CrashnBurn Posted July 18, 2012 Share Posted July 18, 2012 After watching the wobblies on my large boosters, I decided to apply some common structural engineering principles to increase rigidity and also to stabilize the vehicle.First I designed a tension-compression structure to increase rigidity. As there is no way to pre-tension a design in KSP, I decided to use the engine thrust to create the required structural load. This worked beautifully and allowed for a much lighter design. You can watch the structure load and unload as you turn the thrust on and off.However, there was still a good bit of wobble as I got to extreme vehicle heights. So I added a mass-damper, using the observation that the struts will act like springs (you can see them change length as they load and unload). I added a long 'pendulum' mass (as tall as the vehicle), connected at the top of the Tension-Compression structure by structural pylons (little flex) and at the extreme bottom by 4 struts (lots of flex).This addition completely eliminated wobble, even when adding a lot of height and putting the control surfaces and SAS at the extreme ends of the vehicle to try and create instability.Testing with Mechjeb (to stay more consistent between flights) the design maintains consistent stability and rigidity as height increases. I stopped testing at a dozen tanks in the stack, I know, how un-Kerbal of me not to test to failure...but I think you will agree that the vehicle looks quite Kerbalesque, anyway.The craft files requires the Mechjeb plugin.The first pic and craft file are of the 12-stack tension structure without the mass damper.This gets to a 200Km circular orbit easily with plenty of gas to play around or go to the Mun. But expect a bit of wobble.Next Pic and craft file are a shorter model of the same thrust- tensioned structure using the centrally-hung second stage as a pendulum-style mass damper.Just a fast 'first try' at it, I\'m sure it can be refined, but it works well as a proof of concept. Link to comment Share on other sites More sharing options...
Bluejayek Posted July 18, 2012 Share Posted July 18, 2012 Wow, very kerbal craft, I like it.Welcome to the forums! Very good entrance post Link to comment Share on other sites More sharing options...
CrashnBurn Posted July 19, 2012 Author Share Posted July 19, 2012 Thanks Bluejayek. I like to make an entrance. I\'m still new at this, but I\'ll be sure to add to the fun, here. Seems like a great community. Link to comment Share on other sites More sharing options...
Khrissetti Posted July 19, 2012 Share Posted July 19, 2012 Ah, you designed a mass damper similar to the one used in the Tapei 101? Link to comment Share on other sites More sharing options...
CrashnBurn Posted July 19, 2012 Author Share Posted July 19, 2012 Hi Khrissette, yep, you\'re right. I didn\'t know if it would work in the KSP game physics, but apparently it does. Using the second stage to damp the sway of the initial launch and climb costs very little in additional mass. It could possibly be a net improvement in total mass if less stabilizing equipment is required.Even if it didn\'t work, it\'s still quite a Kerbal solution. Link to comment Share on other sites More sharing options...
antbin Posted July 23, 2012 Share Posted July 23, 2012 Link to comment Share on other sites More sharing options...
CrashnBurn Posted July 27, 2012 Author Share Posted July 27, 2012 This mass damper design will work now with the new larger parts in .16 if you use my part.cfg edit for the decouplers. Link to comment Share on other sites More sharing options...
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