Rover Design

[Synapse]

Can somebody talk me through designing a rover for use on Mun/Duna etc? I’ve made a few functional rovers, but the design isn’t very good. I’d like to know how to structurally build them, keep the CoM central, and the best way to attach them to a rocket etc. I’d like to send a rover to Duna now I’ve got the journey down.

I have used the search function already, “rover design†doesn’t bring up anything.

[Colonel_Panic]

Well, it will depend on where you plan to drive them. You'll probably want at least one radioisotope generator and a heavy battery so you have some night time power ability, and some solar cells for maximum daytime endurance. I use subassembly loader to save my rovers, and start building them as attachments to an existing ship so the root piece is the docking port, allowing me to just drop one on to any lifter or lander I have in mind.

I recommend a low center of gravity and wide wheelbase, make it flat, light and stable... add an SAS unit to help keep it level when travelling at high speed, and several octo2 probe cores, to add additional spin torque to help keep it under control and to flip it back over if it takes a tumble. A single RCS tank and a couple thrusters can also help get you un-stuck or reach high places, return the rover to a ship, etc..

I usually use structural panels to give a flat square base to start building on, and struts or girder segments to give a solid frame to attach the wheels to and give it some extra strength and durability.

Check out the Igaluk rover in my signature to see how I build them.

[vincespeedmk2]

Like the colonel says. Low centre of mass is essential if you don't want your rover to roll during turns. If you use the old rover wheels you can mount them above the CoM.

As for descent. For duna, 2 or 3 chutes should do it, but if not then a simple sky crane will sort it.

To build a sky crane. Place a decoupler on the CoM of your rover. Place a one meter truss on the decoupler. Using 4 way symetry place trusses coming off the first. Then place 90 litre tanks on the end off those. Finally, attach your choice of engines to the tanks. Bam DIY sky crane.... DOOOOONE!!!!!

[el_coyoto]

I haven't designed many rovers, but from my experiences :

• They need a CoM as low as possible to avoid flipping over when turning
  
• I build them perfectly symmetrical to avoid trouble, but this is more a matter of preference (so that they drive the same way when you drive backwards).
  If you're as lazy as me, you can even do it in the VAB by using the small rectangle beam (wiki down, can't find the part name, see pictures below). You put a central piece, build one half of your rover, then apply 2x symmetry. You can use 2x symmetry on your "half rover" to put the wheels, then select the "half rover" part and re-apply 2x symmetry to duplicate the "half rover" part.
  
• Landing : I rarely used pure skycranes, but rather landers with big landing legs and struts/girders to leave some clearance for the rover.
  I slap the rover under the lander with a decoupler, and connect the rover+lander to the rest of the rocket with a decoupler under the rover. The consequence is that I have to radially attach the engines of my lander, but this is my standard design anyway (I don't have pictures of it right now, sorry). This make it easier to turn the ship to a manned lander + rover à la Apllo if needed...
  
• Landing (bis) : if you land on a world with an atmosphere, you can estimate the parachutes need thanks to the awesome KSP Chute Calculator.
  
• Driving : in staging mode, the probe that controls your rover will apply torque as on any other ship. While on Kerbin this is not very noticeable, on low grav bodies, the probe core will have enough torque to flip your rover when you turn because you press the 'A' or 'D' key.
  The 2 usual workarounds are : use docking mode or remap your rover control keys to another set of keys (people usually go for IJKL)
  
• Driving (bis) : another trick is to disable steering on the back wheels. This will make the rover behave much more like a normal car and it will not flip over as easily on tight turns.
  
• Driving (ter) : use 'CAPS LOCK' to switch to precision mode. This way, the wheels will turn more gradually and acceleration will be smoother (this can be useful on low grav bodies if you don't like wheelies...)
  

A few examples using more or less the same "backbone":

Light rover : fragile wheels, but light and useful as a scout.

Quite proud of this one. Low and fast. It can do backflips and land on the "roof" without any part being damaged. Seats included to please Jeb...

(I can add pictures of the lander when I get home if you are interested...)

Cheers and happy rovering !

[Benie]

When you say to "keep the CoM low", how low is vital for rovers?

I have this. Using 4 RTGs to weigh it down. This is my Speed Rover, capable of going over 50m/s with the Aerospike engine (which is pretty fast for a rover).

It has KSPX Fuel and Oxidizer Tanks on both sides, and RCS Tanks. It weighs 5.49t. The TWR (whatever that is) is 3.25.

I can get up to 50m/s on Duna fine, with it occasionally shaking due to the terrain, and having the rover "get some air" at times. But I've had several occasions that at 30m/s, it will suddenly start to rotate left and right then the entire thing flips over. By that time it can't be saved.

My question, is the CoM low enough for this? If not, how can I make it lower? And the red lines are Quantum Struts, to securely connect to its lander.

I know legitimately, this thing wouldn't go far without running out of fuel. But my title should explain how I play.

Edited July 11, 2013 by Benie

[NoMrBond]

I like low and wide, because Jebs a leadfoot (we can blame Jeb, right?)

The conventional car layout wasn't Kerb enough either

Edited July 11, 2013 by NoMrBond

[Colonel_Panic]

When you say to "keep the CoM low", how low is vital for rovers?

I have this. Using 4 RTGs to weigh it down. This is my Speed Rover, capable of going over 50m/s with the Aerospike engine (which is pretty fast for a rover).

It has KSPX Fuel and Oxidizer Tanks on both sides, and RCS Tanks. It weighs 5.49t. The TWR (whatever that is) is 3.25.

I can get up to 50m/s on Duna fine, with it occasionally shaking due to the terrain, and having the rover "get some air" at times. But I've had several occasions that at 30m/s, it will suddenly start to rotate left and right then the entire thing flips over. By that time it can't be saved.

My question, is the CoM low enough for this? If not, how can I make it lower? And the red lines are Quantum Struts, to securely connect to its lander.

I know legitimately, this thing wouldn't go far without running out of fuel. But my title should explain how I play.

low is a relative thing to the vehicle's wheelbase. Think of your rover as a pyramid, where the peak is the center of mass, and the wheels are the base. You want it to be wide and flat with shallow sides, so it doesn't tip over when pushed to the side. The more height your COM has, the wider you need the wheelbase to be to compensate. Your craft is narrow, with wheels near the COM, which means it can roll easily. To fix that, you need the wheels to be wide out to the sides, like spider legs, or find a way to push the COM lower, or compensate for rolling forces in other ways.

[Keome]

https://www.dropbox.com/s/mo6zzj73akhvijn/rover1.png

This is a small one Kerbal rover I made using the 1x1 meter square plate as a base. It's got an external seat, solar panels, ASAS and SAS modules, Mechjeb, headlights and enough batteries for limited darkside driving on the Mun and Minmus. A remote version can be made by adding the appropriate remote guidance module to the stack.

In the version shown, it had a tendency to tip over if you braked too hard because the Kerbalnaut was a bit too chubby after eating all of the snacks.

[Colonel_Panic]

https://www.dropbox.com/s/mo6zzj73akhvijn/rover1.png

This is a small one Kerbal rover I made using the 1x1 meter square plate as a base. It's got an external seat, solar panels, ASAS and SAS modules, Mechjeb, headlights and enough batteries for limited darkside driving on the Mun and Minmus. A remote version can be made by adding the appropriate remote guidance module to the stack.

In the version shown, it had a tendency to tip over if you braked too hard because the Kerbalnaut was a bit too chubby after eating all of the snacks.

That's a pretty tall rover with a high center of gravity. It will be prone to tipping. Consider mounting things like the batteries and generators underneath the base panel, and not using the in-line batteries and ASAS as they add height to the rover.

braking will flip any rover. The brakes are just too strong for the physics engine. They should probably fix that.