File Name: center of mass and center of gravity plugin.zip
The dynamics of body center of mass BCoM 3D trajectory during locomotion is crucial to the mechanical understanding of the different gaits.
- OpenRocket center of Mass
- What is Center of Mass: Notes pdf ppt Engineering Mechanics
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The functionality of the previous Naval Architect Pro version is now included in the free evaluation plug-in. The plug-in can be downloaded at Food4Rhino.
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OpenRocket center of Mass
Joined Mar 8, Messages 1 Reaction score 0. Hello everybody, I'm pretty new here, and looking for some advice on using OpenRocket to run a sim of a custom motor. I'm not certain how OpenRocket is supposed to do this, but I'd like to control the center of gravity for the motor, which will change for the first couple seconds of flight as the propellant burns.
My first thought was to write an equation to describe the motor's mass over time, but it would have to be a piecewise function to work during the coast phase as well. I've added a simple mass component, but when I type the equation into the 'mass' box, it just disappears after closing the component window.
What I'm looking for is if anyone else has encountered this issue, or has ideas for a solution. Thanks very much! Joined Sep 21, Messages 1, Reaction score Rocket Stability. Joined Jan 30, Messages 6, Reaction score 1, I think only RockSim can do this, using an.
Unless I am misunderstanding what you want, OpenRocket already has this feature built in. Just make a. That will produce a plot showing 'dynamic' stability, although ideally you would be able to plot a variety of angles of attack as well. During flight, both the CG and the CP move, so stability changes over time. The location of the CP moves rearward during flight, but the CG of course moves forward, so for most rockets it balances out. One big thing you'll notice is that the margin of stability shifts far more for longer, skinner rockets than for shorter, fat rockets.
The first chart is of a Mongoose 54mm on a L, the stability margin changes by 4 calibers during flight, the second one is of a LOC Bullet, the margin changes by only 1 caliber during flight.
Tony See this thread for info on custom motor files: OpenRocket Tom M. Last edited: Jul 26, Joined Sep 6, Messages 2, Reaction score The OP did not ask how to make a rocket stable nor snarky comments on the necessity of his question. He asked how to move the CG of a custom motor as it burns. Yes, this is a real thing, and it was an important consideration in the days of hybrid motors, or when you want moment of inertia information.
I don't think OpenRocket can do it without some user subroutine plugins, which are not easy. As dhbarr mentioned, the RockSim. Buckeye said:. The OP did not ask how to make a rocket stable nor your 2 cents on the necessity of his question. Hmm, how is the graph produced by OpenRocket not what the OP wanted?
It is clearly showing the shift in CG due to the motor burn. I assume it's just using linear consumption of the propellant, which might not be completely accurate, but close enough. The green line is not completely linear but pretty close. The graph shows the CG of the Mongoose moving from 50" behind the nosecone to just over 42" during the motor burn, and then it is static after that. For the Bullet, the CG moves from What am I missing here regarding the OPs request?
Unless the OP is using something other than a solid propellant motor, what is the functional difference? As the motor burns propellent, the CG of the rocket shifts forward as the propellant is burned. Typically the propellent burns along the entire length of the motor in a very nearly linear fashion.
I suppose if it is a 'dual-thrust' motor with a mix of fast and slow burning grains it could vary, as of course would an end-burner, but those are unique cases. I would be very interested in any real-world examples of motors that have substantially different CGs before and during burning, as well as after. And in hearing more from the OP what kind of motor he is using. Every hybrid ever made, for one. JoePfeiffer Well-Known Member.
Joined Jun 15, Messages Reaction score It's pretty straightforward. You need to create a custom motor in. From within OR, it's possible to set a directory for custom motors; of course you need to put the. There doesn't appear to be any support for CG changes during the coast phase; you could model that by simply having an absurdly low thrust for that time. I am curious as to what you're doing that requires modeling motor CG changes, though!
Last edited: Jul 27, There are valid reasons to want to know the CG shift on all motors, including composite. Most of my flights go supersonic. Sometimes I am less than 2 calibers at launch and plan on the shift. Joined May 9, Messages 2, Reaction score Others said this, but for clarity: Unless you are using an end-burner, a hybrid, or a weird mix of grain geometry, the default OR behavior already does exactly what you want.
Kelly Usually remembers to get the pointy end up. JoePfeiffer said:. Yes, but does OR actually read and calculate with the motor CG data found in the. Or, does it just ignore it? I could run a simple test in OR and find out, but I am lazy.
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What is Center of Mass: Notes pdf ppt Engineering Mechanics
When you are running calculation with periodic boundary condition you may end up with situation like in the figure below:. Figure 6 A connected cell in the lattice edge area — periodic boundary conditions are applied. Clearly, what happens is that simply connected cell is wrapped around the lattice edge so part of it is in the region of high values of x coordinate and the other is in the region where x coordinates have low values. A better procedure could be as follows:. Now if after shifting back it turns out that center of mass of a cell lies outside lattice position it in the center of mass by applygin a shift equal to the length of the lattice and whose direction should be such that the center of mass of the cell ends up inside the lattice there is only one such shift and it might be be equal to zero vector. Next we take into account the new pixel either gained or lost and calculate center of mass position for the shifted cell :.
Even if it was reported it doesn't solve the original problem of adjusting the model to have the com in a specified place unless you use trial and error. You need to write an equation for the com dependent on the variable of the geometry you wish to change and then solve it to create the geometry. This is wordy and ends with a relatively small payoff, but what the heck In the offshore oil patch, the center of mass we call it "center of gravity" or "cg" is of continual interest. We calculate it when we lift skids 1 and large modules because the cg will always position itself directly below the hook.
Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content. Dhirendra Yadav. No Comments. What is the center of mass? The center of mass is a position defined relative to an object or system of objects.
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Is there something in Rhino that would help in this process? Any links to boar design groups? You wanna make a preliminary calculation of the weight of the ship without modeling at least a little bit? Suffice it to say, even that would require you to at least model volumes depending on the type of structure. Just search the web.
VMD Community Pages. CG Builder provides a simple set of tools for transforming structures between coarse grained and all-atom representations. CG Builder supports two methods of creating a coarse grained model: A residue-based method, in which two or more particles from an all atom representation map onto a single "bead". A given bead will be placed at the center of mass of the atomic group defining it. Any atoms not defined as part of a CG Bead will be left alone.
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