A related question. How does Doc Brown pay for getting the Delorean (and the train for that matter) converted so it can fly? Perhaps he’s left investments behind in 1985 that have grown enough by 2015 to pay for it?
Hey, he can even go to 2015 first to see what he should invest in in 1985! (Although he’d possibly be against this idea, seeing his reaction to Marty’s sports almanach.)
If I were with Mary Steenburgen I’d never leave bed long enough to invent anything.
Maybe he figured, “What the hell.”
Yeah – I built those as a kid. Why is why I can buy Farley’s hero doing it. But he had to build everything from scratch.
An interesting tidbit of trivia I read mentions that at one point in 1955, there are four DeLoreans.
- The one Marty first when back in in BTTF I
- The one Biff went back in in BTTF II
- The one Marty and Doc both went back in in BTTF II
- The one Doc left for Marty in the cave in BTTF III
Another vague possibility is that he left a bunch of letters at various western union offices to people in the future saying “here’s how to build a time machine. In exchange for this info, please build it and then come pick me up at this time/place in 1886. Then went to that time/place and hoped for the best”.
Ooooh Ooohh Mr. Kotter!
The “1885” Doc sent a similar note to 1955 Doc, telling him how to construct a flux capacitor. 1955 Doc then sent it back on a one-way trip (Think Terminator series), where “1885” Doc retrieved it and used it.
Did he have any friends, anyone he trusted, other than Marty?
No way Doc would do this… he’s on record as saying that time-travel technology is too dangerous to be allowed to continue to exist and insists that Marty destroy the DeLorean as soon as he gets back to 1985.
And then he builds the time-traveling train and starts exploring the space-time continuum. I guess he changed his mind again. 
Though I do agree that he wouldn’t send the specifics of a time machine to random people.
Oddly enough, I was in the grocery store the other day and noticed they still stock 12-packs of Tab. I guess it is still around and popular enough to be stocked.
Having said this, good luck getting one at a cafe.
Some facts:
[ul]
[li]Doc is a student of all sciences, and a proven genius after inventing a time machine.[/li][li]He built a huge fridge out of local materials.[/li][li]He was in the Old West for around six or seven years, judging by the ages of his kids, a very productive part of the tail end of the Second Industrial Revolution.[/li][li]He had the Hoverboard to steal some tech from.[/li][li]He could still visit and/or crib from the DeLorean in the mine, as long as he restored it back to its required condition by the time Marty needs it in 1955.[/li][li]As he perfected recreating the Flux Capacitor, he could Travel to grab more tech from any other era.[/li][/ul]
It seems clear how he managed to build the Time Travelling Locomotive.
Well, by the cartoon series, he carries around a bunch of money from different time periods to give Marty to spend.
I think he’s more against getting rich, but not necessarily against getting what he needs to be time wanderer.
The suitcase of money was taken right from BTTF2.
Aren’t numbers three and four one and the same? The one that’s in the cave in III isn’t in the cave until the one that Doc’s flying around in at the end of II gets whacked by lightning.
No it has been in the mine since Doc put it there in the nineteen century.
I don’t get it though. So there’s a DeLorean already in the mine when Marty and Doc first come back to 1955 from 1985-A (the one where Biff was rich and powerful) in BTTF II? How could it have gotten there? Doc didn’t go back to 1885 until after the DeLorean that Marty and Doc used to get back to 1955 from 1985-A gets hit by lightning near the end of the movie (right before the Western Union guy shows up with a letter from Doc.) This DeLorean and the one in the mine have to be one and the same.
I made/put together crystal radios as a kid.
It seemed pretty simple and easy to do, if you have a crystal.