I've been trying to figure out why SpaceX has changed to active cooling for its Starship.
When I drew some pictures I started to realize what is possibly a brilliant way of using the active cooling to naturally orient the cooled part of Starship towards the heat of re-entry and later to turn to landing.
Phases:
- Launch: all tanks are fueled, the cooling-side of the ship is empty. So the ship is balanced.
- Orbit: the main tanks are empty, except the methane tank: it still has some fuel left in it.
- Re-entry: the cooling-side of the ship is filled by pumping methane in it. The center of mass moves towards that side. This naturally orients the ship towards the heat of re-entry!
- Turn for landing: when methane is pumped out of the side of the ship, its center of mass moves more to the middle (and downwards) which turns the ship with its engines downwards (making it ready for a landing burn)
- Landing: the header tanks contain enough fuel to land. Center of mass is in the middle again (possibly methane is vented in this phase)
- Landed: all tanks are empty.
https://preview.redd.it/64ghei84o0721.png?width=2000&format=png&auto=webp&s=6513a8a3f01149e3cbafb816444fac9d2ada8462
Note: the illustration is not to scale and is not particularly accurate. Its just to clarify the concept.
Regards,
Jeffrey
So you can balance it on your finger instantly.
Hi everyone,
I'm trying to find the center of mass of the area between these to curves. Currently I'm trying to figure out how I can get the first moment of area in the x-direction. However I'm not sure what to do next since the functions f(y) and g(y) have the plus-minus sign in them.
https://preview.redd.it/tgdiyzri9fp41.jpg?width=1860&format=pjpg&auto=webp&s=b25219c9f592bfd3ed2c62b5bb517b0a1dcc83e2
When building a motor boat where should the center of mass be? Should it be a little closer to the front to counteract the motor when it is added? Any response is welcomed!
Also, do we have any idea of the current/projected weight?
Hey Reddit!
I know not even a week goes by without a self balancing robot question being asked, so I was hoping you guys weren't too sick of them and could humor mine too! I'm in the somewhat initial stages of designing and constructing a self balancing robot, and would like to design an LQR controller for it. I have a state space model developed following the proof seen here. I have been able to obtain values for most of the parameters in the A matrix, but was confused about how to measure or calculate the "pendulum" parameters. I'm designing my self balancing robot to look something like this (but bigger) and was wondering how I would measure out the center of mass, and calculate the inertia of the "pendulum".
Can I measure the center of mass out experimentally by using plumb lines? Or is there a better way to calculate it directly considering I know the dimensions of the perspex platforms I'm using, as well as the masses of the objects I'll be placing.
How about inertia? Since the platforms will be cuboids, can I use the inertia equations for cuboids and use the parallel axis theorem to add them up? Could I also approximate the batteries and microcontroller I'll be using to be cuboids and do the same thing too?
I'd also like to apologize in advance if this question is out of the scope of the subreddit, I wasn't sure whether to post this in here or robotics.
Find the x-coordinate of the center of mass of the composite object shown in the figure. The sphere, cylinder, and rectangular solid all have a uniform composition. Their masses and dimensions are: sphere: 200 g, diameter = 10 cm; cylinder: 450 g, length = 14 cm, radius = 5.0 cm; rectangular solid: m = 215 g, length in x-direction = 16 cm, height = 10 cm, depth = 12 cm.?
(Here's an image that was a part of the problem, not completely sure if it'll open): https://preview.redd.it/4lnm04rrhda41.png?width=358&format=png&auto=webp&s=78fe81873d61efc85b3e4cdc11f6d2c7a1cb73e7)
I tried this, but the answer did not match up:
x1m1+x2m2+x3m3 / Total mass of objects
I was thinking it would be the CM of all of the objects, and then averaged, but I'm not completely sure on how to get there.
So, I'm building a knock off Saturn V. I'm using a ps4. I bought the making history expansion, but I have yet to see the LEM cockpit show up in my inventory. I have the origional 2, but I'm not sure 1. What actually comes with the exp. Pack. As far as parts. Compared to the base game I bought.
So I'd like to know, does the Apollo style LEM actually come in the MH expansion for console? Or am I genuinely having an issue?
- In the process of constructing the CM, SM, LEM segment, I usually build the LM first, and work up from there. After those components are finished, I start the stages. Working down till tbe 1st stage.
Everything works great. Its all operating as planned. I'm just wondering, when I lay out the RCS on the CSM, when I use the center of mass tool, it's moving down the rocket as I add stages. Which is fine, only I didn't start at the csm. I started at the LEM. So when I go to dock, I noticed that im having difficulty controlling the csm.
What Ive understood is you need to place the rcs close to center of mass. I noticed too late in the build that in order to take an accurate reading, I'd have to start building the csm first.. or I cant go back later to fix the rcs at center of mass accurately, because the marker is now reading the mass of the LEM or the stages. So it isnt showing me center of mass for the csm when im detached from the LEM.
is there a way to detach the csm from the rest of the build without it becoming a non functioning part? It turns red, i cant attach parts, cant read the center of mass on it, after ive built the main engines etc. The 1st 2nd and 3rd stages stay green. But the csm goes red. And the mass marker stays with the stages.
So is there a work around to fix that issue? Or do i have to just go back and start over with that in mind?
Its late, im tired and I hope im making sense.
Thanks.
https://imgur.com/a/cHsLpXE
Title. The problem is that you start at still on a log both at rest with respect to the shore. Then you start running at 2 meters per second to the other end of the log and stop. The length of the log is 5 meters, out mass is 60 kg and the mass of the log is 540 kg. Find how far the center of the log moved.
The first approach uses the fact that since no external forces are present the position of the center of mass shouldn’t change. So I calculated the center of mass, calculated the distance the person moves and then sets the new center of mass equation equal to the old center of mass. I found the distance we moved by taking the length of the log and dividing by our speed relative to the log (our speed of 2 meters per second plus the logs speed of 0.22 meters per second repeating) to find the time passed until we reach the other end of the log, and multiplied by our speed relative to the shore(our speed of 2 meters per second minus the log speed). I found the speed of the log using conservation of momentum since the system starts with zero momentum vector.
The second approach deals with just conservation of momentum alone, taking that time I mentioned earlier and multiplying it by the logs speed to find the distance the log, and thus the center of the log traveled.
However with center of mass approach I get 0.44 repeating while with purely conservation of momentum approach I get 0.5.
So I just finished a homework problem for my Physics class which involved a dog on a flatboard in the ocean. Basically, you solve the problem with the fact that this dog-flatboard system's COM cannot be changed. But how is this possible? Surely the center of mass would differ if the dog was sitting on the far left of the board vs the far right.
The problem starts with the dog on the far right, so the COM is between the middle of the board and the dog. How then would this not change once the dog moves location?
The book explains it as so: " The canoe and dog form a system; treat each as a particle located at its own com. The system's com cannot move because of internal forces, such as due to the dog's feet pushing on the canoe as the dog moves. "
I'm trying to work on something for a writing project, and I've run into a brick wall. I don't have money nor time to run out and grab some batteries or whatever to build an electromagnetic rod to test this system.
So I wanna ask reddit.
I already tested this with a natural magnet I had sitting around. It pulls everything towards its center mass.
Does a rod turned into a magnet with a coil of wire do the same thing? does it attract all ferrous objects to the center of the rod? Or equally along it's coils?
Using the parallel axis theorem, I=I_cm + Mh^2
The question states that the Mass M of the two spheres is equal, as well as the moment of inertia.
to my understanding h is essentially the r I am solving for, so I try to manipulate the equation to isolate h (aka r),
so I came up with: r = sqrt((I-I_cm)/M)
After watching a few videos and understanding that since the placement of the r I am solving for is in the middle of the sphere, I should think of the start equation as I=I_cm + M(1/2R)^2 ...so r=sqrt(2*(I-I_cm)/M)
But... neither of these were correct. I tried using I as well as substituting MR^2 for I in my answers.
