Speed, tractive effort, tonnages

A cute little diagram I come across in my searching:

While this is for a life size SD40 heavy haul locomotive, I presume the curve demonstrated would be similar for whatever size and scale you are using. Jay tells me that 9kg of H0 scale Broadway Limited Pilbara locos can haul a bucketload of weighted ore cars up a helix no sweat. Again, mod the numbers, you'd probably have the same curve.

That's the general outline for a sand dumper wagon as built by me. The superstructure is wood framing, the dumper part is a upcycled 20L drum, with wheelsets and bearings from DNC Systems in Fairfield. Each wagon would cost approximately $300 - $350 in parts. A 20L drum could carry near on 30kg of wet sand. Add another 10kg (max) for the wagon, and you have a load of 40kg per wagon.

To get to one tonne, you'd need 25 cars. Assuming a length of 700mm including coupler rods between cars, but not including locos, that is a 17.5 metre long train. In terms of costs, that's probably enough for a couple of cartons of Crown left over out of $9,000.

You can see my "three to four tonne" estimate was way out, and while hauling almost two tonnes (now inclusive of locos and batteries, as well as a guards van) for an 25 or so metre long train is definitely a laudable goal, I can feasibly use the overestimate in haulage capacity to go up a steeper grade than a 1 in 40? Perhaps a 1 in 30? Or what about a 1 in 20? At a 1 in 20, I'd definitely need to be able to drop sand on the tracks underneath the wheels as the traction control in the VESCs takes over. This is pretty much an analog to anti-wheelslip technology used in mainline AC traction on the real railway.

I'm guessing I'm going to have to talk to Benjamin about coding up the custom firmware to allow an MU jumper to set slave mode, and traction control activation generate an interrupt pulse to drop sand.

In some ways the above diagram is similar to what I'm trying to do, though certain elements are different. I'm actually using that diagram to guide me in building a 250W brushless DC motor Dutch trike that I would use to ferry Lady Iona to and from the test tracks at Casino Miniature Railway.

Realistically, I'd probably want to haul about ten wagons at a time, 400kg load, plus around a tonne for the loco and guards van, for a length of about ten metres. Cost for wagons - $3,500.

And who says I can't do order of magnitude calculations?