# Controlling the top speed of a train.



## T-Man (May 16, 2008)

Why? Derailment is one reason, too fast and oops. Not what you want to see if you have a fancy self train 7 feet above the floor. Modern throttles are nice so maybe this discussion this mute but it caught my curiosity.

For an HO application the answer is easy. Rob Paisely, in his reversing circuit section talks about diode placement along the track. The farther the engine moves the more diodes in line (between the engine and transformer)and the slower the engine. TO get fancy you can add a few in series and slow the engine for the curves. Operation voltage for HO on the track is around twelve the 1n4001 diode gives a .7 volt decrease 5 of them reduces it to a theoretical 8.5 volts. All this without playing with the throttle.

The diodes are directional So the track will work only in one direction. You will have to double up on diodes for reverse to work. Actually quadruple if you are using them for both sides of a curve . Then you feed power to the four straights for the fastest speed.

Cost wise the best way is to go ebay and get a lot. I got 50 or 100 of them.
Radio Shack is around 1.79 for two. ebay has 100 for 4.75 out of Mass. or less than 3 out of Hong Kong.

It seems more practical for a display or a shelf setup where the train is just running for display than operating on a layout.


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## Southern (Nov 17, 2008)

hum... that is something to think about.

Thanks


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## tankist (Jun 11, 2009)

do i understand it right, is the idea to bridge rails with diodes every set interval?
ehhh, need to read bit into it i guess.


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## T-Man (May 16, 2008)

*Yep*

That is the theory. Each diode causes a voltage drop as the engines moves by the diodes, away from the transformer feed.This can be used to slow for a curve or slow down for a trolley stop with a reverse circuit. I may rig up a simple line and try it. Might make a good video.

The wood is bought and construction begins.


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## T-Man (May 16, 2008)

I set it up like an experiment so I can change things easier.
Some sneak pictures. The terminal blocks are set up to tap into 1,2,or 3 diodes. I may have to make more.










The test platform is an 8 foot slat supported by a slat, cut in half to form a T Then I just slotted it for some plywood pieces. Seen just to the right.


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## tkruger (Jan 18, 2009)

After the curve am I correct that I would need to use a different diode to bring the voltage back up gradually. I would not want to go straight back up to full power, would not look right.

Secondly I have a steep hill with a curve on my layout. I need allot of throttle to make it up but going down Anything more than just minimal is to much. Is there a way to make it different going one way than the other?


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## T-Man (May 16, 2008)

tkruger said:


> After the curve am I correct that I would need to use a different diode to bring the voltage back up gradually. I would not want to go straight back up to full power, would not look right.
> 
> Secondly I have a steep hill with a curve on my layout. I need allot of throttle to make it up but going down Anything more than just minimal is to much. Is there a way to make it different going one way than the other?


Well for full power you need a separate block with it's own feed . I am not sure how realistic you can get it. I am still working on a trial run. You should be able to place a diode so you do not go to full throttle right away. Maybe the trick is not to go with a full throttle to keep the acceleration to a minimum

Diodes are directional so you can have more going one way than the other as in a case of a hill but you need at least one in the opposite direction.

As you can see this does open up some interesting uses. The only way is to try it out.


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## T-Man (May 16, 2008)

*Progress*

The stop diode is installed. The engine travels right to left. After passing the diode the engine stops until the current is reversed. On my engine the pos side is to the right as the engine goes forward.
The track is nailed down with soldered joints for every three pieces. I have a few bumps I need to fix too. 











You can see all the wires joined with banana clips.









Next to install more diodes and make a video.


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## tankist (Jun 11, 2009)

i guess i'm not getting it still.
with possibility to look stupid asking this - why diodes and not resistors? 
price? can't possibly, picked up 10,000 resistors assortment pacakge for 10$ (all hail ebay and china) or is it the "polarity-ability" of a diode (making the train run only one way) 

puzzled. and i have this distinct feeling the answer is "dough!" simple...


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## T-Man (May 16, 2008)

Diodes are directional. That is what makes the train stop in the reverse circuit-the reversed diode. The diodes are easier to calculate, a .7 voltage drop. The transformer varies the voltage for speed. I am a little sketchy here about electronics. I could try something. What resistance would cause the .7 voltage drop?


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## T-Man (May 16, 2008)

*The Premier*

I am still having focus issues. It looks fine in the viewfinder but when I get it to the laptop UGH. SO I made it short and sweet.

The resistors I added were at the beginning by the chimney to the building. Plus I had the speed cranked up, the breaking was better and no problems with derailing. I had to go slow in the beginning because of the derailing issue.
100 ohms stopped the train before it reached the diodes.
Enjoy


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## tankist (Jun 11, 2009)

but not for DCC of course.

how much W the resistors end up dissipating?


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## T-Man (May 16, 2008)

Right no DCC.

No idea? With a transformer and a motor in the circuit . I get 19 volts across the rails with a meter and no running motor with the 10 and 20 ohms.
I rewired the diodes with an extra, so I can reverse plus I added popsicle sticks at the contact points. You cannot see the smaller sticks the video.
The resistors are huge they are rated at 1 watt. I may try again with just resistors to see what point the train stops. It's less than 100 ohms they were wired in before the diodes.
I have to label the runs. I did 12 so it got confusing when I editted.


Explanation of the diode board. and the four boards used in the next picture.










The 10 ohm resistors and the pop sticks for track reference.


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## T-Man (May 16, 2008)

tankist said:


> but not for DCC of course.
> 
> how much W the resistors end up dissipating?


On one test the 10 ohm 1 watt resistor did get warm.
I tried a 47 ohm 1/2 watt and it got really HOT and stopped the train before the diodes. The resistor didn't burn up. I guess it is like breaking the car speed is dissipated by heat.

Remember I am using 19 volts on the Tyco, my MRC only has 10.5 on the rails.
I am not sure if it is doing any good for the transformer.
BTW Nice picture Tankist in the intro thread!


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## tankist (Jun 11, 2009)

that is one of the first things that i noticed about MRR powerpacks, different load and no-load voltage. puzzled me a bit (shamed actually, in distant past i majored in electronics ) but then i realized these are simply not voltage stabilized supplies. 
i'm sure you know you can parallel conect number of resistors so they can share the heat dissipation.


and as far as picture, thanks 
caught red handed - i removed the reticle illumination light from auxilary aiming device and using it as a lamp for reading. (we had the main thermal device running anyways).
while i really happy to have the pic, now i realize how stupid this was. that armor is equipped with automatic fire extinguishing system and there we are doing flash photography. i'm sure having halon extinguisher deploy in my face would have been refreshing. that's what you get when 3 stupid 20-year olds + even stupider 19-year old in charge (yeah, at a point my tank commander was younger then me) given a fully loaded armor.


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## T-Man (May 16, 2008)

I saw the Rob Campbell thread again and have another idea.
For AC control I would use a CW 80 and get power off the Accessory voltage. This is adjustable so you can limit the volrage drawn. 
To get fancy and have a little throlle instad of instant on. I would use the Lionel Controller( that comes in the modern starter sets), It has a whistle and directional control button.

One problem is the plug feed. You need to find a wire with that plug or modify the controller. My guess is that it is the same as a printer power supply. SOmething that uses higher amperage. All you have to do is find one a thrift store or your basement if you have an old printer or scanner.

Or get the set and cut the wire from the 45 watt power pack.


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## gunrunnerjohn (Nov 10, 2010)

The Lionel Legacy has a neat feature that allows you to slow the changes to a very slow speed to simulate the reaction of a real train.

I wonder if you could trigger a variable voltage source when you hit a trigger and slowly reduce the drive voltage to slow the train naturally?


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## T-Man (May 16, 2008)

Sure if you can train a pigeon to press a button.


That is probably half of the Legacy circuit board.


I eventually dropped the idea because of the heat given off. The parts got hot. It was entertaining for a while.


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## gunrunnerjohn (Nov 10, 2010)

Well, when you get half a dozen trains all running on the same circuit, I think the challenge will be a bit steeper. 

I stuck three engines all on the same loop of track and got them all creeping along following each other, then jockeyed the speeds to keep them from meeting. Fun to see at slow motion how busy you are changing channels and trying to keep everything together. 

I will have to try a lashup of three or four engines to see if I can get that working.


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