Not Understanding Rovers

[Chads]

Hello,

 

I'm in a Career mode, and I've unlocked the appropriate parts for rovers, but I can't figure out how I would deliver one to the Mun.  I saw a video where you hang it off an I-beam extending from your landing craft (with a counterweight, of course), but I can't get above 320m/s without entirely losing control of my launch vehicle.  CG seems to be as close to center as possible (I'm eye-balling that, but I don't see any deviation).  I'm using 1.25m rockets, which I'm wondering if that's not large enough for this.

I'm not using KAS but I'm starting to think maybe that'd be the best way to go?

 

Thanks!

[Streetwind]

You probably don't have a problem understanding rovers, you have a problem understanding launch vehicle aerodynamics

The golden rule of rocketry is "heavy stuff at the front, draggy stuff at the back". If your rover generates lots of drag, then the rocket will seek to reverse itself in order to once again follow that rule.

Possible solutions:
- Make the back of your rocket more draggy, such as with fins
- Make the front of your rocket less draggy, such as with a fairing
- Increase your control authority, such as with reaction wheels or gimbaling engines
- Learn how to fly better, by keeping your nose pointed at the prograde vector as much as possible to not give your rocket nose the opportunity to develop sidewards torque

For more detailed advice, try posting a screenshot - we love troubleshooting rockets

[Chads]

Thanks Streetwind!

I was trying to figure out a way to put a fairing on it, but I couldn't get it to work.  I'm assuming it's a problem with drag, and perhaps the fact that the wheels turn (changing the air flow, like ailerons on a plane) while in flight.

It is kind of big, and maybe that's the problem.  I have a Science Jr. on the back, the RoverMate in front of that, 2 panels to make the frame.  It is connected with a Clamp-o-tron Jr.  Getting it connected was a challenge, and I can't entirely recall what the configuration looked like.  I'll look into getting a screenshot.

I'll look at including reaction wheels.  I may have one on it, but perhaps a second would be helpful.

[llanthas]

I actually just attach mine to the top of the lander with a stack separator. Add a fairing around it, to protect during ascent. 

[Tex_NL]

Fairings are a gift from the gods. Anything inside will be free from atmospheric drag.
As long as you keep things balanced it doesn't really matter where/how you carry your rover. On top, on the bottom, on the side. You can even transport rovers in kit form and assembled on-site with KAS.

Once I carried a rover in-line with the lifter and landed vertically. Then tipped the entire thing over on its wheels and detached the landing stage. (Just make sure you do not bust your wheels or bring an engineer that can repair them.)

Edited June 20, 2017 by Tex_NL

[HvP]

Opportunities for creativity abound when delivering rovers. It's one of my favorite challenges.

Small rovers are frequently flown on the top of rockets under a fairing with a skycrane attached. Really tiny rovers can even fit inside of the service bays.

The MK2 and MK3 cargo bays will help you with medium sized rovers, although you may have to land them horizontally with the cargo bay doors facing downwards.

Very large rovers tend to have their own engines attached and are flown as part of the rocket itself. Aerodynamics often forces a launch that is much more straight-up out of the atmosphere before turning to achieve orbit. Alternatively, they can be covered by huge fairings surrounded by large booster rockets on the sides.

One of my favorite ways to deliver rovers is to attach them vertically inside of a kind of sabot -- for example, I-beams on either side that connect to the stack above and below, that have small engines attached, which can be decoupled after landing.

Edited June 20, 2017 by HvP

[bewing]

Launching straight up can minimize aerodynamic instability issues. And as you found, there is always a speed limit that depends on altitude. In your case, make sure you stay below 320 m/s until you are above, say, 13km. That launch profile is inefficient, but all you need to do is bring some extra fuel to make it work.

 

[Chads]

Again, thanks!  Appreciate the ideas.  Still haven't grabbed KAS...I might do that tonight just to have it.  I kind of like the idea of giving my astronauts something to do when they're on the surface.

So, I've heard about the "sky crane" idea in other posts (and I'm aware of its use on Mars with Curiosity).  Not sure what parts that would entail.  I haven't looked at the "stock parts" (or whatever they're called) at this point.  I'll try to track those down.

[nascarlaser1]

I do the same thing as @Tex_NL, @HvP and @llanthas. If your rover is small enough, you can strap it to the top of your rocket, add a small decoupler to the top of it, build a sky crane on top of that, and then cover everything in a fairing. Flying the rocket to your destination, and if your landing off planet (like the mun or minimus) you then use your sky crane as the lander. land the rover, detach the sky crane, and you can then drive around . If your landing on an atmospheric body like Kerbin, you can ditch the sky crane and the decoupler on top, and add some parachutes to land it.

20 minutes ago, Chads said:

Again, thanks!  Appreciate the ideas.  Still haven't grabbed KAS...I might do that tonight just to have it.  I kind of like the idea of giving my astronauts something to do when they're on the surface.

So, I've heard about the "sky crane" idea in other posts (and I'm aware of its use on Mars with Curiosity).  Not sure what parts that would entail.  I haven't looked at the "stock parts" (or whatever they're called) at this point.  I'll try to track those down.

All that the sky crane would require is a small fuel tank and 4 of the twitch radial liquid fuel engines. Add a decoupler under the fuel tank to attach it to your rover. In order to attach it to your rover, you will also need a cuboid strut sticking up from the rover, or have a big enough flat surface.

[HvP]

20 minutes ago, Chads said:

So, I've heard about the "sky crane" idea in other posts (and I'm aware of its use on Mars with Curiosity).  Not sure what parts that would entail.

A sky crane doesn't have to be any more complicated than a fuel tank with a few radially mounted engines and a decoupler underneath to drop the rover from and maybe a probe core or docking port on top so that you have a control point to orient yourself for descent.

A probe core on top of the sky crane will make life easier, so that you can better aim the probe away from your rover when you decouple it. But decoupling just above the surface with the engines still running will do just fine for ditching the delivery vehicle even without a probe core. Separatrons staged with the decoupler will work too.

[EnderKid2]

Although KAS gives you ropes, you wouldn't do it Curiosity-style. Put a decoupler on top of your rover, then put a fuel tank on top with some radial engines>

Basically this:

[HvP]

39 minutes ago, Chads said:

Still haven't grabbed KAS...I might do that tonight just to have it.  I kind of like the idea of giving my astronauts something to do when they're on the surface.

Attaching the wheels is the main difficulty with building a rover with KAS. It's sometimes hard to get them level with each other. But mainly you have to have the main body raised up off the surface so that the wheels don't clip into the ground after attaching them. Bring along one of the KAS ground pylons or other raised structural part and then attach the central body of your rover to that first. It's kind of like putting your car up on a lift. You can then lift the whole rover assembly off of the pylon and then carefully drop the rover on the ground (explosions are common in KAS if some parts are dropped directly onto the ground; always raise them up a little and let them fall to the ground.)

Alternatively, you can build it upside down and then just turn it over when you need to add stuff to the top.

Edited June 20, 2017 by HvP

[Starman4308]

52 minutes ago, bewing said:

Launching straight up can minimize aerodynamic instability issues. And as you found, there is always a speed limit that depends on altitude. In your case, make sure you stay below 320 m/s until you are above, say, 13km. That launch profile is inefficient, but all you need to do is bring some extra fuel to make it work.

 

It's almost like it's 2014 again and we're all building giant asparagus pancakes.

Really, I prefer my mom's buttermilk pancakes, but to each his own.

In practice: most of my current rovers have been sent under a painfully oversized fairing with a skycrane, with the rover parallel to the ground, although my next big one is probably going to be perpendicular and come down under a detachable parachute/ballute system.

[artwhaley]

KAS/KIS are a ton of fun anyway!   And can often save a scrubbed mission.   When you have your massive interplanetary mother ship all ready to go and realize at the last minute you forgot batteries on the lander stage... scrambling a repair mission to spacewalk and install them adds a whole new kind of challenge to the game.  The kerbaltubes and pipe segments are awesome fun for base building too - scrambling around plugging in your various pieces - connecting up your rovers to recharge and such.    

 

Here's Scott Manley in a 'pre-fairings' video showing some examples of rover landing, but wrapping a big fairing around doesn't change it much - though with his big 'counterbalance' effort you may find yourself wanting to launch the lander and the rover and the counterweight on separate launches and connect them in orbit?  

And here's a video of one of my projects that relies on Infernal Robotics.  I did it as a proof of concept for the 'open source parts week' a while back, but keep meaning to clean it up and make it a real thing.  Looks like the download still works though!   The interesting part is at 1:02 or so when you see it deploy.  The rest of the video shows how it's done in Unity, because - open source part week.

 

[HvP]

Another delivery option

[Spricigo]

once upon a time I, like many others instaled KAS...over time I find other option for the functionality KAS provided. For "assemble at the destination" I like this one:

 

[qzgy]

7 minutes ago, Spricigo said:

once upon a time I, like many others instaled KAS...over time I find other option for the functionality KAS provided. For "assemble at the destination" I like this one:

 

That's actually super cool. Definitely a lot easier than KAS.

[Cpt Kerbalkrunch]

As stated by others, a sky-crane can look pretty simple. Nothing ground-breaking here, just a refueling rover (originally meant for Mun, then sent to Minmus as well; finally replaced it later with a more useful model). I also had a very similar rover built vertically on the delivery rocket. It worked pretty well, too, but I must've erased it. Can't find the thing anymore.

 

 

This is a smaller mining-rover, attached with docking ports on the ends instead of the top. The sky-crane is huge because this one went to Tylo. Wasn't sure what I'd need, so I went a little overboard.

 

 

 

 

Edited June 21, 2017 by Cpt Kerbalkrunch

[StrandedonEarth]

You could also have a pair of smallish rovers strapped to the side of your lander, under fairings, then separate them after landing. Then you have two on site!

Edited June 21, 2017 by StrandedonEarth

[Chads]

28 minutes ago, StrandedonEarth said:

You could also have a pair of smallish rovers strapped to the side of your lander, under fairings, then separate them after landing. Then you have two on site!

For when one flips over and becomes useless, right?

 

 

[Spricigo]

30 minutes ago, Chads said:

For when one flips over and becomes useless, right?

Arguable if it had a use before flipping.

[llanthas]

Yeah, rovers are kind of pointless 

[Draalo]

7 hours ago, HvP said:

A probe core on top of the sky crane will make life easier, so that you can better aim the probe away from your rover when you decouple it.

A docking port junior will work too at lower weight

Mount two single Sepatrons separately symetrical (but not two in sym. mode) and set the thrust of one to 85%. Stage them with the decoupler. The asymetric thrust will lift the skycane sideways - eyecatcher

Decoupler force should be set to 1% - otherwise it smashes the rover to the ground and damage the wheels.

 

Small rovers often fit in a 2,5m cargo container. Make a L-shaped holding structure of qubic struts with a decoupler sideways. Attach the rover. After landing open doors and detach.

Edited June 21, 2017 by Draalo

[-Velocity-]

It's extremely easy to combine the function of rover and lander into the same vehicle.  You can even combine more than just lander and rover.  This is rover/science research base/lander/interplanetary transfer ship/ISRU base all rolled into one, for example, for use in the Duna and Kerbin systems:

Spoiler

Drive mode:

Harvest mode:

Flight mode:

 

Notice I have two sets of engines- the primary engines in the back aligned axially and the landing/take-off engines in the middle pointed downward.  This was due to aerodynamic considerations within Duna's atmosphere, but honestly, it might not be worth the trade-off.  If you stay outside of atmospheres, you CERTAINLY only need a single set of engines, and if you are only landing in weak gravity (like, less than 3 m/s^2) then you are better off with LV-N nuclear engines.  In fact, the LV-Ns can be used even for Moho and Duna landing, it just gets more difficult, you start needing a lot of them to get a decent TWR.

Here's another example that only combines the lander and rover functionalities.

Spoiler

As for how to get the rovers into orbit, yes, they can be draggy.  Start a slight gravity turn almost immediately off of the pad so that you never have to make your rocket turn so much below 30 km that there is a greater than 5 or 10 degree difference in the surface prograde vector and where your rocket's nose is pointed. A lot of KSP players in my experience (based on forum surveys I read a long time ago) do not start their gravity turns early enough anyway.  So, as long as you keep your rocket pointed within like 5 to 10 degrees of where the surface velocity vector is pointing, your rocket's control system should have enough authority to overcome the inherent instability of having your center of drag too far forward.  If it DOESN'T, you need to add more control surfaces and/or fins to the back and/or add more engines with thrust vectoring capability.

This is what my ISRU rover looks like on the pad:

Spoiler

If you're wondering how that relatively small rocket gets that huge rover into orbit, it's because I'll launch big things like that with mostly empty fuel tanks and then refill them on Minimus.

And this is that over rover I showed on the pad:

Spoiler

ALSO: Do NOT try to go too fast in the lower atmosphere with that big, front-draggy rover attached to your rocket.  Keep your TWR pretty low, you should have a lift-off TWR below 2, and your TWR shouldn't get much more than 3 or MAYBE 3.5 before going second stage- and that's assuming you aren't controlling the thrust from getting too high, which you actually should, especially in this case (generally, the rule in the lower atmosphere in the stock game is to control your TWR to be around 2).  The slower you go, the easier it is for your thrust-vectoring engines to keep your rocket straight (assuming the rocket is aerodynamically unstable), and slower can also mean being more efficient in the lower atmosphere, especially with a lot of drag.

Edited June 21, 2017 by -Velocity-

[Chads]

Thanks to all for sharing ideas/concepts/pointers/tips!

I marked Velocity's post as "best answer" because, well, I'm new here--I assume something needs to be marked, and I liked all the pics.   

I've contracted both of my kids to try to come up with a neat rover design.  I bought a copy of KSP for my son (a college student), but my daughter only gets to get her hands on it when I'm not playing.

14 hours ago, Spricigo said:

once upon a time I, like many others instaled KAS...over time I find other option for the functionality KAS provided. For "assemble at the destination" I like this one:

 

So, sort of a separate question, but...why can't I find this when I click "Addons and Mods" from the game menu?