[Hamza97]

Try the parameter "ORTSBrakeShoeFriction ( x, y )", where X is speed and Y is friction value. You can use this to adjust the effect you want, and hopefully share with us... :good2:

[steamer_ctn]

Coolhand101, on 01 September 2016 - 03:03 AM, said:

My understanding that wheel skid only applies to steam locos? Can this be also be applied for diesels and electrics to simulate the high retardation effect of cast iron brake shoes at low speeds ?

Wheel slip should occur on all types of rolling stock provided the "right" conditions exist.

The four parameters that mostly influence the wheel slip will be the BrakeForce applied, the friction between the wheel and the rail, the friction between the brakeshoe and wheel, and the weight of the rolling stock.

To confirm that it actually works in Open Rails you could try using "extreme" values for the above to prove the point, and then adjust as per reality.

[Coolhand101]

steamer_ctn, on 02 September 2016 - 03:32 AM, said:

Wheel slip should occur on all types of rolling stock provided the "right" conditions exist.

The four parameters that mostly influence the wheel slip will be the BrakeForce applied, the friction between the wheel and the rail, the friction between the brakeshoe and wheel, and the weight of the rolling stock.

To confirm that it actually works in Open Rails you could try using "extreme" values for the above to prove the point, and then adjust as per reality.

I tested this a while ago. Brake skid does occur with diesels and electrics, but it's the axle brake force being the main factor.

For example, the British rail class 47 locomotive at 40% conditions(snow), applying the brake fully at 95 mph, the axle brake force is 84kN, the running brake force via brake friction is 29kN and the wheelslip percentage is over 70%, so wheel slide occurs.

These are the results

95mph - axle brake force = 84kN - Running brakeforce = 29kN - Wheelslip percentage = 70% - slide = YES
85mph - axle brake force = 84kN - Running brakeforce = 34kN - Wheelslip percentage = 68% - slide = NO
75mph - axle brake force = 84kN - Running brakeforce = 39kN - Wheelslip percentage = 64% - slide = NO
65mph - axle brake force = 84kN - Running brakeforce = 44kN - Wheelslip percentage = 59% - slide = NO
55mph - axle brake force = 84kN - Running brakeforce = 48kN - Wheelslip percentage = 54% - slide = NO
45mph - axle brake force = 84kN - Running brakeforce = 54kN - Wheelslip percentage = 49% - slide = NO
35mph - axle brake force = 84kN - Running brakeforce = 58kN - Wheelslip percentage = 43% - slide = NO
25mph - axle brake force = 84kN - Running brakeforce = 65kN - Wheelslip percentage = 39% - slide = NO
15mph - axle brake force = 84kN - Running brakeforce = 73kN - Wheelslip percentage = 30% - slide = NO
5mph -- axle brake force = 84kN - Running brakeforce = 80kN - Wheelslip percentage = 22% - slide = NO
0mph -- axle brake force = 84kN - Running brakeforce = 84kN - Wheelslip percentage = 19% - slide = NO

Thanks

[Coolhand101]

Hamza97, on 01 September 2016 - 08:01 PM, said:

Try the parameter "ORTSBrakeShoeFriction ( x, y )", where X is speed and Y is friction value. You can use this to adjust the effect you want, and hopefully share with us... :good2:

I have been using this for all my treadbrake stock from when first implemented!

[Coolhand101]

So, the wheels will skid when using steam and wag files via friction coefficient.

I have just tested this for steam engines and wags. The high friction coefficient at low speeds causes the wheels to skid, so this works 100%.

In snow conditions, the brake pipe pressure was dropped from 21in to 5in at 70 mph. At around 15mph, the wheelskid text lit up and skidding was occurring.

Wnen using diesel/electric engine and wags with cast iron tread brakes, OR ignores friction coefficient for wheelskid and applies default 'disc brake' behaviour. This even applies to wags, IF connected to diesel or electric engines.

Can this realistic feature be implemented for diesels and electrics?

Thanks

[steamer_ctn]

Coolhand101, on 03 September 2016 - 05:55 PM, said:

Wnen using diesel/electric engine and wags with cast iron tread brakes, OR ignores friction coefficient for wheelskid and applies default 'disc brake' behaviour. This even applies to wags, IF connected to diesel or electric engines.

Can this realistic feature be implemented for diesels and electrics?

I have done some tests and I can't see that OR is ignoring friction coefficient. The default brakeshoe is cast iron, not a COBRA one.

The wheel skid should work for both diesels and electric locomotives.

To ensure that we are on the same page, can you use the rolling stock and test route from the Coals to Newcastle site.

I have used the 10203 diesel and pass cars (see stock page). The pass cars currently have default cast iron brakeshoes and the loco has COBRA brakeshoes.

In the test route, choose the Basic diesel and the starting point "Top Slope - 25 - Roll". You should be able to release them, start rolling, and then apply them (may need to be an emergency application in winter snowing conditions) to get the train wheels to lock up and slide.

Can you explain your concerns in regard to this test and rolling stock?

Thanks

[Coolhand101]

steamer_ctn, on 05 September 2016 - 02:29 AM, said:

I have done some tests and I can't see that OR is ignoring friction coefficient. The default brakeshoe is cast iron, not a COBRA one.

The wheel skid should work for both diesels and electric locomotives.

To ensure that we are on the same page, can you use the rolling stock and test route from the Coals to Newcastle site.

I have used the 10203 diesel and pass cars (see stock page). The pass cars currently have default cast iron brakeshoes and the loco has COBRA brakeshoes.

In the test route, choose the Basic diesel and the starting point "Top Slope - 25 - Roll". You should be able to release them, start rolling, and then apply them (may need to be an emergency application in winter snowing conditions) to get the train wheels to lock up and slide.

Can you explain your concerns in regard to this test and rolling stock?

Thanks

I have just finished more testing on my own trainsets, and can confirm that coaches attached to the diesel engine DO skid at low speed via increased friction coefficient, i was incorrect on my previous test. However diesel engines do not skid with increasing friction coefficient:

I lowered the weight of the class 47 loco from 122 tons to 32 tons and doubled the brakeforce to 170kN.

Applying full brake around 90MPH, the wheels started to skid due to the HUD wheelslip reading over 70%. Friction coefficient was around 0.15.

At 5 mph, the HUD wheelslip reading was 23% and the friction coefficient was over 0.45. There was no wheel skid.

It appears diesel engines use the HUD wheel slip percentage for wheel skid, and once that reading gets below 70%, wheel skid will never occur again. This is the method used for disc brake trainsets, as the friction coefficient can be as high as 0.38 at 90mph.

With the above test, i was using the class 47 diesel loco and three coaches. Two coaches were cast-iron tread brakes and one coach with disc brakes.

The coach test results:

Applying full brake at 95mph, the disc brake coach skidded straight away due to the high friction coefficient of 0.38. No wheel skid on the tread brake coaches at 0.15 friction.

Applying full brake at 40mph, no wheel skid on any coaches.

Applying full brake at 25mph, no wheel skid on Disc brake coach but wheel skid on both tread brake coaches.

Below 25 mph, again only the tread brake coaches skidded due to the increase friction coefficient with increase brakeforce.

As in my previous test for the class 47 loco, at 95mph, the brakeforce is 29kN with friction at 0.15. At 5mph, the brakeforce is 80kN with friction at 0.45.

As for the diesel engine not skidding at low speed with high friction coefficient and full brake, could this statement in one of your earlier post on this thread be the reason:-

"Diesel and electric locomotives are excluded from this function at the moment as they appear to be covered in the original base advanced adhesion model".

If not, i will download the route and stock you mentioned and test the conditions you have described!


Thanks

[Coolhand101]

I have downloaded the route and stock.

Some observations. My own cast iron brake shoe coaches use a Coefficient of friction of 0.14. Yours use 0.15. All this means is my brake force is slightly less and the wheels will skid at a slightly lower speed.

The default OR braking curve. I never understood why the brakes max out at 25 mph and at 20% brake friction. But the friction continues to rise to 50% without any brake increase?

The loco brakeforce seems to high. I use 75% of the loco weight in kN. For years, i used 65%, but with the added Coefficient of friction, i use 10% more. While your loco does have plastic brake blocks, it has more chance of skidding at high speed as well as low speed, as shown by the wheelslip percentage, even when changing your loco brakeforce to 75%(100kN)loco weight. The wheelslip percentage does not drop as sharp as in cast-iron brakes due to the higher friction coefficient of the composite brake.

However, change the loco brake friction curve from composite brake to cast iron brake, you will see exactly the problem i am getting at low speed with high Coefficient of friction and no wheel slide.

At 100 mph, the brake friction is 10% but wheel slide still occurs. At 20mph the Coefficient of friction is higher but there is no wheelslide. Change the loco brakeforce back up to 150% braking weight( 198kN ) and it's very hard to see what i'm trying to explain, as wheel slide occurs at all speeds, as the wheelslip percentage will always be over 70% at 40% conditions with that full brakeforce

To sum it all up - The loco cast-iron brake should perform as the coach cast-iron brake, meaning wheelslide generally occurs at a lower speed with the same brake pressure due to the higher friction coefficient of this brake for low speeds at the required conditons. This works on steam engines, but not diesel or electrics engine.

Hope this makes sense!

Thanks

[steamer_ctn]

Coolhand101, on 05 September 2016 - 06:13 AM, said:

As for the diesel engine not skidding at low speed with high friction coefficient and full brake, could this statement in one of your earlier post on this thread be the reason:-

"Diesel and electric locomotives are excluded from this function at the moment as they appear to be covered in the original base advanced adhesion model".

This statement meant that the diesel and electric locomotives have a different adhesion model built by a different developer. As far as I can tell the diesel/electric model will produce wheel skid if the brake force exceeds the adhesive weight of the locomotive (indicated by the appearance of the text "Wheel Slip").

I have made a small adjustment in #3616 so that the "Brake Slide" indication in the FORCES HUD now works for diesel and electric locomotives.

Coolhand101, on 05 September 2016 - 09:48 AM, said:

I have downloaded the route and stock.

Thanks, that means that we now have a common base to discuss any concerns on.

Coolhand101, on 05 September 2016 - 09:48 AM, said:

The default OR braking curve. I never understood why the brakes max out at 25 mph and at 20% brake friction. But the friction continues to rise to 50% without any brake increase?

I don't understand this statement.

Have you seen the brakeshoe coefficient curves on this page?

Coolhand101, on 05 September 2016 - 09:48 AM, said:

However, change the loco brake friction curve from composite brake to cast iron brake, you will see exactly the problem i am getting at low speed with high Coefficient of friction and no wheel slide.

I am able to get wheel skid to happen at speeds of 15mph with both cast iron and COBRA brakeshoes under the conditions indicated in the post above.

Coolhand101, on 05 September 2016 - 09:48 AM, said:

To sum it all up - The loco cast-iron brake should perform as the coach cast-iron brake, meaning wheelslide generally occurs at a lower speed with the same brake pressure due to the higher friction coefficient of this brake for low speeds at the required conditons. This works on steam engines, but not diesel or electrics engine.

Within reason this appears to be the case for my testing of diesel and electric locomotives.

I am sorry, but I must be missing something. Can you describe a single simple test that we can both undertake to clearly see the problem?

Thanks

[Coolhand101]

steamer_ctn, on 06 September 2016 - 02:41 AM, said:

I don't understand this statement.

Have you seen the brakeshoe coefficient curves on this page?

Yes i have. If you look the performance HUD for the coaches from your site, the brakeforce stops increasing at 25 mph and at 20% brake friction. Below 25mph, the brake friction will increase to 50% at zero speed, but there is no difference in brakeforce below 25mph. Or am i missing something obvious?

steamer_ctn, on 06 September 2016 - 02:41 AM, said:

I am able to get wheel skid to happen at speeds of 15mph with both cast iron and COBRA brakeshoes under the conditions indicated in the post above.

I take it this is using the brake force of 150% loco weight? If so, the wheelslip indicator will always be over 70% at any speed range even with cast iron brakes. The braking friction could be at zero and you will still get wheelslide.

steamer_ctn, on 06 September 2016 - 02:41 AM, said:

Within reason this appears to be the case for my testing of diesel and electric locomotives.

I am sorry, but I must be missing something. Can you describe a single simple test that we can both undertake to clearly see the problem?

Yes, with the diesel default brake force of 199kN, use this brake shoe curve with 0.49 at 0 mph and 0.01 at 75mph, so :

ORTSBrakeShoeFriction ( 0.0 0.49 8.0 0.436 16.1 0.01 24.1 0.01 32.2 0.01 40.2 0.01 48.3 0.01 56.3 0.01 64.4 0.01 72.2 0.01 80.5 0.01 88.5 0.01 96.6 0.01 104.6 0.01 )

Apply full brake once down the slope at a speed over 100mph. I guarantee that wheelside will occur at 0.01 brake friction with very little brakeforce at 0.01! Why, because the wheelslip indicator is over 70% and the diesel own computations is not using the friction coefficient to skid the wheels.

Hope i got the above test right :blush2:

Thanks