Dynamic fan brake

That's true, for my Super-Chuffer I had to obtain a license from MTH for their patent.

I did the resistor trick to my Porter.  You don't really need a relay, you can just control the fan, and a reed switch can handle the 30-40ma used by the smoke motor.  I'm using a 100 ohm resistor across the motor and a reed switch to generate the chuffs.  It's not as effective as the method used in my Super-Chuffer, there I use a FET across the motor to drop a direct short of less than an ohm across the motor, it stops the motor in it's tracks!  I added the resistor after I posted the thread below.  The one thing I've noticed is the screen in the stack tends to diffuse the smoke and slow it down too much, it looks much better with the stack top off.  I'm thinking of just removing the screen...

K-Line Porter TMCC Conversion Project

If you go with the relay option, note that you only need an SPDT arrangement.

There also are SPDT reed switches but they are harder to find, fewer packaging options, more expensive, etc.

If as you say you have more time than money, it's worth experimenting with GRJ's resistor method using just an SPST reed.  My experience is you really want hard braking to get distinct puffs.  To get hard braking with the resistor+SPST, the resistor must be quite small (a few Ohms rather than 100); but that resistor would consume serious power (more than the motor) since you must drive both the resistor and motor (in parallel).

The resistor works OK at slow speeds, for faster speeds the relay will certainly do a better job.  Go for the ultimate, install a Super-Chuffer.

GRJ, l've been meaning to ask you if you've considered back-emf control of the fan motor to achieve the puffing behavior for example in this video - I tried to time-tag video to start at the point of interest - but if not working go to 1:55 minutes into video.

To my knowledge most if not all implementations simply hard-brake the DC motor to a stop between puffs.  Whereas if you watch the video what's really going on is there's a steady stream of smoke with puffs that are additive to the stream.  So to implement this behavior I think you'd want to run the fan at some constant speed (e.g., whatever speed used for idle when engine stopped), then accelerate the fan to puff, then quickly brake it but only back to the constant speed.  I think to implement this I'm imagining back-emf sensing which would require an A/D channel and some code.

Now this may all seem over the top but then again you are calling it the Super Chuffer.  Again, I've never seen this implemented in a model train but if you have I'd like to see a video.

Stan, I think this was suggested before.  However, that would be a whole new board as it would require a different PIC with more I/O channels and more discrete components.  If I were going to do something like this, I'd probably also consider regulating the smoke resistor as part of the package.  Obviously, anything can be done, but I don't think that's on my plate right now.

Stan, thank you for the tip on SPDT.  Other than the space to eliminate a relay, is there any advantage to experimenting with a resistor? If just shorting the fan would also result in hard braking - I think I'll look at the relay or SPDT reed switch.   I doubt I have more time than money but I'd rather do an enjoyable project like this than do unenjoyable things to make more money just to spend

GRJ, Thank you for the tip on the smoke screen.  Nice to know what to do while the engine is open!  I checked out your thread on the TMCC conversion and things look tight even in the tender.  I have the same tender you used from the Lionel Pioneer set.  When/if I open the Porter, I'll probably go TMCC as well. The whistle board from a Docksider will probably fit and works with most ERR TMCC packages - though it only provide whistle (and some people do not like it - I think it is great for these small engines).

I don't think the Dockside whistle will work with the MiniCommander II, but it should work with the Cruise Commander Lite, that one has the 5V logic output when the horn is blowing.

gunrunnerjohn posted:

Stan, I think this was suggested before...

Can you remember the reference?  But don't waste time if not easy to recall.  I'm just curious if someone has actually implemented it so I can see a video.  Talk is cheap!

andy b posted:

...

Other than the space to eliminate a relay, is there any advantage to experimenting with a resistor? If just shorting the fan would also result in hard braking - I think I'll look at the relay or SPDT reed switch.   I doubt I have more time than money but I'd rather do an enjoyable project like this than do unenjoyable things to make more money just to spend

...

If you have space for the relay that's the path I'd take.  I see no advantage to the resistor method other than simplicity.

Whether it be via a relay or some other method I think you'll find you need a method to shorten/extend the length of time the fan pulses.  If you only have a reed switch, the fan pulses will be the length of the time the magnet is over the switch....obviously.  If you think about it, this is probably not what you want.  Specifically, think of the limiting cases of the stopped engine and the fast moving engine.  For example, if stopped the fan will be solid on or solid off depending on whether it came to rest with the magnet just over the switch (or not); most implementations go to a idle stream of smoke.

To dig a little deeper, I think you'll discover that when you work through all the scenarios you'll conclude that you ought to figure out a way to drive the motor with solid-state components.  That is, it takes 2 inexpensive transistors to implement an SPDT switch to drive a DC motor.  This has its advantages over an electro-mechanical SPDT relay that is chattering quite rapidly when the engine is going at a good clip.

Then after you go around in circles a few times tuning/tweaking circuits to get the timing just right for various speed scenarios, you come to the conclusion you should have just done it with a programmed microcontroller chip.  Then you have the V-8 moment when you conclude you should have just purchased a Super-Chuffer.

stan2004 posted:

Then you have the V-8 moment when you conclude you should have just purchased a Super-Chuffer.

I was waiting for someone else to say this.

Super-Chuffer recommended by 2 out of 2 experts! 

Thank you both for sharing your knowledge and coming up with new products on this forum.  It is truly enjoyable to read and learn. 

Maybe 1 1/2 Andy, I have a vested interest in getting people to use them.   Stan is a more unbiased observation, he doesn't have a dog in the fight.