Doddys HaupWerkstatte - My build thread

[John Candy]

I have (after a year or so of frustrating R&D), got the doors to work on my G class (later Q23) District line motor car.

Well done.....this I must see!

Regards,
John.

[Doddy]

to see if I can.

After a pleasent weekend photographing ex-LT1938 tube stock on the I-O-W. I decided to see how to drive the 2'  7" wheels from an ex-DVD motor.

First the new Griffon Hovercraft




And delapidated tube stock at St Johns Depot




And a bite to eat at the Ryde Pier cafe - well in order! Service was excellent and freshly cooked food - delicious!



After establishing that the wheels axle needs to turn at 500rpm to achieve a prototypical 45 mph, the DVD motor is rated at 6500 rpm. Calculating a double reduction gearbox using this website proved useful.

http://www.smex.net.au/Reference/Ratios02.php

Prior to that Ineeded to understand the relationship between an Axles rotational  speed and Miles Per Hour. So back to the PC and a short blast on an Excel spreadsheet.




Using the SMEX calculator I derived a 13:1 double reduction gearbox configuration.



I don't intend building a tube train, but found the process helpful to get my mind around gearbox design. I trust others will find the information useful to them.

Doddy

[Peaky 556]

"...the DVD motor is rated at 6500 rpm."

Just capturing a line from Doddy's workings, as a general comment to anybody thinking of designing or choosing their own gearbox or ratio, it is not appropriate to use the free running speed of the motor.   Not that I'm assuming the 6500 rpm is the free running speed in Doddy's case, but the reality is that maximum power is achieved at about 50% of free running speed. 

Consequently if we hope to work a small power unit hard to get the top speed we want, it's probably wise to gear the motor for 50% revs at the speed we want.  Then if power is a bit marginal, it's more likely to run as we want, and if it's overpowered, it's just a matter of treading gently on the 'go' pedal.

Generally these thoughts are a bit academic though, as most suppliers of motor-gearbox units wouldn't tell you the speeds or ratios anyway!

Regards,
Tim

[Doddy]

My thoughts exactly Tim, many thanks for drawing them out.

Your assumption of my using a maximum speed at 6500rpm is therefore correct.

In the case of any potential 1938 'Tube' car, I envisaged that I would not want it operating much (if at all) above a scale 35mph, so the 50% powerloss would have been almost irrelevant in my particular case.

As for monitoring the motor speed, I just treated myself to one of those hand held laser gadgets you use yourself to count the rpm on spindles - cost £8.72 inc p+p comes complete from Guangdong with a Chinese 'dump Trump' cap and flag.

Doddy

[Doddy]

Normally, I am on the ball so to speak, but cannot identify where this photo was taken.

Any takers?

[John Candy]

Fort William

John.

[Doddy]

Just recently I saw a photo from this DVD and decided to get a copy, fortunately the MIBA website still has them, they are rather old as the former Big Boy of Dobwalls Theme Park was presented.



The stock of Dobwalls was dispersed across the globe many years ago, I seem to remember that the Big Boy sold for about £250,000.
Nonetheless, Bob Symes (Robert Alexander Baron Schutzmann von Schutzmansdorff (6 May 1924 – 19 January 2015)) introduces another Austrian chap whose father built a rather nice 1:27.5 scale Railway in his garden.











If this is what can be done in 52mm gauge (1:27.5) then G3 (1:22.58) offers just that little bit extra scope for railway modelling. Either way, to see a near G3 scale train in this environment is truly heart warming and one that I find rather inspirational.

[IanT]

1:22.58 Doddy - what happened to 1:22.6 ?

IanT

P.S. Like the railway though...

[Doddy]

Here we go around the Mulberry bush . . .

1 foot = 304.8 mm

304.8 mm / 13.5 mm = 22.577777777

[cabbage]

Sorry Robert but the metre is now defined as a numner of Cadmium Red wavelengths and your accuracy is still way out...

Regards

Ralph

[IanT]

I'm afraid not - G3 is 2.5" gauge and we model UK standard gauge at 4ft 81/2" - all imperial measurements

That's 56.5"/2.5" = 22.6.

No (Metric) Mulberry Bushes were involved (or harmed) in this calculation...

Regards,

IanT

[Doddy]

This is the third time we have had this dicussion and I for one, I am thoroughly sick and tired of this pedantic discourse. Clearly you have a bee in your bonnet that needs to be cleared out.


If it is so wrong in your mind, then why not (for the second or third time of asking) get the G3 society website updated with the correct information? It does not appear on the technical standards webpage either.




Perhaps a word in the ear of the webmaster to make the changes needed? . . .  Ooops my bad!

[John Candy]

Oh dear!

Let's not "nitpick" over fractions of a mm (or thousandths of an inch) .... very few of our models are likely to be precisely to scale anyway ...... measuring and cutting, material shrinkage (resin and plastics) all contrive to introduce errors....add to that the fact that a great many of the available "scale" drawings include errors.
There is a body of opinion which says, "if it looks right", then that's good enough.

John.

[IanT]

I don't see any problem with the Website.

Between the wars, most G3 modellers moved to 17/32" scale (from 1/2") as it was very much nearer the correct ratio and also gave a bit more space. With the advent of metrication - some (including myself) found 13.5mm to be a convenient ratio to work to. Now 17/32 = 13.494mm and 13.5mm = 0.5315" (17/32" = 0.53125") - so they are not exactly the same but are very close. A 30ft loco built to 17/32nd would be 404.82mm long, at 13.5mm it would be 405mm long and at (an exact) scale of 1:22.6 it would be 404.6mm long. So, I agree that there is virtually no difference in practice whether one uses one of the "rules-of-thumb" or the correct scaling factor. However - if you are going to use a scaling factor - why not use the right one?

These days I use 22.6 because it is so very simple to draw in CAD a full sized prototype and then just simply scale it by 22.6. I also find it convenient to just divide any full sized measurement by 22.6 to get its scale equivalent - although I will then probably convert it into mm most of the time.

As to a bee in my bonnet - well initially I thought I was just pointing out a simple fact. However, having meditated on the issue, I've decide I probably do have a bit a buzz in my noggin. It probably started many years ago when GRS started calling Gauge 3 - "G64" - because I guess they didn't want to call it "G63.5".

It died away for a while but resurfaced a year or two ago, when the G3S announced on it's banners that the scale was 1:22.5 (same as LGB).

And then there was the most recent occasion when Garden Rail insisted on heading their Sentinel article as being a "1:22.5" scale article - and also actually changed the text to say I'd designed the loco at 1:22.5 - which as you may have gathered from above was incorrect - the Sentinel was most definitely scaled at 1:22.6.

What's the practical difference, well not a lot at all really - but why change things that don't need to be changed.

Gauge 3 is blessed with having a single gauge and scale and in that we are unique when compared to the larger model railway gauges G0 & G1. If someone wants to build at 1:22.58 or 1:22.3 - then of course they are very welcome to do so - I really don't care. But if you are going to post things as "facts" then let's try to stick to the actual scale ratios.

Regards,

IanT

[Doddy]

Posting things as facts when the blinkers are on and the facts not properly represented on the G3 website really irks when you then get repeatedly criticised for making an observation.
In the absence of specifically stating the scale ratio on the G3 website and its corresponding technical pages leaves everything open to debate.