i was just wondering how does a TAT IV build reasonably well stack up against say an MRC power pack ( like 2500 with momentum/brake) .
reason i ask, is that ive been reading a lot about throttles and ive been toying with the idea of building it myself, was just wondering if it was worth the effort.
Bearing in mind that the TAT-IV was a DC controller, built with discrete transistors (some of which may now be unavailable), I believe it would have been easier to tailor to the performance of a specific locomotive.
One example. The acceleration rate could be adjusted to locomotive load - by turning a dial, you could simulate the difference between a light locomotive, the same locomotive pulling a short train and the same locomotive pulling maximum tonnage. My MRC pack has a fixed 'all or nothing' acceleration rate.
The other side is that someone whose knowledge of electronics is more current than mine could probably redesign the TAT-IV into a TAT-V with integrated circuits instead of discrete components, thereby easing construction while retaining the flexibility of the original.
Whether the increased flexibility would warrant the complexity and cost of construction, deponent saith not...
Chuck (Modeling Central Japan in September, 1964)
As I recall an MRC 2500 is one of the first Tech II series of throttles that is itself rather primative by today's standards. I believe the answer to your question is that the TAT-IV or even better a TAT-V allows the operator to have more control over what the system is actually doing. The MRC is mostly pre-set and automatic. On the TAT There isn't just "a" momentum but momentum adjustments. There is not just "a" pulse but controls for the pulse.
Personally I would highly recommend spending the time to understand and build such a throttle. The knowledge gained is applicable in many other areas of this and other hobbies. It wasn't until I built a transistorized electronic throttle in 1975 that I truely began to understand how and why motors in toy trains work the way they do and how a controller can greatly effect that. This knowledge has helped me design a throttle that simulates other things like fuel consumption, hot brakes, engine overheating, etc. I use the concept in both model railroading and slot car racing controllers. Likewise it can be applied to decoder design.
I never built a TAT IV, but I do remember being impressed with the schematics when they appeared in MR years ago. I'd expect the TAT IV design to have as good momentum as anything. If memory serves the circuit did some pulse power things at low throttle settings. If you want to built one, it will work with modern transistors. As long as the transistor is the same "sex" NPN or PNP, and the same physical size (power rating goes with size) you should be alright. Transistors have improved since the TAT IV came out and I would expect any run of the store transistor to have better gain and withstand greater voltages than they did back in the 1970's. Plus a 12 volt throttle won't stress any transistor made today.
David Starr www.newsnorthwoods.blogspot.com
ranchero i was just wondering how does a TAT IV build reasonably well stack up against say an MRC power pack ( like 2500 with momentum/brake) . reason i ask, is that ive been reading a lot about throttles and ive been toying with the idea of building it myself, was just wondering if it was worth the effort.
What my brother TT of Japanese modeling fame said.
An MRC Tech 2 2500 is a basic transistor throttle with fixed momentum and brake added. MRC used "mild" pulses in their Tech series throttles to avoid motor over-heating and damage. The trade-off for the mild pulses is not getting the ultimate in tie crawling slow speed. The MRC Controlmaster throttle series had more adjustments and would be more comparable to the TAT.
The TAT series - I have only seen the articles on 3 and 4 - were designed to run a locomotive as realistically as possible on DC. To that end, almost every key parameter is adjustable in the throttle - very much an analog version of today's DCC decoders with extensive CV tables.
The problem with using a TAT is that the settings will be different for each locomotive - just like you alter the CV tables on an individual basis. IIRC, there was an early command control system or IC-based DC throttle that allowed you to pre-program key settings into an individual chip for each locomotive that you plugged into the throttle. The other hassle with using a TAT is that the multitude of adjustments and controls makes a walk-around version very awkward.
Most commercial DC throttles reduce the number of adjustments to just a very few, especially if walk-around control is anticipated. The remainder are pre-selected for you - if that circuitry module exists. Momentum and brake settings are typically preset in commercial throttles, with just on/off selection provided. As you go up in price on commercial throttles, the number of adjustments typically increases.
IMHO, key adjustable features of a throttle would be:
Note that all these are available in a decent DCC decoder.
The nice to have features (not necessarily adjustable/available in the TAT):
Note that this second group is much more difficult to implement. DCC decoders are locked into pulse width modulation without DC insertion for motor power due to heat sinking and space constraints. Otherwise, decent DCC decoders offer all the key features, and are individually programmed for the locomotive they are installed in. The other advantage of DCC decoders is the ability to use BEMF. BEMF is less practical to implement in a DC throttle due to noise and momentary dropouts in the BEMF signal transmission to the throttle.
There are DC throttle circuits posted on line today that offer various subsets of the TAT features, and which would be easier to build (see http://www.awrr.com/throttle.html and http://home.cogeco.ca/~rpaisley4/Throttles.html for some examples).
My questions before recommending the building of a TAT IV would be
Personally, I decided to build a very simple walk-around transistor throttle as a trial. It has only a pot with a nice knob and a toggle for the reversing relay in the handheld case. The handheld case connects to the layout with a 4 prong plug and a coiled telephone handset cord. I found out simplicity in a walk-around throttle should not be under-estimated. The throttle did everything I needed it to do on my small layouts. Photos are posted with the Yahoo Basic Model Railroading Group (http://groups.yahoo.com/group/basicmodelrailroading/). The rest, which is a heat-sinked Darlington transistor, the reversing relay, and a broken (DC side is broke) AHM trainset power pack for power lives under the layout. There is no momentum or brake or special pulses.
I never got around to building anything fancier. My dad passed on to me his MRC Tech 2 add-on handheld throttle, which does have more features. I should be trying that out in the next month or two.
my thoughts, your choices
Fred W
I never used a TAT-IV - before my time. But MR featured an updated kit version with ICs etc. 15 or so years ago, called indeed the TAT-V. I purchased and built four of them, and they are the best throttles I've ever used. TAT stands for "true action" and 1:1 scale railroaders will tell you that most control of a train in motion is with the brake; this is just how the TAT-V works. Accelerate to your chosen running spedd, then select "Coast", and then use brake applications - whenever you release the brake the loco automatically returns to the original running speed. Momentum and pulse are easily dialled with a small potentiometer - much more convenient than setting CVs. Min and max voltage require a small screwdriver; they would be much easier to set if they also had a numbered dial instead. I set up a spreadsheet on an old laptop, dialled up these values for the loco of the moment, and it was quick work to set them. The more esoteric controls I have never found of much use - the midway default settings worked fine with all my locos. I understand that when the TAT-IV predecessor was first designed, these settings could indeed noticeably improve the performance of the open frame motors and sloppy gear trains of that day.
You have never learned how smooth and quiet a quality loco can be until you run it on a TAT-V and I assume the same was true of the TAT-IV (for which you almost certainly can no longer obtain certain critical parts). The purity of the filtered DC is awesome and I believe unmatched by any other DC design. As for DCC, even with the modern decoders the loco sounds like a washing machine compared with running on the TAT-V.
Having said all that, I still use them for a couple of situations but the lack of memory walk-around is just crippling. The fellow did in fact design a memory walkaround version and I bought two but sadly they have never worked for more than a few hours, at which point either the directional relay, or the "brains" IC, or both, blow. After returning them a couple of times for warranty service and replcing these parts a couple of times myselg, I gave up - clearly some fundamental design flaw there.
Does anybody have a schematic for the original TAT-IV throttle? I built one when it first was introduced. It still works, but I never labeled the controls, and cannot find either the original article by Lynn Westcott or my hand drawn "as built" schematic.
I have a copy of the original Feb 1962 TAT IV throttle that I can copy and email to you if you are still interested.
rdemalcolm I have a copy of the original Feb 1962 TAT IV throttle that I can copy and email to you if you are still interested.
rancheroreason i ask, is that ive been reading a lot about throttles and ive been toying with the idea of building it myself, was just wondering if it was worth the effort.
I think there were two significant features of the TAT throttles: - the use of pulses for better low speed performance and - indirect control of the throttle to simulate momentum and brake.Momentum required electronic control of the throttle; one reason for a transistor throttle instead of one using a rheostat. (I thought i read an article where a motor controlled the rheostat for the same purpose).But the TAT could have implemented a pulse width modulated throttle also controlled by a momentum/brake circuit.As someone already mentioned, one drawback is that TAT parameters needed to be adjusted for different engines and different train lengths. Today, each DCC engine has its own throttle with stored parameters controled using a picoprocessor.While I learned a lot about circuits and throttles by reading and re-reading the TAT articles, todays technology is superior in many ways. A TAT-like throttle could be built using integrated circuits, but more simply using a Pic like processor. And understanding picoprocessors has more application on todays model railroads. They are used in DCC throttles and decoders.One thing lacking in todays decoders is somehow accounting for train length and adjusting accelleration accordingly. I believe train length/weight could be determined by current draw.
greg - Philadelphia & Reading / Reading