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Werdna

Trouble flying straight in drag race - any tips?

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I'm new to the game and figuring it out, but getting my drone to fly straight in drag racing is driving me nuts.  I feel like I'm designing balanced ships that are top/bottom mirrored, with fuel tanks in the middle line (even with core) in case they weigh less when fuel is used, but my ships very quickly drift down or up as if there is random air drag or something wrong with my balance.  Does the center of mass moving left or right from fuel usage matter if thrusters are balanced?

Am I missing something?  Is it randomness caused by fuel use shifting center of mass unevenly?  If so... I notice identical design ships tend to always drift the same direction, so it doesn't seem random.  Is it possible to get a drone to fly straight over a long distance (without sensors and corrections) in the drag race?  If not, I guess sensors are needed.  If yes, could it be that there something is about the attachment "lines/connectors" between parts that is causing the imbalance -- they hide behind the drone, but do they have mass that enters the equation?  Or am I just experiencing floppiness that causes random drift?

I've had some success and gotten some models to finish in about 11 seconds using afterburners and regular thrusters, but the balancing seems wonky, and several bounce off the top and bottom walls/rails and are just lucky to cross the finish line.  Sometimes something like adding one more pair of symmetrical thrusters (leaving center of mass where it is) will change the direction (to top or bottom) of drift.  Strange. 

Any tips?  What am I missing?  This is driving me nuts.  It doesn't help that I'm not great at using sensors (I'm using the laser pointer ones to sense wall and trigger perpendicular thrust into core)... they tend to under-correct and then over-correct and I end up faceplanting the wall.

Thanks,

Werdna 

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As additional information: this problem appears on the Sagittarius drag strip with only one thruster on each side of a drone core and a fuel tank behind, as the craft ends just a few metres North of its starting position. Adding thrusters adds some slight turning, and heavy parts behind the craft make it collide with the wall rather quickly, even with the ship perfectly balanced around its stern-prow axis.

Placing a small, supplementary piece to the right of a craft's centre of mass seems to solve this (roughly). I believe I cannot prove much more useful than that, and I assume this behaviour is not intended by the developers.

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I've fiddled with it a bit more.  Made a nice symmetrical design with 6 thrusters, 6 afterburners, and 3 large fuel tanks that drifted left (up, while flying to the right) and crashed about half way through.  I took a thruster on the left side and moved it the smallest fraction away from the core to imbalance the center of mass.  This caused a very quick crash.  So then I went back to the original design and pulled a number of the thrusters/ABs on the left/top and moved them aft to keep mass centered around the spine, but further back on the left/top side.  I'm attaching am image.  This seemed to correct the drift for the most part (it pulled a little right/down, then stabilized), but it seems a little crazy to have to do this.

 

 

Nimbatus_Screenshot_201905021242296916.png

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Garr! My tip is to concentrate as much of your thrust as close to center line as possible, all attached to the core. While an update a while back helped to reduce thrust inconsistencies in units attached to things other than the core, it still happens. In my experience, anything attached directly to the core has a much more stable thrust pattern than anything else. Placing as many thrusters as possible near centerline reduces the effect of inconsistent thruster performance by mitigating the rate that any given thruster can turn your drone.    

Many drag racers are also attaching their fuel to a chain of a few springs or more. In addition to reducing overall drag, this creates a pendulum effect that provides a modicum of passive steering to the drone.  

Soon, you'll be fiddling with ways to achieve near instant afterburner activation. Get ready for some spectacular wrecks. :) 

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It's a mess... even putting things closer to center doesn't help that much.  The drift seems very random. 

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Using the tip about springs and central thrusters...  This guy really wants to go left... crashes into top and stabilizes.  Got my best time with it so far.

 

Nimbatus_Screenshot_201905021506139981.png

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so are all these issues with stability bugs or intentional?

Kerbal Space Program, for example, punishes you for imbalanced design, but it seems a lot more forgiving.

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Glad it's going better. Here are a few more tips to increase your times.

Add another spring and push your fuel farther out. Don't worry about fuel being on center line. Use the extra room to move your afterburners closer to centerline.

Prioritize your afterburners for centerline. The regular thrusters are low priority. You want as much thrust near the center as possible. With the number of thrusters you're using, you should be able to get every afterburner no more than one unit off the center. 

Put your logic on a release and set it to release at the start. Use the extra space for more centerline thrusters.   

Your fuel is overlapping. This is probably a bad idea unless you know something I don't. 

You'll probably still need to adjust a few thrusters for a more reliable run. 

Many of the record setters only complete the course once out of a pile of false starts. The faster the drone, the more instability becomes an issue. 

If you absolutely can't prevent your drone from hitting a wall, use guidance. A wall strike will cost you more than the extra weight. You can make top ten easy even with guidance. 

Eventually, you may want to give up regular thrusters entirely :) 

 

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Thanks. What do you mean by "put your logic on a release and set it to release at the start?"  Do you mean to jettison the button at launch?  Does it still work if it's not attached?  By the same logic, should I detach/decouple thrusters when I hit 150 using speed sensor?  I see that shotgun/magnet start is something I need to learn, but maybe as a bridge to that?

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Aye, jettison the button. It's wireless. You could do this with regular thrusters as well, but since you're moving on to using shotguns, you won't need thrusters anymore. You want increased recoil and multiple projectiles. 

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My best design has a single long chain of springs for the fuel, but in previous designs I used 2 chains and whenever I had my drone drift I would fix it by tweaking the strength of a spring on the opposite side. It results in your drone going off-center and then returning, which loses you a few milliseconds that can cost you when you get to the top 10 or 20.

Getting your balanced design to fly straight takes some trial and error unfortunately, and it gets worse once you add shotguns as your starter.

I've heard @Markus say that Unity doesn't resolve some calculations with perfect precision, so this drift might be because of that. If it is, it might not be fixable.

Final tip, don't use a button. Try using the empty/full keystrokes on fuel tanks (at least 2) instead.

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I'm not a coding expert, but if I understand it correctly, the PhysX Engine (which Unity uses) uses randomness and approximations to be faster. So it's inherently imprecise :/ But that's also the reason it still runs reasonably fast enough for our use-case  :)

There are other physics engines which are more suited for games like nimbatus, but those did not exist when Nimbatus started (2013) so we're locked to what we have.

Great infos here on this thread. Another thing which might work. Try to have most of the applied forces in front of the center of mass, so that it's dragging it and not pushing. Otherwise it's like trying to balance a long stick on a finger.

For stability one single VTOL thruster in the front might already be enough to keep your drone stable.

Another tip: Buttons are wireless. This means you can but a button on a decoupler and let it split off in the beginning and you still have a button which works without adding mass. Depends if you're close to the part limit though. In that case just use the "is fuel full" trick as trigger.

 

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