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· DT
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8,026 Posts
I was reading the manual of the DCC controller that I have been recently playing with. I see that it has 28 speed steps with pre determined speed values. These values from 2 to 255 look like this:


Obviously programmed this in for a train.

This is the acceleration curve of a Porsche Carrera:


So we need to reprogram the DCC chips for cars.

Something like this:


For better acceleration.

The programming is done by changing values of CV 67 through to CV 94. This can be modified for each chip in each car so one can adjust the acceleration characteristics based on the original car.
 

· DT
Joined
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8,026 Posts
QUOTE (RC45 @ 27 Jul 2004, 01:36)For fear of repeating these things, but this is one of the first custom configurations I have spoken about when ever I arrived at a slot car forum.
I didn't see that Paul, not here I presume...
Please don't hesitate to repeat yourself if it will make things more clear.

What values have you used to reprogram the Speed steps?

This whole exercise explains why the car was not accelerating and decelerating correctly using the default settings. I must now go and reprogram the chips.


This is what is should (roughly) look like:


Here's the data:

CV#StepTrainValueCar Value
6701002002
6802004040
6903006066
7004009090
7105013110
7206018124
7307024140
7408031153
7509039164
7610048173
7711058182
7812069190
7913080197
8014090205
8115100212
8216110220
8317120226
8418130230
8519140235
8620150240
8721160245
8822170248
8923180252
9024195254
9125210257
9226225258
9327240259
9428255260
 

· DT
Joined
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8,026 Posts
CV2 is minimum speed: set to 0 (or no volts)
CV5 is maximum speed: set to 255 (full voltage applied)

CV3 is acceleration: value 0 to 255, one unit corresponds to 32/1000 seconds, the time it takes until the loco/car decoder internally switches over to the next higher speed step.

CV4 is brake delay: value 0 to 255, one unit corresponds to 32/1000 seconds, the time it takes until the loco/car decoder internally switches over to the next lower speed step.

Note: initially my CV3 did not equal my CV4 and turning the speed knob say a quarter turn to the right would take it to a certain speed, but bringing it back by a quarter would not bring it to where it started. This is very disconcerting for slot cars as the control is much more erratic than trains.

CV67 to CV94 are the speed steps. Hence the graph.

Within CV29 there are configuration settings such as direction, speed steps (27 or 28), whether or not to allow analogic running and and whether or not to read from the speed table (CV67 to CV94) or whether to calculate it automatically.

The 14 speed steps is an old setting, now widely replaced with 27 or 28 steps.

To come back to what I was saying:

I think they are important and the shape is relevant to the vehicle. One can say that the voltage applied is in proportion to the speed. No volts, no speed; max-volts, max-speed - it's not going to go faster.

Think of a big steam train: The fireman opens her up from a standing start at the station; chu, chu, chu; The Revs slowly increase; it slowly starts moving gathering speed as momentum gathers and the cylinders start working to the optimum.

Think of a car: Light and nimble; hurtling off the start line at high revs; peaking 20 to 30 seconds down the road going flat out. We measure acceleration within the first 60mph/100kph because after that it really does take a while to go still faster.
 

· DT
Joined
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8,026 Posts
Discussion Starter · #14 ·
QUOTE (astro @ 27 Jul 2004, 19:18)The porsche acceleration curve is a red herring and not related to what the graph represents
I beg to disagree. It represents the convex shape of a vehicle that has a better power to weight ratio than a heavy cast iron train that need momentum to get moving.

The correct graph may need to be flatter or more pronounced, but I'm sure that it's convex as opposed to concave or linear.
 
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