Is anyone using a TAT (True Action Throttle)?

Model Railroader Electronics and DCC
1

I would like to know if it is possible to set the TAT brake while working a light throttle; and increase the throttle, or add more brake to make a precise stop. This is the way the 12 inch scale trains were operated to make precise stops or control slack action.

The reason I am interested in this is that none of the DCC decoders seem to be able to simulate this. Either the throttle will not work with the brakes set; or the brakes will not work with the throttle open; or there is not a seperate release on the brake.

From what I read, it appears that the TAT will simulate working the throttle and brake together. Has anyone done this?

Thanks

2

Rick,

What a ‘Blast from the Past’! I built one of the original TAT IV throttles, and a later TAT V throttle. Here is my take on them. They are nice to ‘putz’ around with. Your will need to adjust for each locomotive and each combinations of locomotives and keep a log - then use these values to set up for operation. Running MU diesels can involve time consuming setup measurements.

For operation when I was into DC - I found that a good hand-held with a nice top-side toggle switch for direction was perfect for single hand operation. The ‘memory’ feature was basically a ‘decay’ circuit, and the brake position just added different resistor values to each of the braking rates. I later standardized on MRC Control Master 20 throttles - Big enough to have the power to run 3-4 Athearn engines in MU, decent memory control for running un-plugged, and basic rock solid MRC performance. I had 4 of these units on the layout.

DCC - I converted to DCC years ago, and the ability to speed match engines & run real MU was a big seller. not to mention getting rid of the block control issues. I guess I have never really thought about applying power with a brake set on a model train layout. The DCC control is so precise, I can creep a train into a yard track and get a precise stop.

I understand what you are talking about with increasing power with a small set of the brakes - On the prototype it is many times called ‘power braking’ In my time as a train service employee back in the late 60’s, we always used power braking . Now most railroads frown upon power braking, and if the engine has telemetry capability; You might hear from a trainmaster of the power desk about your actions and that you are burning up fuel and brake shoes with your actions.

Jim

3

Jim,

BNSF calls it stretch braking and tolerates it in some situations. Power Braking is Stretch Braking above notch 5.

Anyway, I do like the drama of stretch braking with steam locomotives. There have been descriptions of this in various articles, the best being on page 58 of Model Railroad Planning-1995. This was a straight train order meet; so the train taking the siding stretch braked to a crawl, so that the head brakeman could run ahead and line the switch. The opposing train stretch braked to slow its speed until it could be seen that the other train was in the clear and the switch lined back for the main… then the brakes were released and the throttle opened to get back to speed. This drama would not “lip sync” with any DCC sound system, so I am wondering if a TAT could simulate the action. If so, it might be possible to include a TAT circuit as part of a redesigned DCC sound decoder.

It may also be possible to adjust a TAT so that the train will runaway down hill unless the brake is used. This feature would make it interesting running through a sag. Were you able to try this with a TAT?

Thanks,

Rick

4

Rick,

I sold both TAT throttles and the power supplies at a train show over 20 years ago! Tht TAT throttle braking was just a resistor added to each of the 3 actual brake modes and affected how fast the power would run down until the train came to a complete stop I would have to review the circuit, but IIRC, the LAP and 3 BRAKE positions may just cut out the actual pot in the throttle circuit. I remember if you were in LAP, the engine would eventually come to a stop. Each of the BRAKE positions had that happen sooner. The more current the engine would draw would make the coasting stop faster.

When I worked for the ‘Q’, the older engineers would set about 10 lbs on the train line and them ‘pull’ the train down Langdon Hill. Most of the younger guys would on set 5-7 lbs and ride the DB to control the speed down the hill. A friend’s husband is still an engineer and with the new DB’s, they just use the DB to control the train all the way down!

Jim

5

With the NCE DCC (and any other system that has accelerate/decelerate buttons), couldn’t you use momentum and the decelerate button to simmulate the braling action? It would be nice if the manufacturers would give you the option to use this control as an “actual” brake.

6

There would have to be some way for the throttle to know that the train was sitting on a slope.

7

That’s what BEMF is for. Sountraxx uses it to get rod clank on steam locos, so they don’t keep chuffing downhill.

With all motive power AND braking in the loco, you can;t ever get a true stretch braking action. All the TAT throttles did when ‘working against the brake’ was reduce the braking rate as you increased the throttle with the brake on. Really all you’re doing is working against the independent brake.

I once fantasized about how ro get more prototypical train action, but because physics doesn;t scale, it probably wouldn;t work in anything smaller than O scale, and probably not even well there - maybe G scale. To wit, a caboose with a decoder of some sort would have a spur gear driven flywheel and either a small motor to oppose it or an actual electronic brake - a psuedo-motor with magnets and coils on the flywheel shaft would probably work. In the loco end, it would need to be either a multi thread worm or spur gears, such that the loco would NOT stop if the motor shut off - and in fact could potentially run away down hill if no brake were applied. Loco would either reverset he main motor or have a second motor or brake mechanism for the independent. Heavy trains might need more cars like the caboose for more momentum plus more braking. You would then have downhill coasting, plus seperate train brakes and an independent on the loco.

Electro-mechanically - I think this is very possible. How well it would work in practice - well, that’s the big question. Certainly not in lighter, smaller scales, even if it would fit. Heavy O scale or larger - I think it could. Much larger than G scale, and you already have that - Inch and inch and a half scale generally does have functional braking, at least on rider cars, otherwise you couldn’t stop them.

–Randy

8

I have considered powered trucks under the caboose, steam locomotive tender, and maybe a few freight cars. Silent decoders are cheaper than many RTR freight cars! The powered tender has potential in that it would allow the drivers to slip if the throttle was opened too fast[:)]. Some states required a riding car up front and many railroads included a boxcar for LCL. Again, it would help if the feedback on a TAT could be adjusted to produce a runaway on a down grade unless the “brake” was used.

But this gets complicated. The brake simulation would have to be part of a seperate but linked speed control. Some sort of SmartPhone or JMRI application might be needed… and that stuff is way over my head.

The MRC remote, that is used to control the Athearn Challenger on DC, is a handy little push-button throttle. There is some of the throttle and brake action in touching the Slow button when coming into a coupling.

9

I recall reading on the HOn3 Yahoo Group that Steven Hatch (Railway Engineering) had come up with CV settings on Tsunami decoders to operate/switch by just blipping the accelerate and brake buttons. I’d have to search the archives for a better understanding and/or more info. I’m still on DC (soon to change), and switch with a non-momentum throttle.

Fred W

10

In doing more reading, it appears that the TATs do isolate the throttle function when the brake switch is moved into a brake position. This was corrected by Dennis Blunt by adding a brake circuit that did not cut out the throttle (“Add a brakestand to your cab”, Model Railroader, August 1968, pp 47-51). This followed a great article on “Airbrake Valve Action” (pp 40 - 46) that mentioned working throttle against brake to keep slack stretched.

Despite all that effort, Linn Westcott did not include the more realistic brake circuit in the TAT IV (Model Railroader, March 1969, pp 12 - 26). Westcott was more concerned about perfecting pulse power application. Not long after this, the first developments of Command Control began to appear and interest in DC transistor throttles began to fade. So far, none of the DCC systems have attempted to simulate realistic brake action and are only begining to suggest appropriate sound effects.

11

Rick is correct – I’ve just been reviewing older MRs re the TAT IV, and the brake in all of the Westcott TATs disconnected the throttle pot from the amplifier when the brake was applied. This was done via switch SB, which connects to R via RA in “run” and via R5 in “booster.” All other brake positions connect either to nothing (“lap”) or some braking rate (a resistor which decays the momentum capacitor).

I’m not sure what a TAT V is – to me it always was a TAT IV with NPN power transistors In any event, I’m exploring using them again with modifications I will call TAT VI. This replaces SR (the dpdt reversing switch) with a 6p.19t. wafer set up as an actual power reverse for a steam locomotive. The first two poles are wired for reversing – just a more complicated dpdt with center-off in the “10” position. The “booster” setting is moved from SB to SR (pole 3, positions 1 and 19 – the “company notch”). This setting controls the pulse only (SR booster pole attaches either to point 8 – booster off – or point 9 – booster on – on the diagram) – the SB1 attachment simply goes directly to RA but around a new switch, RT (see infra). The next two poles, 4 & 5, affect the water and fuel capacitors (new!) – proposed time-delay circuits using a small Darlington amplifier and an SCR trigger. I worked out the fuel circuit last night, and what the SCR does is turn off a medium power transistor inserted between SB and RA (the “run” connection – see supra). If you don’t visit the coal dock every so often (or the oil plug), the fuel capacitor (used as an electrical sponge) will charge to the point of triggering the SCR through the Darlington, which cuts the line from SB to RA and converts “run” to “lap” (you coast to a stop and stay there till someone fills you up!). But, I have not yet figured out exactly where to attac

12

Rick Mugele
It may also be possible to adjust a TAT so that the train will runaway down hill unless the brake is used. This feature would make it interesting running through a sag. Were you able to try this with a TAT?

“There would have to be some way for the throttle to know that the train was sitting on a slope.”

I recall something like this could be done by turning up the voltage regulator, potentiometer RR.

13

A follow-up to my previous post (if you’re still listening):

I looked up the Blunt braking article over the weekend; I also pulled my Transitrol manual on TAT IV construction (still have it!). The proto-brake circuit is a drop-in unit – works in the TAT III as described in Blunt’s MR article and in the TAT IV as described in the Transitrol directions.

If you are modifying an existing unit, set SB permanently to release and drop in the Blunt brake (it connects to the plus and minus busses and to the point where SB, SD/C1, and R3 come together). No other modifications are necessary.

If you are building from scratch, eliminate SB and all its resistors (R5 to R8). Connect RA directly to R3 at the junction with SD/C1 and add the “middle” brake connection. The pulse switch, SP, in auto mode now connects directly to the Squelch, and there is no “booster.”

In Blunt’s own words, his brake circuit does allow one to work the throttle against the brake, since braking no longer disconnects RT from R3.

FYI: The Transitrol manual has a simplified circuit for the brake which eliminates the independent brake but does allow something like independent braking by other means. Essentially, Blunt throws away the bottom half of his circuit.

This should answer your precise question. Hope it helps.

P.S. If you have it, look up th

14

Wouldn’t true “stretch braking” be impossible anyway, since the cars don’t have brakes?

15

Pretty much. But I once had an idea (probably only good for O scale or larger) of putting a spur geared free running but low torque motor in a caboosee, with a decoder. Loco would also have spur gears, so it can run away downhill without the brakes set. Loco would also need a good size flywheel. Add resistence across the motor to be the independent brake. Apply power in the reverse direction of movement to the caboose motor and it would be the train brake.

–Randy

16

Yes and no: Not only do the cars not have brakes, but it is not possible to separate the automatic and independent brake, no matter what system you have.

That’s the “yes.”

But, it’s also true that, unless you are running cars with MKD4 couplers, there really is no slack in the train; and, since most cars use MKD5&10s, viz., Athearn, that means there is no slack in the train.

However, by using the throttle against the brake, you can simulate the action of a train, e.g., coming out of a curve; and, the most important feature of the proto brake is that, by using the throttle against the brake, and using the independent brake, you can do switching with the momentum on (it’s possible with skill to actually spot cars).

In the old days, this always was the great bugaboo of momentum throttles: They were good for road work, but you needed something like the Fyffe pure-pulse throttle in the yard or on the local. The Blunt circuit appears to cure this (N.B.: I have not tried it yet).

Re using spur gears, I would not recommend this! There is no way to install spur gears in that way which is not noisy.

A better idea: Use a coreless neodymium motor with a large flywheel connected to the caboose trucks via a worm or flea drive. Since all you’re trying to do is put some drag into the train, a small one of these motors, e.g., the Maxon RE15, probably would work. The main engineering problem would be synchronizing the gearing with the gearing of the locomotive. Or, you might experiment with something like the old Athearn Hi-F rubber-band drive (I still remember how my brother’s Hustler scooted when the power was cut off). Also, you might want

17

What #5’s are you using that have no slack? All of my cars have #5’s, the only place I haven’t been able to always use a 5 is on some locos and a very few random older cars, but they usually mean using an over or underset shank or a longer shank variation. ANd if I take a 20 car train and push adn pull on the caboose witht he loco stopped - theres PLENTY of slack! Once the the things I like to do, with a properly set up loco, is start off so slowly so you can hear and see the slack being stretched.

You can certainly do spur gears that aren’t noisy - the key is using the proper materials on the two gears.

–Randy

18

5&10s have only the slack in the knuckle (which I would not consider a lot). 4s have a compression spring for the centering device, plus a little pellet to slip inside the spring to prevent it from compressing so much it fails. 4s actually behave more like real couplers in that, when pulled, the shank actually extends from the pocket. If you use 4s, you actually can (with a good-enough throttle) pull the slack from the train, car by car (how a real engine has to do it to avoid snapping a drawbar).

Try a few; I think you will appreciate the difference.

Re spur gears, all I know here is my own experience plus the word of people like Dave at North West Short Line (who does gearing for a living). But, there is no point in arguing this. If your units are quiet enough, then use what suits you.

I do suspect you will get both quieter and more effective results with either the coreless motor or the Hi-F drive. Whatever the verdict on the spur gears, I can guarantee the rubber bands will be all but silent.

19

I haven’t built any of this, it’s just a crazy idea I’ve had for more years then I care to count. Coreless motors might be the way to go, though I’d think excessive use of the brakes would kill them pretty qucik from overheating. Might combine the flywheel and brake in one, using a magnetic material for the flywheel, or embedding bits of a magnetic metal in a brass flywheel (obviously needs to be carefully built and balanced) and a stationary electromagnet energized to various levels. Doesn’t need much to simulate the drag of the train brakes. Can;t use too big of a flywheel either, you want it to shove, but not shove the train off the track. I think you’re pretty safe from stringlining, at least with properly weighted cars with body mount couplers - I’ve seen some pretty rough train handling with the cars wrapped around reverse curves at on the club layout and no stringlining. Sometimes not the operator’s fault, if someone else in the same power district shorts, instant stop, then instant acceleration when the short clears. I think it takes some very bad track work and some really extreme starts and stops to make that happen.

I don;t see this working very well in HO. S or O maybe. Or just go to 1" or 1.5" scale and have actual working train brakes and forget simulations.

–Randy