Duncan's 7mm Workbench - Connoisseur 4F Tender Cab

[Fastdax]

Ian Kirk Coach

 

The driving brake coach has had some grime applied to the nooks and crannies. I did this using my lazy-man's approach to muck - slap it on liberally then clean it off so that it clings to the bits that would have been missed by the cleaner's rag:

 

 

 

The more you wipe it, the cleaner it becomes.

The paint is Wickes tester pots of emulsion. It's a mix of dark grey and orangey/brown. Even when it's been drying for some hours, it can be shifted with damp kitchen roll or cotton bud.

The interior has been finished with painted seats and self-adhesive stickers for pictures and mirrors. Red for third class:

 

 

The front pipework has also been painted. As best I can find out, the vacuum brake pipes and engine bell cables were in red, faded to pinkish, and the vacuum regulator pipe was yellow, faded to whiteish:

 

 

This will be toned down under another layer of muck.

 

Edited December 26, 2023 by Fastdax
Reinstating photos.

[Fastdax]

Ian Kirk Coach

 

At last it looks like we're getting somewhere!

 

Decals are on. Well - on the body sides at least. Technically there should be lettering to say "Pull & Push" and "Engine Bell" on the driving cab end, but I can't find anyone who makes decals like this.

 

The cab end has had some weathering, as has the underframe and bogies. A whitemetal lamp with a hole bored in the bottom hooks neatly over a lamp iron, just as per the prototype :-)

 

 

The roof isn't screwed down tight, thus the gap above the windows. I also need to add all the glazing - separately, as each group of 3 windows sit at different levels inside, necessitating 3 individual bits.

 

Meanwhile, here's a quick video of the BR(M) Pull Push train arriving in Offerston Quay's station:

 

 

 

 

Edited December 26, 2023 by Fastdax
Reinstating photos.

[Fastdax]

Radio Controlled Austin K8 Van

 

Lately I have been inspired by @Giles Favell's wonderful radio-controlled 7mm scale vehicles. His exploits in this parish, on YouTube and in MRJ #256 and #271 are to be wholly admired.

 

In what follows, I give due thanks and acknowledgement to Giles' expertise and instructions, as my attempt is based heavily on his words of wisdom.

 

For a while I've had a British Railways Austin K8 van by Oxford die-cast, so I thought I'd give it a try to make it r/c. It has a capacious van body to get all the r/c gear in. I'm not so skilled or ambitious as Mr. Favell as to attempt an Austin car yet! It has proper rubber tyres as well (important!)

 

 

Most of the engineering required is concerned with the front axle. This needs free-rotating hubs, steering and 3-point compensation to keep all the wheels on the road at all times.

 

The wheels are plastic with bosses for 2mm axles, so I carefully removed the bosses leaving a 5mm drill mark as deep as I dared, until it just broke through the face of the wheel. Then I could lube up the hub ball-races and dummy stub axles and epoxy them into the wheel backs, making sure they stayed perpendicular to the wheel. The trick with these vehicles is to get the steering pivot (the king pin) as far into the back of the wheel as possible, so the wheels turn on the spot without travelling forwards or backwards in the wheel well. That's why I got the hubs as far into the front wheels as possible.

 

The lube allowed me to remove the dummy axles when the epoxy had set, leaving the ball race hopefully still free to spin.

 

 

 

 

The van was dismantled, showing that the floor is in two parts - an upper and a lower. I glued them firmly together to be a rigid base for the butchery which would be necessary to get the axles in.

 

 

While the body was in bits, I cut out the rear doors as I want to make them operate under radio control. This Oxford die-cast metal is tough stuff and I had to hack into the bodyshell quite crudely with a razor saw to get the doors out. I'll fill in the extra cuts in the roof later. And paint in where I have ruined Oxford's nice finish.

 

 

Offerston Quay has a road vehicle route from off-stage at the right-hand end, over the railway line, and to the warehouse at the left-hand end. I want this van to be able to drive through the scene, do a three-point turn, open its rear doors and back up to the loading dock before closing the doors and returning once more to the right-hand end.

 

Whether I can achieve this, we shall see!

 

I've reached my 10Mb upload limit for this post. More soon.

 

Edited December 26, 2023 by Fastdax
Reinstating photos.

[Fastdax]

Front Axle

 

I made the rocking, steering front axle as simple as possible since I don't have a lathe or milling machine. I also soft-soldered everything together. Giles did give me a demo of silver-soldering at Warley a few years ago but I'm hoping regular soft solder is strong enough.

 

The front axle is basically four layers of 1mm x 3mm brass strip, soldered together in a sandwich. The top and bottom layers have rounded ends and 0.8mm holes for the kingpins. The middle two layers are shorter and are just for spacing. I set the kingpin holes 31mm apart as this should give an overall width of the front axle that replicates the original die-cast model.

 

The steering stub axles are short lengths of 1.5mm square brass, with 0.5mm brass strip soldered on for steering arms. This 2mm sandwich fits nicely between the axle top and bottom plates.

 

The steering arms have the holes for the cross-shaft linking to each other and to the steering servo set slightly inwards to form a proper Ackermann steering angle. This allows the inner wheel to steer more sharply than the outer, which is useful when negotiating tight turns. There should be a straight line from the kingpin, through the hole in the steering arm, to the centre of the back axle.

 

The square 1.5mm stub axles are a tight fit in the 2mm ID bearings in the wheels, needing only a very slight wipe with a file on the corners to get them to push in tightly. (Pythagoras says that the diagonal of the 1.5mm section is 2.12mm).

 

 

The swivel kingpins are actually a single piece of 0.8mm nickel-silver wire, bent up at the ends. This avoids having to solder in close proximity to the moving bits. The wire is held in its centre by a blob of glue, which can be broken if I ever need to dismantle the axle.

 

A short length of 1.6mm ID brass tube soldered across the top of the axle forms a rocking pivot:

 

 

 

I mounted the axle on a length of 1.6mm brass rod, which I superglued to different places on the floor pan until the ride height looked right. A lot of hacking of the plastic floor pan was needed to allow the front wheels to rock and turn fully:

 

 

I'll fix the rod more permanently with epoxy and add a front bearing later.

 

A tiny Hobbyking 5320S 1.7g servo is set into the floor to be the steering actuator:

 

 

Edited December 27, 2023 by Fastdax
Reinstating photos.

[34006]

Looking good Duncan.

 

atb

Phil.

[Giles]

This is first-class stuff! And looks neater than the bits I churn out.....!

[Fastdax]

1 hour ago, Giles said:

This is first-class stuff! And looks neater than the bits I churn out.....!

 

Not sure about that Giles, but many thanks anyway!

 

[georgeT]

interesting approach Duncan watching with interest, great stuff...

[Fastdax]

Back Axle

 

The motor/gearbox unit is a ubiquitous 150RPM N20 gearmotor from ebay, as are the nylon 3D-printed bevel gears with 2mm inside diameter.

 

The gears fit on the 2mm nickel-silver rear axle with a bit of boring out. The motor output shaft is 3mm so I had to drill through one gear, hoping that the 2mm hole would self-centre the 3mm drill bit. It did - sort of. The final gear wobbles a bit but stays in mesh with the axle gear. For rear axle bearings I simply used the Oxford axle location. It's a good fit for the 2mm axle.

 

The motor unit was epoxied to the floor pan, with a few bits of packing to get it pointing directly at the axle. A lot of the plastic floor had to be removed to allow this.

 

 

 

The previous picture also shows the modified steering cross-shaft whose shape stops the wheels turning too far. By varying the amount of bend in the 0.8mm wire, I can set the front tracking. I also made a front support for the front axle rocking shaft.

 

The battery is a bit overkill at 1000mAh but it's what I had in stock already. It fits neatly to the van floor between the wheel arches. It should run the van for days!

 

 

On the side of the steering servo is a tiny distribution board made from Veroboard. This allows all the positive and the negative connections to be made easily. For a circuit, I used Giles' diagram in MRJ #271. I haven't got the radio gear yet, but I should be able to wire the motor to the battery to see what top speed looks like.

 

Edited December 27, 2023 by Fastdax
Reinstating photos.

[Fastdax]

Brake Lights and Test Run

 

Here's the rather messy result of cutting out the back doors and reattaching them using 0.6mm nickel-silver wire as hinge pins. I drilled through the cast hinge bodies on the van's rear panel and superglued the hinge pins to the doors.

 

 

When cutting out the doors, I also had to cut off the rear light / number-plate panel. This gave me the opportunity to drill through the lights 0.8mm then 2mm:

 

 

And embed 2mm red LEDs into the floor pan for brake lights.

 

 

Normally this panel would be removed from the chassis with the bodywork but, like this, it can stay connected permanently to the radio receiver (when it arrives). There's a bit of cleaning up of filler and paint to do, but the LEDs give a good impression of the "Dalek's eye" brake light covers. One nice feature of the radio receiver I've ordered (Deltang Rx41D) is that it automatically lights the brake lamps when decelerating.

 

 

I also added an on/off switch and wired the motor through this to the battery. Now we can see what the full 3.7V produces in terms of speed:

 

 

I think this looks like a very reasonable top speed.

 

Edited December 27, 2023 by Fastdax
Reinstating photos.

[Joner]

That is excellent, well done with the mod.

[Fastdax]

39 minutes ago, Joner said:

That is excellent, well done with the mod.

 

Thanks Joner!

 

[34006]

Thats definately the dog's do - dads,Duncan.

 

atb

Phil.

[Fastdax]

Thanks Phil. It's very satisfying to see what started out as a toy move under its own power.

 

[Fastdax]

Austin K8 Test Run With Radio Control

 

The radio gear arrived and was fitted to hook up the motor, steering servo and rear door servo.

 

Then, of course, I had to take it for a test run:

 

 

 

[NeilHB]

Absolutely fantastic Duncan! 

[Joner]

Amazing. That is brilliant.  I was expecting something a lot quicker and less realistic than that.  Doors were a surprise for me, didn't know you were planning that as well.

 

As we're social distancing you'll have to give yourself a well deserved pat on  the back.

 

Top marks 

[Giles]

That's a proper job! The doors are great! Lovely to see it rocking and rolling at it goes down the road.....

 

I've started fitting my transmitters with extension sleeves to the sticks to get finer control, which helps.

[Fastdax]

25 minutes ago, Giles said:

That's a proper job! The doors are great! Lovely to see it rocking and rolling at it goes down the road.....

 

I've started fitting my transmitters with extension sleeves to the sticks to get finer control, which helps.

 Thanks Giles.

 

I do find that the N20 gearmotor needs to see a higher voltage to start than it needs to keep running, which can lead to a sudden take-off from stationary. Longer sticks may well help me here.

 

I'm also experimenting with the throttle response curve in the Jumper T8SG transmitter that I'm using.

 

[Fastdax]

11 hours ago, NeilHB said:

Absolutely fantastic Duncan! 

 

Thanks Neil!

 

[Fastdax]

10 hours ago, Joner said:

Amazing. That is brilliant.  I was expecting something a lot quicker and less realistic than that.  Doors were a surprise for me, didn't know you were planning that as well.

 

As we're social distancing you'll have to give yourself a well deserved pat on  the back.

 

Top marks 

 

Thanks Joner!

 

[Adrian Stevenson]

Very clever indeed. The doors opening is a great idea.

 

Well done!

 

Cheers, Ade.

[Fastdax]

11 minutes ago, Adrian Stevenson said:

Very clever indeed. The doors opening is a great idea.

 

Well done!

 

Cheers, Ade.

 

Thanks Ade!

 

I made the doors open so that there's an excuse for the van to back up to the warehouse loading platform, while hiding that fact that there's no subsequent movement before it departs again.

 

I did consider having the van push a small crate out through the doors but that's getting silly.

 

 

[Giles]

What voltage/speed gearmotor are you using?

 

[Fastdax]

53 minutes ago, Giles said:

What voltage/speed gearmotor are you using?

 

 

6V 150RPM, run from a 3.7V 1S LiPo.

 

I could have gone for 100RPM but, in hindsight, it would have reduced the top speed to a crawl. These BR van drivers are impatient!