Rover uncontrollable on Mun

[Gilead]

Hi! I recently designed a rover to scan for resources after I put the M700 Survey Scanner around Mun.

I tested the rover on the KSC and it is very easy to control, it drives well. But when I got to Mun, it was another story, the slightest change in direction makes the rover leave the ground and bounce around ! And even when going straight at low speed the wheels spend more time in the air then on the ground.

Here are some pictures.

Btw, I know I went overboard with solar panels and batteries ^^

I have never designed rovers before, and I have no idea what I did wrong.

Thanks in advance for your help.

Edited May 6, 2018 by Gilead

[bewing]

Well, you didn't really do anything wrong. Driving in a low-G environment it is extremely difficult. Unless you go really slow -- you will spend a lot of time in the air, and you will spend some of your time upside-down on the ground.

So these are extra design considerations you need to take into account when you build your rover. It helps if it has a reaction wheel so that you can spin it upright in the air, so that it will mostly land back on its wheels. It helps if it has some mechanism (reaction wheels, RCS, or some clever mechanical contraption) so that it can flip itself back upright when it lands upside-down. Some players build their rovers so that they have wheels on the top, too -- and then they don't care about landing up vs. down. Alternately, you can make your rover extremely large, with a low CoM and a super-wide wheelbase. This makes the rover hard to flip in the first place, and averages out the bumps in the terrain.

Alternately, some players put a small rocket/RCS/ion engine on top of their rovers, pushing down. To supply the missing gravity, in a sense. You can activate the engine when you are just about to take a jump, or when you get otherwise bounced into the air.

Adding the reaction wheel also allows you to flash SAS on and off. If you get bounced into the air, and you are starting to rotate, you flash on the SAS -- and it stops the rotation for you.

So overall, designing a functional Munrover is a whole new kettle o' fish beyond designing rockets and spaceplanes. New learning curves and the whole bit.

 

[pquade]

Something in 1.4.x introduced into the rover equation a different behavior than previous.

Rovers that I had previously been able to drive on both Mun and Minmus suddenly are way more twitchy.

[bewing]

There was a Unity upgrade for version 1.4. Every time the KSP Unity engine gets upgraded, it changes the way wheels and suspensions work. So the rovers all need to be retuned a bit for version 1.4. Additionally, through version 1.4.2 there was an undocking bug that made rovers extra bouncy just after they undock. But none of that should affect newly built rovers in 1.4.3.

 

 

[Geonovast]

You can actually test for close to Mun conditions at the KSC.  Using the F12 menu, you can "hack gravity" to temporarily give Kerbin the Mun's gravity.

Pretty sure this would muck up stuff in orbit, so I would do the testing in a separate sandbox save specifically for that reason.

[mystifeid]

If you ever get sick of being hands on all the time - some contracts may require a round trip of 50km or more - the stability control in the rover autopilot module of mechjeb seems to do a pretty darn good job of always landing on all four wheels. My rovers tend to be on the heavier side (15t - 20t) and I find it very amusing to let mj drive me around at 25 - 30ms^-1 taking huge jumps along the way.

[Serenity]

1 hour ago, Gilead said:

Hi! I recently designed a rover to scan for resources after I put the M700 Survey Scanner around Mun.

Nice little rover.

1)Play with SAS, turn it on see how things go

2)Introduce RCS for downforce

3)Turn friction control to Override and set it to maximum, see if that helps

4)Wider is better

5)Turn only in front wheels

6)Testing, testing and testing

[Gilead]

45 minutes ago, Geonovast said:

You can actually test for close to Mun conditions at the KSC.  Using the F12 menu, you can "hack gravity" to temporarily give Kerbin the Mun's gravity.

Thx, but I installed HyperEdit, so I can send my rover on the Mun easily on my sandbox tests save.

Ok, so I tried adding Dawn engines on the top pushing down, and I put reaction wheels on both ends of the rover... New problems... When I it [W] to go forward, the ship starts spinning on itself (like a satellite would for example) and the wheels don't spin.

So I removed the reaction wheels. With both Dawn engines pushing at full throttle I can drive kinda correctly at 10 to 12 m/s on Mun but all hell breaks lose when I go down a slope.

I'm gonna try the approach with wheels on top, to see if it's better.

EDIT: I tried the aforementioned technique, and I got stuck sideways!  I'm pretty sure I wouldn't have managed to do it if I tried xD

 

Edited May 6, 2018 by Gilead

[bewing]

1 hour ago, Gilead said:

New problems... When I it [W] to go forward, the ship starts spinning on itself (like a satellite would for example) and the wheels don't spin.

In Settings/Input/Vessel/Wheels, you can change the "W to go forward" to some other key, so that it does not conflict with the reaction wheel.

 

Edited May 6, 2018 by bewing

[Serenity]

14 minutes ago, bewing said:

In Settings/Input/Vessel/Wheels, you can change the "W to go forward" to some other key, so that it does not conflict with the reaction wheel.

I read somewhere if you switch to docking mode it fixes that, is it correct? I have to try it.

[Gilead]

14 hours ago, bewing said:

In Settings/Input/Vessel/Wheels, you can change the "W to go forward" to some other key, so that it does not conflict with the reaction wheel.

I checked that, my rover works with the new keys, but still hard to control.

14 hours ago, Boyster said:

I read somewhere if you switch to docking mode it fixes that, is it correct? I have to try it.

Tried that, switched to docking mode, tried to move, nothing happened.

[mystifeid]

On 5/8/2018 at 12:43 AM, Gilead said:

Tried that, switched to docking mode, tried to move, nothing happened.

If, after switching to docking mode, you hit the space key to change to rotational control then the keys will work but I doubt you will notice any difference from staging mode.

Anyway, I made something that looks as much like your rover as I could and took it to the moon. First was one with no reaction wheel but unfortunately, the SAS from the probe core provided almost zero rotational authority once the wheels left the surface and it was quickly consumed in a ball of fire. However, the simple addition of an Advanced Inline Stabilizer made a big difference. To overcome the rover dipping forward I used caps-lock to turn on soft controls (pitch/yaw/roll markers turn blue) and took to tapping the wsad keys instead of holding them. It was pretty easy to get it moving at 30ms^-1 and taking some big jumps. Recovery was also easy. I think it's important to always be planning how to put all four wheels back down on the surface at the same time (and in the direction you are moving) and to do this you need something that can rotate the rover on all three axes. Engines pushing down won't cut it. This means either SAS or RCS or both and if you have to pick just one it would be SAS.

 

This was a jump 80m off the surface. First bounce was 10m back up again but it soon settled. Doubtless, there are probably many things you could do to make it better but I ended up driving it around for quite a while and the more I got used to it the more I enjoyed it.

[Corona688]

If it can jump 80m off the surface it's probably overpowered.  Consider turning off some of those motor wheels.

[Gilead]

Thank you everybody!

I think I got the hang of it, it is drivable with an Advanced Inline Stabilizer and soft control. I just need to drive it a while to improve my driving skills.

[ArmoredLipid]

Switch your SAS to stability assist only; pilot will attempt to orient your entire rover in whatever direction you selected.

[putnamto]

with my rovers that have the medium size reaction wheel i usually drive with SAS off, and the Reaction wheel turned off also, then i try to keep speeds beetween 15-20ms, but i slow down to 10-13 when taking turns or she rolls. but when she rolls i just turn on the reaction wheel and flipper upright.

reaction wheels are also good for when you get inevitibly board of the loooooooong drive and decide to hit every bump you can for airtime, then you can use the reaction wheel to reorient yourself so you dont become a pile of garbage on the surface.