Rover Steering to use Ackerman Principle.

[OTehNoes]

Hey guys, I actually just made an account to put this forward!

I managed to get my first rover/car onto the Mun the other day, after much effort to get it onto the surface successfully, I started driving around, only to have it flip over almost immediately, and I figured out the problem.

The steering on KSP does not use the Ackerman principle, and so the wheels scrub upon cornering.

To those of you who do not understand the ackerman principle, it is where the inside wheel of a car during a turn has to turn at a tighter angle to follow a tighter turning circle than the outside wheel, as shown by the diagram below.

Instead in game, the wheels are attempting to follow a path more like this (MS paint ftw)

As a result, as soon as the path stops being the width of the axle, the wheels begin to scrub, and in a low gravity environment such as on the Mun, this causes vehicles to flip.

I've managed to slightly counter this affect by crudely adjusting castor angles though I'm yet to test a design like this in a lower gravity environment.

So what I propose is adding this system into the game, I wouldn't have thought it would be too hard to do as it can all be worked out as you can see on this Wiki page explaining it, its all relative to the centre of the rear axle.

Sorry for the wall of text though I hope my explanations made sense!

Thanks for reading guys, I hope this is taken into consideration!

Edited July 26, 2013 by OTehNoes

[basbr]

i see what you'r getting at, but adding something like that would be very hard because the wheels are placed by the player and there position is not known ahead of time

for example, you say its all relative to the centre of the rear axle. how do you define the rear axle if the vehicle has 6 wheels or 2. what if the wheels are angled.

I see the problem and there is no easy way to solve it.

I suggest driving a little more careful and having rovers with low centre of gravity

[OTehNoes]

Well it applies only really to 4 wheeled cars as 3 wheelers can sort of get around it, or at least lessen the effect. And I honestly tried driving as carefully as I could, but this kept happening. Was a real shame as it took so much effort just to get it up there!

[OTehNoes]

Also maybe I should have been more specific, I mean things more like a car than say a rover. The Apollo 16 rover had 4 wheel double ackerman steering, maybe that could be the easier option? As both front and rear axles would follow the same circles?

[OdinYggd]

KSP rovers already use 4-wheel steering unless configured not to by turning off steering on some of the wheels.

Generally though if you are having problems with a rover flipping over, you're driving too fast for your current conditions.

It also helps to keep your rovers as wide and low to the ground as possible so that they are resistant to tipping, and many designs use small engines or ions to provide downforce for improved traction and stability.

[CombatWombat]

Rover wheels have such rudimentary slip-angle "simulation" that this wouldn't do much of anything. Ackerman adjustment is barely noticeable even in dedicated racing simulations that put the bulk of their development time into their tire physics.

In KSP the wheels struggle just to stay above the collision mesh of the terrain, most of the time.

[Arran]

I understand what you'r saying, but the wheels in KSP work differently..

First of all, biggest problem, KSP dont use differentials, so wheels all turn at same speeds in corners, unlike normal cars/trucks do. So the shrubs in corners and thus give the strange cornering effects. Then since the wheel are independed without differential powered the effect gets even stranger.

I dont think there is an easy fix for this, nor i doubt it can be modded in the manner how wheels are supposed too work.

Changing wheel angles doesnt help much, since the effect isnt simulated, and can lead even too that they can break easier from the rover.

hence this isnt a racing sim like iRacing for example

Flipping over can be solved by making the wheelbase wider, and flipping on breaking can be solved by making the wheelbase longer, but this doesnt allways be a working sollution if you try too squeeze the rover into a tiny space on a rocker/spaceplane.

So this only works for "fun-rovers"..

As i said, this isnt a driving sim, so you prolly need to work here with limitations

[Scoundrel]

CombatWombat is correct in that the flipping isn't because of the Ackerman Principle - which wouldn't induce flipping anyways. It's simply a solution to reduce the wear and tear on tires and running gear, and to improve turning performance. Without Ackerman geometry a rover simply would have pronounced understeer rather than flipping. What causes the flipping is the tires not breaking traction when they should, and that is simply because KSP's physics model for the wheels (including those bizarre torque curves) is pretty primitive... enough that whenever I try to do BOE calcs for my rovers, they always leave me scratching my head, lol.

Bobcat's DEMVs have much better stiction/traction modelling, if you want to compare. Personally I prefer how Squad handles rover building better, but I would love it if Bobcat wrote a plugin to hijack Squad's wheel physics so we got the best of both worlds. IMHO Squad has a lot of other things to make/fix before they should turn their attention back to the wheels.

Flipping over can be solved by making the wheelbase wider...

Wheelbase is made longer, track is made wider.

That said, I agree with your post.

Edited July 27, 2013 by Scoundrel

[OTehNoes]

Well guys thanks for the responses! I guess you're right! As I said the problem only really became evident once I was in a lower gravity environment, though I wouldn't say the design was particularly prone to flipping otherwise, it had a fairly square wheelbase and low centre of mass, yet when driving on the Mun, I couldn't go faster than about 1m/s before it began to flip and tumble through the air (or lack of ha!).

But hey, I am a petrol head, maybe I just need to learn to slow down every once in a while!

[Comrade Jenkens]

Keep in mind that real rovers like curiosity don't go fast.

[OTehNoes]

I'm talking about things more like the Apollo Rover, a space buggy if you will.

I'm not talking so much about rovers similar to curiosity's design.

[OTehNoes]

Not to mention flips were happening at low speeds, 1.5m/s maybe.

[boomerdog2000]

In the meantime you could consider adding outriggers of a sort in between where your front and rear wheels are then setting those middle wheels to not turn to reduce flipping.