Author Topic: GWR City class loco  (Read 311 times)

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Offline 753

GWR City class loco
« on: May 04 2019 14:15 »
 Considering the wheels for the City I could not find a supplier of GWR 6’ 8” plain drivers, I could buy crank boss ones and cut out crank pin area but by the time you pay for a set of drivers and then rework them I thought it just as easy to make them and save a few quid for other items required.
This the test wheel, and I am quite pleased with it!

Mike




Offline MikeWilliams

Re: GWR City class loco
« Reply #1 on: May 04 2019 15:38 »
Very nice Mike.  So that is CNC milled from solid ... aluminium?

Mike

Offline 753

Re: GWR City class loco
« Reply #2 on: May 04 2019 16:34 »
Mike

Yes 1/4" thick ali with a 3mm end mill so you have a slow feed as ali is very sticky with small cutters, lots of suds!

I will have to order in some 4"dia  BMS for the tyres, if I cut out the centres they should be big enough for the tender tyres?

Mike

Offline 753

Re: GWR City class loco
« Reply #3 on: May 05 2019 15:50 »
Researching details on the City I found a very nice image of an original build, and an interesting comparison with the rebuilt version.
I prefer the original less busy, cleaner lines, and no top feed.

Mike







Offline 753

Re: GWR City class loco
« Reply #4 on: May 11 2019 10:03 »
Advice sought regarding powering the City, I have a Mabuchi motor rated at 6-18v and am considering using a lead acid battery which will fit well in the tender and I would think will have more power than NiCad’s. What amp range would this kind of motor pull under load?
That way I can add specific weight to the loco if needed i.e. front or back.
Thanks

Mike

Offline John Candy

Re: GWR City class loco
« Reply #5 on: May 11 2019 18:17 »
I have not used lead acid cells in a model loco but Ralph is keen on SLAs and will no doubt give some advice.

I use Ni-MH cell packs rated at 2.3Ah which power either Buehler or Mabuchi motors with a 24V max. rating. I find that a 16.8V nominal pack (which fully charges to around 19V) will run for at least 2 hours with a reasonable load in tow, so the average current drawn would be around 1A.
I now fuse my locos 5A and have yet to blow a fuse.

 On the advice of Brian Jones (supplier of Mac 5 ESC), I fitted my first-built G3 loco (LNER/GC N5 0-6-2T) with a thermal cutout rated at 1.6A and that has only once tripped, when the loco stalled.

Photos of the "guts" of Calcutta's tender below : Mtroniks Viper Loco 10 HV esc and "MyLocoSound" card included.

Regards,
John
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline Peaky 556

Re: GWR City class loco
« Reply #6 on: May 11 2019 21:47 »
Advice sought regarding powering the City, I have a Mabuchi motor rated at 6-18v and am considering using a lead acid battery which will fit well in the tender and I would think will have more power than NiCad’s. What amp range would this kind of motor pull under load?
That way I can add specific weight to the loco if needed i.e. front or back.
Thanks
Mike
Mike, look at the Mabuchi website which will tell you certain performance data for each type of motor.  Beyond these basics I find Mabuchi a pain in the neck, as they seem very secretive and selective about who is permitted to register on their site to see further info!  Hardly a good business model... I’m still awaiting “approval” after several days!  Moan over, I support the use of sealed lead-acid (SLA) batteries, but partly because their weight over the driving wheels gives good tractive effort.  So without much weight in the loco you may suffer considerable wheelslip unless very carefully controlled!
Rgds, Tim

Offline 753

Re: GWR City class loco
« Reply #7 on: May 12 2019 14:36 »
John and Tim thanks for your suggestions, I had thought about weight distribution over the whole loco, and as there are only four drivers you may be right to get maximum weight over them. I think some experimentation once the chassis are complete is the way forward.

Mike

Offline 753

Re: GWR City class loco
« Reply #8 on: May 16 2019 15:16 »
Considering the comments and suggestions regarding suspension / compensation in earlier posts, most applied to six coupled inside framed locos.

The City has outside frames and they need to be modelled faithfully, as there was no room for gear between inside and outside frames, that meant introducing inside axle boxes for springs / beams to bare on thus doubling friction and restricting movement.

The obvious solution to modelling outside axle boxes / horns was to make them work, the chassis now has sprung axle boxes on all four driving wheels
The motor / gearbox is mounted on a slotted cross beam between the inside frames allowing the module to move in the vertical plane and pivot in the horizontal plane. This combination should keep all four drivers in contact with the rails thus providing traction?

The motor and gearbox were made from component’s found on e-bay total cost £18.98.

Mike