7mm BR Derby Type 2 x2

[SteveO]

In preparation for my Autumn/Winter project on my Rats I thought I'd start a thread to get some feedback and research sorted so I know what I'm doing when I get there.

I have two of these Beattie resin models to work on; a (badly, and not be me!) built model that I'm in the process of dismantling and stripping and a kit - or part of. Both will be 32B locos, numbers to be decided and research on individual locos is required. They will both be represented within their first year in revenue ('59-'60).



First up is the built model I have. It's been built and painted quite badly so a full strip is required. Due to the way it's been assembled I'll need to replace all the grills with new etches, if I can get hold of any from Mr Beattie or find any replacements from elsewhere (JLRT maybe?). I'll avoid the use of household cleaning products to strip the paint this time (!) and use something more appropriate. ModelStrip seems to be a popular choice though I'm unsure of its suitability on resin – advice required on that.

Next up is the part-kit. This has been supplied with all the castings but no etches, so I'm in the same boat with this as the other one regarding replacement grills, etc.

Before I start on the bodies I'd like to get rolling chassis designed and etched/fabricated. I'm planning a simple ladderframe design for both which all DCC electrics and sound will be fixed to (incidentally, I'm also going to use the same design for the NBL Type 2 I've just bought). I'm also playing with the idea of incorporating the buffer beams into the chassis but I'm not sure this will work very well or is even necessary – advice required here too.

Meanwhile, I've got plenty of reading to do. Research is probably one of the best parts of building models as you really get to know the history and finer details of what you're building so I'm looking forward to it. If anyone's got any advice or knowledge they want to pass on about these kits in particular or advice in general, especially about finding replacement parts, I'd be grateful.

 

[SteveO]

I've been playing with bogie designs tonight and have come to realise just how tight the space is in there with a horizontal motor - in this case a Mashima 1824, which I've just bought 6 of.

The basic design below, shown actual size, has a single compensated axle. At the moment it doesn't have a spring as I'm relying on the weight being distributed evenly from the bogie pivot to keep the frame level. I'm not sure how this will react with power applied though. I've cut away parts of the frame that are not required but I will probably reinforce the design with support underneath. The reason I've cut away the front and back is to avoid having a huge face when all I need is somewhere to stick the frame crossbar.



The configuration shown here is designed to incorporate Steph's gearboxes but now I have a visual I can see that I'm going to have to raise the bogie pivot quite some distance to clear the motor. I'm beginning to have doubts about whether this will work. Before I start designing the chassis frames I need to sort out the bogie problem.

 

[Steph Dale]

Steve,
Have you got any chassis parts included in the kit we/I can have a look at?
I'm not hugely familiar with Classes 24, 25 I must admit, so it'd be helpful to see what you've got to start with.
Steph

 

[SteveO]

Hello Steph, the only 'chassis' parts included in the kit are cross members that form the support for the bogie pivot. These are then glued onto the body sides. It all looks very ambiguous to me and open to error. On the built model I have the cross members are not even perpendicular to the body sides! Obviously, when I build the chassis for these and the NBL I won't need these cross members so I can do what I like in regards to supporting the bogies.

From what I've put together above the only way this is going to work is if I build a bridge over the motor and put the bogie pivot on that. It raises the centre of gravity and the angle of pivotal rotation quite a bit so I'm not sure how that's going to perform.

 

[Steph Dale]

Steve,

Aha, I think I see where you're coming from!

The CofG remains roughly where it was, but I agree the centre of rotation of the bogie may be a little higher than you were originally expecting. It's not actually all that high (it'll all happily fit below the floor of a DMU, for example). This actually has an advantage in some ways; it's possible to get all the weight into the fueltank and lower body, so it's below the centre of rotation which actually improves stability of the model as a whole.

Looking at your bogie layout I can see you've chosen to make the free gearbox the compensated one, it's probably simpler to swap that around and make the motor-mounted gearbox the one that moves. That way all you have to do is loosely restrain the back of the motor to prevent the gearbox rotating around the axle. It also negates any issue with torque through the gearbox causing any unwelcome movement in your bogie suspension.

I can also see your concerns with the distances between the back of the motor and the gearbox. Well, it does all fit, although you may find you'll have to shorten the rear motor shaft a little, depending upon which exact variant of the motors you have. I have a suitable 'ball drive' set of components in my lists to allow this drive to happen.

I'll take a few minutes this afternoon to look at the layout of my projected 8'6" drive bogie in your prototypes and see if I can offer further help or insight.

Steph

 

[Simon Dunkley]

From what I've put together above the only way this is going to work is if I build a bridge over the motor and put the bogie pivot on that. It raises the centre of gravity and the angle of pivotal rotation quite a bit so I'm not sure how that's going to perform.

Can you not have the gearbox "upside-down", i.e. with the worm under the axle?

 

[Steph Dale]

Can you not have the gearbox "upside-down", i.e. with the worm under the axle?

Nope - the motor casing will then be below the height of the rails...

Steve,

Here are a couple of views I've just prepared. First up, the gearboxes on their own shown at real size on a Class 24/25 bogie:


And here's a view showing the first draft I'm currently working on to produce my own compensated 'universal' 8'6" drive bogie:


In either case they look pretty good to me - the bogie pivot can be nicely hidden between the chassis rails, with the fuel/water tanks fully weighted the balance of the loco will be pretty close to ideal. Of course your view may differ from mine...!

A suggestion for making the frame therefore would be to use two sections/strips as the longitudinal members in the chassis, which should be able to go pretty close to scale centres and can run from bufferbeam to bufferbeam. On their top surfaces you could mount the pads for the bogie and body fixings. From their lower edges you can mount the tank brackets, etc. Which should be a relatively straightforward and quick method of construction. The amount of detail you then choose to ladle onto what's effectively a 'scale' underframe (and the true purpose of this drive system) is then up to you.

I hope that's some help. I've certainly found it useful and encouraging to have a more detailed quick look at another application and I'm very interested to know what you think

Cheers,

Steph

 

[SteveO]

Steph, your Universal bogie design looks very interesting. In fact, it looks so interesting I will halt development of my own until you've firmed up your design to a finished prototype – or I'll help prototype it for you as I'll be after 6 of these beasties!

My only slight concern – well, not really a concern, more of something to think about – is what will be visible between the bogie and the body. It looks like there's a fair amount going on in that space with pipe routes, etc so it may not be an issue.

I'll start basic planning of the chassis rails and what I'll need to fix to it and where I can fix the body to it – those cross members supplied in the kit may have a use after all!

While we're talking chassis', does anyone know the bogie pivot centres of both Derby Type 2s and NBL Type 2s? It would be very handy if they were the same so I could share a common chassis deign, or worst case make it slightly adjustable, rather than designing a chassis for them each.

I really appreciate your input so far Steph.

 

[Steph Dale]

My only slight concern – well, not really a concern, more of something to think about – is what will be visible between the bogie and the body. It looks like there's a fair amount going on in that space with pipe routes, etc so it may not be an issue.

Steve,
I'm sure there's stuff missing from the Carter drawing I used; blower ducts and similar items. The chassis rails also extend downwards into the dragbox assembly, but the outline isn't shown clearly if at all. The height of the motor is actually in a pretty 'dark' area of the loco (between the pivot and the fueltanks) so I think you'll get away with it. Perhaps I may also be permitted to point out that were you wanting to use alternative drive systems they typically have even less 'daylight' in this area.

While we're talking chassis', does anyone know the bogie pivot centres of both Derby Type 2s and NBL Type 2s? It would be very handy if they were the same so I could share a common chassis deign, or worst case make it slightly adjustable, rather than designing a chassis for them each.

Carter gives the Cl25 as 28' and the Cl22 as 23' - so it looks like two different chassis to me. No reason that the same components shouldn't be used for both though. It might be worth tracking down build, scrapping, works or accident photos to help work out what the underframe and bogie arrangements look like. I must admit on my current planning (Class 50) I've been relatively lucky to find that 1/25 of the Class have turned over in accidents* and so have reasonably clear views of what the underframes look like.

Steph

* I feel I can get away with that comment on the grounds that there were no fatalities or serious injuries in either case.

 

[SteveO]

...The height of the motor is actually in a pretty 'dark' area of the loco (between the pivot and the fueltanks) so I think you'll get away with it...

Steph, after looking at it for a while I think you're right, plus as the motor is quite narrow in relation to the body it's going to be well hidden, especially with plenty of matt black and rail grime.

So, in the case of bogies for all three locos, I'm in your hands. I'll be very happy to help out with testing/development so I'll wait on your call if you need me. Meanwhile, as soon as you've firmed up the dimensioning I'd appreciate a working drawing so I can finalise my chassis design (which is not going to be prototypical, but purely functional). If you need any 1824 motors to test application, let me know – I have a box full of them!

 

[SteveO]

Just in case it all goes off the rails with Steph's Universal motor bogie, I played around with a couple alternatives. I have no idea what the gear ratios would end up like or even if the first one would even be feasible but it was a worthwhile scribble just to see what could fit. I'm quite intrigued by the top one actually and wonder if it could actually be done.



I also did a rough draft of the common chassis. There's quite a difference between the bogie pivot centres on the Derby and NBL but as the difference would only hang over the bogie frame it would be possible to use this chassis for both loco types. I've yet to determine the optimal width. I need another visit to the loft to measure the bodies of both.

 

[alcazar]

Sorry if this is obvious, but if you have the gears on the same sides, won't it make the two wheels turn in opposite directions?

 

[SteveO]

Sorry if this is obvious, but if you have the gears on the same sides, won't it make the two wheels turn in opposite directions?

Sorry old bean, I don't follow...

 

[iploffy]

not if you mount them on opposing sides of the axle

 

[iploffy]

ask Dai he did a class 87 the same way

 

[Dog Star]

not if you mount them on opposing sides of the axle

On opposing sides of the same axle?

 

[iploffy]

I meant opposite sides on either axles so both wheel sets rotate in the same direction, doggers you know what I mean

 

[Dog Star]

I meant opposite sides on either axles so both wheel sets rotate in the same direction...

Maybe we need to wait until Prof Steph of the Gearbox-o-matic comes along to explain... he has patent-pending eh, Gromit.

regards, Prof Barking-plain-Mad

 

[SteveO]

Well, as logic would dictate, and a brief perusal at the gearbox confirms, the gearsets can be mounted either way in the box, so making sure your drive is contiguous is in the way you assemble them. Essentially the ploffessor is correct.

 

[SteveO]

Like I said in post 10, I quite like the arrangement of the motor and gearbox in the top design so I had a little play earlier. Shown below is a plan and elevation diagram of how I envisage it. It's far too complicated for me to work out the final ratio or even how it would be compensated, but I quite like it for compactness (I haven't yet thought about the casing either). The grey areas are the gear meshes. Thoughts and critique are appreciated.