Stratzenblitz75

That's an interesting hypothesis, and some of my data seems to support it. For example, when the thruster is exerting a force slightly greater than static friction, I get the jittering behavior. In this case, the physics inaccuracies you talked about would cause the parts to randomly wobble slower than the craft, causing them to exert their static friction and "stick". When the craft reaches a certain speed, the jittering and random turning stops completely. In this case, the parts would be well within the realms of kinetic friction, and thus, random inaccuracies don't cause the parts to exert static friction. Not sure how I'd test this either. I'd have to play around in game and experiment with this kinetic-static speed boundary.

Yep, I've encountered this annoying behavior as well. Take this rocket for example: This thing masses at over 2000 tons, yet, its rotating and walking around the launchpad on its own. However, when you remove the heat-sheilds on the bottom and let it rest on the MK2-3 fuel tank, it doesn't move at all. From this, it appears that the mass of the part(s) that contacts the ground plays a big part in what forces it experiences. A heavy object resting on a part with low mass will jitter and walk around, while a massive object resting directly on the ground won't. The more I think about it, the more I'm leaning towards stock-joints being the problem. If I recall correctly, the strength of the joint depends on the mass of the part, right? That would explain why a part with less mass would exhibit this behavior, while one with a large mass would not. I'm thinking that because the joint of a small mass part is weaker, it exacerbates some kind of bug in the stock-joint that causes the part to jitter when in contact with a force. Hmm... More experiments are definitely necessary. I wonder if this behavior still occurs when a part is resting on top of another stationary part instead of the ground? Is part-to-part friction different from part-to-ground friction?

--- Introduction --- During the whole 1.1 slippery/explodey wheels, I began experimenting with alternatives to the buggy wheels. In particular, I began playing with skids made of I-beams and structural panels. I haven’t really seen skids in KSP before, and thus, had no idea how to make them. So, I began running through prototypes, testing all sorts of skid configurations, trying to find the lightest, most durable, and least draggy setup. Through this testing, I found something odd. One of my skid configurations did significantly better than all the others I tested: Here is one of my standard skids: And here is the odd skid: As you can see, my standard skid only started moving when the engine thrust reached 18.7 Kn. By contrast, the other skid design started moving at about 13 Kn of thrust. Can you spot the difference? The standard skid is resting on the flat side of skids, while the other skid is resting on the vertices of the skids. In reality, between dry surfaces, friction does not depend on contact area. If you decrease contact area, you decrease the area for friction to act upon, but you also increase the pressure on the area. Turns out, this decrease of area is exactly canceled by the increased pressure. Thus, the force of static friction stays the same for a given mass, no matter how you vary the contact area. Most of the time. I’m sure there are cases where this isn’t true, but for the most part, it is a good approximation. So, what’s going on here? Why does reducing the contact area appear to lower the static friction in KSP? Is there some sort of flaw in KSP’s friction system? --- Building the test rigs --- Curious, I began designing a series of test rigs to experiment with this phenomenon. I wanted to eliminate as many external variables as possible, so I built the rigs to the following guidelines: 1. Engine must be as close to the ground as possible to minimize torque 2. CoM must be as close to the ground as possible to minimize torque 3. Mass must stay constant Here is what I came up with: There are four structural panels on the bottom of the rig which can be angled to decrease contact area. I then built two more variations of the rig. One where only the edges of the panels contact the ground: And one where only the vertices of the panels contact the ground: All of the rigs have the same mass. --- Running the tests --- To perform the experiments, I will load each variation onto the runway, enable infinite fuel, throttle the engine until the rig starts accelerating, and then take note of the engine’s thrust. As of Newton’s third law, this force is equal to the force of static friction of the rig. Now all we have to do is run the tests… Wait a minute… What’s going on here? Why are the panels jittering everywhere? And why is it turning? Why does the speed keep changing? Sigh… This was going to be more difficult than I thought. So, let’s, replace the 4 panels with just one panel. The mass stays the same, and contact area stays the same. Success! Looks like the rig overcame static friction at 9.7 Kn. Let’s keep note of that number for the next tests. Alright, now to test the edge contact area rig: Huh, about 9.5 Kn again. So far, it looks like KSP is doing quite well. Finally, let’s try the vertices contact area rig: Would you look at that! It only took 4.8 Kn to overcome static friction, about half the force of other 2 tests. --- Conclusion --- For most cases, it seems that KSP handles the force of friction realistically. However, in cases where only the vertices of a part touch the ground, the force of friction is drastically reduced. Why is this? My guess is that since the plates are perfect shapes, their vertices essentially have an infinitely small contact area, confusing KSP’s friction calculation in some way. Then again, an edge of a perfect shape should also have an infinitely small surface area, and as you saw from my second test, the edges produced the same force of friction as the flat plate. So, at this point, I really have no idea what could be causing this. And that isn’t to mention all of the other oddities I noticed during these tests. For example, the jittering plates in my first test. This jitter seems to increase with the number of parts touching the ground, but why? The parts are very sturdy: After all, they are steel plates fixed to a single steel beam and thus, they don’t move very much when put under pressure. Despite this, friction causes them to jitter, causing all sorts of random movements in the craft. On top of all this, it seems friction on terrain differs significantly from friction on the runway! For one the static friction is much higher (Which makes sense, grass/dirt/sand would exert more friction than flat concrete). Additionally, the jittering is much, much worse on terrain. Parts will quite visibly jolt back and forth. However, this jittering will completely stop once the craft reaches a certain speed. --- Final Words --- In the end, I am left with more questions than answers. While I did learn a little about how contact area effects friction in KSP, these experiments have revealed a bizarre world of KSP that I’ve never noticed before. A world where the simple act of sliding metal plates against a flat surface creates jittering, phantom forces, and physics-defying skids that glide effortlessly across the ground. On that note, I want to encourage you all to help me explore KSP’s friction. Download my test rigs and try to replicate my results. Conduct your own experiments. Try testing parts other than structural panels. KSP’s friction is obviously much more complicated than it seems, so maybe with some group effort, we can come to understand how it actually works. Thanks for reading everyone! -Stratzenblitz75

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I think you are looking for @achroma's cinematic, "Delivery & The Jabberwocky": Honestly one of my favorite KSP videos of all time. Achroma breathes so much life into his worlds and stories, it just leaves me awe-struck. Highly recommend checking out his other videos as well; lots of creative, crazy and beautiful designs there. ...Now about that virtual cookie.

I've been having a lot of fun with skids recently. I don't think they offer much advantages over wheels, but still, they are fun to play around with:

First, let me say that this mod is simply gorgeous! You've done an incredible job revamping the stock system without sacrificing too much performance. So, thank you for continuing to update this mod into 1.1 pre-release. Now, I have seen one problem with mod so far: Eve looks far too pink (Ignore my ship undergoing unplanned disassembly): I am running the latest 1.1 pre-release, Windows 64 bit version. I am also using the High-Resolution version of SVE. Is anyone else experiencing this?

Ahh, SRBs are quite fun indeed! Some tips I've learned in my SRB adventures: 1: Seperatrons are great for fine-tuning. All you have to know is how much Delta-V they give your ship, and then you create a maneuver node with exactly that much delta-V (Adding radial or normal components as necessary) 2: You can fine tune interplanetary transfers by timing the ejection burn. A split-second change in when you start your burn can influence your ejection angle, and thus, your solar trajectory. With enough quick-loading and quick-saving, you can find the exact timing that will give you an encounter. 3: You don't have to do a powered landing. On airless bodies with low gravity such as the Mun, or Eeloo, you can build a lithobraking landing system that can take hits of up to 100 m/s. On planets with atmospheres such as Eve or Duna, you can use wings.

Today, I messed around in the 1.1 pre-release:

First video of April! This time, I have some fun with part clipping:

No-one has mentioned @Vaos Human? His attention to detail is simply incredible. The camera angles, the awesome craft designs, the sound effects, the stories, the editing, the narration... It all comes together to make a very immersive experience. His Solar Nations series has to be one of my favorite KSP series:

Today, I went fast:

Well, I figured I could get another video out before April, so I gave Jeb a vacation. After all the things I've put him through, its only fair.

Today, I gave Jeb a vacation:

The first thing I did was throw out all my habits of reducing part-count and built a giant 500 part mun-base chock full of useless features. And, it ran at 20+ FPS. The rocket actually files in REAL TIME. Did you hear? REAL TIME. No 45 minutes of time dilation for a 15 minute launch. No stepping away to eat lunch while Mechjeb flies it. No horrible, painful-to-look-at low FPS. No, for once, I actually ENJOYED flying a giant rocket myself... It almost brings a tear to my eye... THIS is what I've always wanted KSP to be!

And here I was, wondering why my video got sudden surge of activity. Honestly wasn't expecting this at all! Thanks so much for the feature!

Here is my most recent close-call: Literally used all of my fuel in this mission, mainly because I didn't include solar panels and thus, had to run the engine during reentry to get electric power.

Today, I went to the Mun and Minmus with a rocket-powered SSTO:

Another month, another video! For march, I decide to fly a rocket powered SSTO to the Mun and Minmus using FAR... Without refueling!

^^^THIS^^^ Blender is an incredible non-linear video editor and I use it for all my videos. Best of all, its free! Can't recommend it enough. Although, it is somewhat complicated to get the hang of. You'll definitely have to watch some tutorials to get you started.

Well, I guess I made this thing: When I came up with the idea, I honesty did not expect it to work at all. You can imagine how surprised I was when it didn't nosedive into the ground immediately. Ah, the crazy things you can do in this game. KSP, never change.* *Except for fixing bugs, improving performance, adding parts etc.

Thanks! I will consider it. After all, these videos don't seem to be getting any attention in this subfourm... Then again, since they are technically "mission reports", I am not sure they would fit in the challenges section.

When your own YouTube URL calls you a "Dork": "https://www.youtube.com/watch?v=O8N5nJkDork"

Today, I went to Tylo:

A new video just before the end of the month! To celebrate this leap day, I decided to cram a Tylo lander into a MK2 Cargo bay: