Best motor / gearbox for OO GWR locos

[The Fatadder]

I am hoping for a bit of motor / gearbox advice.

 

 

After deciding that I should be building rather than buying more of the locomotives for Brent, I have just purchased a part built kit for a 4700 class 2-8-0 by PDK.  Last night I started trying to work out how I am going to power the kit. 

 

The model came with a Branchlines gearbox, along with a Mashima 14 by 30 motor, I also have a Mashima 14 by 32 and a 14 by 24 available, along with a High Level Roadrunner and Roadrunner Plus

 

My key requirement is that the motor must fit within the firebox, a DCC decoder will have to fit in the resin boiler (given that the tender body is solid preventing my usual tender location).  The latter also prevents any thought of a tender motor / cardan shaft arrangement.)  I defiantly do not want to Stop correcting "compromise" the lower half of the boiler, so cutting to clear the motor is out of the question.)  There is approximately 34mm by 14.5mm hole inside the firebox, tapering down to 12.9mm at the firebox wall.

 

The model needs to be able to handle 8 brass coaches, or an equivalent length of milk tanks at appropriate speeds.

 

I am hoping that someone more experienced may have some advice as to a good motor gearbox combination, with no preference on brand etc

 

 

I can fit the 14 24 into the model by sliding it into the boiler, however I don't see how I could do this with the motor attached to the chassis.  a 14 by 20 would fit horizontally in the firebox (with the rear shaft cut down).  Would this have enough power?

 

Finally, I cut down the rear motor shaft to approx. 2mm of length.  Can this be taken any shorter?

[Gordon A]

If you use the right High Level gearbox the motor can be raised so that its centre line matches that of the boiler.

 

The motor gear box assembly should be able to be rotated on the driven access to facilitate the fitting of the body.

 

On the High Level site is a printable plan of all their gear boxes to full size so you can match the gearbox to your requirements.

 

Gordon A

[Miss Prism]

I suggest you download the High Level gearbox planner, and start rotating various configurations (with bits of paper) and overlaying them on the loco drawing, for example:

 

 

 

[k22009]

I suggest you download the High Level gearbox planner, and start rotating various configurations (with bits of paper) and overlaying them on the loco drawing, for example:

 

47xx-drive.gif

 

If you can print the High Level Gearbox planner onto tracing paper it's an easy job to hold over a drawing of the 47xx then to see the best configuration.

 

Dave

[DCB]

As the 47XX used a standard 3500 or 4000 gallon tender I would use a different tender with the biggest baddest Mashima I could lay my hands on driving the loco via a U/J and driveshaft under the cab floor.   I have decided to go this route with my 28XX after serious motor and gear meshing issues and after reading of Guy Williams original Pendon 28XX.

 

We run a Cotswold 47XX with an MW005 and around 30:1 gears and the performance is most disappointing, it can't even haul the same trains as modified weighted Triang Halls without their magnadhesion as the motor lacks torque and stalls.

 

Isn't Hornby or Heljan or someone making a 47XX

[34theletterbetweenB&D]

...The model needs to be able to handle 8 brass coaches, or an equivalent length of milk tanks at appropriate speeds. I am hoping that someone more experienced may have some advice as to a good motor gearbox combination...

 Is your 'appropriate speed' = will achieve a scale 60mph with the heaviest train you plan to run? (Understanding 60mph to be about as much as was safe with this locomotive.)

On this question hangs the motor rpm and gearbox ratios that would meet your requirement.

 

...I can fit the 14 24 into the model by sliding it into the boiler, however I don't see how I could do this with the motor attached to the chassis.  a 14 by 20 would fit horizontally in the firebox (with the rear shaft cut down).  Would this have enough power?...

 If you allow the motor and gearbox to be secured on the rear axle alone, the resulting hinging action might allow the body to take a small part of the end of the 1424 motor in the boiler, while still being able to remove and replace the body. A couple of pieces of foam, one above the motor, one below, to clamp it physically between boiler top and the frame when assembled, might aid in reducing the resulting extra wear on the gearbox. (The torque reaction is otherwise all going into deforming the gearbox frame.) Assessment of whether this clamping is successful may be audible in gear noise reduction.

 

With the proviso that the rolling chassis and gear train is free rolling, a 1420 on 40:1 to 50:1 should result in a scale 60mph capable loco, and one that you can assemble the motor and  gearbox fixed in the frame, and still have the body lift off easily. With enough weight installed for adequate traction with your 8 brass carriages I suspect that motor will get pretty warm.

 

But I would look to 'steal' some space at the backhead in order to fit in the 1424 conventionally with the motor and gearbox fixed to the frame. Remove the backhead from the boiler, and replace in sheet metal, intruding into the cab perhaps a millimetre or so more than it should.? A little 'nibble' can make a big difference. Then the gearbox goes on the third axle and the rear of the motor is concealed in the cab

 

 

...I cut down the rear motor shaft to approx. 2mm of length.  Can this be taken any shorter?...

 It could have been. So long as the cut end of the shaft cannot enter the bearing you are good. The difficulty in trimming off a little more - if that is the intent of this question - is that you now have very little to hold, in order to protect the bearing during the cutting operation.

[B15nac]

I used a high level gearbox in mine it is a very tight fit in there though

[The Fatadder]

Thanks for the advice,

 

I will have a play later on and see what I can manage.  Unfortunatly the instructions (or at least the pages supplied with the kit) only had drawings of the body, so its a bit more difficult to use the High Level planning info.

 

I will try and work out the gear ratios of the various gearbox options I have already got and ensure they are suitable, my expectation is that I will go with the Roadrunner+ given the extra flexibility of the final drive.

 

Yes, I would be looking to get performance which matches 60mph max speed on a passenger working, so a hot motor is going to be something of a concern giving its close proximity to the sides of the resin firebox.  I think I will see what can be done about thinning the firebox sides to at least give it a little more space.  If not I will go back to looking at positioning the 1424 into the boiler

[Miss Prism]

If you need to fill the boiler and firebox with lead for best loco balance and adhesion, then a tender-mounted motor and UJ transmission is the optimum, as David suggests. Here's a modest Mashima in a small tender for Steve Duckworth's Caley 812 (described in a recent Snooze). This sort of transmission needs quite a bit of planning. A 4000g tender could take a large slow-revving Maxon, which would reduce the gear space requirement.

 

 

 

 

 

 

 

 

[Gordon A]

As the 47XX used a standard 3500 or 4000 gallon tender I would use a different tender with the biggest baddest Mashima I could lay my hands on driving the loco via a U/J and driveshaft under the cab floor.   I have decided to go this route with my 28XX after serious motor and gear meshing issues and after reading of Guy Williams original Pendon 28XX.

 

We run a Cotswold 47XX with an MW005 and around 30:1 gears and the performance is most disappointing, it can't even haul the same trains as modified weighted Triang Halls without their magnadhesion as the motor lacks torque and stalls.

 

Isn't Hornby or Heljan or someone making a 47XX

 

I thought using 30:1 gears on steam outlines went out years ago.

45 or 50 : 1 would be better.

 

Gordon A

[Barclay]

I built a Robinson 04 2-8-0 from a Pro-Scale kit and had a similar dilemma. In the end I made the Smokebox/boiler/firebox as a separate unit. During assembly the cab/running plate go on over the motor, then the boiler unit is carefully located, threading the motor inside it, and is  located by a brass peg on the cab front. A bolt under the smokebox secures it down. Invisible to the naked eye!

[polybear]

An email to Phil King at PDK may give some useful info too.
HTH

Brian