Re to Tuning Engines for double heading
paul roth
double heading. This way you can actually select the engines you wish to
join together rather than have to work with engines that just happen to
be close in electrical signature (amp. draw). Sounds as these is the best
solution yet.
Paul
--
kr...@railnet.nshore.ORG (paul roth)
Railnet BBS +1 216 786 0476
Steven Bellovin
> I like the idea of a pot or rheostat on engines to fine tune them for
> double heading. This way you can actually select the engines you wish to
> join together rather than have to work with engines that just happen to
> be close in electrical signature (amp. draw). Sounds as these is the best
> solution yet.
Yah -- but at, say, 8 volts and currents ranging from .7 amps to 1.2
amps, you have a motor resistance ranging from ~6.67 amps to 11.4 amps.
So your trim pot has to be 5 amps at most. Worse yet, you're talking
about 10 amps at least here, and more if you want to allow for flat-out
12 volt running. Besides -- where is all that heat going to go?
Plastic engine shells don't make very good heat sinks, at least not more
than once...
A solution, if any, will have to be more sophisticated than a simple pot.
William Adams
[idea of using a pot for tuning engines]
OK OK, I'll recant. I didn't think it through enough before I
posted, the resistor value would be small and the resistor would
be dissipating around 1 watt of power (aren't those dynamic brake
fans functional on your models? :)
Maybe one could use a small resistor network to help spread the
power over enough resistors to keep them from blowing, (would
have to wire them in parallel to get small resistance, then in
series to ease individual power dissipation). But then you'd
still be generating the same amount of heat which would have
to be sinked somehow (air vents/rails).
But the goal is to make both of the engines look the same to
the power supply, right? So if the voltage is dropped at
the motor (say from diodes, as Leo mentioned) then the
motor draws less current and may match an engine with normally
lower draw. With this, how about replacing the diode(s) with
their fixed V drops with a rheostat (as Paul mentioned) for better
control? I know nothing of rheostat characteristics, so don't
know the consequences of power/heat/whatever in this case.
Or, if I may clutter the net with another idea, could one build a
transistor circuit using a small pot to vary the base current
(in a BJT) which then moderates the collector-emitter current
(going to the motor)? Transistors capable of handling 1+ watt are
common and could probably be heatsinked to the metal chassis
of the model (assuming it has one). Before I get blasted on this,
it's just an idea... I never really was an electronic circuits guy,
I'm a digital person.
Bill
wad...@faraday.ece.cmu.edu
Carnegie Mellon University
Leo Pesce
>
> Yah -- but at, say, 8 volts and currents ranging from .7 amps to 1.2
> amps, you have a motor resistance ranging from ~6.67 amps to 11.4 amps.
> So your trim pot has to be 5 amps at most. Worse yet, you're talking
> about 10 amps at least here, and more if you want to allow for flat-out
> 12 volt running. Besides -- where is all that heat going to go?
> Plastic engine shells don't make very good heat sinks, at least not more
> than once...
>
> A solution, if any, will have to be more sophisticated than a simple pot.
Steven is right, the potentiometer will not work. The heat generated will melt it right away. I was talking to a
friend of mine about this problem and the conclusion we reached is that the only way to solve the problem is to
have an electronic module. This is no different than putting a digital system in the engines, like the Marklyn,
which allows you to set the voltages for each engine to run the same speed, except that this module would be set up
specifically for each engine and it would run only on non-digital layout. Then again, it could be built to
standards so that it could be switched to be used either on non-digital or digital layouts. But where are the
standards (NMRA? Lentz? Marklyn?).
My friend also said that another solution would be a combination diodes/wound wire resistor. The heat problem still
exists, but the resistor now should be handling smaller voltages. He mentioned though that the speed
characteristics would not be a linear change as the voltage is increased/decreased.
As for the heat problem, a solution may be in the Proto2000 FA1 fan system. It means that each engine must have
seethrough grills and a way to pushh the heat out through them. A very difficult task in HO and with plastic
bodies.
Leo Pesce
Timothy Allen Rumph
One solution is to use a computer controlled command control system. This would
allow the computer to control each locomotive in such a way that everything runs
together smoothly regardless of the DC responce of the individual engines, as
long as you don't try to run the consist fast than the slowest loco will go.
This should also improve reliability of pushers and mid train helpers.
The cheap and dirty way: Run heavy trains with all the power at the front end
and put the faster locos in front, so all the couplers will be in tension at
all times. This works OK if the differance between the engines is not to bad.
If it is a gross mismatch, one or locos may not run at all.
Tim R.
Amateur Radio Club
I'm relatively new to this e-mail and newsgroup thing (almost a day now) but
I've been frittering around with diodes in constant lighting circuits for
several years now and thought I'd offer my ideas/discoveries. A rectifier
diode has an approx. forward voltage drop of 0.7 volts. putting two diodes
together gives a 1.4 volt drop. When this is put in series with a motor,
it drops the voltage to the motor by 1.4 volts. Hence, when the throttle is
putting out 12 volts, the motor is only seeing 10.6 volts which slows it down.
In this sense, the diode acts like a resistor that only affects voltage, not
current draw. When the throttle is putting out 1.4V the motor sees 0V
since the initial 1.4V is absorbed by the internal resistance of the diodes.
Anything over 1.4V is passed through the diodes as if they weren't there.
However, current is not affected by the diodes. If the motor draws 0.5A,
it will still draw 0.5A with the diodes. Current draw is a characteristic
of the motor and the only way to change it is to remotor the loco. In my
opinion, diodes are better than resistors in that one doesn't have to go
through the calculations of finding the "ideal" resistance and sufficient
power dissipation. Diodes provide a consistient 0.7V drop regardless of
the motor draw or mfr. Just keep adding diodes until the speeds are
equivalent (shouldn't need more than 6 - 3 in each direction). The only
thing that you have to worry about is that the current rating of the diode
is greater than the current draw of the motor. (not really a problem as
the standard 1 amp 1N4001 diodes are suitable for all HO applications)
Hope my two cents sheds some light on an otherwise mind-boggling subject.
C. Thomasson
Univ. of Manitoba
um...@ccu.umanitoba.ca
Dave Scanlon
: >
: >[idea of using a pot for tuning engines]
If you assume that each motor has a freewheeling speed proportional to
voltage than the resistive technique sounds good. Yet if you want the
motors to start rotating at the same rail voltage, the diode aproach
all for compensating for the difference in startup threshhold.
If engine rpm (no load) can be modeled as:
RPM = V(rail) * constant1 - V(threshold constant)
Then depending on the value of the constants you may want diodes
and/or resistors.
I imagine a more precise motor model would lead to a non-linear
equation and thus a non-linear circuit would be best.
--
Dave Scanlon Internet: d.sc...@medtronic.com
MS-T415 UUCP: uunet!medtron!ds0000
Medtronic, Inc VOICE: 1-612-574-6022
7000 Central Ave NE.
Minneapolis, MN 55432-3576
Kershner Wyatt
>Good stuff deleted on resistors and diodes and doubleheading concepts...
Fascinating discussion. Now let me ask the more elementary questions (which
I'm sure everyone except me knows...) Doubleheading is something I think
all of us try to do, long before we worry about equalizing the pulling power,
starting speed, etc. I imagine that most of us put the faster loco in front,
so that it pulls the couplers tight. Sometimes it's a problem, sometimes not.
I have seen the resistor concept before, but never gotten around to worrying
about it. Diodes are something I'll have to look a bit more at.
The questions:
How does one tell when the speeds are equal? See if the locos stay the
same distance from each other when running independent on the same
track?
Would a central pickup point wiring the motors together provide a solution?
What's the best way to doublehead two Atlas n-scale Pacifics? Replace the
non-functioning front coupler with Kadees? Maybe for once, I would have
enough pulling power for my heavyweight passenger cars on hills...
Thanks for the patience in answering the basic questions.
Kershner
--
Kershner Wyatt
kwy...@ccscola.ColumbiaSC.ncr.com
My opinions are my own and aren't necessarily my employer's.
Leo Pesce
>
> [deleted]
>
> How does one tell when the speeds are equal? See if the locos stay the
> same distance from each other when running independent on the same
> track?
>
> Would a central pickup point wiring the motors together provide a solution?
>
> What's the best way to doublehead two Atlas n-scale Pacifics? Replace the
> non-functioning front coupler with Kadees? Maybe for once, I would have
> enough pulling power for my heavyweight passenger cars on hills...
>
> Thanks for the patience in answering the basic questions.
>
> Kershner
1st question: Yes. Put two engines on a long straight and apply power.
If the engines stay close to each other with a small speed difference,
do not worry about putting any resistors/pots/diodes in them. You have
to remember that a layout has curves and hills, so each engine will at
some point change speed. That means that speed on a layout is a
relative thing. That is because most of us use constant power. On the
other hand, with digital control, one can control an engine like a
cruise control on a car. On my car (my first with C.C.) no matter what
the road condition (up or down), it maintains the same speed.
2nd question: No. Speed depends on a lot of factors: motor, gears,
power truck frictions, dirty wheels, dirty top rail, etc. etc. Engines
connected electrically (I think the term is 'mued' ??) via small
wires, mean that no matter what the condition of the track or wheels
are, if there are wheels making good contact with the rails, all
engines will be powered with the same voltage (this makes spectacular
scenes when the lead engine derails, the engine will still run, almost
real, no?). This is very good if you have plastic frogs for example.
3rd question. I do not know specifically (I model in HO), but knowing
the reputation of Kadee couplers, I would say YES. I would suggest to
put a dummy coupler instead of a Kadee (please no flames, it is just a
suggestion) that couples with Kadees, so when you run the engines by
themselves, the couples does not stick out too much.
A note: As suggested by other people, put the faster engine in front.
One reason is if you have Kadee magnets between the rails and you have
a slower engine in front, it may uncouple and go on by itself. (now
how can a slower engine run away from the rest of the train ?!?!?)
At the club, we found that a Kato/Athearn combination work best with
Kato (Atlas,Kato,Stewart) in front. That also works with Roco (Atlas).
Also Kato/Roco (read Stewart/Atlas) combination works very well and it
does not matter what is in front. Spectrum/Proto2000 work well
together, but not with any other manufacturer; for some reason they
are geared very different and run much slower than Kato/Roco/Athearn.
Walthers SW1 being a switcher runs most of the time by itself,
although I run it with the Atlas S2 and they run nicely(we du not run
them together because one is letterd SP and the other WP).
BTW, we run the trains at 7 to 10 volts. When we use Spectrum and/or
Proto2000, we have to increase to 12 to 14 volts so the train can
travel at the same (approximately) speed. Or power system goes up to
18 volts.
Sorry about the lengthy response but sometimes I get carried away.
Leo Pesce
Leo Pesce
>
>>2nd question: No. Speed depends on a lot of factors: motor, gears,
>>power truck frictions, dirty wheels, dirty top rail, etc. etc. Engines
>>connected electrically (I think the term is 'mued' ??) via small
>>wires, mean that no matter what the condition of the track or wheels
>>are, if there are wheels making good contact with the rails, all
>>engines will be powered with the same voltage (this makes spectacular
>>scenes when the lead engine derails, the engine will still run, almost
>>real, no?). This is very good if you have plastic frogs for example
>
>
>divide the power between the motors...??
>
>
Yes, it is a benefit, but to a point. You have to maintain most of the
engines together during operation, since the wires are plugged and
unplugged manually.
Leo Pesce