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In lugnet.lego, Ben Fleskes wrote:
> Has anyone adapted two NXT units to drive a train yet?
Not exactly, that I know of, *yet*...
The biggest problem in running a train would be hiding the NXT - I saw only one
good solution to hiding the RCX in a boxcar, and the NXT is bigger, as are the
motors. You could use an old motor (or even a 9V train motor) with a legacy
converter cable, but if what you're looking for is a migration pathway to
actively produced electronics, you need to do without. Besides, the NXT motors
would give you very good speed control.
Two other options exist. One, power the truck with a PF motor (they are rather
powerful) run from the NXT by a converter cable (this solves the bulky motor
problem but you still have the bulky NXT on-board). Or two, command the Hobby
train or PF drive system via IR from an NXT using the Hitechnic IRLink. Yes,
this gets back to the problem of IR (and range), but it might have some very
interesting possibilities so I wanted to mention it.
> One NXT as a controller talks bluetooth to the other
> NXT that drives the train.
Note that you could network several NXT together this way, and run a slew of
automated accessories as well as sensor, points, etc. Especially with the
ability of the NXT with the IRLink to command the PF motors, that implies the
possibility of one NXT commanding 11 motors: 3 NXT motors with positional
feedback, and 8 PF motors (two on each of four channels). Could be interesting.
> I've been itching to try it but I only have one NXT
> and I'm not that familiar with the programming interface.
Where are you located? I know a number of folks (on either side of the Atlantic)
who have more than one NXT, and some idea of how to program them for BT. For
that matter, what do you want to do? In NXT-G, I could likely whip up some
simple coding for you, or you can take a look at my remote control example up on
Steve Hassenplug's webpage, near the bottom:
http://www.teamhassenplug.org/NXT/
To just look, you could look at the BTRC.png and Remote.png images in my
Brickshelf gallery:
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=191310
--
Brian Davis
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In lugnet.lego, Brian Davis wrote:
> Two other options exist...
Oh, for shame, Brian. Letting me think up an option that you passed right over
(and a really cool one at that). With the legacy converter cables, you could
power the _track_ with an NXT. Hook the track up as if it was a motor, using
the standard leads connected to the legacy cable, run the NXT off the Li-Poly
pack with an AC adapter hooked up, and then you can sit anywhere in the layout
with a remote unit that'll let you start and stop the trains at whim. Now, if
you can get _one_ NXT to slave multiple NXTs, you could run as many as three
loops off a single remote, using the three motor leads to give you three
different throttles. Now, granted, you might not be able to run large loops
without slaving multiple NXTs to a single throttle and spacing them around the
track to provide boosted power, but I don't have the necessary parts or
experience to tinker around with this idea to see what really is possible beyond
spending ~$600 to produce the equivalent of an IR train without the
line-of-sight restriction.
But being able to incorporate some portion of this concept into the next
generation of trains would go a long ways towards getting the trainheads to
support the changeover, if grudgingly.
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In lugnet.lego, David Laswell wrote:
> In lugnet.lego, Brian Davis wrote:
>
> > Two other options exist...
>
> Oh, for shame, Brian. Letting me think up an option that you passed right over
> (and a really cool one at that). With the legacy converter cables, you could
> power the _track_ with an NXT.
I believe the options being discussed were in relation to the use of non-metal
track, which is all that will be produced by LEGO in the foreseeable future.
ROSCO
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In lugnet.lego, David Laswell wrote:
> Letting me think up an option that you passed right over...
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.
> With the legacy converter cables, you could power the
> _track_ with an NXT.
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!
...but it depends on conductive track, which is going away.
> run the NXT off the Li-Poly pack with an AC adapter
> hooked up
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).
> But being able to incorporate some portion of this concept into the next
> generation of trains would go a long ways towards getting the trainheads to
> support the changeover, if grudgingly.
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.
--
Brian Davis
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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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In lugnet.lego, David Laswell wrote:
> 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.
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 of what the peak voltage is, which for a system driven by the NXT
will be slightly lower than what I *think* the peak voltage is from a train
controler, but not by much.
> I'm not sure a 1:3 pulse of power would be enough to sustain
> a desirable speed on many AFOL trains.
You lost me here. I was proposing pulsing the power ("pulse width modulation")
on a motor output, to simulate a more standard PWM scheme. With an NXT motor
attached, you might actually get away without a bunch of rapid "on off" command
in the software, because by watching the motor encoders for feedback the
firmware on the NXt would do it for you. The neat thing about this second is
that when the train hits a hill and tries to draw more power, the amount of
power to the NXT motor on the circuit with it will drop, and it will slow down
just like the train... until the NXT firmware detects this, and increase the
power out to maintain a constant speed on the motor. I've not tested this, but
it's a possibility that might be very interesting for NXT-driven 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.
Use an on-screen menu and the on-brick buttons to select which bank of loops to
control, and then use the three motors as three inputs to "set the throttle".
No, you wouldn't have a console of nine analog-appearing throttles sitting in
front of you, but it would certainly work. Start small is good, and I agree...
but I'm pointing out the level of flexibility inherent in the system.
> > 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.
And this is a good reason, but it would need more testing to see what the limits
are. Conservative is good, but very few of us have 4 NXTs to try this out with
as yet (yeah, I do know a few folks who could, but theytend to be hyperactively
busy with their HW).
> 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...
I agree... but if you are using conductive tracks, use good old analog train
controlers. If you want automation, you could control the train controler with
an NXT motor (if you've got the hardware, this gets around a number of
problems). And since folks have run their trains using LDCC off an RCX, running
a similar set-up off an NXT using the Li-ion battery and a wall wart should be
easy in terms of power (the transformer is the limit in the system, and if it
could power 1.5 amps out of the RCX under LDCC, it should certainly handle
something similar for the NXT).
> they'll never get the LTC's to switch over to a system
> that requires constant line-of-sight to keep a train
> moving.
I agree, but it's not large buildings that worry me, but tunnels and multi-level
layouts. If the Hobby train IR remote is anything like the PF remote, just point
it at the ceiling. I can control my PF Bulldozer from the other side of a island
counter just by pointing it up at the ceiling and bouncing the IR. But no way
will it work for tunnels. Yes, a system that allows the reciever to enter a
"latched on" state would be ideal... and while you're at it, if the PF receiver
(in the new yet-to-be-seen trains, for instance) could do PWM, then other than
battery life a lot of the problems have been solved: you could use IR to "talk"
to a receiver on a train going by, and set it's speed. The train then holds its
speed until the next communication window.
--
Brian "not actually a train-head" Davis
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In lugnet.lego, Brian Davis wrote:
> 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 of what the peak voltage is, which for a
> system driven by the NXT will be slightly lower than what I *think* the peak
> voltage is from a train controler, but not by much.
So it sounds like a single loop should be no problem under most situations,
since I'm not sure I've heard of anyone running three motors on a single train
(there's the same issue with how much amperage a power regulator can push).
> > I'm not sure a 1:3 pulse of power would be enough to sustain
> > a desirable speed on many AFOL trains.
>
> You lost me here. I was proposing pulsing the power ("pulse width
> modulation") on a motor output, to simulate a more standard PWM scheme. With
> an NXT motor attached, you might actually get away without a bunch of
> rapid "on off" command in the software, because by watching the motor
> encoders for feedback the firmware on the NXt would do it for you.
It sounds like what you'd want to do is run three loops where only one loop is
receiving power at any given moment. Based on that, what I was saying is that
I'm not sure a train will run nicely if it's only getting power 1/3rd of the
time. It seems like if you're giving it full power for one second and no power
for two seconds, it's roughly equivalent to giving it a steady 33% power.
> Use an on-screen menu and the on-brick buttons to select which bank of loops
> to control, and then use the three motors as three inputs to "set the
> throttle". No, you wouldn't have a console of nine analog-appearing
> throttles sitting in front of you, but it would certainly work. Start small
> is good, and I agree... but I'm pointing out the level of flexibility
> inherent in the system.
Well, if you don't mind the fact that many people would have difficulty
operating it under emergency circumstances (such as one train derailing over the
tracks of another approaching train). And don't ever hand it to anyone whose
VCR still flashes "12:00". Actually, if you include the use of buttons in the
control scheme, you could control four single-loop NXTs by using three motors as
analog throttle controls, and the left/right arrow buttons as a fourth digital
throttle.
> And this is a good reason, but it would need more testing to see what the
> limits are. Conservative is good, but very few of us have 4 NXTs to try this
> out with as yet (yeah, I do know a few folks who could, but theytend to be
> hyperactively busy with their HW).
No one person should need to own all involved NXT bricks. Since this is
something that would ultimately likely appeal more to an LTC than a robotics
group, having a few members donate NXT bricks for any shows would allow one
person to do all of the programming without having to drop a bunch of extra cash
on the project. For instance, in our club, Steve Ringe does a lot of work with
the older Mindstorms, but I doubt he'd have bought four NXT sets (I'm not sure
he's even bought one), but all told I believe our club has at least six within
the greater Detroit area (more if you include all of our far-flung members).
> I agree, but it's not large buildings that worry me, but tunnels and multi-
> level layouts. If the Hobby train IR remote is anything like the PF remote,
> just point it at the ceiling. I can control my PF Bulldozer from the other
> side of a island counter just by pointing it up at the ceiling and bouncing
> the IR. But no way will it work for tunnels.
Heh. So I guess that wouldn't work at all for one of Ringe's more devious
systems...
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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
Some precisions here:
- NXT stall current is 2A but only for a short time: internal thermal protection
will trip at a current much lower than that (exact value depends on temperature
and overload duration). A practical value is about 1A
- NXT motor driver itself limits the current around 1A too.
Philo
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In lugnet.lego, Philippe Hurbain wrote:
> A practical value is about 1A - NXT motor driver itself
> limits the current around 1A too.
Ah, thank you - so running two stalled train motors would exceed the NXT output,
but running one train motor up to a stall conditions should be fine. Out of
curiosity, along with the output limitations on the NXT (1 A) and RCX (500 mA),
does anyone have the output limitations (voltage and current) on the train
transformer?
--
Brian Davis
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In lugnet.lego, David Laswell wrote:
> So it sounds like a single loop should be no problem under
> most situations... there's the same issue with how much
> amperage a power regulator can push.
Philo kindly corrected me, pointing out that the NXT outputs are regulated down
to 1 A, so you couldn't run a dual-truck train all the way to stall. You could
still get a good bit of the way there, however. Does anyone know what the peak
voltage and current a train regulator can put out is?
While somebody is at it, the next time a large train is run up an incline that
is going around a bend at the same time, what is the train regulator actually
putting out? Do you ever see a train regulator running "full on" and the train
is just making it (i.e., near the limits of the system)? We had this issue with
the RCX powering the GBC trains, in that if we ever do go to "full power" (and
from the RCX, that's 500 mA, max), we get instant train wreck (usually with
impressive colateral damage, but that's a different thread).
> It sounds like what you'd want to do is run three loops
> where only one loop is receiving power at any given moment.
Ah, I see. What I was talking about was running three loops in parallel, pulsing
the power to each of them, not rapidly switching between the three from a single
port. PWM under software control isn't as smooth as you'd like, particularly at
low powers, but it might actually be good enough using the NXT motor encoder
feedback trick. It needs to be tried.
> Well, if you don't mind the fact that many people would
> have difficulty operating it under emergency circumstances
> (such as one train derailing over the tracks of another
> approaching train).
Program in a global kill switch: if the touch sensor is pushed, stop *all*
trains on *all* slave NXTs. Ideal? No... but if what you want is handling an
emergency, that will do it. My primary point is that if you are using a series
of true computers, there's a lot of possibilities.
As an example, let's say a slave NXT is running three loops under steady-state
conditions, and suddenly notices either its internal battery voltage jump up
(I'm not sure how much that would happen if it's plugged in), or one of the
loops suddenly starts running under a "no load" or "light load" condition. The
slave can correctly assume that something has happened to that train, and if
that loop crosses any others, can shut down not just that loop, but the
intersecting ones as well, "safing" that section of the layout (possibly an
out-of-sight section) before sending a message back to the master NXT for user
display. Incidently, since the master NXT isn't doing anything power-intensive
like running the motors, you could wear it on your belt like a big pager,
controling the layout from anywhere you happen to be. Your control center is
mobile.
> Actually, if you include the use of buttons in the
> control scheme...
There are four sensor inputs as well... any one of which could read an old-style
rotation sensor. If you are OK with different style throttles, you could easily
run seven (three motors, four rotation sensors) or more (gang touch sensors,
using pairs of touch sensors for throttle up / throttle down. You can probably
stack three or four touch sensors off every sensor input port, leading to
perhaps 6 up/down throttles from just touch sensors on sensor ports alone).
> No one person should need to own all involved NXT bricks.
No, but to learn how to program this stuff you really need at least two. I find
BT messaging between NXTs to be fairly easy, and very simple under NXT-G... but
that's because I've had the experience. You really need at least two to work out
the kinks on such a remote control scheme, and probably more (response times
change as you add more NXTs into the system).
> So I guess that wouldn't work at all for one of Ringe's
> more devious systems...
Really, if the PF system is going to be embedded into trains, having a "latch
on" mode would be ideal, and solve many problems. It doesn't even have to be an
"exposed" mode to kids, just a behavior that the IR receiver can produce when
properly commanded (like by an IRLink from a NXT, or a special "train remote").
OK, I'd also love non-line-of-sight solutions like compact BT between the train
and the remote, or just good old RC... but I don't know if those are in the
pipe. I'm pretty sure IR is already in the system :-).
--
Brian Davis
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In lugnet.lego, Brian Davis wrote:
> In lugnet.lego, Philippe Hurbain wrote:
>
> > A practical value is about 1A - NXT motor driver itself
> > limits the current around 1A too.
>
> Ah, thank you - so running two stalled train motors would exceed the NXT output,
> but running one train motor up to a stall conditions should be fine. Out of
> curiosity, along with the output limitations on the NXT (1 A) and RCX (500 mA),
> does anyone have the output limitations (voltage and current) on the train
> transformer?
The linear regulator inside is a 1.5A version if I remember well, but I may be
wrong. Cross posted to lugnet.trains trying to get train guru opinion...
Philo
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In lugnet.lego, Philippe Hurbain wrote:
> In lugnet.lego, Brian Davis wrote:
> > In lugnet.lego, Philippe Hurbain wrote:
> >
> > > A practical value is about 1A - NXT motor driver itself
> > > limits the current around 1A too.
> >
> > Ah, thank you - so running two stalled train motors would exceed the NXT output,
> > but running one train motor up to a stall conditions should be fine. Out of
> > curiosity, along with the output limitations on the NXT (1 A) and RCX (500 mA),
> > does anyone have the output limitations (voltage and current) on the train
> > transformer?
>
> The linear regulator inside is a 1.5A version if I remember well, but I may be
> wrong. Cross posted to lugnet.trains trying to get train guru opinion...
>
> Philo
At BayLTC we usually run four train motors on one loop using stock Controller
with a 1.2 amp wall wart.
Bruce
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In lugnet.lego, Philippe Hurbain wrote:
> In lugnet.lego, Brian Davis wrote:
> > In lugnet.lego, Philippe Hurbain wrote:
> >
> > > A practical value is about 1A - NXT motor driver itself
> > > limits the current around 1A too.
> >
> > Ah, thank you - so running two stalled train motors would exceed the NXT output,
> > but running one train motor up to a stall conditions should be fine. Out of
> > curiosity, along with the output limitations on the NXT (1 A) and RCX (500 mA),
> > does anyone have the output limitations (voltage and current) on the train
> > transformer?
>
> The linear regulator inside is a 1.5A version if I remember well, but I may be
> wrong. Cross posted to lugnet.trains trying to get train guru opinion...
The Australian LEGO wall wart is marked 10V @ 7VA on the secondary. I don't
recall all the stuff I learnt about the relationship between VA and W, but that
seems to me to indicate about 0.7A. I believe this generally reduces as load
increases, but again I don't recall all that stuff... Philo?
M>ltc uses a home-built 3A transformer for our displays.
ROSCO
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> The Australian LEGO wall wart is marked 10V @ 7VA on the secondary. I don't
> recall all the stuff I learnt about the relationship between VA and W, but that
> seems to me to indicate about 0.7A. I believe this generally reduces as load
> increases, but again I don't recall all that stuff... Philo?
You are right, the main limitation probably comes from wall wart... You are
essentially right for the 0.7A current (though it is not hard limit, rather a
safety one).
Philo
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