Minimum size flywheel for PS/2 Conversion

I did a Weaver 3 rail Hudson and it's one of smoothest runners I have. Had to jury rig a tack  holder and used the largest strips that came with the kit. Getting the smoke unit in the thing was not fun but doable. If I remember correctly there's a large lead weight in the thing that gets in the way at times.  Does  it run the same speed as all other MTH engines??  I doubt it but it's a keeper.  I think Chuck S   may  have done one as well, The small  flywheel is between the motor and gear box on mine. go for it.

I figured it would probably work.  I got the Hikel worksheet they created and computed the number of strips I needed based on a Premier Hudson I have for repair, it ends up being 12 stripes, so I don't think the encoder should have any issue, the stripes will be plenty large.  I was impressed with the gear ratio, if I used more stripes, it would be a great slow runner. :-)  Using the worksheet, I'm supposed to end up with something that close to scale MPH, so maybe it will be.

What I do for tach readers in locomotives with oddball motors and flywheels is just bond a fiberglass board piece to the motor and then glue a spacer to that to position the reader at the correct distance.  I've done that on quite a few conversions, none of the supplied tach holders work all that well on most brass locomotives.

Thanks for the reply, I'm ripping the wiring out and moving forward.

I've converted many a large scale locos by having to make flywheels for them and when it comes to steamers, the number of black stripes needed are all over the place! I've had some brass locos that I fitted 1.5" flywheels to that took 40 black stripes to get the speed right. Some diesels with 1" flywheels need 11 blacks. I've seen some MTH One-Gauge steamers where only the black stripes were painted on a bare brass flywheel. 

As near as I can tell, I'm going to need 12 stripes, so I think I'm a go.

Did the loco coast well before the conversion?  My suggestion would be to install a larger flywheel.  Doing so would probably benefit operation in other ways.  

Regarding the high-rpm performance of the tach reader-- Most brass locos have a gearbox which is separate from the frame.  If necessary you could replace the whole gearbox with a 0.6 mod ball-bearing gearbox from NWSL.  That unit has a gear ratio of 23:1 which is pretty close to MTH's OEM ratios.  However replacing the gearbox would be an expensive proposition, and a fair amount of work.

I know you stated that this is a 2-rail Hudson, but what is the vintage?  I'm excited to discover that some locos were geared so low from the factory.  If it's not too much trouble, a few pics would be great.  Thanks for sharing!

If there is room for a larger flywheel, rather than replace the existing one, make a ring that fits over the the one you have. Make it out of plastic so if not perfectly concentric it would have minimal effect on balance. Ten minute job if you have a lathe.

Pete

If the gear ratio is twice as low as the engine whose sound file you are using the smaller fly wheel should not hurt if you use a larger tape that results in half the stripe on your small fly wheel.  Which I believe you alluded too.

The flywheel needs to turn twice for the equivalent scale speed, so half the stripes will force the processor to apply more voltage to turn it twice as fast.

Should be smooth even at low speeds.  I have seen similar results with Williams Brass that had low gear ratios. G

No room for a larger flywheel, that would take cosmetic surgery.  I'm not entirely sure of the exact Weaver model number as it's in a 3-rail box, but it's clearly a factory 2-rail locomotive.  It's fairly old, I can tell you that.  I had to go re-verify that it really was 45:1, because I haven't seen one with that high a gear ratio either.  I think it's probably 44:1 on a recheck, still really impressive.

Here's a few shots of the chassis and box.

Interesting isolation motor mount. Too bad you don't have more room for a larger flywheel. The set screw would allow an easy swap. Is there room in the cab area for a motor with a rear mounted flywheel?

Pete

No room in the back.  I'm proceeding with the existing flywheel.  Given the high gear ratio, I'll only need 12 stripes on the flywheel, so my concern about the sensor is probably moot.  I have to rig a holder for the tach reader, other than that it looks simple.  This isn't my locomotive, and spending someone else's money to do mods that probably aren't necessary isn't in the cards.   Now I just have to figure out how to cut the end off the huge brass cylinder that is the weight from the boiler so the fan driven smoke unit fits.

Have not seen many larger motors with rear mounted flywheels.  All the 500 series or Pittmans use the shown set up.  If that is a 540 or 550 I would look to swap to a 545 or 555.  The 0 are 3 pole, 5 would be 5 pole.   G

Dremel cut blade, but wear gloves and do it in a trash can, lots of lead powder.  G

No lead George, it's really a big brass cylinder.  They're usually lead, so I was surprised to find this one in there.   Of course, the downside is it's much harder than lead, so it's harder to cut. 

I have done a couple as Gregg said, I used the larger stripes tach tape. It runs smooth but the SMPH is off. You won't be double heading a Streamlined Hudson with anything so it didn't have to be perfect. Even with the tiny flywheel it worked fine.

It's an RS-550 motor, but unless I have to, it's not changing.   The fact that it's going to only have 12 stripes means it'll be running faster for a given speed, that should smooth things out, even being a 3-pole motor.  Again, I'd be spending someone else's money.

Here's my solution to the non-standard tach reader mounting.  This has been used in a number of locomotives, never failed me yet.  CA Adhesive is great stuff.

GRJ, over 10 years ago I updated a Weaver brass USRA 0-6-0 switcher.  As I recall, the flywheel was about 22mm.  I made a tape for that diameter, with the same number of stripes, but the tach reader couldn't read it, and MTH told be that the smallest readable size stripes it could read were those on the 277mm tape.  SO that's what I used.  The speed is off, but I do have DCS control.  I also left the Seuthe smoke unit as is, as the boiler was too small to monkey with.  Used a diesel kit and submini-connectors between loco & tender.  Tach reader bracket was epoxied to motor shell.

Gun. john,

Why are you using MTH?

RJR, I only have 12 stripes on the tape, they're nice and fat.  Since the gearing is 44:1 on this locomotive, that's what I calculate with the Hikel cheat-sheet for computing custom tach tapes.  I also have the pages of custom tach tapes they posted some time back, so it's just a matter of finding the right tape and printing a copy on label stock.  I have used the small single element MTH smoke unit in some very small locomotives, I really try to fit them in if possible.

Joe, I have a lot of MTH DCS stuff, why would you presume I didn't have MTH?    However, this isn't my locomotive, you'll notice it's a 2-rail model.  I'm just doing upgrades on a few of these for a customer.

GRJ, I have neen told thT tach readrrs havr bren modified snd now can read finet stripes yhan they used to.  Don't knoe if that's factual.

PS/3 may have redesigned circuitry for the tach reader input, but I haven't heard anything about the performance changing.  That could well be possible.

 I could have guessed you have MTH products. I would have bet you'd recommend a TMCC install, that's all.

I think you'll come up with the correct striping once you pace the engine with another and see how she does.

 I have a 2 rl Weaver right here doing on upgrade on it, and the flywheel size seems regular to me. It's hard to know exactly what each release had.

one note that may help, if you are way out on the tach, the board will try to read and usually will stop. I've seen it stumble as it expects a result from the engine at a given output. It appears like it knows something is off!

When I'm doing my own stuff, I do both PS/2 and TMCC, depending on the specific locomotive.  Of course, when I'm doing other folks stuff, I do what they want.  I don't see many people running 2-Rail TMCC, though it's certainly possible.  All the 2-Rail stuff I've done has been PS/2 upgrades.  I have people converting from TMCC to PS/2, and I have people converting from PS/2 to TMCC.  The customer is always right.