Mun ground circumnavigation fail - Tips ?

[Cairol]

Today I tried to solve the Elcano ground circumnavigation challenge on the Mun. Just for fun because I enjoyed the mission reports of the successful players.

My rover has 2 kerbals, a pilot and an engineer, front bumpers, two small and one (ugly) medium KIS cargo container with loads of spare parts.

It has ruggedized wheels, back up landing gears, a large fuel cell, a front and rear fuel tank (probably oversized, as the cell seems to be pretty efficient),

solar cells for the day time, remote tech antennas mainly just because, some batteries, lights, a winch at the front, RCS was only for safe landing, but I kept it just in case...

I was able to drive about 10 km with speeds of 10 - 25 m/s.

At that point, my rover has had about 20 flat tires, was down to about 50% of its initial parts, having encountered several nearly deadly rollovers and non-optimal landings.

It was driving on it's rear backup tires, lost the medium cargo container, one of two fuel tanks and dozens of solar cells with it, was practically unsteerable

due to the shifted CoM because of the loss of the rear fuel tank and practically a dead thing.

So I aborted the haul and went back to the drawing board.

How did you (the successful ones) manage to keep your vehicle from rolling over and getting destroyed while moving at higher speeds over the bumpy Mun surface?

I read of 100 m/s fast vehicles...

Mine is in constant danger to loose control when moving faster than 10-15 m/s.

Edited September 13, 2015 by Cairol

[Nansuchao]

A safe speed is under 10 m/s for a rover. Try to build wide with and as low as possible CoM and remember, go slow...

[Cairol]

Hm. From what I read, the guys used to drive 20-40 m/s on the Mun.

My rover can drive 25 m/s max. at even terrain. But if it hits a bump and jumps at this speed, it's pretty much done for when landing, if I'm not super lucky with my controls.

I know this is not a race. I'll take it more careful on my next try and improve my design.

But I really wonder how you can handle those speeds at 0.17 g even for a minute without taking off and crashing miserably.

Or how you can let MechJeb drive the rover and go drink some coffee. I also tried it. It's suicide.

The only thing MJ does good for me, is keeping the given heading. That's useful.

Edited September 9, 2015 by Cairol

[ajburges]

A few observations I've had with rovers:

Any part on the outside (or on a bay wall) with an impact resistance of less than your driving speed is fodder. Keep fragile parts enclosed. For this reason, Mk2 and Mk3 fuselages make great rovers.

A wheel that takes a collision on its own will pop, either accept that or work to minimize the scenarios where one wheel takes all the abuse. Landing gear in front can help if you don't mind the aesthetics.

Time warp is king. A 10 m/s rover that can travel under 4x physics warp covers terrian just as fast as one that goes 20 m/s at 2x. 20 m/s is fast by terrestrial standards, but is dead slow by orbital standards.

[The_Rocketeer]

I haven't completed a circumnavigation of mun, but I have driven an equivalent distance on an indirect route gathering science. The frustration of repeated accidents still haunts me whenever I contemplate a new mun rover design.

From that experience I learned that in my non-RCS-stabilised rover, speeds in excess of 10m/s are safe-ish, in excess of 15m/s are risky, in excess of 20m/s are pushing your luck and in excess of 30m/s are downright reckless. That didn't stop me from occasionally hitting 35m/s or even 40m/s on the flat straight-aways when I knew I had a quicksave in my pocket, but it did make me take the slopes with great care and pick my route with a view to minimising my exposure to rugged terrain.

I also have a circumnavigation of Kerbin underway, and again quicksaves are my saving grace. It only takes one bad bounce and the trip's over... and that despite measures I've taken to improve the suspension (using landing gear to supplement the ruggedised wheels). Even on Kerbin I'm taking my life in my hands exceeding 30m/s.

On Mun you can do a few things like use RCS thrusters that point to the ground to keep you firmly stuck to the surface at speed, but if you hit a bump it's actually lifting and braking thrust that you're going to want, to slow you before you crash down again. Also, don't trust the SAS to do anything except kill rotation - u need to steer yourself into the gentlest landing you can.

Lastly, downhill is by far the worst for getting a bad shimmy on. Always take these bits with care, and don't be fooled into thinking a gentle slope means nice smooth ground with no sharp angles. It doesn't, and any extra speed you allow here is going to bite you hard.

Edit: Also, for reference keep in mind that the RL Lunar Roving Vehicle reached only 4.9 m/s (11.2 mph), and it didn't have inflatable tyres to burst, it used steel mesh wheels.

Edited September 9, 2015 by The_Rocketeer

[Hagen von Tronje]

Hey hey hey, a topic where I know useful things!

On design:

- I feel like your CoM is pretty high, at least for what I like. If you want more ground clearance, you gotta spread the wheelbase. You have a good idea with the I beams, try longer ones and see how it works. Or just stick the wheels out the side. But really you could bring your "belly" down to where your suspension currently is, if you clothesline that undercarriage you're toast anyway so no reason to feel like you need to protect the fuselage.

- Don't forget to tweak your wheels! Steering with wheels that have enabled motors is method #1 to flip any rover. If you're using Claw's brake bugfix (you probably should, it really is a bugfix and really does help), you may need to tweak brakes to have enough to stop you but not so much to flip you.

- Downthrusters. RCS thrusters are a popular choice, but I've found the most efficient method for me personally is to use either Twitch or Puff engines. This is because you can limit their thrust and throttle them for on-the-fly, as-strong-as-you-need-it downforce. Other engines work, including Dawn, Ant, etc, I just find those two to be the preferred type for me. See comments on driving below.

- Ballast. Does that sound crazy? Actual mass = "free downforce." Assuming of course that mass is keeping your CoM low. Fortunately, KSP gives us an ideal ballast in the form of LFO, which is dense, transferable, and fuels the downthrusters. If you're concerned about putting more mass up, you can send it up with empty tanks, then dock and fill it on the Mun. For a circumnavigation attempt, you are almost surely going to want to carry lots of fuel for downthrusters anyway, and maybe want/need to refill them too. The only downside to more mass is that impacts will be more damaging to wheels, huge n' heavy rovers will break stock wheels with regularity just bumping into terrain edges.

- Moar wheels. This also sounds crazy, who drives cars with six or eight wheels? Folks who need lots of traction, that's who - dualies. We don't have dualie wheels, or a great selection of wheels of differing profile, so we make do with more wheels. The trick here is simple - more area contacting the ground = more traction. Hence why tanks use treads (among other reasons). Worth mentioning that the motors in the wheels, true to life, seem to have really amazing torque, they will do their top speed of 25m/s even with pretty heavy loads!

- Minor factoid I remembered: 1 RTG = 1 fully powered wheel. Unpowered wheels don't use juice even if they have steering enabled and powered wheels only consume EC when actually running the motor. Not that you have to use RTGs but this is a nice thing to know. However you don't have to have full power at all times, especially on Mun where you can coast nearly 90% of the time without hardly losing speed, so in practice you may need less power than you think. Not that I mind your overengineering, I admire it!

Driving:

- What it really comes down to at all times is traction. Downforce is about traction. Flipping is about losing traction, or getting uneven traction. Think of traction like a resource; any action you take uses part of your traction budget. Accelerating, braking, turning, all use traction, just like in real life. Unlike driving on a well maintained highway under Earth gravity, your total traction budget may subject to change without notice, which is what trips folks up (besides the fact that driving on Mun gravity reduces it significantly already). The problem is you can't see this resource, you have to guess at it. However, without seeing it you can still know that when you turn, you should neither accelerate nor brake, for example.

- An extension of traction is slope. Going uphill gives you better traction, gravity is pulling you down the slope, and you are driving into it, so your wheels get good contact with the ground. So long as the slope isn't flipping you backwards, going uphill will be to your advantage in low gravity. Going downhill is of course the opposite; you are driving "off" the slope so your wheels have poor ground contact and hence poor traction. As a result you can go faster uphill but must take it easy going downhill; I advise coasting, tapping the brakes or reverse as needed to control speed, and engaging downthrusters if needed.

- Avoid driving parallel to slopes, this is yet another wonderful way to roll your rover. Whenever possible you probably want to go into slopes straight on; when tackling more severe slopes where doing that is itself hazardous, you can snake up or down the slope, but you must be very careful, and practically stop when you make the S turns. Such maneuvers should be have a very wide "wavelength", just swerving back and forth in a generally forward direction is usually worse than just driving straight forward, but going in very broad waves can let you ascend or descend unreasonably steep slopes if the rover has a low enough CoM to not roll over while doing so.

- Downthrusters are not something you have to run all the time. You don't want to, that's a waste of fuel. You'll need them when you make turns, when going downhill sometimes, and when you want to brake faster. Plan your turns; on the Mun, you should drop speed below 15m/s or so, then engage downthrusters, then begin a turn to a planned heading. Once you're stable on the new heading, turn off downthrusters. If you used engines with a throttle, like the Twitch, you can selectively use minor downforce for simple corrections, or heavy downforce for emergency evasive driving or if you panic. After a little driving, you should get a pretty good feel for how your rover behaves in the environment you've put it in, and how much downforce you want at which speed to make desired turns. Keep in mind the simple rule that the more downforce you use, the more traction budget you have, the more aggressively you can spend said traction (such as with a much tighter turn radius).

- SAS stability totally works in a rover. Keep it on, and when it tries doing a little correction steering, don't immediately override it. Even driving a straight line is much easier with SAS on. You probably do this already, but if not, I'm not kidding, it's great!

- Driving fast mostly means driving a straight line either gently uphill or on extremely level ground, and having enough downforce to deal with whatever terrain variances you encounter. On Minmus's flats, this a cakewalk, no downthrusters needed just don't make sudden high speed turns. On most of the Mun, this means jockeying the downthrusters diligently without being wasteful of them, and also picking out reasonably straightline paths between craters and holding to those vectors as well as terrain allows. Rough terrain is rough terrain, though - if you want to drive up and down mountains, you go slow up and slower down.

Really truly speedy rovers that go even 50m/s+ consistently are gonna use all landing gear or mod wheels in all likelihood and IMO are a whole different category of build. They're much harder to make, harder to drive, and typically less versatile (rover wheels have potentially unlimited "dV" while rocket sleds do not, to say nothing of the difference in how speed is being acquired). They sure are fun though! But I'll let you in on a secret: physics warp can totally work with a rover. At x2, you should have mostly normal physics still, and in fact I almost always drive on x2 even when making cautious maneuvers. x4 might require you to bugtest the rover to make sure it doesn't do wacky crap when the physics inconsistencies from that warp level creep in, but you can absolutely speed across gentle terrain at x4 in many places. One great thing about this is that you get the "let's go faster" feeling but so far as the game is concerned, you're still driving whatever your actual speed is, so you won't actually be any more prone to going off the rails than normal, provided you can keep it in hand (and it doesn't spontaneously explode, many part combinations seem to do this so really do bugtest this).

Sorry it's long and I ramble. I bet you can tell I love rovers. I hope this helps, and good luck in your adventures!

Edited September 9, 2015 by Hagen von Tronje

[Pax Kerbana]

Unlike common held opinion, a recent excursion demonstrated something I had noticed but had been unable to put my finger on.

I think the key to successful roving is MORE mass, reaction wheel, and RCS thrusters. Base modules I move around easily with a tiny rover under a big module but my Kerbaled rovers always seem unwieldy. The base modules are a little tippy but they are predictably so. Light rovers are squirley and have difficulty on slopes.

Reaction wheels are used to correct orientation of a jumping rover and to increase traction on slopes, otherwise keep it off. RCS only necessary for occasional rotation control and for forward/back assist. RCS is also the emergency brake because let's face it, the regular brakes are useless. RCS is not to be used for flying/hover!

[JTpopcorn]

To make stuff not boom make a skeleton around the outside out of I beams. Quicksaving is your friend, as well as SAS but dont overdo it.

[Sharpy]

A good method to bring your CoM way down is to attach a bunch of jet engines pointed upwards as your ballast. Their CoM is actually outside them, quite a bit into whatever they attach to. So if you point them upwards, you can move your CoM below the ground!

Also, good reaction wheels (and possibly RCS), and two-handed driving. Reassign Rover Controls to a different set of keys than WSAD, then drive using both sets of controls - keeping your left hand on Q/E and W/S to use the reaction wheel to level your rover.

Steep slopes will be your bane. You will really want some engines or RCS on front and back.

(I didn't do ElCano, but I drove a rover 30km through one of large craters and a canyon...)

[Cairol]

I use SAS permanently. I have RCS equipped. But I intended to use it for better control above the ground if I lift off at some point.

(but the MK2 Cockpit actually has enough reaction wheel torque on its own)

Didn't think of using RCS for increasing my ground traction...

My rover is already pretty heavy. It has a mass of 15 t with full tanks at 1g. (= 2.5 t on Mun) But the CoM could be lower, I guess.

I try to not drive through larger craters. Because up/down/slope driving is my enemy.

The tip with phys warp seems good for a slow rover. But I fear the kraken. So I pretty much never ever use this.

I'm currently trying my slightly optmized design.

If it does not work out, I'll make a more drastic redesign to incorporate some of your suggestions.

Edited September 10, 2015 by Cairol

[Kelderek]

My tip: bring along as much patience as you can.

[xendelaar]

How long does it take to perform a typical circumnavigation trip? This thread ignited some interest in me but it still sounds like a 2 hour waiting game. ... (even without all the crashes). The engineering part sounds like a really cool challenge though.

[Hagen von Tronje]

How long does it take to perform a typical circumnavigation trip? This thread ignited some interest in me but it still sounds like a 2 hour waiting game. ... (even without all the crashes). The engineering part sounds like a really cool challenge though.

Depends on where it is and what you'e driving. Minmus in a rocket sled could probably be done in a few hours. My Kerbin route took me 45+ real time hours (not game hours, it took me 11 days in game, I used physics warp frequently), maybe more, that's just an estimate.

It's not just a waiting game, though. You will likely encounter some very hostile terrain at some point, and getting through that often takes some resourcefulness, particularly if you don't want to pull your hair out. However, they are typically very lengthy missions, for obvious reasons.

If you'd like to try an Elcano, I suggest Minmus. It's got some of the smoothest terrain, it's got flats that will let you shave hours off your drive, it's got interesting sights (at least IMO), and the low g does provide an engineering/driving challenge to overcome. It's also one of the prettier and less oppressive places to drive IMO. If ends up boring you, it only takes a few hours to complete and you'll have it under your belt rather than giving up, and if you like it...there are a lot of planets and moons!

One nice thing is that because Elcanos are meant to be adventure challenges and mod parts are permitted and even encouraged, the nature of the drive is up to you! You can choose to set a land speed record on flats or you can choose to go mountaineering or boating, you can take a caravan through the desert, you can drive a train! You decide which mountains you climb, which gullies you dive into, which glitched terrain you endure for the wacky screenshot. You even determine the conditions you drive under, you can do all daylight driving or take the night as it comes, and all of those things completely change the character of the challenge.

[xendelaar]

Thanks hagen for your kind reply. You've convinced me to try and circumnavigate minmus. I'm currently working on the cave man challenge but when I'm done with that i will try to circumnavigate minmus. I can't wait.

I do have to read up on the whole braking bug issue. Never heard about that before.

On a side note. ...aren't the biggest rover wheels capable of withstanding a velocity of 200 m/s ? (I can't check because I'm not at home) It sounds like they would work well in these situations.

[xendelaar]

45+ hours. .. for one mission. .. that's impressive man! You must have some real patience and determination skills.

[Hagen von Tronje]

Thanks hagen for your kind reply. You've convinced me to try and circumnavigate minmus. I'm currently working on the cave man challenge but when I'm done with that i will try to circumnavigate minmus. I can't wait.

I do have to read up on the whole braking bug issue. Never heard about that before.

On a side note. ...aren't the biggest rover wheels capable of withstanding a velocity of 200 m/s ? (I can't check because I'm not at home) It sounds like they would work well in these situations.

The braking bug is probably the source of a LOT of gripes about rovers. Whenever you tweak a wheel, the brakes will go to a fraction of their effectiveness, and will never go back to full, ever. The bugfix gives you the normal braking torque range, so you can tweak them anywhere from dangerously stiff to nice and gentle.

Out of stock rover wheels, the tiny wheels can take 20m/s, the balloon and ruggedized wheels can take 60m/s, and the huge XL3 wheels can take a paltry 30m/s, not that they can go that fast. The huge wheels also work on a cantilever and have all the maneuverability of a drunken cow, if you can do an Elcano with those, my hat off to you and mad respect, I can barely make a functioning rover with them.

Unfortunately with stock wheels there's little question that the ruggedized are the wheels of choice. Balloon wheels are actually almost as good, main problem is, they're the same thing, just slightly inferior, and offer no even situational advantage that I know of. They're even more power hungry!

Wheels themselves are actually really durable though, I've almost never had a wheel be the thing that blew up on me. They can be repaired infinitely in the field even in stock so feel free to use them as bumpers, I certainly have and they work great for that. I find it's a lot more common for impacts to transfer force through the wheel, jamming it into the chassis and blowing that up, or for minor irregularities in the terrain to poke up and rack your undercarriage or chassis and blow it up that way (they can be REALLY hard to see unless you're driving with your camera down under the vehicle!), hence the conflicting interests of ground clearance and low CoM.

I look forward to seeing your Elcano! I might also suggest, if you're not already, consider visual enhancement mods. I know that sounds meaningless, but when you spend dozens of hours looking at a planet, it's nice if it's fun to look at!

[tbarcello]

Check out this video. It travels 10-15 m/s no trouble, but faster - dangerous.

[Starwhip]

I find that the large landing gear have some ridiculous tolerances (I'm 99% sure they're invulnerable actually, unless you slam them into the ground at a high enough vertical speed. Watch out for that, it's orders of magnitude more dangerous than horizontal speed.)

This was one of my Elcano run vehicle iterations. Ridiculously fast. The vessel in my signatureWhoops, sorry, forgot about that. Here it is: Silverfish, which I am currently using can safely travel at around 70 m/s. If and when I do a Mun/Minmus run, I'm going to adapt one of those designs to have artificial downforce (most likely with ions). They're very strong.

Edited September 11, 2015 by Starwhip

[Motokid600]

If it wasn't for a challenge I'd say cheat. I cfg edit the max speed and breaking points of the ruggedized wheels to 999999. Works great. With it I can make rovers that cruise at 100m/s. It's fun as all hell and at that point the lost challenge with the hacked wheels is offset by the difficulty of controlling a rover at those speeds.

I like getting places fast. It makes roving in ksp practical and just plain fun.

[cephalo]

The main hazard on the Mun is that the map is rather low res from a rover point of view. Occasionally this leads to invisible sharp angles that will launch one of your wheels and send you spinning. The bottom of a rolling valley can look smooth but geometrically might be like driving into a wall (It's not a U shape, it's a V shape). It would be easy to drive fast there if not for these invisible traps.

[Branjoman]

To help with COM issues, the RAPIER actually has a bugged/incorrect COM - its centre of mass is quite a ways in front of it, instead of inside it. Place some on cubic girders on top and clip them in the fuselage (for aesthetics of course).

[Cairol]

@cephalo

It's exactly how you say. I always angle my camera in a way so I can better detect those pesky spots early.

But it does not work out every time, because the Muns surface has a pretty uniform texture that makes the feeling for depth of the terrain difficult.

@Branjoman

I won't abuse such things knowingly. My pride dictates me to go down with a good conscience.

I chose the Mun, because I think it's a good start for a circumnvigation.

It's not that big and it's gravity is more forgiving than that on Kerbin but not so delicate like that on Minmus.

I could imagine, going a bit too fast on Minmus could lead to making an orbit if you overlooked some small hill. XD

[Motokid600]

The Mun is difficult for circumnavigation because it has a different terrain system then all the other planets making it very hazardous. The best place for roving? Eeloo easily. Place is as flat and featurless as it gets.

[xendelaar]

Hagen, I've got Planet Shine. Are there any other visual enhancement mods available at the moment?

I just finished the cave man challenge so I'm up for the Elcano Challenge. I'm building my rig as we speak. I Can't wait to test my rover

[Hagen von Tronje]

Hagen, I've got Planet Shine. Are there any other visual enhancement mods available at the moment?

I just finished the cave man challenge so I'm up for the Elcano Challenge. I'm building my rig as we speak. I Can't wait to test my rover

http://forum.kerbalspaceprogram.com/threads/102145-0-25-Astronomer-s-Visual-Pack-Interstellar-V2

AVP is what I use, provides a range of nice effects from auroras (on multiple planets), dust storms, snowstorms, clouds at multiple altitudes, the works. Everything is optional/configurable so if you start running out of memory or if one of the effects bothers you, you can remove it.