Hot answers tagged

96

It has more to do with the rocker bogie suspension than anything else. The system is designed to be used at slow speed of around 10 cm/s, so as to minimize dynamic shocks and consequential damage to the vehicle when surmounting sizable obstacles. In exchange for moving slowly, the rover is able to climb rocks that are double the wheel diameter (normal ...


39

This seems like a softball question but is surprisingly subtle. There are some excellent answers here, but I can add some basic rigor. The reason the rovers move so slow is essentially the need to be cautious with a multi-million-dollar piece of equipment. But there are some other design constraints worth mentioning. Energy is simply the worst bottleneck ...


26

I'm not such an expert in physics, but I can think of a few reasons: Power. The amount of power you need to do a task is inversely proportional to the time it takes to do that task. I think it is well known that doing something faster requires more power, otherwise you could do everything infinitely fast at no cost. Computation Speed. The statement about ...


19

One reason is because of the communications delay between Earth and Mars. The round trip time for signals from Earth to Mars is several minutes, which means that you can't teleoperate the robot in realtime. That means that the robot needs some autonomous obstacle avoidance capability to help prevent it from getting stuck or otherwise in trouble. The ...


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

I think you've taken a good first step; you've divided the problem into a mobile platform (which has uncertainty of position and must navigate) and the arm (which has a fair certainty of position in real time, through encoders). I have looked at papers related to robots architecture [...] but I have yet to find information on how to have the low level ...


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

You're making two mistakes that I can see, both related to the idea of "shrinking" the set of front or back wheels into a single wheel. Rather than thinking of Ackermann steering as (conceptually) a single wheel, imagine expanding the single front wheel of a tricycle into 2 wheels. At first, the tire gets wider, then splits into two tires, then they get ...


7

You have the right idea, just be sure to design for the servo to bear the moment force (aka torque) generated by the load at Y = 4 inches from the joint, not the 2.5 pounds of what you're trying to hold. $\tau = r*F*\sin(\theta)$ Where: r is the displacement (your 4 inch arm) F is the magnitude of the force (2.5 pounds + the gripper) Theta is the angle ...


7

While the answer by freeman01in references a useful presentation (alternative source) on the practical application aspect of your question, it is probably worth answering the specific question in the title too, in terms of first principles. From the Wikipedia Power page: In physics, power is the rate at which energy is transferred, used, or transformed. The ...


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

A good presentation on how to size your motors for a mobile robot is Sizing Electric Motors for Mobile Robotics from the Central Illinois Robotics Club. The general procedure outlined there includes the following steps: Step One: Determine total applied force at worst case Step Two: Calculate power requirement Step Three: Calculate torque and speed ...


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 want to mount the batteries as close to the center of the hub and as close to the center both horizontally and vertically. The closer it is, the less the controller has to work to keep the craft horizontally balanced and the less battery power you will use.


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

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 ...


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 ...


Only top voted, non community-wiki answers of a minimum length are eligible