New to me

Forum for discussion relating to the M2/M3 and M16 US Half Track
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Jerry Carducci
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Re: New to me

Post by Jerry Carducci »

I spent some time with the driver's and right side armored doors. I was looking to add either the cast metal latch details, the latch that secures upper and lower panels together; or make functional versions.

I quickly became apparent that no matter which option I chose, neither would fit where they needed to be because of the upper steel cross member.
It took a while but I finally found an image that showed this area which is set in a bit.

Not wanting to chop and whittle my way into a corner by altering the kit parts, I first decided to scour the web looking for the curious miniature
steel angle as the one used in the kit but finding none. So door number two was to cut a section of square steel tubing. I received two lengths of angle for my efforts and milled and ground them as needed. For the left and right hand cross members I introduced a slight bend to allow the clearance needed for the latch works.

At for the latches themselves, the biggest challenge was to make a long slot just wide enough for a small handle to pass and the latch bar to slide freely. Alignment of the top and bottom sections wasn't quite trivial.

There's actually some level of detail yet to added but it's very hot in my garage these last days.

Jerry
Attachments
prog0611_06.jpg
prog0611_05.jpg
prog0611_04.jpg
prog0611_03.jpg
prog0611_02.jpg
prog0611_01.jpg
http://tanks.linite.com/ - RC tanks: stay home, build a tank and save a life!

User avatar
Jerry Carducci
Posts: 694
Joined: Sun Apr 05, 2020 7:38 pm
Location: The People's Paradise of California, the former Golden State
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Re: New to me

Post by Jerry Carducci »

Between hot days here I've continued to work on the small bits surrounding the cab doors, all the various latches and related bits. I wanted to
make these functional as I mentioned previously and happily I've been able to do that while being able to use materials that are not out of line
with the overall scale proportions of the originals. So there's that.

The one disappointing aspect of this project remains the tracks, unfortunately a key aspect that really dictates the overall tone of it all.

I attempted to modify one of the tracks, actually the roller chain basis to not have the retaining clip as the longer pins were causing grief.
I had feared and that fear became a reality that the master link pins were/are a very hard steel, not surprisingly so, that resisted my attempts
to form rivet heads thereby eliminating the need for the retaining clip and the added length of the pins in one stroke. In essence I ended up damaging
one of the two tracks as the efforts did not hold up as expected. I believe if I had thought of this before assembling the track with rubber loops I could
have tried to anneal the pins and attempt the riveting then however you know the nature of hindsight...

The second track issue which really surprised my while I'd heard of it and actually seen it prior is how quickly one of the track loops split at the the 'ribs'
not once but in two places on the left outer loop. This was on the intact track on which I'd not tried my master pin modification. Unlike other challenges I don't believe I have a cure for this yet. I believe the root causes are far too rigid rubber loop and the roller chain basis is far too coarse putting enormous stress on the rubber when bending around idler and sprocket. This failure occurred after less than 20 minutes total run time and at very low speeds- albeit at maximum throttle- the best speed the machine is able to muster.The assembled tracks are far too rigid to purpose in my opinion. This stresses the rubber to the breaking point and it puts such a load on the motor as to barely achieve any realistic speed. The ESC rated to handle fairly high current levels gets very hot, too hot to touch, after a short time in operation.

All this has been disheartening but my enthusiasm for this model remains; it is such an unusual, interesting machine; I wish further developments had been made for this. I'm probably going to cut short my detail work on this after a while and leave it to the side as I decide what to do about the track issue; whatever the solution is it won't be a quick, over night sort of thing...

Jerry
Attachments
prog0617_06.jpg
prog0617_05.jpg
prog0617_04.jpg
Splits may be seen towards the forward upper part of the drive sprocket and just to the rear of the idler ( with the red handled pliers in the background)...
Splits may be seen towards the forward upper part of the drive sprocket and just to the rear of the idler ( with the red handled pliers in the background)...
http://tanks.linite.com/ - RC tanks: stay home, build a tank and save a life!

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Jerry Carducci
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Re: New to me

Post by Jerry Carducci »

I've had a number of conversations with fellow owners of the US half-track. All have some level of concern for the tracks. To use the chosen
lyric of all fatalists everywhere; 'it is what it is'.

As soon as I knew something needed to be done my first inclination was to think, 'Hmm.... can I reproduce a miniature track using scaled down
methods used for the original?' The answer being 'possibly' also brought with it probably a good long project with much trial and error to find properly flexible fine steel 'rope', making a vulcanizing mold (not that difficult), how to heat that mold then how to make the guides, attach them and everything else that goes along with it. So I decided to save that idea as a project for when I've run out of other projects....

Right on the heels of that though was 1) using industrial tooth belts, or timing belts if you prefer followed by 2) 3D printing the belt using TPU filament.

Door number 2 requires STL file for the track which is extant and finding a fellow modeler with a printer of sufficient capacity, minimally 400 x 400mm or purchasing the same. This thought is still being pursued.

That leaves Door number 1, timing belts. Seems like a viable option all things considered. in parallel I cast about for for belts of appropriate dimensions and once I determined that I sent off for two.

For a task like this I consider it from the most basic implementation and add features or modifications there as needed as it goes into test.

The belts arrived today, after several annoying delays, rendered largely moot however due unbearable heat in my shop (108F) over the last week..

Without anything else I tore open the packages and proceeded to fit them to the model, just as is; they were just snug enough to fit as I'd planned;
no adjustment to the track tensioner. No guides. No relieved center section of the belt to remove teeth from the central 9-12mm as would be appropriate for a more 'scale' appearance. The belts are 53mm wide- nearly identical to the OEM tracks.

Just as is.

I was very encouraged that this has a chance to work with hopefully minimal alterations to belt or model and looks 'decent' as well. Yes, in the brief
test the left side belt wanted to work its way off but that was fully expected with no guides.Oddly the right side belt never moved from its lateral starting position. I will take my time deciding how to mount guides that will also engage the existing sprocket but I will try locktite 410- my experience with the steel /rubber bonding capabilities has made me a believer. We'll see how that works but I have other ideas in that regard as well.

Jerry

Attachments
belt test_02.jpg
belt test_01.jpg
http://tanks.linite.com/ - RC tanks: stay home, build a tank and save a life!

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