Here We Go... Nonneminstre Hibberd Planet

[Armchair Modeller]

Starting with a Nonneminstre Hibberd Planet Kit

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Well, that photo above is more or less what it should look like, but at the moment it is just a body kit, as supplied by Nonneminstre Models.

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However, my P4 train set needs trains! The kit is designed to fit a motor bogie, but that would look very obvious below footplate level. I did get as far as starting a scratchbuilt chassis some time ago.......

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......but like most things I ever do with locos, I wasn't totally happy with it. One problem was that the design relied on a long chain of spur gears to get the drive to both axles. It looked more like a cheap clock that a loco chassis when it was assembled - not at all elegant. There was no room to hide the motor, so it would have been vaguely visible inside the cab. The other problem was that the prototype is built on wagon principles, with a frame at buffer level and W irons for the wheels. This means that there is lots of space underneath and very little is hidden. To do a good job, I really needed to keep all but the final drive around buffer height or above - and not in the cab, if at all possible.

On the plus side (I must try to think positively!) the compensation arrangement, with a transverse beam on one side of the chassis, worked well. The chassis seemed to ride more elegantly than a wagon I tried with the more usual one-axle compensated W-irons. The final gear deliberately looked a lot like the gear on the prototype's chain drive too. That's two features worth considering for 'Mark Two'.

So what to do? Well, firstly I bought a Ruston 48DS kit, hoping for inspiration. I wasn't completely happy with that either (see other topic) - aren't I hard to please?! Back to the drawing board then!

There are a few other issues I need to resolve before I finish this project, like couplings, loco livery etc.

I do have ideas, but they will have to wait until the next instalment.

[Mike Garwood]

Had you thought of this method?

http://www.clag.org.uk/axle-hung.html

Just a thought.

Mike

[Armchair Modeller]

Many thanks Mike.

I had seen these ideas before, but completely forgotten about them. They may well provide inspiration for some other projects - however, they look a little too bulky for my Hibberd Planet loco, where the wheels are more or less at the extreme ends of the chassis (Mini-style ) so any form of gearbox will be very visible.

I am happy to experiment on this one, so if my own preference fails miserably, I may come back to this idea. It's not like I am building or rebuilding a chassis for a Beyer Garratt, so the cost of failure is relatively low.

[Armchair Modeller]

The appearance of the Hibberd Planet modelled in the Nonneminstre kit is very deceptive. The body is basically a modern casing on what is really a Simplex-based design. The bonnet hides the radiator, whilst the engine and gearbox are mounted transversely in the middle of the chassis. It is easier to suss out the internal layout from early locos, which were less thoroughly enclosed. Here is a photo from http://www.bermudarailway.net showing the position of the motor in the centre, with chains leading down to the large gearwheels on the driving axles.

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(all historic photos on this site stated as out of copyright)


So, contrary to my comment in the first entry about not wanting the motor to stick into the cab area, the motor should actually be there in its entirety, although partly submerged in the underframe. The photo does neatly illustrate the point about most of the area between the wheels being fresh air. A motor bogie or any inside framed motorised chassis would look totally wrong, in my opinion.

The good news is that the kit should make it relatively easy to hide a working outside-framed underframe within the cosmetic one supplied in the kit. The frames of the real locomotives were well spread out to allow room for the loco springs between the frames and the outside face of the wheels. Here is a close up of one of the real w-irons. You can probably just make out the leaves of the spring through the hole just above the axlebox.

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Here is a rough sketch showing an end view of the proposed chassis

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This shows the wheels and axles held in place by the working frames (green) hidden inside the cosmetic frames supplied in the kit (red) The drive would consist of large gear wheels on the axles, driven by small gear wheels hidden in the upper part of the frames, which would be linked to the motor. A large gear wheel on each axle is very prominent in views of the real loco, so what I am proposing will be a moderate representation of the real thing.

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One of the working frames would pivot in the centre to provide compensation. The other would be fixed. The short wheelbase of the loco should mean that the up and down movement of the ends of the axles held in the compensated frame will be very small. Given that the other end of each axle would be rigidly held in the fixed frame, then the up and down movement at the point where the gears mesh should be minimal.

That then is the general idea. Great in theory (at least to me!), but there's only one way to find out if it will work...........

........more in the next installment!

The reason for using compensation is for good electrical pickup, by the way, rather than just to keep the loco on the track. Springing would give unpredictable movement for each axle, making gearboxes essential, I assume, to ensure good meshing of the gears. These would far more obviously look wrong than the final drive I am proposing.

If I sound as if I know what I am talking about, I do apologise. I am only guessing/bluffing/whatever!