Evening all, I've just had one of the new Dapol class 43 in "fag packet " livery. On dc doesn't seem to fast on full power, I timed it over a meter which took 3.3 seconds which by my reckoning is about a scale 100 mph. I then put a rails of Sheffield n18 decoder it in tried again, exactly the same. I'm still a novice on dcc, but I've tried playing with cv5 value, 100 top speed very slow, set it to max 255 and top speed is the same a scale 100mph. Anyone any ideas why it won't do a scale 125mph it's about 20% down so pretty noticeable, I'd expect 1m of track in about 2.5 seconds for a scale 125mph rather than 3.3 or 100mph.

As an aside, anyone know where I can get a full list of the cv's for a rails N18 decoder? Seems nothing on there website. Thanks.

Probably nothing to do with DCC.

Run it in firstly on DC and time it - it may be the mechanism is tight. I've seen particular tightness on some on the worm drives, so they may want freeing or lubricating.

DCC won't fix a model that needs work on DC.

Cheers,
Alan

When they made the change to Next-18 PCBs a couple of batches ago they resolved the running height issue on the power cars (older models sat much higher than the mk3s), but introduced a problem with the bogies rubbing on the underframe. I've noticed that the newer ones appear slower as well, and I'll wager it's because of the drag on the bogies/unframe.

Make sure you follow any suggested lubrication instructions and run-in the model in to bed in the drivetrain.  Some models do loosen up a little as part of running-in.

The max speed the model runs at on DCC is unlikely to be significantly different to the speed on DC unless your DCC is running at an unusually/inappropriately high voltage compared to your DC controller.  For the equivalent of a "nominal" 12V DC model railway, DCC  is usually set at somewhere around 15V-16V to allow for a little voltage loss within the decoder.

Quote from: njee20 on August 20, 2021, 08:49:44 PM
When they made the change to Next-18 PCBs a couple of batches ago they resolved the running height issue on the power cars (older models sat much higher than the mk3s), but introduced a problem with the bogies rubbing on the underframe. .

This was always a problem, just few seem to have noticed it until now - there's no evidence of a ride height or tooling change - they appear identical to older batches - I was modifying the underframes to clear on the first batches of Dapol HSTs because of this.

Cheers,
Alan

There was a very clear change in the ride height, which coincided with people talking about the issue with the drag, it certainly became more prevalent.

The ride height is most notably dictated by the wipers on the chassis block - it's likely they are just set differently on newer models - as I've looked at this also and used it to slightly reduce the height (though frankly, my units haven't exhibited any major issue in this area).

Mind you, another thing I do to most Mk3s (certainly earlier production ones) is bend out the bad bow in the bogie sides, which seems universal on some of the early ones, this would slightly lift their ride height.

Nominally on the power cars, there would be no rubbing, but clearances would still be very tight. However, the chassis bases tend to be slightly distorted, particularly at the power car front ends, such that rubbing is common on all batches I've seen, old or new.

There's no appreciable design change*, as I've had a Next18 unit apart, precisely because it had a very tight front worm. That Next18 unit now runs considerably faster than some of my earlier models (which now want the worms checking also!). This can be identified by removing the bogies and seeing if there's freedom for the worm shafts to move a little a long their axis. If they are tight on this sliding, they may need freeing up.

Cheers,
Alan

* apart from change to Next18 equipped PCB from the NEM651 6 pin.

Yep, entirely probable it's assembly, not construction differences. I've recently swapped bodies around between original 2011 release and a current one and the body sits lower. Anyway, I'd be checking the interface between bogies and chassis, which has definitely been a more prevalent issue on recent releases. OP can disregard if he wishes.

Generally drag is worst off the dummy car for the flange clash in my experience; the PC motor tends to have the power to overcome its own drag.

But I would agree that doing the standard modification of opening out the base of the chassis to clear all wheels at all possible bogie angles is desirable - it's a standard mod I do to any new HST to my fleet, as is the un-bowing of Mk3 bogies, and in recent times checking the stiffness of worm shafts and bearings. Even if correcting drag does not help speed, drag will cause the motor to draw more current, run hotter and ultimately reduce its lifespan. Given HSTs are run a full tilt generally, the motors already can get hammered, so everything to ease this is worth doing.

Before any of that, running in is the first thing to make sure is done properly, as out of the box they tend to be tighter and slower with un-bedded in brushes etc. Of course, undertake no modification until you are happy to take the risk, as it can't be warranty returned thereafter....

Cheers,
Alan

Thanks for all the thought and ideas. I should of poster it had about 40mins in each direction left for 10 mins at 25%,50,75 and 100% power. I tried dcc just out of curiosity with the higher track voltage and tweaking the cv5 to max to see if a few more volts would increase the speed.
Try and get in the loft and check clearances as above tomorrow otherwise will have to assume track work has been carried out and top speed limited....after all I've got all sorts of rolling stock from pendolinos to the n class so a bit more imagination won't go amiss...