This is part of why I like reading the old MR's, to see how we got to where we are today.
In the early 60's, Linn Westcott developed the TAT III transistor throttle. One of its features was an automatically adjusting pulse that adapted to the needs of the motor - back EMF.
In Jan 65 there is an article by Dave Fyffe on a new throttle circuit that used continuously controlled pulses to drive the motor - one glance at the output waveform shown with the article and this is clearly pulse width modulation.
What's old is new again. I'm sure I will shortly come across the first article where one fo these genuiuses combined both.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Something like the below?
http://www3.sympatico.ca/kstapleton3/851.HTM
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Yes - I remember reading articles about CTC years ago and I think there was something called Astrac. I remember how clunky these were and now we have DCC. What will the future hold?
There's never time to do it right, but always time to do it over.....
I have no doubts DCC will become antiquated in the coming years..
I highly suspect something similar to R/C will be used..
I'm kinda surprise DCC is still "modern".
Larry
Conductor.
Summerset Ry.
"Stay Alert, Don't get hurt Safety First!"
I remember those articles too, but I thought " who would want to use these electronic devices to control a model train?". Here I am, 71 years old and fully involved in DCC and sound. Now have over 12 sound locos and almost 60 locos, half of which are now DCC. You just never know when something will hit you? I love it and can't wait to get my layout finished; then I can get more rolling stock and buildings to work on!
-Bob
PS: If it wasn't for guys like Randy and Candell and few others I would still be running DC! Thanks Guys.
Life is what happens while you are making other plans!
Didn't MTH patent all this stuff?
Simon Modelling CB&Q and Wabash See my slowly evolving layout on my picturetrail site http://www.picturetrail.com/simontrains and our videos at http://www.youtube.com/user/MrCrispybake?feature=mhum
simon1966 Didn't MTH patent all this stuff?
No, but they still won their lawsuits.
Alton Junction
building your own throttle is just one aspect of the hobby. But I think DCC takes that away unless you're interested in building your own dcc compatible decoder or controller. Of course you don't have to use DCC.
While pulse width modulation seems to be the typical method dcc decoders use to control engine speed, I was told this is not the best method. It isn't that difficult to build a PWM throttle with circuitry similar to TAT, but Westcott decided that pulse injection and DC control were better. I think DCC uses PWM because it is least expensive and easily supported with the picoprocessors available today.
(I read the MTH has lawsuits with Lionel and Union Pacific, nothing to do with throttle control).
greg - Philadelphia & Reading / Reading
gregc (I read the MTH has lawsuits with Lionel and Union Pacific, nothing to do with throttle control).
They sent letters to the DCC community long before they entered the HO market which resulted in some companies disabling features like BEMF. It is probably best explained by reading this thread.
http://cs.trains.com/mrr/f/88/t/21838.aspx?PageIndex=7
My comment was tounge in cheek following this debacle several years ago.
richg1998 Something like the below? http://www3.sympatico.ca/kstapleton3/851.HTM Rich
That there is a modern IC version of Fyffe's throttle. Fyffe used a then-new Unijunctions transistor to make the initial sawtooth wave and then used that to modulate th etrack drive, I think there were a total of 7 other transistors. The one UJT was approximately $8 at the time, more than half the total cost of the throttle. In today's money, that entire throttle costs about the same as what that one transistor cost.
Edit - I went back and looked at prices - that fully assembled VrioPulse is less expensive than that one tranistor when inflation is calculated in. That $8 in 1965 would be arounf $55 today!
simon1966They sent letters to the DCC community long before they entered the HO market which resulted in some companies disabling features like BEMF. It is probably best explained by reading this thread.http://cs.trains.com/mrr/f/88/t/21838.aspx?PageIndex=7
While the thread doesn't explain what prompted the OP, various responses seemed to highlite the belief that anything not compatible with NMRA standard would not be well received.
While i'm no expert, i'm not sure there's a big enough market to support mutiple systems such as DCC. Standards allow multiple manufacturers to get a piece of the market and incentive for innovation to reduce cost. But if there were two incompatible systems, splitting the existing market, i doubt manufacturers could make enough economically to profit from it, and i wonder if any hobbyists could afford replacing their existing investment with an alternate one.
Of course DCC doesn't prevent approaches other that PWM, but wouldn't any other approach require that each decoder contain a linear power regulator (a complete transistor throttle).
in other words, it seems to me that it would be very expensive to replace DCC and this will inhibit alternate approaches in both communication and power control.
gregc While the thread doesn't explain what prompted the OP
While the thread doesn't explain what prompted the OP
The OP was prompted by fairly unbridled vitriol being directed towards MTH on this forum, and others, by the smaller scale community. MTH was without doubt losing the PR battle at the time, and this was evidently an attempt to blunt the damage. Given that over the years MTH has been forced by market conditions to make their locomotives more DCC compatible, I would say that to date, they have failed to gain any significant penetration of the market with the DCS command system.
Counter EMF or back EMF is heavily used with DC motor control. Its in no way precise, but in model railroading, it works. Often where speed control is important, and additional encoder is used.
I personally don't really care for back EMF for normal operation. I really like having to increase the throttle to go up a grade. As I pass the summit, I need to back off on the throttle as the weight of the train becomes more downhill. This makes operation more realistic. At least if you are a train follower like me.
Some people like a control station and operate their layout from there. I suppose that they would like back EMF more than me.
For automatic operation, back EMF could allow a control system to operate the trains more precisely. Particularly if the train control has two way communication unlike DCC.
-Marc
The most common anti-BEMF arguement, and pretty much patently false. WHiel BEMF CAN be used liek that, to make an absolute cruise control where the speed varies not one bit regardless of grade or weight of train, that is NOT the primary use, except possibly among the 100% fully automated layout crowd - displays like Miniatur Wunderland, where it is critical that all traisn move at the known speeds at all time.
A better use, which I woudl argue is useful to EVERYONE, is overcomign gear train resistence, espcially in steam locos. Models are always a compromise - no real loco has the mix of gears we have in electric model locos. Real steam locos glide away at very slight speeds (assuming at least a halfway competent engineer at the throttle). Even the best engineered drive train and valve motion will have some stickiness. You cna polish and tune all you like, there still we be some there, resulting in some jerkiness at the slowest possible speed. A proper BEMF implementation will not only drive through any stickiness, it will also reduce the minimum operating speed, for far better slow starts and stops. This is not the same as having cruise control.
As for 2-way, sure it opens up some possibilities, but it's really not needed for fine tunign the running, not with a processor more powerful that computers of not all that long ago right on board the loco. Back pre-DCC, the TAT V throttle introduced the idea of tunign the performance for each specific loco, with the ability to use DIP headers with fixed resistors replicating the settings on the various adjustment potentiometers. Switch locos, switch to that loco's resitor pack, and the throttle was tuned to it. That's all unnecessary with DCC since the tuning is done right in the decoder, on board the loco, and is always with it.
Interesting the discussions spawned form simply noting the first published occurrence of using solid state PWM for model railroad control. It's not even close tot he first PWM - WAY back, there were several control options that used electromechanical means, with a spinnign disk with contacts and a wiper arm that was moved to be the throttle. This was an attempt to get pulse power without the rectifier - but in reality they were getting pulse width modulation drive.
SteelMonsters Counter EMF or back EMF is heavily used with DC motor control. Its in no way precise, but in model railroading, it works. Often where speed control is important, and additional encoder is used. I personally don't really care for back EMF for normal operation. I really like having to increase the throttle to go up a grade. As I pass the summit, I need to back off on the throttle as the weight of the train becomes more downhill. This makes operation more realistic. At least if you are a train follower like me. -Marc
The biggest problem with Back EMF is that as the motor heats up and cools down, so the resistence of the windings which alters the BEMF feedback load. So what might have worked perfect when you first started running your loco, might not be so smooth when running it 30 minutes later.
Encoders are of little improvement though. They introduce a moving mechanical component which is limited in resolution. So if you are traveling really slow, your encoder feedback may not be that accurate.
As to your second concern, you can turn on the BEMF cutout, which slowly turns off back EMF above certain throttle speeds. This means you get the best of both worlds: Nice steady slow speed operation, and speed changes for hills at higher speeds.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
This is why I like TCS decoders, their BEMF is self-adjusting. And it really does do something, it's not just a marketign gimmick. The first few minutes of runnign a loco with a new decoder installed, the slow speed is a bit rough, but it soon settles down. It's not warm up - it still runs nicely the next time, even if it's been a month since it turned a wheel. And they have the cutout feature so at road speed there is little or no BEMF for that 'crusie control' effect.
To be honest, I've never really noticed much differnece in operation of an otherwise broken-in loco from first run to hours later. I can;t run logn enough trains to make things really work on my home layout, but at the club I can pull enough of a train that the motors do defintiely get warm after a little while.
Grades have an effect on all operation, starting from a stop, slow speed, and faster speeds. For this, I don't care to have BEMF
Speed tables and motor kick were supposed to help compensate for a cheap locomotive. I suppose that if that is what you run, BEMF might help somewhat. In higher quality locomotives, I find the bigger issue to be a momentary loss of power continuity. That is a different problem with a different solution. Either packing in some kind of rechargeable battery or a set of supercapacitors like the TCS Keep Alive.
I may be dating myself, but I bought most of the parts to build the TAT IV (?). Reading the artical by L Wescott got me interested.
Through the years I did not build the throttle and than the Digitrax "Big Boy" came on the market and I bought it. Was that the late '90's?
Hard to believe.
simon1966 gregc While the thread doesn't explain what prompted the OP The OP was prompted by fairly unbridled vitriol being directed towards MTH on this forum, and others, by the smaller scale community.
The OP was prompted by fairly unbridled vitriol being directed towards MTH on this forum, and others, by the smaller scale community.