I'm inclined to agree with you, Steve, as they come out of the box, Heljan locos are mighty beasts -certainly in 4mm! And kit or scratch build is going to be the more easy route to start with, as you say, you can plan where to put the batteries and LCU.
To answer some of the recent posts, if I may. You could certainly put batteries in a trailing wagon or coach and connect it through to the loco. However, our design principles include that the loco power should be self contained as with the prototype as, agreeing with Phill, you would need to have the wagon permanently coupled. We have thought about having a small battery in the loco and other batteries in the wagons and connect them up when coupling, but we haven't done any research on this yet.
Steve rightly mentions that there are larger batteries than the 2200mAh that we have fitted to the 4mm locos. In the larger scales (7mm and up) we can use different package shapes and we can configure them to fit diesel bodies. The LCU doesn't increase proportionately in physical size so you have relatively more space for the power pack in a 7mm loco.
Certainly a more efficient motor should reduce battery consumption but there are other aspects that you may want to consider first. I chose to fit the 4mm Heljan diesel locos to see how easy it would be to convert an RTR
loco (see post above). In encountering the Buhler motor I wondered why such a powerful motor was necessary until someone told me that a significant amount of torque was required to overcome the frictional force of an unsprung bogie.
Another important consideration is the efficiency of the gears in transmitting the load.
The other aspect (I am told) is that RTR models are designed with the toy market as well as the finescale modeller in mind and ruggedness has to be built in. Many modellers still expect the loco to respond at rates of acceleration far higher than the full sized loco and this requires extra power. With my 4mm conversions, even with the weight of the battery replacing the Buhler motor, I was expecting the loco to struggle under power but I was able to pull quite a respectable train at realistic speeds with the Mashima motor working on two axles only. If I tried to accelerate instantly, I got wheel spin and very little forward movement. However, when I notch up gently, as per the prototype, the loco responds, lifts its load and gently accelerates. It is a whole different driving experience!
Next year, we will install Protocab in a 7mm Heljan and I will report our findings here and on our website. Meanwhile I have recently acquired another Hymek in 4mm and I intend to replace the mazak chassis with brass and put two sprung power bogies in to see what difference this makes.
We are still building our understanding of model loco efficiency and a number of trials with our dynamometer will enable us to determine how best to overcome power losses and build in efficient power handling circuitry.
Thanks for the various posts, they all add to our understanding of your requirements. We aim to satisfy them in due course.
Best regards
Tony Hagon
Acc+Ess Ltd