Live Diesel 1/12th scale

[dewintondave]

when you do eventually get round to encasing the engine you will probably need to consider forced cooling. The engine was originally designed to be forced cooled by an airplane propeller or in an RC car you generally need to keep moving to prevent overheating.

I have been thinking of a fan cooling system. But, with the rich setting required for good smoke effects comes excellent cooling from all that evaporating excess methanol. Plus, castor oil provides fantastic high temperature lubrication.

The black coloured engine helps radiate heat, and the frame absorbs quite a bit of the heat too. The engine is only idling and not making much power.

Best wishes,
David.

[Boustrophedon]

From an engineering point of view one should never put a flywheel at the end of a shaft, particularly with a single cylinder engine. you are going to get torsional vibrations at some revs or other.

Worm gears are always less than 50% efficient, typically less than 25%, just saying.

[dewintondave]

From an engineering point of view one should never put a flywheel at the end of a shaft, particularly with a single cylinder engine. you are going to get torsional vibrations at some revs or other.

Worm gears are always less than 50% efficient, typically less than 25%, just saying.

Thank you for that.

In practice the large flywheel had little desired effect and wouldn't stay attached to the shaft; when the engine was stopped it would be spinning freely for quite a while.

Gear efficiency is not an issue with the loco really, it is far too powerful as it is.

Anyway, the gearing as you see it was to determine the required ratio. I've recently been busy cutting Mod 1 spur gears, an enjoyable and slow process.

Best wishes,
David.

[dewintondave]

I have been working quietly behind the scenes for months. We now have a primary gearbox fitted with a 4-stage spur gear reduction. The gears are quite massive and the whole box weighs quite a bit. Here's a short video of me powering-up the box using the lathe.



Best wishes,
Dave.

[dewintondave]

On Sunday we had a fine outdoor test of the new clutch and gearbox.





I've been green and plumbed the excess engine oil from the muffler into the gearbox. The gearbox covers are to stop oil-spray and dirt getting in, and are not air-tight. Along with the oil, a fair amount of exhaust is also being pumped into the gearbox and wafts out of all the gaps. At the end of the run, there was a lot of oil in the gearbox, Klotz Benol castor oil.

This was the first run since March. The torque output is fantastic even with the clutch partially engaged. In the video you can see me putting some resistance on the output pins, it doesn't stop the drive even when not fully engaged. The drive is very smooth, I'm expecting some smooth starts when the loco has a final drive...

Best wishes,

Dave.

[dewintondave]

After yet more months of behind the scenes work I can now reveal the final transmission set-up.



The gears are in constant mesh and are connected to their shafts by sliding dog-clutches. The gears on the jackshaft are Loctited to the shaft, the other gears rotate on their shaft unless engaged by a clutch.



I have built a three-speed gearbox.



As with Dave Watkins' "Detritus", reversing is accomplished by the opposing bevel gears. Unlike an automotive gearbox the three gears are available in forwards and reverse. The bevel gears were bought on eBay, and are the only gears I didn't cut myself.

There are four gear levers, one for reverse, one for 2nd gear, one for 3rd & 1st gears, and one for forward gear. I have to bring reverse fully out of gear before engaging forwards or else both gears will be engaged, and that would cause issues


Best wishes,

Dave.

[GTB]

 I have to bring reverse fully out of gear before engaging forwards or else both gears will be engaged, and that would cause issues  :)

Very nice work.

I've not had to machine gears yet, are you using commercial volute cutters, or do you make your own?

It's a bit hard to work out from the photos, but could you fix the bevel gears on a sliding sleeve so they move together?

That would mean only one lever is needed for direction change, removing the risk of putting a few gears into low earth orbit in a moment of distraction.......

Graeme

[Big Jim]

Wow.
I take my hat off to you.

[dewintondave]

I've not had to machine gears yet, are you using commercial volute cutters, or do you make your own?

It's a bit hard to work out from the photos, but could you fix the bevel gears on a sliding sleeve so they move together?

Hi Graeme,

I'm using a homemade cutter as detailed in this excellent resource: http://www.helicron.net/workshop/gearcutting/method/

It's very satisfying making gears, but very slow. Some of the gears were made four at a time. I ended up roughing out each tooth in one pass at .09" depth with a single tooth cutter, then finishing in one pass at .097" with the hob detailed on the website. The gears come out heavily burred and require about an hours fettling.

The bevel gears are both in mesh all the time and freely rotating on the shaft. The dog clutches need about 2.5 mm of movement to bring them fully in and out of engagement. If the levers were connected I'd need about 5 mm of travel at each side so there wouldn't be any double engagement. I just didn't have the room.

Best wishes,
Dave.

[GTB]

I'm using a homemade cutter as detailed in this excellent resource: http://www.helicron.net/workshop/gearcutting/method/  

Thanks Dave,

I found that site a while back while searching for something else and have a printout stashed in the files. Good to know the method works, as it seems to be within the limits of my machining abilities......

Machining burrs are one of those things sent to try us, I think.

Graeme

[Dannypenguin]

Thats impressive

[dewintondave]

I've had to extend the frames forwards 10 mm.  The front of the carby was directly inline with the front buffer beam.  The engine couldn't go back any further...

The chassis with one side frame off for lengthening.


Now the frame is 10 mm longer.


The graceful new lines.


Best wishes,
Dave

[dewintondave]

The rear suspension is far too bouncy. Some things are good being bouncy but not this loco.



As a trial I had used a gauge 1 inside frame type suspension, it doesn't look the best on this application.

Here we are, I'm making horn plates for a new suspension arrangement on both axles.



Best wishes,
Dave.

[Dr. Bond of the DVLR]

How does the new system work - equalizing beams?

[andymctractor]

Superb stuff.  
That is the only loco chassis I've ever seen in any scale that could not look any better by fitting a body.  Its almost a shame to cover it up.

[dewintondave]

How does the new system work - equalizing beams?

Axle boxes sliding between the horn plates. I want to try a leaf spring arrangement, if that fails it will have to be the usual coil springs on top of the axle boxes.

I was recently re-watching the 16 mm assoc videos, I loved your DVLR films they were magic :-)

[dewintondave]

Superb stuff.  
That is the only loco chassis I've ever seen in any scale that could not look any better by fitting a body.  Its almost a shame to cover it up.

Thanks Andy, that's great.

There will be plenty of works to see through the cab doors. I didn't manage to keep everything below floor height

[dewintondave]

Milling the axle box slots out of the first frame side.



Here's the new horn plates in position on one of the frames.

Front


Back


My project this week is to make some axle boxes.

[dewintondave]

Here are two new axle boxes. I shall think about the springing and the keeper plate before I start on the other frame.

[dewintondave]

I had to use coil springs as I couldn't fit leaf springs in.





Now I have to do it all over again for the second frame