Speed and acceleration problem

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Tom@Crewe
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Speed and acceleration problem

Postby Tom@Crewe » Sat Jul 18, 2020 6:35 am

I have an NCE Power Cab and two loco's - Both are Bachmann one is a Jinty and a class 08 both fitted with Zimo MX648R chips with sound and all is well EXCEPT.........the Jinty run's well with good acceleration and deceleration and being a shunting layout I do a max speed of 8 on the controller but the 08 with 8 on the controller is very very slow to accelerate and decelerate, I have input the Cv's 2 to 6 the same as the Jinty but no good. What do I need to be looking at to match the Jinty performance.
Never enough time...........

mjb1961
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Re: Speed and acceleration problem

Postby mjb1961 » Sat Jul 18, 2020 8:39 am

Hi,,,in real life the 08 class wouldn't be a fast train,I think this has come up before on the forum ,I've got an 08 dcc fitted and that is slow .

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SRman
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Re: Speed and acceleration problem

Postby SRman » Sat Jul 18, 2020 9:03 am

The gearing on both Bachmann and Hornby 08s is very low and they have heavy flywheels. Simply putting the same settings as the Jinty is not guaranteed to match the different mechanisms.

Try entirely different settings, particularly in CVs 3 and 4 for the 08. If you want more rapid acceleration and deceleration, put lower values in to each then test. Repeat until you are happy with these.

Similarly with CVs 5 and 6 for top and mid-voltages.

I have just spent an hour or so playing with these settings to try and speed match two ostensibly identical units that seem to have quite different characteristics to each other, with one being a lot more free-running than the other. Take your time and just keep fine-tuning until you are content with the results.

Bigmet
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Re: Speed and acceleration problem

Postby Bigmet » Sat Jul 18, 2020 9:54 am

Tom@Crewe wrote:... What do I need to be looking at to match the Jinty performance.

Your layout, so your choice: but in reality a class 08 performed very differently from a steam shunter like the Jinty.

The 08 will accelerate smoothly and steadily up to the 15mph max that was the standard top speed. That's roughly 100mm a second flat out in OO.

The Jinty will go off like a startled rabbit with no load and graft up to 50mph if allowed a long enough run on the main line with a modest load (they were regularly used in suburban passenger service pre WWII).

My 08s have a CV5 value of about 40 (from 250 steps) CV6 at 20, CV's 3 and 4 at about 30. That replicates the smooth and steady, never very fast performance of reality. In many yards they never did more than jog along at 7 or 8 mph.

My 0-6-0T shunting types are all set for scale of around 50mph, and both Bachmann and Hornby models need the CV5 value set somewhere in the 100 to 150 range to limit them to that, with CV6 about three quarters what CV5 is set to (they accelerate well from low speed, not so well once over 20mph). I change the CV 3 and 4 values according to whether they are being used in a yard for shunting, or going for a run on a trip freight. Shunting was done very briskly indeed by most crews, whereas a run with a load was a far more pedestrian affair.

Dad-1
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Re: Speed and acceleration problem

Postby Dad-1 » Sat Jul 18, 2020 11:39 am

Perhaps I'm a dinosaur, but I know some people try to match loco responses from their controllers.
I often wonder why ?
Each different locomotive had different performance parameters, even sister locomotives were different (So I'm told by an old driver)
I used to have 2 cars, A Daewoo Matiz 796 cc and a Jaguar 'X' with 2500 cc. Obviously each had a very different acceleration and speed.
Well that's what I expect from my different locos. I need to learn the response of each and drive to their strengths, or weaknesses.

Some may say I'm not exploiting what DCC can offer - Well as I'm happy with it so that's the way it stays.
I do have small track measurement markers, a speed chart and a stop watch. That way I know exactly what steady speeds one of
my trains is running at. It's usually under 15 mph on my small layout and freight never more that 45 mph on the big layout.

Just another example of the different approaches we railway modellers have.

Geoff T.
Remember ... I know nothing about railways.
viewtopic.php?f=22&t=32187 and Another on viewtopic.php?f=22&t=28436&start=60&st=0&sk=t&sd=a

Tom@Crewe
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Re: Speed and acceleration problem

Postby Tom@Crewe » Sat Jul 18, 2020 1:35 pm

Bigmet wrote:My 08s have a CV5 value of about 40 (from 250 steps) CV6 at 20, CV's 3 and 4 at about 30. That replicates the smooth and steady, never very fast performance of reality. In many yards they never did more than jog along at 7 or 8 mph.


I put these numbers in and it does 6 inches in 26.22 seconds that's 0.99mph (according to online calculator)
Never enough time...........

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Peterm
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Re: Speed and acceleration problem

Postby Peterm » Sun Jul 19, 2020 3:04 am

Tom@Crewe wrote:
Bigmet wrote:My 08s have a CV5 value of about 40 (from 250 steps) CV6 at 20, CV's 3 and 4 at about 30. That replicates the smooth and steady, never very fast performance of reality. In many yards they never did more than jog along at 7 or 8 mph.


I put these numbers in and it does 6 inches in 26.22 seconds that's 0.99mph (according to online calculator)


So try raising the CV5 value by 5 until you get what you think is right for top speed. Then adjust 6 until you're happy with that. CV3 for acceleration can be what you want, but Bigmet's suggestion of 30 should be a good starting point.
I have two 08's one Bachmann and one Hornby. I've adjusted CV4 to 160 and activated the brake on F2 so I have complete control.
Pete.

Tom@Crewe
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Re: Speed and acceleration problem

Postby Tom@Crewe » Sun Jul 19, 2020 11:34 am

OK messing about with CV's and my settings seem way out But! the Gronk is better controllable for my layout

CV2 - 0
CV3 - 60
CV4 - 60
CV5 - 255
CV6 - 112

On full power it now does the 6 inches in 1.46 seconds that's about 18mph
acceleration and deceleration are a good steady rate.

The Gronk will never be asked to do full speed as it's a shunting layout, still not as nimble as the Jinty but as pointed out the real thing never was.
I am happy now, I just need to remember that when operating one loco then the other to change my operating style. (or slow the Jinty down to match?)

Still open to more tips and advice
Never enough time...........

Bigmet
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Re: Speed and acceleration problem

Postby Bigmet » Sun Jul 19, 2020 6:02 pm

Tom,

The right CV settings are those that produce the performance you want on your layout.

(I have my DCC system set to deliver 15V at the motor terminals, to make some 'slugs' among the traction achieve scale maximum speed. My 08s are actually set CV5=30, but I boosted that by a third for what I suggested, thinking of DCC systems producing 12V at the motor terminals.)

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RAF96
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Re: Speed and acceleration problem

Postby RAF96 » Mon Jul 20, 2020 9:03 am

Surely the installed decoder decides what max voltage the motor and function outputs see. You can set what controller output track voltage you like within any particular decoder limits and the onboard gubbins will take the output voltage down to design spec.

E.g. TTS decoders have a system limit of 27volts, but the motor only ever sees a max of 12v PWM. My Elite controller puts 15v DCC onto the track.
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Bigmet
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Re: Speed and acceleration problem

Postby Bigmet » Mon Jul 20, 2020 11:00 am

Tom@Crewe wrote:...I just need to remember that when operating one loco then the other to change my operating style. (or slow the Jinty down to match?)

Still open to more tips and advice

It is entirely your own decision how to operate your layout, whatever system you use: steam, clockwork, electric, magic moonbeams...

Personally, because I have a main line set up and the express trains should belt along at the then 90mph speed limit, I set up the fast locos to achieve this; 'plus a bit' in the case of the most speedy. Then there's the middling group, set for the typical 70mph maximum, and the slow group, which for my purposes are limited to 40mph. (And finally the diesel shunters which are set to the specific maximum speeds they were rated for, don't have to match anything else as they potter around yards.)

I match the speed curves on groups of steamers so that they will run together smoothly to 20 mph, so that 'trots' of steam locos can go on and off shed together; and all the diesel traction worked in multiple is matched throughout the speed range.

Happily the Bachmann DMU models that are essential for my operation preented no trouble at all in this respect, very uniform performance on DC, so easy to set up in DCC, almost install decoder and walk away and they move 'as one'.

The same cannot be said for the assortment of Bachmann, Dapol, Heljan and Hornby diesel models; all of them have very good centre motor drives that perform beautifully, when assessed individually. Some match very closely when set to matching start, maximum and mid range speeds using the default speed curve, and minimal further adjustment is the most that is required. But others do not, and may end up needing a custom speed curve to make them move like 'one of us'.

There is one exception. For the amusement of occasional children (some in their 70s) the very naughty Thomas is capable of about 200mph.

RAF96 wrote:Surely the installed decoder decides what max voltage the motor and function outputs see. You can set what controller output track voltage you like within any particular decoder limits and the onboard gubbins will take the output voltage down to design spec.

E.g. TTS decoders have a system limit of 27volts, but the motor only ever sees a max of 12v PWM. My Elite controller puts 15v DCC onto the track.


In my experience, (Lenz system, mainly Lenz decoders, some ESU and Zimo) altering the DCC track voltage varies the voltage at the motor terminals in direct proportion. I deliberately increased the DCC system track voltage output from the factory setting, in order to enable three RTR mechanism designs and a couple of kit builds to move at scale maximum speed, and this was successful in giving them the speed capability I required.

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Roger (RJ)
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Re: Speed and acceleration problem

Postby Roger (RJ) » Mon Jul 20, 2020 6:30 pm

Most decoders apply track voltage minus approximately 1.4volts to the decoder, the 1.4volts is lost in the electronics, mainly the bridge rectifier on the decoder pcb AFAIK.

There are a few which do actually regulate motor voltage, which I believe may be user selectable via CVs.

Bigmet
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Re: Speed and acceleration problem

Postby Bigmet » Tue Jul 21, 2020 1:30 pm

Roger (RJ) wrote:...There are a few (decoders) which do actually regulate motor voltage, which I believe may be user selectable via CVs.

Definitely is or has been a feature on some Zimo decoders. Never bothered to look into it as performance is more than stable enough.

Roger (RJ) wrote:Most decoders apply track voltage minus approximately 1.4volts to the decoder, the 1.4volts is lost in the electronics, mainly the bridge rectifier on the decoder pcb AFAIK...


The standard 1.4V loss in the rectifying bridge, and on the Lenz decoder I tested on a scope, another 1.8V 'lost' (10% of the DCC track voltage about neutral with the DCC system set to deliver 18V about neutral). Except it isn't lost, in that is the 'reserve' that means that even when the motor is at speed step 28/128, the BEMF control has some extra power to call on to maintain motor speed if the load on the loco increases, as on a rising gradient. There is an 'EMF switch' on CV50 which enables this to be disabled, and then the maximum motor voltage rises to approximately 1.6V less than the DCC voltage about neutral: the supply isn't continuous, there's a brief zero volts interval at the nominal 23kHz motor supply frequency, which slightly reduces the net motor supply voltage to a little below what you would expect if it was just the loss in the rectifying bridge.

(I should add that the scope wasn't calibrated, so some small variances in values might be expected if compared to other's findings. Keen though he was, the scope didn't go off to an NPL registered facility for regular recal. after my father retired...)

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Peterm
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Re: Speed and acceleration problem

Postby Peterm » Wed Jul 22, 2020 1:38 am

Bigmet wrote:
Roger (RJ) wrote:...There are a few (decoders) which do actually regulate motor voltage, which I believe may be user selectable via CVs.

Definitely is or has been a feature on some Zimo decoders. Never bothered to look into it as performance is more than stable enough.
)


Yes, with Zimo CV57 will adjust the top volts that the motor sees and with my Lenz system I've adjusted the track volts to 14.5 for safety with stay alive cap's.
Pete.

Bigmet
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Re: Speed and acceleration problem

Postby Bigmet » Wed Jul 22, 2020 9:46 am

Dad-1 wrote:...I know some people try to match loco responses from their controllers.I often wonder why ?...

Thought I had replied to this question, but must have failed to press the submit button.

Very much a 'what your operation requires' thing in my opinion.

Firstly I don't want to generally drive the trains as such, my interest is in recreating the operation of train services going by, stopping or through, as the timetable requires. This requires automation, and uniform performance is helpful for this.

That's before we get to the ability to run groups of locos together at matching speed: slowly for the steam locos coming off or going on shed in a 'trot' to reduce track occupancy as the real railway did (those I will drive!); and for MU'ing diesel traction where you don't want them 'fighting' at any point in the speed range.

My ultimate plan is that my driving will be restricted to shunting type operations and reversing the inner suburban services at the country end terminus; plus any out of course events from the randomness generator such as a loco 'failed' and needing replacement. The automated main line services will supply the exciting spectacle on the theatre set.

Possibly all this is because I never had ambitions to drive a loco (or a car come to that, given the choice!). No, had I joined BR - and it was a career choice I examined - operational control would have been my career ambition. (I achieved that elsewhere in very different businesses.)


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