Problems getting diesel-electric to work

[Manichean]

I'm trying to set up a diesel-electric powertrain, but I'm having big issues getting the ratio of engines -> generators -> motors set up right.

I want to have two medium motors running two large propellers. The generators should supply enough juice so I can run the motors on, say, half speed without draining the batteries.

I tried setting up two large engines with two medium generators to supply the electricity, so a ratio of 1 large engine -> 2 medium generators -> 1 medium motor. But I found that I can barely get the large engine to crank one medium generator with a gearbox.

I set up some tests, and basically figured out that I can't, under any circumstances, get the engine to crank the generator at any appreciable RPS. The only setup that marginally works is putting a 1:3 gearbox between them, then the engine is barely able to run at about 8 RPS at full throttle. I'm guessing there is not enough torque there to run the generator, but even doing things like putting a clutch in between engine and gearbox to help ramp up the generator, or putting an additonal small motor on the generator that runs for spinning up the generator and then stops, don't work.

I've also tried looking for diesel-electric guides or tutorials but it seems that they are pretty much all outdated, or I'm doing something fundamentally wrong that's just not covered in the tutorials. Question: Is diesel-electric fundamentally broken right now? Or is there something I'm not getting?

[Ra-Ra-Rasputin]

Despite its namesake, the medium motor is actually the rough equivalent of the power output of the large engine. One medium motor can suck up ~ 500 generator charge.
My recommendation is to instead utilize clusters of small motors. This allows you to delete them individually to reduce power drain until you find equilibrium.

This only becomes a problem in huge builds, as wiring the clusters of small motors becomes frankly, painful.

If you want, i can take a personal look at the craft in question

[Manichean]

I was wondering more about the optimal setup for generators, although clustering small motors helps a bit. In the tutorials I've seen, people use a large engine to run four medium generators through two 1:3 gearboxes. I can't even get one large engine to crank one medium generator through two gearboxes. My best output is around 150 electricity or so from one medium generator being driven by one large engine with a 1:3 gearbox, with the engine running at around 7-8 RPS. I feel it should be more, since AFAIK I should have 500 or so electricity generated for a medium motor to run full throttle, and people say diesel-electric is supposed to be super efficient...

[Ra-Ra-Rasputin]

Those tutorials are probably outdated. You can run 2 medium generators with one large engine, but i don't remember the gearing off the top of my head. Could be somewhere around 1:2. Whatever makes the large engine settle at around 12 RPS

[Manichean]

I played around on my testbed a little more.

- Generally, torque seems to be more like the amount of torque needed to turn everything on that pipe network than the torque output by the engine. An engine outputs torque even when it is not running, and if I engage a clutch with nothing running on that power network, the torque in that network rises.

- I can get a large engine to crank 3 medium generators with a 1:2 gearing. It will even start under full load, which is convenient.
- I can get a large engine to crank 1 large generator using the same gearing, but that seems to be the max. It will output a little more electricity than the three medium gens.

- Electrical motors consume electricity in proportion to the torque they have to turn. I used generators not connected to power as a load in my testbed. A large generator requires more electricity for the motor to turn. A medium motor turning a large generator will consume more electricity than a large generator provides when turning at 10 RPS.

[Ra-Ra-Rasputin]

A word about the torque meter, it doesn't measure torque applied, it measures the total torque of the system against applied force. You're not seeing the engine apply torque, you're seeing the amount of torque that is present in the system. Unfortunately the name of the component is totally misleading in this sense, it can't measure torque delivery.

Imagine the torque meter has a spring that pushes on the thing it's attached to, and measures the resistance. You can get very high values by attaching the torque meter to a bunch of wheels, for instance. Since there's no one-way power delivery, you'll have to map out the torques of things by yourself. It's something i'm working on in my engine design guide, the engine section is already done on that part, but power curves is going to be another beast to conquer altogether.

There is also a torque curve to engines, despite what reddit is so keen to claim about that. They're assuming the torque meter also measures delivered torque correctly. But if you apply a constant valued variable brake to an engine running at 10 rps, then do the same to one running at 20rps, you'll see a significant difference in how it reacts. To actually measure the torque output, you need a dyno with consistent results. It's possible with the variable brake, but it has taken me a few weeks of design to get a testbed for power consumers that behaves consistently.

[RiftHunter4]

My diesel electric train uses a medium engine, a 1:3 gearbox, a large generator, 2 large batteries, and a medium motor. I had the engine running at about 10-15 RPS via a PID to provide power to the batteries. Was able to reach the Arctic with full battery and 50% fuel. Top speed was 120 MPH.

For efficiency, I find that running a medium motor at low RPS is pretty good. I only saw a 10 MPH increase moving from 30% to 100% throttle. Motor's electrical consumption is directly related to their RPS, so lower RPS can mean better efficiency.

[Manichean]

Thank you both. I think I understand enough of what I'm doing now to get something set up.

[Ra-Ra-Rasputin]

Originally posted by RiftHunter4:

For efficiency, I find that running a medium motor at low RPS is pretty good. I only saw a 10 MPH increase moving from 30% to 100% throttle. Motor's electrical consumption is directly related to their RPS, so lower RPS can mean better efficiency.

There's a fun thing about the electric motors that isn't easy to figure out at all; they're hard-limited to 20 RPS. The only way a gearbox affects an electric motor any way is by allowing this cap to go higher. Be very careful when lifting the gearbox ratios, as the engine does have to work harder. Try sneaking a 1:2 gearbox in there and you'll see the difference.