepper motor" might be an acceptable direction, but it'll probably end up simply being the ...


3

The solution is actually not quite linear. There are at least two cases: 1) The fastest solution does not require maximum turning at all times. 2) The fastest solution does require maximum turning at all times. For an example of 1), consider the goal is straight ahead of the drone. For an example of 2), consider the goal is very close, but straight behind ...


3

The mechanical answers above are correct. The inherent stability problems with single large motors are exchanged for dynamic comtrol over 12 dimensions of acceleration, yaw, pitch, roll which can be partially coupled (the translational amd rotational matrix) where one is presented with a simplified diagonal inertial frame to build a dynamic model with. In ...


3

In my personal experience, I hate Google SketchUp. I Recommend that you use CAD Solidworks. Google SketchUp is not meant for gear design. In Solidworks, you are able to create gears however you may and also make it function on a three-dimensional visual on your computer screen. *I personally recommend this to you with great honestly.


3

7 is diameter of propeller in inches and 4.5 is pitch of propeller in inches. Unless mentioned, propeller parameters are mentioned in inches. The Pitch of a propeller is distance covered by the propeller in one full rotation hence measured in inches. This is similar to pitch of a screw.


3

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 rotational velocity back into linear velocity. I don't think the Ftotal calculation is correct because your estimated weight isn't correct. Kg is a unit of mass, ...


3

To answer your questions directly, the X-shape is not the only design that will work. There are many variations of frame design around a number of rotors that can range from 3 to (in some cases) 8. Since it hasn't been mentioned in the other answers, I want to point out that perhaps the biggest reason for the X shape is to keep the weight in the center, ...


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