Braking - Rate of Deceleration

Modern disk brakes give a constant braking force and thus rate of deceleration over the entire speed range (bar the last couple of mph before stopping), but traditional tread brakes do not. They give a higher rate of deceleration at low speed and a lower rate as speed increases.Is there any way this feature can be replicated in MSTS?Stewart

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RE: Braking - Rate of Deceleration, chucksc, Aug-27-03, 09:38 AM, (1) RE: Braking - Rate of Deceleration, nxpanel, Aug-28-03, 09:58 AM, (3) RE: Braking - Rate of Deceleration, jtr1962, Aug-27-03, 10:54 PM, (2) RE: Braking - Rate of Deceleration, Captain Bazza, Aug-29-03, 00:58 AM, (4) RE: Braking - Rate of Deceleration, xlspecial261, Aug-30-03, 05:45 PM, (5) RE: Braking - Rate of Deceleration, jtr1962, Aug-30-03, 10:04 PM, (6) RE: Braking - Rate of Deceleration, plainsman, Aug-30-03, 10:13 PM, (7) RE: Braking - Rate of Deceleration, xlspecial261, Aug-31-03, 00:08 AM, (9) RE: Braking - Rate of Deceleration, derekmorton, Aug-31-03, 02:33 AM, (10) RE: Braking - Rate of Deceleration, xlspecial261, Aug-31-03, 01:15 PM, (11) RE: Braking - Rate of Deceleration, derekmorton, Aug-31-03, 05:09 PM, (12) RE: Braking - Rate of Deceleration, xlspecial261, Aug-31-03, 06:25 PM, (13) RE: Braking - Rate of Deceleration, derekmorton, Aug-30-03, 11:32 PM, (8)

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Yeah you can re-write the garbage physics engine Kujo wrote! Seriously, welcome to our world Stewart. Some pretty sharp people have been trying to "tune around" the bugs in the physics engine since day one and this particular "undocumented feature" has yet to be solved....Chuck Schneider
(Virtual) CEO
North American (Virtual) Locomotive Works

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Hello ChuckThank you for the welcome.I had a suspicion that was going to be the answer. Of course, it will be rectified in MSTS2.......... !!Many Thanks
Stewart

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Another undocumented finding regarding braking which was bought to my attention by Clem Tillier is the fact that in the real world adhesion is dramatically lower at TGV speeds than at low speeds. In MSTS, it is the same at all speeds. Hopefully this will be corrected in MSTS2 along with about 1001 other errors or omissions in train physics, especially curvature resistance. How on earth could they possibly have let that one slip by???

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Yeah, don't beat your brains out too much, the sim seems to have a mind of its own, it never seems consistent between sessions, or even on any particular day. The physics change at the whim of some as yet undiscovered bug. Extensive testing has led me to the conclusion that no matter how much tweaking you do, the results may vary too much to be of use.Yours, in frustration...................I could say more, but this is a family rated site afterall. <Sobs into fourth glass of cheap red wine.>

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>Another undocumented finding regarding braking which was
>bought to my attention by Clem Tillier is the fact that in
>the real world adhesion is dramatically lower at TGV speeds
>than at low speeds. In MSTS, it is the same at all speeds.
>Hopefully this will be corrected in MSTS2 along with about
>1001 other errors or omissions in train physics, especially
>curvature resistance. How on earth could they possibly have
>let that one slip by??? You don't need TGV speeds to lower the adheasion. AC4400's slip like the devil at 40MPH in the rain and hold the rail at 10MPH under the same conditions.Go figure.

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Interesting. Could this be due to the actual wheel-rail physics or some quirk in the way the wheel slip control system computer handles wheel slip in the rain? Do DC locomotives behave the same way? Obviously no way to duplicate this in MSTS but it sounds like something worth studying in case MSTS2 has the ability to make adhesion speed-dependent.

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Hi Joe,
I am suspicious this is largely a software issue. The computer probably has some speed dependant programing that kicks out even if wheels slip above a certain speed? Another of the 117 things we just can't model in version 1.
Bob

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>Hi Joe,
>I am suspicious this is largely a software issue. The
>computer probably has some speed dependant programing that
>kicks out even if wheels slip above a certain speed? Another
>of the 117 things we just can't model in version 1.
>Bob I think this is a big part of it Bob. I've had AC4400's derate down as low as 1500HP due to wheelslip at 40MPH. Not fun with their slowloading characteristics.I think the wheelslip system simply cannot react fast enough at high speed. Not all locos slip this bad at that speed though. 90MAC's don't, but they have a different inverter setup, basically controlling 3 axles each. May have something to do with it.The thing that REALLY makes no sense though is the fact that SD60's, only 200HP down to an AC4400 at that speed (CP's derate to 4000HP at 25MPH), do not have this problem. Sometimes they will start singing, but never completely lose traction like the AC4400's do. Watching the Locomotive Monitor under these condictions is interesting. You can watch all six axles jumping all over the place on the TE and speed numbers. It's not just the lead axle.It should be noted for those who are just learning some of this stuff, that tractive effort drops off as speed increases. A locomotive may hold the rail at 160K TE at 4 MPH, but spins out at 45K TE at 40MPH.It's an interesting question that I wish I had more answers too.Todd

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>I think the wheelslip system simply cannot react fast enough
>at high speed. Not all locos slip this bad at that speed
>though. 90MAC's don't, but they have a different inverter
>setup, basically controlling 3 axles each. May have
>something to do with it.
>
>The thing that REALLY makes no sense though is the fact that
>SD60's, only 200HP down to an AC4400 at that speedWould it not be unfair to compare DC with AC here as DC would be condidered to be dumb in comparison.But further, if an SD60 can outpul an AC4400 at 40mph in the wet, then GE have a big problem.>A locomotive may hold the rail at 160K TE at 4 MPH, but spins out at 45K TE at 40MPH. I have a lot of trouble with that problem, I would have expected the traction to increase with the speed of the axle. ie its harder and takes a LOT more power to spin an axle as it spins at a higher speed.Derek

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"Would it not be unfair to compare DC with AC here as DC would be condidered to be dumb in comparison.But further, if an SD60 can outpul an AC4400 at 40mph in the wet, then GE have a big problem."It has been stated before that the main advantage of AC is the low speed tractive effort. They do not pull any better than a DC locomotive in the higher speed ranges. Perhaps even worse than DC without entering rain or snow to the equation. To me they just don't seem to pull as well above 50MPH. Why this would be I have no idea.A couple good examples of railroads understanding this trait are the massive orders for SD70M's and Dash9's placed by UP and BNSF respectively.I think my experiences show that is not unfair to compare the "dumb" DC with the "advanced" AC at higher speeds.Todd

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>I think my experiences show that is not unfair to compare
>the "dumb" DC with the "advanced" AC at higher speeds. Todd,I wasn't questioning your experience here.Just trying to understand the vageries of AC and DC as appears to you on the road, I have no experience here.Derek

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All I can really do is relate what seems to happen with them. I do not know enough of the inner workings of the systems, especially the AC's, to be able to say exactly what is going on.DC's are pretty straightforward. One axle slips, it draws current away from the others. The load drops and the load meter and governor react. (SD50 and 60's are bit more sophisticated than this)AC's? The computers do a bunch of stuff. Much has been made of the slow loading characteristics of AC, but I believe a part of that is the prime mover design on the GE. NS Dash9's I have operated are not a lot different when it comes to loading characteristics. 90's load much slower, in the lower notches anyway, than UP 70M's however, so perhaps AC is a portion of it.Also, emissions requirements have slowed loading on both brands. Neither reacts like something from the 70's, although GE's have always loaded slower than a comparable 2 stroke EMD.But I digress. Wheelslip at speed is a phenomenon that I do not have all the answers for. I've had SD40-2's hold the rail while lugging a potash drag uphill out of a siding then slip at 30 MPH. Not a bad slip mind you, but you can hear the singing of wheelcreep.If someone has more answers for this, I would love to hear it. It's something I have long been curious about.
Todd

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Jo,>Interesting. Could this be due to the actual wheel-rail
>physics or some quirk in the way the wheel slip control
>system computer handles wheel slip in the rain?My understanding is that maximum grip happens at 11% slip, and with AC control and ground radar it is easy to achieve this.
Perhaps the wedge of water at 40mph is enough to list the front axle and cause slip.>Do DC locomotives behave the same way?No, as dc cannot control the axle speed like the ac brothers and that accounts for the big difference in MTS and CTE.Derek

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