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B-80 excessive sinking in the front


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Maybe the sinking of narrow wheels is exaggerated in the game or the tractor is too front-heavy, but it's hard to imagine a tractor like this would be useful in real life.  This is what happens after the tractor is spawned in the swamp before even being driven.

20201104235047_1.thumb.jpg.a090a4f5bf34e49348577f6766aed501.jpg

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I see that from legendary downgrade (not upgrade) of game physics. Actually it is caused by gravity anomaly. In mud atoms have too much space between each other and this cause gravity anomaly.

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@rarumWell this game for sure doesn't simulate mud atoms but it is likely caused by the new ground pressure calculations.  I suspect they are exaggerated and maybe they don't account for the fact that when a wheel pushes down on the mud harder, the mud also pushes back harder, so it's not exactly more pressure = faster sinking.

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Already wrote about this.

On 8/26/2020 at 10:37 PM, Alex Cameron said:

No, the translator conveyed the essence of the question surprisingly accurately.


In version 1.5.1, the B-80 could drive until it ran into deep mud (and could still get out, in mild cases), and in 1.6.1 it cuts through the mud. This problem did not exist, which means that the issue is clearly not in the mass of the wheel. The B-130 does the same, but not so obvious.
Cars with wider wheels do not sink into the mud. For this, the tire pressure was added to the game, so that when the wheels are deflated, the resistance to immersion in mud increases. Well, logically, this is how it should work.
So there should be such a parameter. 
🤔

2717.gif

At the same time, I found a solution.

 

On 8/26/2020 at 10:56 PM, Alex Cameron said:

SO. In the parameters of the wheels, vehicles have the following item: "Width = x.xxx". The default value for B-80 is 0.172, and if you change it to 0.355, the tractor stops falling into the mud. Checkmate. This means that the mud has a parameter that considers that the thinner the wheel, the faster it will sink in the mud. It remains to correct the absurdity of this parameter.

1111.gif

Now you can do the same, parameter 300 is enough.

Edited by Alex Cameron
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Thanks.  Yes that would be a temporary fix for one vehicle.  But I'd rather have this fixed in the calculations so that real tire widths can be used and they still behave realistically.

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@Trackrod_STHello, can you help me with something, please?  I'm trying to calculate where b-80's center of mass should be.  Can you look over the data and tell me where the COM should be?
From my calculation it seems that it's placed where it should be. But PressureLine says that it should be pulled backwards.  And the 3000 kg front axle is really strange. Also should the tyres be wider?

Here's the data from b-80's manual:
operational weight: 6500 kg
weight on the front axle: 1220 kg
weight on the rear axle: 2550 kg
wheelbase: 2475 mm

Tyres:
It has 9.00R20 tyres, which have а widht of: 262 mm  (from kama's website, I couldn't find what MTZ-80's tyres are called).
The tyres in game however are only: 172 wide.

In game the tractor has two main bodies with the following weight:
Chassis: 3600 kg
Front axle: 3000 kg

Here's something funny - the tractor sinks even in the editor:

Capture1.thumb.JPG.7f51daa1c11054ce18364cd358b887c9.JPG


So, what i did was:
Changed the front axle weight to: 1220
Changed the chassis weight to: 5280
And I moved the COM backwards - and this fixed the issue with the sinking front wheels.

The red dot - shows where the default COM is
The yellow dot - is where the 0.0 center is
The green dot - is where I moved the COM to

Capture3.thumb.jpg.90578eec4344646ec4d1115e75bbe98f.jpg

Edited by Truckwolf
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@TruckwolfI don't know if the center of mass would be that far back.  It would seem that tractor would tip backwards very easily.  RWD tractors don't tip that easily (I've watched many mud-running tractor shows) but they also don't sink in the front like the ST tractor does.  It's also important to take into account the wheel mass.  Those huge rear wheels must have a significant effect on the center of mass.

Edited by Unster
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@Alex CameronI settled on using 0.28 width on the front wheels.  They still sink somewhat, but not as bad as with the stock settings.  I didn't want to go any higher because then the tire tracks get oversized.

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My COM is totally wrong, but it is what it took to prevent the front wheels from sinking (with the default tyre width). We need to readjust everything to find what is realsitic and what it would take to prevent it from sinking. Trackrod knows his technical stuff and owns tractors IRL, so I decided to ask him. And I am taking such interest in b-80 only for the learning experience.  (I much prefer MTZ-82 by pokemone)

Regarding the wheels: the default COM is not taking them into account.  
The front wheels weight: 2 x 100 = 200 kg
The rear wheels weight: 2 x 600 = 1200 kg
Should I be adding this weight to weight on the front and rear axle?

 

Edited by Truckwolf
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1 hour ago, Truckwolf said:

hould I be adding this weight to weight on the front and rear axle?

Theoretically yes, but the wheel weights were never realistic in this game, at least not for the scouts.  100 and 600 are some of the usual template wheel masses, and if they are in kg they are much too heavy as scout wheels, and I wouldn't trust them to be accurate for bigger trucks either.  Besides, we don't even know if the wheel mass is added correctly to the vehicle mass.  Remember that questionable behavior where trucks with light wheels seem to be heavier, judging by their compressed suspension.  But that may have to do with how the wheel-less chassis weight is calculated.

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@Trackrod_ST Found this -> (LINK)
ТРАКТОРЫ СЕЛЬСКОХОЗЯЙСТВЕННЫЕ Определение положения центра тяжести
Agricultural tractors. Measurement of the centre of gravity position

Capture_tractor.JPG.a5bea0aa6b559dbe8ced5c510ce38202.JPG
Capture_tractor2.JPG.93873f5d929be9b81ca7ed2ce33bd43c.JPG

X is the distance from the rear axle centerline to the center of mass.
d is the wheelbase
m is the weight on the front axle
F is the reaction force on the front axle.  

Edited by Truckwolf
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Looks like these are MTZ-80's tyres:  9.00R20 - ФБел-311
And their width is: 234 mm
(LINK)
EDIT: Actually, those are MTZ-80x's tyres. MTZ-80 has 7.5R20 tyres which are only 190 mm wide.
But since the "0.234" tire tracks fit perfectly the in-game wheels - we're going to ignore this fact for the sake of stopping the front wheels from sinking.

I did some tests, now I realise why does the front axle weight so much. WIth "1220" front axle the tractor is difficult to control. It climbed the steepest hill on Psix's proving ground without overturning, but it was very difficult to keep it straight.
I then returned the default mass values. The tractor was easy to control again, although curiously this hurt it's climbing capability, it took a lot of effort to get over the steepest hill.

Whether the front axle weighted "1220" or "3000" the tractor's front wheels didn't sink under the tractor's weight in the bog on the default proving gound. I only moved the COM to where I've shown above - on the orange dot, and made the wheels "0.234" wide.

Tinkering is so much fun! I hope I am on the right track with this though...

Edited by Truckwolf
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@TruckwolfFrom your pictures it looks like the sign on the x-coordinate for the COM is reversed.  It's 0.487.  -0.487 would be pretty much spot on if your calculation is correct.  But I've already tried that value and it didn't really help with the front wheel sinking.

Edit: It does help in combination with the greater tire width.  Now that I've moved the COM more to the rear, I can get away with 0.24 front tire width and not sink excessively.  The tire tracks are still a little fat for the tires, but not too bad.  You may also want to reduce the substance friction on the rear tires to compensate for the added weight over them so they aren't OP.

Edited by Unster
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@Truckwolf You have been busy.

First off. This game tractor has permanent diff lock. This simply would not work on a real tracktor and is why I have no interest in it..

Looking at my tractors, they have a roughly 0.4./ 0.6, front / rear, axle weight.

Using the same, this would give 1422 kg on the B80 front axle and its 7.50 x 20 tyres.

BUT.

With a diff lock on, this combination would simply not be able to turn, as it would push the front wheels sideways.

The only way to get over this is to increase the weight on the front wheels (3 ton you say) and consequent reduction to the rear. This will make it turn, but at a sacrifice to the traction. Add 2 ton to the lift arms and you're back to square one.

 

..

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Yeah, I have been.  Spintires tends to suck me in and I can tinker with it for hours. Time just flies by. Which isn't great when you're procrastinating on your work with Spintires. 😁
Like PressureLine said: "If it's wrong, it bugs me. If it's wrong and I know I can fix it, it bugs me even more."
Except that PL is brilliant and I'm a pudding head who managed to screw up both of the equations. The easier one for the front axle offset I messed up by using the operational weight instead of the construction weight (1220+2550=3770). The second equation from the manual I messed up by dividing m by d instead of the other way around (I've edited my post above to remove my stupid bs)

So, here's where the COM on the b-80 should be:

(EDITED OUT, proper calculation below)

Edited by Truckwolf
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I recalculated the COM using the game's wheelbase:
It's "-0.3035" However to be on the safe side I've moved the X COM to "-0.4".  

This is a list of changes in the attached xml files that give B-80 some much needed TLC. It's front wheels no longer sink in the mud as soon as it is spawned. And it's front loader won't bury it in the mud either.

COM offset moved  "-0.4"

CenterOfMassOffset="(-0.4; -0.5476; 0)"

And I took some of the weight on the front axle and moved it to the chassis. It's possible to decrease it even further but then the front wheels start feeling slippery and the tractor becomes difficult to steer.

Mass="4500"
ModelFrame="BoneChassis"

Mass="2000"
ModelFrame="BoneAxleFront"

Changed the front tyre width to: "0.234"

Width="0.234"

Changed the rear tyre width to: "0.394"

Width="0.394"

Gave it some very slight suspension travel, as suggested by PressureLine: 

SuspensionMin="-0.025"

Decreased the b80_front_loader mass from "1300" to "500". It was making the front wheels sink even with corrected tyre width and COM.

Mass="300" ModelFrame="BoneRoot">
Mass="100" ModelFrame="BoneArm">
Mass="50" ModelFrame="BoneGrappler">
Mass="50" ModelFrame="BoneHook">

I also disabled Difflock="always", based on what Trackrod said.

DiffLockType="Default"

The lifting arms on the rear can only be lifted up by "-2" degrees. In reality they're supposed to go much higher. They don't have collisions, but the handle of the attached trailer does. I've found myself in a situation where the arms drove tthe trailer's handle into the ground and it got stuck there.
So I increased it's angle to -8, this is the last possible value before clipping starts to occur at the back of the tractor and at the hitch.

	AxisLocal="(0;0;1)"
	MinLimit="-8"
	MaxLimit="10"
	Name="Grabber"
	Type="Hinge"

- -
Now it doesn't sink under it's own weight when spawned in the bog. (once I spawned it in the deepest part and actually it was the rear wheels that sank a little bit).
It also doesn't roll backwards on steep hills.
Here's a screenshot:

mtz-801.thumb.png.6835f08184d8874155762f8c7df4f234.png


And here are the xml files if anyone wants to give it a try. I am not making any claims to have "fixed it", I am still learning.  Let me know if It can be improved further. According to PressureLine the gear ratios need fixing.

b80_front_wheel.xml

b80_rear_wheel.xml

b80_front_loader.xml

b80.xml

Edited by Truckwolf
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I don't really care if the COM is exactly where it should be, as long as it's close to reality.  Yesterday I moved my COM to -0.3 which happens to be within Truckwolf's latest calculated range.  But I also reduced the substance friction of the rear tires to 1.2.  That's important if you don't want the tractor to unrealistically climb out of any mud hole.  1.2 is still grippy with most of the weight over the rear.

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15 hours ago, Trackrod_ST said:

With a diff lock on, this combination would simply not be able to turn, as it would push the front wheels sideways.

Probably not with a hard diff lock, but something like limited-slip or auto-lockers would be very useful on a RWD tractor in real life.  I'm not a tractor expert but I've been watching RWD tractors racing on hilly mud tracks, and I never saw one wheel spinning faster than the other.  So I think they probably have some sort of traction control.

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@Truckwolf wow what a great work you did here. i would love to test the settings or even test 1.6.2 but found no time at the moment. but i really like how the communitiy helps to game to stay alive.

When i read your researches for the B-80 troubles i come to one conclusion - the base game is not programmed with any research to real specs. They try to programm it that it works in some way in there engine.

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@Unster

Just to make it clear. (Real life).

I has an axle diff lock, but not a "Permanent Lock" of any kind. The ability to turn tight is essential in field work and this is aided by differential brakes, which can stop the inner wheel, thereby doubling the outer wheel speed and make it, turn on a dime, as they say.

The d/l is only for use in a straight line. The d/b can also be used as a traction aid, as can hydraulic weight transfer.

@Truckwolf

If you add a trailer, or any kind of weight to the lift arms, max 2 ton, then the front wheels will come off the ground. Weight is added ahead of the front wheels to balance this. (RL).

I'm guessing, this game tracktor was made to do this in the first place, hence the heavy front axle.

...

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@Trackrod_ST That's just the thing I was going to ask you about.  This type of trailer, that weights this much, is expected to lift the front wheels off the ground? And this will be countered by using a counterweight? That's 2 tons in real life or in-game?

I found the trailer that PressureLine was talking about. (LINK) 
It's a bit of a spazz, when spawned it slams it's handle/arm into the ground before moving into place onto the tractor's hitch. It weights 1500 + 5000 worth of medium logs = 6500 kg.  It does indeed lift the front wheels. I also thought about adding a counterweight. MTZ-82 has a really nice one, but there's a special rack where it fits. I could slap it onto b-80....but it'll be just slapped on.  However, there's another way to solve this - installing the grabber. It's weight is enough to keep the front wheels on the ground.
So this is realistic? Or  has this trailer revealed a flaw in the center of mass positioning?  The real life MTZ doesn't have anything so humongous. Here's a catalog of compatible trailers (LINK)
b-80_semitrailer.thumb.png.a2abe2854fe1537abecab73252f6bca2.png

This is what PressureLine said regarding traction:
PressureLine06/27/2020
".... the 'cart' trailers suck for the B80, because they put almost no weight on the rear axle of the tractor
which means you gain a whole load of weight, but no extra traction...
This trailer is great though. This style of trailer not this exact specific trailer"

PressureLine06/27/2020
" it's that the wheels on the trailers support 100% of the load weight and theres no practical way to make the tractor heavier over it's drive wheels
so the B80 weighs 3600kg
lets say that 2/3 of that is over the drive wheels, and that we get a 0.75 coeff of friction
so thats 2400kg*0.75 = 1800kg/18kN of tractive force max
which is fine if you're only driving around a 3.6 tonne tractor but lets add 2700kg of of 'Agricultural Flatbed' (info pulled from game files) and 3100kg of logs (again, from game files) we've almost tripled the weight of the combination, and gotten 0% extra traction"

PressureLine06/27/2020
"but on the trailer i posted above, lets assume that the weights are all the same, but that the trailer puts 50% (I could work it out, but I can't be bothered) of the weight of itself and it's load onto the drive wheels of the tractor
so that's an additional 2900kg of force pushing down on the drive wheels
which almost doubles our max tractive effort"

Edited by Truckwolf
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