7mm Steph's 'Western' - real workbench...
- Thread starter Steph Dale
- Start date
Steph Dale
Western Thunderer
Well, passing current across a wear surface will tend to introduce electro-erosion in to the mix. Reducing area and lubricant selection can reduce this dramatically. The contact areas on a ball race are very small indeed so electro-erosion can be a bit of a problem. Adding AC in to the mix with DCC does increase the probably of an arc being struck within the bearing and this could be one of the mechanisms by which 'cold welding' can take place. This can, in worst case, lead to a siezed bearing (although not likely in our applications). The cold welding effect will lead to high wear and electro-deposition at a microscopic level; this will soon be enough to negate the fitting of ball races.
A good example can be seen at many main line railway stations. Look at the track where an electric loco is taking a lot of power at slow speed and you'll see the surface of the rail is pretty rough. That's the effect of putting a lot of AC power across a heavily loaded surface.
Steph
S
SteveO
Guest
Not even just the worm? 26:1 is quite appealing. Are they cut the same and the same dimensions?
Steph Dale
Western Thunderer
Steve,
Although many kit manufacturers seem to believe that the provision of an etched gearbox is down to getting the meshing and fixing centres somewhere near where they should be and then expecting the builder to miraculously produce a sweet-running mechanism, it isn't quite true.
Critical dimensions in the gearboxes I do include meshing centres, motor mounting centres, worm length, gear diameter, worm diameter, gear tooth face width, gear overall width, thickness of fret material used, run out of worm and gear, lubrication type, machining tolerances in parts. There has been some significant brain power and design trading to get where we are with the current 'boxes.
You'll note, for instance, that unlike other etched gearboxes the Blines 13:1 gearboxes don't have easy means to adjust mesh of the gears. They don't need it; it's designed in.
The long and short of it is that if you change any of the components from those specified the gearbox will either not work or will be a pain to assemble.
There will eventually be gearboxes available from yours truly which use Romford or Markits gears (as Roxey do) and they will have to include means to adjust the mesh of the gears; there is quite some variation in the worm dimensions used in the Markits gears; we're just not there yet, with one major design issue still to be resolved.
A 13:1 gearbox is a good ratio for a modern-traction prototype, allowing running up to scale speeds if desired. At these lower ratios the gears are pretty efficient and so slow running or haulage isn't compromised.
Steph
S
SteveO
Guest
Thanks, that explains a little more. The reason I was looking is that I'm worried slightly about slow-speed control, especially with a small high-revving motor like the 1824. I would hate to have built a nice-looking model only for it to have to launch at rocket speed because that was all the motor and gearing combination was capable of. 26:1 looks a very good compromise between high top speed and low speed control.
Steph Dale
Western Thunderer
I've managed to get a bit more done tonight. First up is a quick shot of the motor/gearbox units, pretty much ready to fit now; just tails to wire on and the prop shafts need shortening to length. Split axles in place and (with prop shafts unclipped) bench run. Happy bunny 
:
The major assembly of the evening (prepare to be underwhelmed) was to make up the bogie mounting. I started by opening the holes in the fret to take the screws, deburred, then assembled the fret components themselves. There's a modification required (to remove one side of the bridge), which was accomplished with piercing saw and cleaned up with needle files. I then shortened the 4 small bogie fixing screws, using two of the supplied nuts as a length gauge/deburring tool. With that job done the nuts are soldered in to place on the mounting, followed by the main bogie fixing screw. After an aggressive clean under hot water the overhanging part of the screw head was filed off - an easy job with a 10" flat 2nd cut file. It's always worth having a couple of full size files in the tool box isn't it? By the way, the nuts appear to be BZP steel, luckily I have Baker's fluid available otherwise I have no idea how they could be soldered, brass would have been so much more sensible...:
In order to make the bogie mounts a nice snug fit I increased the countersink for the screw heads in the bogie side frames. Well, I say 'increased'; in fact it appears that the tooling was probably designed around using cheese head screws, but it all worked out okay. The bogie mounting assembly was retained in place to act as a spacer as I gently worked a countersink bit around the hole. A quick trial run and hey presto; the position of the motor becomes clear. You'll note that the tube spacer, plasticard spacer and bogie mounting all work to strengthen the frame:
I decided to quickly check the location of the motor. One reason for that was to confirm whether I can get the motor in/out through the top of the frame (check), through the bottom of the frame (check), that everything fits (check) and that assembly can proceed pretty much as defined in the instructions from here (check):
I'm pretty pleased with that. Time to shorten the prop shafts and go for a trial assembly methinks. More next time!
Steph
:The major assembly of the evening (prepare to be underwhelmed) was to make up the bogie mounting. I started by opening the holes in the fret to take the screws, deburred, then assembled the fret components themselves. There's a modification required (to remove one side of the bridge), which was accomplished with piercing saw and cleaned up with needle files. I then shortened the 4 small bogie fixing screws, using two of the supplied nuts as a length gauge/deburring tool. With that job done the nuts are soldered in to place on the mounting, followed by the main bogie fixing screw. After an aggressive clean under hot water the overhanging part of the screw head was filed off - an easy job with a 10" flat 2nd cut file. It's always worth having a couple of full size files in the tool box isn't it? By the way, the nuts appear to be BZP steel, luckily I have Baker's fluid available otherwise I have no idea how they could be soldered, brass would have been so much more sensible...:
In order to make the bogie mounts a nice snug fit I increased the countersink for the screw heads in the bogie side frames. Well, I say 'increased'; in fact it appears that the tooling was probably designed around using cheese head screws, but it all worked out okay. The bogie mounting assembly was retained in place to act as a spacer as I gently worked a countersink bit around the hole. A quick trial run and hey presto; the position of the motor becomes clear. You'll note that the tube spacer, plasticard spacer and bogie mounting all work to strengthen the frame:
I decided to quickly check the location of the motor. One reason for that was to confirm whether I can get the motor in/out through the top of the frame (check), through the bottom of the frame (check), that everything fits (check) and that assembly can proceed pretty much as defined in the instructions from here (check):
I'm pretty pleased with that. Time to shorten the prop shafts and go for a trial assembly methinks. More next time!
Steph
Locomodels
Western Thunderer
InvernessTMD
Western Thunderer
Steph, Ive got a Peter Clark MPV to build and he recommends the ABC traction motors, but I want to do it as per the real thing and have the drive under the load bed with a driveshaft to the bogie, these look ideal...
Steph Dale
Western Thunderer
Thanks guys!
Si,
You'll have a PM in the next day or two...
Steph
Si,
You'll have a PM in the next day or two...
Steph
InvernessTMD
Western Thunderer
I shall look out for it!
Cheers
Cheers