Vessel Symmetry with Radial Mounted "Legs"

[_alphaBeta_]

I'm trying to build a vessel like this. Some of the tutorials also use radially embedded tanks that are then connected to engines etc. I've been trying to figure out how to stage these into orbit.

 

I'm having a difficult time of using the symmetry tools once I try to add components to either of the two legs. As an example, I want to add a radial decoupler to both sides of both legs. Here's what happens:

Only thing I can figure is build one side with no symmetry and then "detach" it temporarily from the main rocket. Then add the entire piece with 2x radial symmetry. This "works" but there's further complications with some of the radial decouplers showing up twice in the staging and placing structs is still problematic since they don't seem to hold symmetry around the whole vessel like that description of the mode says. Is there an easier way to build a design like this?

[AHHans]

When placing a part with symmetry enabled, then at the top left - below the "place a part", "move a part", "rotate a part", and "set root" buttons - you get a field saying either "Vessel" or "Parent". That means that the (radial) symmetry will be done around (only) the parent part, or around the whole vessel. Except that this doesn't seem to work... It usually only does symmetry around the last part that was placed without symmetry.

In a case like your example I would place one pair of decouplers (in radial symmetry around the vessel) on one side of the side-tanks, and then another one on the other side of the tanks (where there isn't one already).

4 hours ago, _alphaBeta_ said:

This "works" but there's further complications with some of the radial decouplers showing up twice in the staging

Most of the time a symmetry-group of decouplers (or engines or whatever) show up in the staging list with only one symbol (and a small number saying how many there are in that group). But when that group is selected, e.g. by clicking on it in the staging list, then it shows up with one symbol for each part, with small numbers from one to the number of the parts.

[Fierce Wolf]

Beware of putting legs on that ship, it's too tall and will fall to one side upon landing. Try for a shorter lander with 4 legs.

[_alphaBeta_]

7 hours ago, AHHans said:

When placing a part with symmetry enabled, then at the top left - below the "place a part", "move a part", "rotate a part", and "set root" buttons - you get a field saying either "Vessel" or "Parent". That means that the (radial) symmetry will be done around (only) the parent part, or around the whole vessel. Except that this doesn't seem to work... It usually only does symmetry around the last part that was placed without symmetry.

In a case like your example I would place one pair of decouplers (in radial symmetry around the vessel) on one side of the side-tanks, and then another one on the other side of the tanks (where there isn't one already).

Most of the time a symmetry-group of decouplers (or engines or whatever) show up in the staging list with only one symbol (and a small number saying how many there are in that group). But when that group is selected, e.g. by clicking on it in the staging list, then it shows up with one symbol for each part, with small numbers from one to the number of the parts.

I also thought the "parent" and "vessel" modes would be what I'm after, but I haven't found a situation yet where they actually accomplish anything different. Granted I just started playing, but they're not currently bugged are they?

The symmetry groups are what got a bit wonky during numerous tries to get the game to accept my intended symmetry. Some of the same radial decouplers were listed in two different groups. This was especially misleading with engines since adjusting parameters were only applying, to say, half the engines (you should have seen that liftoff). Sometimes the symmetry also seemed to fixate around a single part when I didn't want it to (really want around the whole vessel), and pulling off and reattaching whole sections of the vessel was the only way to reset the behavior.

Given all of this, it feels like a design like this is outside the normal parameters of what the game is expecting, or I'm using the tools incorrectly (hence my original questions). I never would have thought to try a design like this, especially considering it's essentially squishing multiple parts into the same physical space. Feels a bit gamey and hacky, but then I noticed the first Mun landing tutorial has radially mounted fuel tanks that provide two terrier engines. So i thought perhaps this is an expected area of play, even before some of the other connector types become active in the research tree. But building them seems problematic. Is this type of construction mainstream, or am I really outside the parameters of the game?

 

2 hours ago, Fierce Wolf said:

Beware of putting legs on that ship, it's too tall and will fall to one side upon landing. Try for a shorter lander with 4 legs.

I'm not trying to land this, just looking for more power without my overall rocket being so long. I just got heavier rocketry and the corresponding fuel tanks, so perhaps that will help. I'm still struggling getting higher stages up into orbit with enough fuel. Short of establishing an orbiting fueling station, bringing up fuel in batches and topping off exploration vessels before they leave LKO, I can only think of building larger lower stages to get something like the Mun landing tutorial vessel into orbit with a fuel tank.

[Fierce Wolf]

9 hours ago, _alphaBeta_ said:

I'm still struggling getting higher stages up into orbit with enough fuel.

I found the Terrier to be the early magical tool beginers need to reach farther. Try one!

[AHHans]

14 hours ago, _alphaBeta_ said:

I'm still struggling getting higher stages up into orbit with enough fuel.

Well, IMHO most of the fun of the game is designing your own craft, so instead of pointing you to other craft I can give you some general tips:

• Design your craft from the top down:
  • What do you need to return to Kerbin, what non-rocketry parts (science parts) do you need for your mission
  • (What do you need to land and get back to Kerbin? Only applicable once you actually want to land on Minmus, the Mun or so!)
  • What (how much dV!) do you need for maneuvering in orbit?
  • What kind of booster will get that into orbit.
• A few grams at the top of the rocket cost as much as a ton of the bottom of the rocket. So try to shave of as much weight as possible at the top without compromising your mission. (Do you need all that monopropellant and ablator?) But still keep a healthy safety margin. (Yes, getting that balance right is literally rocket science!)
• A good booster will need ca. 3200 m/s vacuum dV to get into Kerbin orbit.
  • You'll need a TWR of at least 1.3 at the start of the first stage to get off the launchpad fast enough.
  • At a TWR larger than about 2 you are loosing efficiency, you either waste efficiency by ascending too steeply or by getting too fast too low in the atmosphere.
  • (On airless worlds a high TWR doesn't have an efficiency penalty.)
• As @Fierce Wolf already hinted at: different engines are good for different stages.
  • Solid rocket boosters are great for getting you off the launchpad, but most (and all that were available before 1.8) loose they utility quickly.
  • The reliant and swivel are good lifter engines, but at best mediocre in vacuum.(*)
  • The terrier is useless in atmosphere but great in vacuum. (I use it a lot even in late game!)
  • Have a look at the Isp values of the engines in different circumstances (in atmosphere and in vacuum) to figure out which engine to use when.

(*) The reliant and swivel are also outclassed by later game engines like the skipper, mainsail, or vector as first stage lifter engines. But early in the game they are what you have.