Looking to get into XMR. A few questions.

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Looking to get into XMR. A few questions.

Postby Andy Miller » Fri Nov 15, 2013 8:02 pm

I recently came across XMR a few days and I am really excited about what it provides. My main purpose would be to create a car that other games don't currently have the ability to simulate. My team and I created a highly successful mod in rFactor for dirt late models but rFactor falls short on many aspects of a late model and we had to fudge the physics quite a bit to get something passable.

I can get more technical information if needed but would this be a platform that we could simulate something like a dirt late model on and if so which license would allow us to do so? I'm going to try and find some more information on my own through reading but I figured someone who has made a car for XMR might be able to shed some light.

Thanks!
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Re: Looking to get into XMR. A few questions.

Postby Eugene Cojocar » Fri Nov 15, 2013 8:32 pm

Welcome to the forum, Andy!

I think it's possible to simulate dirt late models although I never tested them.
Any technical information about the dirt late model would be great of course.
At one time I created for XMR and tested off-road 4x4 cars. They were very nice but gave up that idea to focus on the road/sport cars and tires for the asphalt.
If it's for your personal use then the Pro license is enough to create cars and physics.
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Re: Looking to get into XMR. A few questions.

Postby Andy Miller » Fri Nov 15, 2013 9:14 pm

Thanks for the information. I honestly don't know that much technically about late models so I'm going to try and get our physics guy to come over and give his input on that matter. I do know that our biggest struggle with rFactor has been suspension and tire model. The suspensions are pretty limited in rFactor so we've been trying to find another platform to do a true late model.
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Re: Looking to get into XMR. A few questions.

Postby Andy Miller » Fri Nov 15, 2013 11:51 pm

Ive sent him a message but in the mean time this is essentially what we want to create. Again I know nothing about suspensions. (This might something common and Im just dumb)

http://www.stockcarracing.com/techarticles/39098_four_link_tips_advice/
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Re: Looking to get into XMR. A few questions.

Postby Eugene Cojocar » Sat Nov 16, 2013 6:16 am

Thanks for the link, although it contains only general information.
It seems the cars have significant roll steer effect.
I'd like to create a test model (physics model) of the car if you give me basic information (even approximate) like:
mass, centre of mass, mass distribution, wheels sizes, steering system, brakes, engine, suspension (max travel, stiffness, anti roll bars, bump and rebound numbers). Also the basic information about the tires would be nice especially. At least the max values of the lateral and longitudinal forces on the stated load.
You can find all the parameters in the VehiclePhysics demo except for the tire model which is not available in the demo.
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Re: Looking to get into XMR. A few questions.

Postby SoBe92 » Wed Nov 20, 2013 3:57 am

Eugene Cojocar wrote:Thanks for the link, although it contains only general information.
It seems the cars have significant roll steer effect.
I'd like to create a test model (physics model) of the car if you give me basic information (even approximate) like:
mass, centre of mass, mass distribution, wheels sizes, steering system, brakes, engine, suspension (max travel, stiffness, anti roll bars, bump and rebound numbers). Also the basic information about the tires would be nice especially. At least the max values of the lateral and longitudinal forces on the stated load.
You can find all the parameters in the VehiclePhysics demo except for the tire model which is not available in the demo.


I can answer most of the questions you have.
Mass should be around 2300lbs with the weight distribution being 53-56% rear weight and 53-55% left side weight.
Wheels are 15" rim that is 14" wide with a 5" backspace or offset (from rear) weighing just over 10lbs.
Tires are bias ply with really flexible sidewalls and 11" tread width / 29.0" diameter and 92" cir. with some stagger options being within a few inches the smallest being around 88" running air pressures from 6-12 lbs.

Steering is rack and pinion with tie rods attaching to a steering arm on the front lower side of the spindles with unequal length a-arms roughly based off a ford front strut front end.

brakes are disc brake with 4 piston calipers and 1.25" wide rotors. the rf caliper has an optional shut off.

Engine is a american v-8 alum. heads and block. 410-460 cubic inches pushing 900 hp and 700 ft lbs of torque. running on racing fuel through a 850 cfm carb.

suspension on front should be 7" stroke shocks double adjustable with a 2.5" coil over
rf should see 4-5" of compression with little to no rebound from ride height. the spring rates are 450-250lbs per inch.
lf should see 1-2" of compression and full extension from ride height (this will result in the tire lifting off the ground) with spring rates 450-600lbs
Rear shocks will be 9" stroke shocks
rr should see 4-5" of compression with 1-3" of ext from ride height with a spring rate of 150-275lbs
lr should see 1-2" of compression with full extension with a spring rate of 100-275lbs

the rear suspension is what would best be called a floated 4 link with a torque arm.

top left link is 18" c to c at an angle of 28 deg downhill to the rear end attachment point or what we call a birdcage. the birdcage top attachment point is 4.5" from axle center line. the bottom left link is 15" c to c and is mounted at a 5 deg downhill angle to the bottom of the birdcage at 4.5" from axle center line. the birdcage is fully rotationally floated and the shocks mount to it in both front and behind the rear end housing. at a height of 6" below axle center line and 5" behind and in front of center line. the lr spring would be mounted behind on a coil over at an inboard 15 degree angle. there would also be a second shock attached on the front side of the birdcage at the same angle.

top right link is also 18" c to c at an angle of 20 deg downhill to a birdcage at the same 4.5 from axle center line the bottom link would be 15" c to c at 2 degrees downhill to the 4.5 below center line.

the lateral movement is controlled through a panhard bar from front right side of pinion to left side of chassis. roughly 21" c to c at a 8" split (lower to the ground at pinion).

the torque arm attach to the rear end housing to control axle wrap. it has a damper shock mounted with a coil over spring at 35" from center line forward and centered in the chassis. this damper shock will have a 300lb spring on it and sees 3" of compression travel and 3" of rebound travel.
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Re: Looking to get into XMR. A few questions.

Postby Eugene Cojocar » Wed Nov 20, 2013 9:13 am

Thanks for the info.
I hope to begin to work on it in 1-2 weeks.
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Re: Looking to get into XMR. A few questions.

Postby SoBe92 » Fri Nov 22, 2013 3:10 am

Not a Problem. I can get most everything for you. Tire data on the other hand they don't hand out to us.
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Re: Looking to get into XMR. A few questions.

Postby Eugene Cojocar » Fri Nov 22, 2013 8:24 am

Seems the tire behavior is close to a dirt road.
Anyway, I think that finding a suitable tire model for the cars is not a difficult task with the VehiclePhysics.
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Re: Looking to get into XMR. A few questions.

Postby grobed » Sun Mar 16, 2014 8:20 pm

How would you handle the differences between left and right sides for oval cars like the above mentioned late models. I too would be interested in building models of circle track cars but only see physics for front to rear distributions. You can compensate roll stiffness mathematically for differing spring rates, but I do not see where xmr differentiates between left and right shocks.
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