Chieftain MK3 Build

[David Battson]

Finishing the lower hull front end.
New idler brackets and towing eyes were firmly embedded into the original kit front before covering over with the new toe plate. The gap between the two was in filled with strips of aluminium sheet.
John, I’ve tried to follow the Armortek ethos as much as possible and although the finished armour is maybe more composite than homogeneous, it should at least be dent proof !

Underside front in progress

Underside front 2

Underside front 1

Oops

The bracing between the hull side and inner face of the idler bracket extension form a very complicated set of angles, so rather than attempting to make new, the kit idler brackets were trimmed down to leave just the supporting webs. Hopefully this means the new arrangement should be at least as strong as the original kit.

Idler bracket

A new waste hatch finishes off the planned lower hull details. The diagonal groove above the hatch was cut in the hull side to replicate the join between hull side and glacis casting on the real thing. Weld detailing needs to be added to both.

Waste hatch

Waste hatch 1

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David

[simon_manning]

Staggering build, A wrestling match of Metal, do not stop, regards simon.

[John Clarke]

Super detailing David, tiny details that will be rarely, if ever attempted on the model. The front end looks brillant, capturing the fat lip very well.
The Armortek ethos in some areas of Chieftain is way way over the top they really out did themselves, the turret, a crippling weight for lone worker. The thought of thinning it out briefly passed though my head like the pain though the back.
But no, I'd hate to deprive the next owner of that privilege.

The Armortek model usually out lives the owner.

Eagerly waiting for the next installment.

[David Battson]

A little more progress on Chieftain with the front Idler Wheel assemblies.

The shape of the swing arm housing was modified from a tapered to stepped appearance as per the real thing. A few details added like the inner bearing retaining plate underneath and a scale thickness end cap to replace the m8 nut on the pivot shaft.
To ensure everything was properly aligned prior to drilling the bolt holes, the two housings were threaded onto a steel bar supported at either end on equally sized spacers. Before disassembly, locating pins were added to make sure the exact same housing positions could be repeated on the final build.

original assembly

idler assembly

aligning the idler swing arm housings

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The outer idler wheel was reprofiled to exaggerate the ogee step shape and an undercut added to the inside of the outer rim like the real thing. Casting numbers are on the to do list for another day. The kit the idler comprises two convex shape wheels placed back to back, whereas on the real thing the inner wheel profile is concave. My initial plan to simply reverse the inner wheel didn't work out, so instead I made up a new inner wheel from scratch to the required shape. The inner wheel was finished off with a backplate/oil seal detail to hide the RS bearing.

idler wheel - outer

idler wheel - inner

idlers

[Phil Woollard]

Excellent work David you should be very pleased with what you have achieved

[Phil Woollard]

Looking forward to the next post!

[John Clarke]

Brillant! Detailing's fantastic.
I think you've done a wonderful job on the nose of the hull. Capturing the smiley edge is work of art. .
Thoroughly enjoying the build. Dished inner idler wheel, never noticed even when crawling under the tank.
Though in my defense I wasn't looking for it. I'm probably not the only one either.

[David Battson]

Next a look at the suspension springs, before installing the swing arms.

With the suspension at full drop the kit spring assembly loses contact with the swing arms. Although the spring assembly can't escape from the suspension housing, it doesn't always reseat properly when the swing arms move back up and grip it again.

kit spring install

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Simply lengthening the inner spring to maintain contact at full drop is not an option, as the large outer spring bottoms out on the swing arm, forcing the spring end caps off the pivot points.
As an alternative solution, I made up a spring-loaded end cap, with a small degree of articulation which enabled the spring end caps to maintain contact with the swing arms at all times.

Initial end cap components

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Initial end cap 1

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initial mod install

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Whilst this initial solution worked well with the kit springs, it really only addressed the symptoms and not the cause - so before making another 5 end caps I had a rethink of the problem.
The spring rate of the kit spring unit is such that only a relatively small amount of compression is required before it can support the weight of the model.
The advantage of this design is that the kit will always have the correct ride height, whether it's empty shell built for static display, or fully kitted out with heavy motors and lead acid batteries. The disadvantage is that the model ride is quite harsh and 'jolty', compared to the real thing which appears a bit smoother and 'springier'.
To change the ride characteristics, I designed an alternative spring with a spring rate almost 4 times less than that of the kit. The kit end caps were modified to take the new smaller diameter spring and bronze bush added to the free end. The smaller diameter also meant the spring no longer bottomed out and so no need for any articulation in the connecting rod. The free end of the connecting rod was drilled and tapped for an M4 retaining bolt. This bolt holds the spring in the compressed state for ease of installation and then removed once the spring is in place.

revised spring unit components

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revised spring unit 1

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revised spring unit

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revised mod install

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The advantage of this alternative is that it should give almost 4 times the suspension travel for a given load. However, the disadvantages are the spring needs to be compressed significantly more to support the weight of the model and the ride height is far more dependent on the model weight. As a result, I won't really know how successful my design is until the model is fully built and loaded up - it may well require some more fine tuning to get the required look.

alternative spring comparison

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[John Clarke]

Gad zooks, did you remove the internal spring on each unit?
I must admit it is disappointing that the suspension unit does fall apart if not held in place by the fitting of the tracks. I did my own thing to stop that happening.
When the initial builds began there were a lot mods performed by builders to increase road wheel travel, but I came to the conclusion that wheel height and travel is what it is, while not overloading the model, in use it should be fine.

[John Clarke]

Ahh, I should have added, the track length comes into it too, more suspension travel should/could need more track links and therefore cause a saggy track.
Chieftain's tracks are normally quite tort.
I wonder how tort the tracks were on the Chieftain You tube clip on "New toy" topic I put up recently, when the Hip Hop boys threw a track..
Which is why I'm going with Armorteks general setup. It looks ok other than the aforementioned problem.

[Gary Richardson]

Hi David

I just found this build while looking for something else but have found it captivating. Your modifications and attention to detail are superb. looking forward to following this build as you progress.

Regards
Gary

[David Battson]

Hi John,
Many thanks for your observations. You are correct, I have dropped the inner spring in an effort to reduce the overall spring rate and give the model a bit more of a 'floaty' ride like the real thing. As you can't scale material properties, any solution is always going to be a bit of a compromise - for example the real thing actually had three springs.
I'm hoping that longer spring length will in fact help maintain track tension, by pushing the swing arms down to full travel when the weight is off the wheels, such as when the tank crests at the top of a steep slope. However, the tension and weight of the iron tracks is a concern, from experience if the springs are too weak, the tendency is for the front and rear road wheels to be lifted off the ground even when the tank is at rest.
For me the scale movement of these heavyweight monsters is all part of the Armortek USP compared to plastic and smaller scale alternatives, so it's an improvement worth pursuing. Unfortunately, I won't know whether this modification will make things better or worse until the model is up and running at its finished weight, which could be a long time in the future. Although I've modified the end caps, it won't be too difficult to make some new spring seats to take the original kit springs, so there's a plan B if it all goes pear shaped...,.time will tell.
David

[David Battson]

Hi Gary,
Thank you for your kind words and interest. I have some more ideas in mind and will try to keep the posts going, unlike my Comet thread of some years back - I must really finish that off someday.
I fear though Chieftain is going to be a long build, so in the meantime, I'm looking forward to your Churchill build as inspiration.
David

[John Clarke]

Constantly wowed by your build and knowledge David, but I think you may be pushed to get a floating Chieftain. Unless your going to be shaving weight.
The Chieftain is prototype Mk1 heavy.
Now Comet, no problem with crests, independent Christy suspension, speed, it's all there.
Ours is a super little tank.

[Charles A Stewart]

Good evening David.
PM' sent to you as requested.

Charles