Armortek

Thanks (and yes Chris,I agree. I'll lose some of it with the weathering).

I finally ran out of enthusiasm for weathering the tracks and thought of Dennis' suggestion about running them through mud. I couldn't get red Vietnamese mud online but I got this Japanese stuff which looks close enough.......



Fitted the tracks. I thought I'd done a good alignment check on the running gear. It would be near impossible to misalign the Armortek parts but I found I had to resort to trims to get the tracks to run at equal speeds with no steering applied. This is a sure sign of a problem and on measuring, I found I'd got a banana track on one side:



It's due to the replacement one piece idler I'd made. It was almost three mm off track centre:



It's now that you regret using high strength Loctite.... I managed to disassemble the idler arm and reduce its width and adjust the idler axle to shift the wheel across:



Sorted:



No excuse now for not giving it the first trial run, except that I might be invited to mow the lawn.

Regards

Stephen

Time for the model to start gaining its identity.

There are several ways to apply markings from stencils to hand painting but I tend to prefer creating decals. It give a lot more control over the colour and detail but there are pitfalls. It's important to take account of how the real marking were applied. Decals replicate stencils well but if a marking was hand painted, I'd use a mask and apply it with an airbrush, touching it up by hand.

First stage in creating decals is to select reference photos:





I then enlarge details of the markings, cut and paste them into Powerpoint and then create a copy, noting the little details such as the misplaced 0 in the front registration number:



There are more powerful programmes out there and some like Adobe Illustrator have bitmap to vector tracing which in theory make it easier to get an exact likeness. I prefer to struggle on with .ppt as it does all I need. The design is then printed on decal film. Most copiers and printers can't paint white and the decals tend to be quite thin, so I tend to apply white backgrounds, either with acrylic or using white decal film:




It's important to give the decal sheet at least two coats of an acrylic varnish or the ink can run when wetted. I then apply the decals and give them another coat of acrylic matt to seal:



This is where research is rewarding. In this early photo, 169064 has the unit marking for the deployed squadron of 1st Armoured Regimeent on the fuel tank (number 106 on a rectangle of red and yellow):



In this picture taken in 1970, towards the end of its time in Vietnam, the unit marking has been replaced with the Formation Sign for 1st Australian Task Force (kangaroo on a gold shield):



This sign was introduced in October 1969 and although it was intended to be used on AFVs, with the exception of this photo, I haven't seen it on Centurions tanks, although it does appear on ARVs. I then found this photo:


Although I can't be 100% certain that this is 169064 or exactly when the photo was taken, it is marked 22 in the same distinctive style as 064 and has other common features. I've consulted former crew members and I think we now agree it probably is 064 and was taken in late 1969, at just the time when the Formation Sign for 1 ATF was introduced. On the original high definition photo, a Formation Sign can be made out. All of which is to say that I enjoy the research and the link with the former crews and want to get the model right for them. Result:



Regards

Stephen

Stephen,

Very interesting research, especially the change in badge, once again demonstrating the value of going back to contemporary photos. Did you hand draw a vector outline for each stencilled number or did you use a font and kern to match the spacing of the original?

We have discussed before the question of different length tow ropes on 100gal Tank equipped LR vehicles. The two photos in your post show a tow rope mounted high up on the fuel tank and apparently pulled taught, unlike some of the loosely mounted examples. Is this especially tidy stowage of the longer LR rope or evidence of the shorter type rope being used on LR vehicles?

Has anyone in Aus discovered the part number for the LR tow rope?

cheers Fabrice

Fabrice

Mike Cecil advises that the stencil sets were supplied by contract to the workshop that did the rebuild, in this case, the ARN and bridge markings on 064 were done at Bandiana. Markings on Australian Cents vary enormously in font, numeral thickness and even spacing, though the latter tends to be reasonably consistent between stencil sets. Stencil sets were supplied to Army under contract and were cut from brass sheet with slip-join edges, hence the spacing is pretty much the same. Then there are the ‘signwritten’ ARNs, done by the workshop’s signwriter, which have no gaps like those done by stencil, or the unit’s ‘best’ painter, which have no gaps, but are often rough and conform to no known font.

I used a TT font which was very close to the one used on 064. I had to adjust the numeral 6 by shifting the gap. This shows how (and also shows how I made the kangaroo). For the latter, I traced the outline of an enlargement using the Freeform Draw tool and then used Edit Points to smooth and correct it to the one on 064.



Re tow ropes, I'm yet to be convinced there were two different lengths. I tried to get the staff of the Sappers' Museum to go out and check the part number on their AVLB, which has both the external tank and a fitted tow rope but they seemed unable to oblige. Anyone with access to an AVLB might establish whether the tow rope is a different part number to one for the gun tank.

Regards

Stephen

Final marking for now is the callsign applied to the external tank. For the period concerned (the tour in Vietnam of B Squadron, 1st Armoured Regiment in 1969, the full callsign was applied, signifying the squadron (2), the troop (2) and the troop corporal's tank (B) ie 22B. The marking was hand painted so to replicate this, I created a suitably rough artwork in Powerpoint and printed it on Friskfilm:



Cut out, this was then used as a spray mask:



Final markings, with some initial weathering:



Regards

Stephen

Hi Stephen
This is very interesting I have been making a stencil to do the bull on the comet.
This I have cut from 0.5 mm thick plastic card.
I wish I had seen this before I struggled cutting that out.

regards

Derek

Clearing my desk at work, I found a small spring coil intended for a name badge. Clearly, it was intended in another life to be used for the infantry/tank telephone of a one sixth Centurion....

I based the phone handset on a one sixth walkie talkie radio, cut down and remodelled:









Installing the mechanism was easy once I'd found some low profile M2.5 set screws:

Positioning was critical but works OK. Only problem was how to grab the handset once inside the box - I couldn't think of a better way than a piece of silk thread. Totally mad but fun to do.










Regards

Stephen

This week building an Armortek tank produced a moment which will live with me for a very long time. I've been in contact with a number of former crewmen of Centurion ARN 169064. One of the most generous has been David Hay, who served in Vietnam with B Sqn, 1st Armd Regt in 1968/69.







David recorded his impressions of operations in Centurion for the Australian War Memorial here (click on "sound" half way down):

https://www.awm.gov.au/collection/S02607/

On 6th June 1969, elements of 33 Regt, a regular North Vietnamese Army unit, occupied the village of Binh Ba and engaged Australian Forces. In the two day battle, David's tank was hit twice in a close in fight in the village by RPG-7, one of which penetrated the turret:



David and Leigh are in UK to restore a portrait of a First World War Gunner Officer to his family, having found in at an auction in Melbourne. That's as they say, another story. En route, they came to see the model of his tank.

I'd managed to get her running and threw the turret together and the sun shone:













David was the operator/loader on 22B, although he also trained as a gunner. The Tank Museum cut in half Cent brought back some memories:



David recorded an interview with the author Simon Dunstan and the Curator Stuart Wheeler gave him a tour of the Restoration and Conservation Facility:



Then that moment...I'd replaced the Armortek/Benedini sounds with actual recordings of Australian Centurions in Vietnam. These include radio traffic recorded during the Battle of Binh Ba. I left David to listen - to his own voice from forty five years ago, calling for Dustoff for his wounded commander. (Three of the crew, including David, were hospitalised after the battle). He simply said "it made the hairs on the back of my neck stand up".

The model now carries David's signature and there is space on the other transmission decks for his fellow surviving crew mates:





Thank you David.

These models touch a lot of people in unexpected and memorable ways.

Stephen

Hi Stephen.

Excellent story and a real one off addition to the final model.

Great stuff.
Cheers Paul.

Wow Stephen. Nice to have one of the crew visit you.

All the best, you're doing a great job.

Good to hear from you, Paul and Ray. Greetings for ANZAC Day on Saturday.

While I had the turret assembled, I though I'd have a look at the range of elevation for the main armament and its mechanism. The real Centurion achieved +18/- 10. The maximum elevation is only important for the ability to fire long range HE, although in Vietnam, surprisingly, there were operations in the Long Hai Hills which tested the maximum elevationllimits. The more critical and difficult parameter is depression. It's difficult because the turret roof limits travel at the breech end and it's tactically important because you need gun depression to fire hull down, ie sitting on the back of a slope with the hull protected from the enemy view.

So I was interested to measure the kit out of the box at +7.5/-13 deg, normal to the mantlet mounting plate. That plate though is mounted at 10 deg off the vertical, so the actual achievable figures are +17.5/-3:





I decided to remove material from the top of the mantlet mounting plate and start a process of incrementally removing material from the rear of the mantlet:





I found I also needed to remove some material from the gun trunnion mountings - it was a process of trial and error, moving in small increments.





The depression stop is a bit more complex. First there is a lip which needs removing on the front surface of the turret casting. The casting is very hard and far too big for my mill, so I had to use a corundum disk in a Proxxon Long Necked Grinder:



Once the casting is flush with the mantlet mounting plate, the same process of removing material from the back surface of the mantlet got me to the 10 deg of depression required:





With that all done, I can now look at the leadscrew mechanism. The elevation mechanism needs to be absolutely solid, with no lost movement, if the muzzle is not to bounce with the tank moving. So I'm looking to eliminate any play, any flexibility in the elevation lever arm and motor mount.

Regards.

Stephen

Stephen,

Fantastic effort linking the vehicle crew to your research and model. So glad they brought some southern sunshine up to this hemisphere. Certainly seems to have got the grass/daisies growing

Unless there has been a coup, Stuart is the new Historian at the moment. I am sure the Curator would be following his own rules and wearing a Hi Vis vest!

Re killing muzzle jiggle, consider using big R/C car shock absorbers (linking gun cradle to turret casting)and careful counter-balancing to reduce this artifact. Researching gyro-stabilization may be worthwhile as the hardware for this has dropped hugely due to model helicopter and now civilian drone applications.

cheers,
Fabrice

As always a great job of research and detail: my compliments, Stephen!
The particular handset of the radio is a little gem!

Ciao,
Iacopo

Thanks Fabrice and Iacopo. Research on stabilisation continues.

Great day out at Tiger Day yesterday, crowds around the Armortek display and lots of interest. Smiles all round and good to catch up with everyone after a long winter hibernation. Roll on Tank Fest - it would be good to see some of Battle Group North (and Paul, we won't even react if the F word is mentioned.....)

A couple of pics of 064 in passing:





Regards

Stephen

Although crude gun stabilisers were introduced late in World War 2 (in the Sherman M4 for example), Centurion was the first production tank in the world to be equipped with a practical two axis stabilisation system. The 20 pdr introduced in the Mark 3 was stabilised in elevation and traverse. I've long wanted to replicate this, at least in elevation.

The design has very much been by trial and error but the starting point was a couple of core requirements: the gun has to be balanced to minimise the power required to move it (which is turn allows the elevation motor to achieve quick response rates) and secondly, given the mass of the balanced gun, it needs to be damped to eliminate bounce and feedback loops. First stage was to commission the new elevation mechanism. This didn't seem difficult as others have done it successfully. Stage two was the stabilisation itself and this presented a few more challenges. I decided early on only to attempt stabilisation in elevation.

Replacing the elevation mechanism. The leadscrew setup is never going to be responsive enough to support stabilisation. Direct drive by servo linkage depends on a powerful, responsive digital servo. The Cent gun elevation range is +18/-10 deg. To keep the servo lever arm short, in order to maximise torque, the geometry worked out at a required throw of 29mm at 60mm from the rear face of the mantlet, using a 20mm servo arm:



This really determined the layout of the new elevation bracket. I hope Mark won't mind me saying that I found an alternative use for the Comet long bins:



The gun needs to be counter-balanced, so I brazed up a receptacle and added just over a kilo of lead:



That's a lot of mass and therefore momentum and early tests confirmed the need for some damping. I needed the longest travel shock dampers available and found these from Modelsport UK:



http://www.modelsport.co.uk/index.php?p ... Aq_P8P8HAQ

You only need damping, not rebound, so I removed the springs, selected the smallest aperture pistons and thickest shock oil to give the stiffest damping available:



I drilled and tapped the mantlet rear face M5, mounted the new elevation bracket and installed the dampers with new mountings bolted to the turret floor plate:



The tops of the dampers act on spigots machined from M5 set screws:



To give this overall setup:



I added a temporary linkage machined from 12mm alu square bar but it isn't really rigid enough and I've ordered some M3 bar and a pair of ball ends and spigots for the final build standard, to eliminate all lost motion and slop:




The high voltage digital servos is an MKS HV777 from Jettstream UK:

http://www.jettstreamuk.co.uk/mks-hv-servos.html

Mounted on a new bracket bolted to the turret floor:



Once the end points were sorted, this setup has proved to all I needed, fast, responsive and well damped. The only outstanding issue is to deal with the electrical noise generated by the digital servo, which is heard through the sound system.

The big test was the stab itself. I reviewed a lot of available gyros. Cardinal spec points are: single channel, capable of vertical mounting (ie not a heading hold yaw damper), fast, responsive and low power draw and low cost. I settled on the Futaba GYA 430, supplied by Nexus UK:

http://www.nexusmodels.co.uk/radio-sets ... l?___SID=U

I also asked Nexus to supply an onboard servo power analyser:

http://www.nexusmodels.co.uk/electrics- ... 60470.html







I'll save the pain of installing and setting up the gyro to another post but after a day of fiddling and confronting Futaba "Jinglish" and with some help from Nexus and Ripmax, I can say it worked. I've not yet worked out the best place to mount the gyro and this is critical because, unlike a model aircraft, the rates of displacement of a one sixth tank are more difficult to sense correctly and I've found I needed to turn up the gyro gain to 140%, the maximum, to get the correct response. It will need to be tuned once everything is finally installed in the tank and run over a test circuit.

I'm now trying to convert a video from .mts to .mp4 to upload.

Now for a beer or two.

Regards

Stephen