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In lugnet.lego, Brian Davis wrote:
> As Ross mentioned, I was focused more on the "future" of trains, and if it's
> going to be done in LEGO, it looks like it will be done without conductive
> track.
Fair enough, but clearly the idea has sparked some interest, so I'm sure I'll
see it get put into use at some point.
> Absolutely, but you could do better. Run a single loop off a single output,
> and either pulse the power to it (this is how Steve and I do the GBC trains
> on standard 9V now, emulating PWM at a software level), or hook up a NXT
> motor to it as well, unloaded (that would require special split power cables
> I think) to function as a rotation sensor for feedback. You also *might* be
> able to run it as a "normal" motor in an unregulated mode - to be honest,
> I've not played with this. Now each NXT can run *three* loops; NXT ports can
> pour out current. So with three slave NXTs under the command of a single NXT
> master, you could selectively power at least nine loops or track segments.
> Very cool!
The ports may be able to pour out power, as you say, but I'd say it's equally
well established that large trains with heavy cars will suck it like water in a
desert. I'd be leary of running more than one loop off a single NXT's output,
and I'm not sure a 1:3 pulse of power would be enough to sustain a desirable
speed on many AFOL trains. While it might be possible to pull off nine loops, I
think your first problem would be in setting up independant control of all nine
through a single control NXT. All it has is three inputs, each of which would
accept one motor. Each motor can only have one setting, so unless you want to
slave three loops to a single throttle, that puts a strict 3-loop limit on each
control NXT to begin with. The second problem would be that unless you limit
yourself to short trains, I'd be concerned that this setup would be more likely
to burn out train motors. Slaving one loop per NXT allows each loop to draw
full current from a single NXT (though you might find that you have to slave a
second NXT to the same throttle to provide boosted power on a large loop).
> ...but it depends on conductive track, which is going away.
Yeah, but I don't expect the train clubs to start dumping it outright.
> There may be a problem here, in that the AC power supplied through the Li-ion
> limits the motor ports (in other words, you can draw more current from the
> three ports together than the wall transformer can supply in a steady-state
> situation).
Again getting back to a reason for limiting this to one loop per slave unit, and
three loops per control unit. You've got three basic choices for how to provide
current. Use alkalines to get higher voltage than a rechargable, though they'll
get expensive over time _and_ they drop voltage as they're used. Use the
Li-Poly pack with an AC adapter so that if you can limit the draw you can run it
indefinitely, or if you can't you'll at least be able to supplement the initial
charge. Use rechargable AAs to get the worst of both worlds. I mean, I suppose
you could go all-out on this and use regular Lithium AAs, but those are way more
expensive than alkalines, though they do also last a lot longer (not sure they
last long enough to spend $10 per pair, though...). Remember, this is a system
where train clubs will turn the trains on in the morning and let them run for
maybe eight hours straight in a single day, with the only breaks being to swap
out trains or to recover from a derailment. I don't think a battery-only
solution is going to cut it, and I also don't think most LTC's have much need to
actually power more than three regular lines. I think MichLTC set a club record
at NMRA when we had a grand total of seven loops running in a single show (three
regular, two elevated, and two underground).
> Well, like I said, the NXT can talk to both the IR Hobby train and the PF
> system (which it looks like will be in the future trains) via the IRLink, so
> the communication and control is already availible, just via IR.
Yeah, they'll never get the LTC's to switch over to a system that requires
constant line-of-sight to keep a train moving. Have you ever seen Jim Garret's
buildings? The Fisher Building has a large enough footprint that a train will
travel about 11' from the time it passes behind one end of the building to the
time it emerges from the other side. And in a normal layout, you could only
count on about 1' of clearance before it passes behind another building. Add in
the trigonometric problems (a single IR control unit cannot have a direct shot
down every street on a large layout unless you've conned someone into chasing it
around for the entire show), and you will have _very_ brief moments of control
over a very long run. Now, if the motor stays switched on until the IR control
specifically switches it off, that's less of an issue as all it means is you'd
have very brief moments during which you could adjust the speed up or down
(unless you did so from the outside), but if it requires a constant signal to
stay powered up, every building it passes behind will cause it to stall out a
bit, and large ones will stop it completely.
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Message has 1 Reply:
 | | Re: The Future of Trains
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| (...) Stalled, the train motor pulls 950 mA, while the stall current of the NXT motor is a whopping 2 Amps. So a single NXT motor output should easily handle a twin-engine train loaded to the point where it stalls the engine(s)... there's the matter (...) (17 years ago, 7-Oct-07, to lugnet.lego, lugnet.robotics.nxt)
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Message is in Reply To:
| | Re: The Future of Trains
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| (...) As Ross mentioned, I was focused more on the "future" of trains, and if it's going to be done in LEGO, it looks like it will be done without conductive track. (...) Absolutely, but you could do better. Run a single loop off a single output, (...) (17 years ago, 6-Oct-07, to lugnet.lego, lugnet.robotics.nxt)
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