SD80Mac physics

[plainsman]

I had a request for an SD80Mac physics update for OR. I am attaching the file. This uses some ideas Joe Realmuto and I came up with, which is one step further improvement over the files I put in the library. I tried the files and they work quite nicely for me (except the old dynamic braking specs need some work in how they are used in OR).
BTW, to get close to prototypical performance, you will have to use shift plus x for sanding with this.

[Gary54]

Bob,

Thanks for the SD80Mac physics update for OR.

You have mentioned the importance of auto-sanding to the proper running of the AC engines in a number of previous posts. Is there a speed threshold value at which sanding becomes critical? I see that the updated physics file includes the line, "Sanding ( 25mph )." While I'm not very familiar with the the details of *.eng files, that value seems higher than other *.eng files that I have looked at.

Again, thanks for the SD80Mac physics as well as all of your contributions to the physics of modern freight operations.

Gary

I guess what I am asking

[plainsman]

Hi Gary,
Good point! Yes the sanding speed in OR has to be MUCH higher than MSTS. OR treats adhesion very differently than MSTS. Essentially the V4.7 and newer MSTS files implemented auto-sanding and traction control with the adhesion line. While this file I just posted tries to do some of that, it is still necessary to use shift plus x when your speed drops below about 14 mph on dry rail and up to 25 mph on wet rail. BTW, that is with the adhesion slider at 101 and environment turned down to 6 or less.
Another thing, OR treats the couplers very differently than MSTS (a lot of that was sorely needed) so the coupler line is very different in OR, particularly the r0 line. In OR the first value in the line must be 0. The second value, at this point, needs to be 8-12. I expect the coupler physics to become a bit more robust as OR matures. OR needs a lot more work on the coupler, to get realistic slack action. The couplers were done by folks that were much more focused on high speed passenger trains than long freight operation. It will get better as the community requests slack to operate more prototypically. It is now possible to use actual break strength in OR couplers. The AC files use the latest 2014 heavy coupler ratings. The Alco files use a less robust coupler. I am waiting to see if anyone experiences an appropriate broken coupler with these files??

[Gary54]

Thanks for the discussion, Bob. I really look forward to where this will take us, especially as it relates to heavy North American freight operations.

One more question regarding auto-sanding and how it actually works. Are the AC units set up so that when a lower threshold speed limit is reached, the engine automatically begins to sand the rails?

Thanks.

Gary

[plainsman]

Hi Gary,
The way this works in actual use, the locomotives have radar or other equipment to measure actual forward speed. The computer compares this against the angular velocity of the wheels (how fast the wheels are turning). From this it can determine the amount of creep or wheelslip. The computer then adds sanding as the wheelslip approaches a threshold percentage. The sand is abrasive to the rail surface, and accelerates wear on the wheel flange, so railroads don't want to use it unless needed.

[Gary54]

Thanks, Bob. Hopefully, this will be implemented into OR relatively soon.

Gary

[baldwin]

It probably can be added relatively easily as there is already wheelslip detection in place. Just needs some code developed to add autosand along with an ORTS instruction in the eng file. Something for the future.