1/8th Scale Merkava MkIII Dor Dalet

[jdflute]

Hi All, 

So this is a long term project that I have worked on and off (Mainly off) since 2007. In my defense it has been interrupted by a cyclone, the birth of my second son, job hunting as a result of the GFC, moving countries and life just getting in the way.

But it's back, and I will finish it thanks to the wonders of modern technology, however first things first and like all good stories I need to start at the beginning. Just be warned, these are probably going to be a long first posts just bringing everyone up to date.....

 

 

[Vaastav]

This looks like an interesting thing.

I shall hop on to the bus if you don't mind.

[Corsairfoxfouruncle]

1 hour ago, Vaastav said:

This looks like an interesting thing.

I shall hop on to the bus if you don't mind.

Me too... Merkava’s are my favorite MBT’s. 

[jdflute]

So the build starts in 2mm aluminium sheet which I cut and folded to make the tub and install a ladder chassis for the suspension system.

Unfortunately I cut it some 10cm short, so I had to cut and fold a new chassis. Doh!!

 

Next came the upper deck, again from 2mm sheet aluminium



I found an good, all aluminium lazy susan at my local hardware store which I used as a turret ring, just about the right diameter with only minor tweaks to the deck.

At this point in time I discovered that the Academy kit I had been using as a guide was considerable wrong, which resulted in me having to remake the entire front deck



Rough detailing of the front deck has been aided by the application of some paint, without which I struggle to see the wood from the trees.

The rear door proved to be a challenge as is a clam shell two piece system. Again, due to a total lack of CAD skills, the final product was developed by trial and error

The biggest problem I found was making the mechanism rigid enough whilst allowing for smooth friction free movement. The servo has a speed control and limit modification fitted to it, so that I can slooooow it’s movement down and stop it exactly where I want, control will be off the undercarriage toggle switch on the transmitter.







The tracks and sprockets were purchased (OK I cheated, so shoot me) from Kenny Kong in China. They are in fact 1/8th scale Chieftain tracks, but since the Merkava was developed after the British had withdrawn their loaned Chieftains, they are surprisingly similar.

 

From there I was able to develop the road wheels. Each of these have been fabricated from two 4” nylon casters, with one face sliced off (ask me how much molten nylon hurts, I dare you). Detail was then added with a little bit of milling and polymorph plastic.

 

If you imagine that they begin life as two nylon 4” castors, I cut off one side of each of them, and butt them together, spaced with some large washers. The nylon is as hard as steel and a real @%*&#!#$ to work with, and in the end I used a diamond tile cutter disc on an angle grinder cooling all the time with water.
The bolts go through both sets of wheels and allow me to fine tune alignment of the wheel to keep it true, and the detail is added using molded polymorph and miniature brass fixings from http://www.microfasteners.com in the States

https://drive.google.com/uc?export=download&id=1npSP4RLQZRxcHn5mTS-9_fWMTRgAxb4S

 

The paint is added solely for me to see imperfections

I have also prototyped an idler wheel out of one of my son’s bicycle trainer wheels. 

 

Using my pillar drill as a makeshift milling machine, I was able to thin the wearing surface by 50% getting rid of the grooves in the process. Then it was a case of shaping more detail with the ‘mill’ until it resembled something approximating the real thing.

The motors and chain drive are now installed, two 300W 24V scooter motors with integrated gearboxes from the manufacturer in China.

 

Jd

Edited January 28, 2020 by jdflute

[Corsairfoxfouruncle]

Very Impressive work on display here, its not quite as large as I thought it would be ? Big no doubt but I somehow thought it would be larger. 

[jdflute]

The mechanism to the headlights came next, here they are in the closed position.

 

 

The Merkava stows the lights when not in use, and these have to be manually opened by the crew. Being a lazy sort, I decided to have them pop up at the flick of a switch, so using some micro servos mounted just behind the motors and some cable push rods, they will now pop up and (eventually) switch on when I want them to.

 

 

On to the control arms and I tried several designs, the shocks and springs came courtesy of Tower Hobbies and I ended up making the control arms out of 25mm square bar. I did think of trying to add detail, but to be honest, no one will see the arms when it is finished and I have a real problem getting enthusiastic over the idea of manually filing down twelve lumps of aluminium. Unfortunately this is where a home made mill just doesn’t cut it.

 

 

Well after making the sixth trailing arm, I needed a break from filing, so I set about putting it all together, on one side at least.
 

 

 

The first of a few idler wheel mount and track tensioners came next, but the finished version came out quite well

 

 

 

Something to remember at this point is that at the time I had no knowledge of CAD so this is all designed in my head and roughly sketched up on scraps of paper. Therefore a lot, and I really mean a LOT of trial and error ensues. 

 

Test fitting of the tracks came next and then the side skirts

 

 

 

Paint added to help my eyes

 

 

 

Detailing to the upper deck has come along



But the real achievement is the fabrication of the rear stowage basket frames

The last on shows the quick release system.

 

So I had five weeks by myself and a fair amount of time spent working on the Merkava.
I am pretty happy with the revised drive train, the motor mounts are solid and the cross bracing has provided me with a solid esc mount that doubles as a large heat-sink.
This has also freed up some space in the front compartment for me to fit a smoker, planned to be a water based fogger, with a fill point under the drivers hatch and the exhaust on the front right hand side.
The micro servos driving the headlights has been replaced by a single standard jobbie, incorporating a micro switch to control power to the LED’s. I just need to do the final connection to the servo arm, and wire up the headlights, and make the headlights and fit the headlights and, and, and.



Next section houses a couple of speakers and the control box.
At the back I have reworked the rear door mechanism with the two micro servos and a landing gear mixer/slow unit which has freed up a lot of space.

The door itself has changed considerably over the summer, internally I ripped out the original mechanism and have fitted two micro servos (previously driving the headlights) with a mixer/servo slow unit. Along with finishing the external detailing, I added two micro switches to the mechanism. One will turn on an internal light (red) and the other will trigger the sound card with some radio messages



I decided to switch from lead acid to Li-Po batteries and this gives me more space in the back and so I have another thing to think about...........

 

 

Heading back around to the front, I installed the drive sprocket covers, carved some tow hitches and detailed the top deck with hinges and latches.

 

 

The right hand side received some additional detailing to the side skirt mounts, along with completing all the rivets to the skirts themselves.

 

At the rear I completed the stowage bins and mud flaps on both sides as well as fitted the baskets either side of the rear door. I also added two track links to the bottom half of the fuel cells, but you’ll have to look closely to find them.

 

 

 

On top, I added a shovel and a few more latches and bits of detail, so all in all quite productive.



Next involved spending a little cash and getting bits and bobs to try and get the Merkava moving again, literally speaking.



Two 24v 8Ah lipo batteries to begin with

Wiring up the control box with a watt/amp meter



The monster 805 servo modded to 360 degree and fitted to a spring tensioner



The esc hiding behind the headlight servo



And for the finale, my sound system 

 

 

 

[jdflute]

 

I spent a few weeks on the internal electronics, wiring up the control box and making sure the different output voltages were correct.



The control box distributes and regulates power to the different and disparate components



The primary voltage is 24V which powers the two scooter motors (main on/off switch under the drivers hatch). The red switches control the smoke (24v), sound and fans (12v) and servos and receiver (6v). The display provides watt/amp/volt info depending on the menu I choose.
To the left of the box is a 1/4 scale servo with a wheel mounted and modified to turn 360 degrees and this is wired into a headinglock gyroscope (little blue box located in the middle of the red switches)

 

 

The video shows the proof of concept for the turret rotation, the speed looks about right to me for a modern tank but it is difficult to judge without a turret in place. The small movement at the end of the video is the gyro doing what it is supposed to do, I was manually moving the hull and the gyro was moving the turret ring to stay in it's original location. The idea is that wherever I point the turret it will stay in this position independent of the movement of the hull. I'll have to fine tune the gyro at some point, because it is way too sensitive at the moment.

 

I took some fresh photos without a flash so it is easier to see some of the detail, most don't need descriptions

 

 

 

As I previously said, the track and drive sprocket is from a chieftain, but I have milled out the hubs and added bolts to try and come close to the real thing.

 

 

 

 

The rear door and stowage baskets are getting there and but I need to wire in the tail lights. I also haven't decided weather to continue with the baskets in thin copper sheet as seen on the left or make them in fabric.

Here is some video of the rear door working from the inside...

http://youtu.be/DvHP6rso2H4

and then an outside view

http://youtu.be/odMuK-eflMk

http://youtu.be/8z8w1ciY4TM

 

And finally some general shots

 

 

 

 

 

 

 

Edited January 28, 2020 by jdflute

[jdflute]

Here is the final historical post that brings the project up to present day.....

 

Headlights come next; I stole some lego lights off my boys, not that they would notice,

 

 

 

 

 

 

 

I wasn't happy with the original flaps so remade them in a thinner aluminium.

I switched over to the internals, mainly wiring and re-jigging components so that they fit together and I successfully tested both the smoke and sound components. The smoker uses an ultrasound water mister which is designed not to upset the wife, but provide at least the semblance of exhaust smoke, albeit white.
The sound is definitely loud, I need to programme the unit before I can really test its potential, trouble is that it is quite a complex system so I expect a lot of trial and error.
The headlight system is pretty much complete with just a 5 minute job to install a microswitch remaining
The other internal part I have spent a bit of time on is the interior as viewed from the rear door.

 

 

The view from above,

 

And the view through the back door

The brown fibreglass shell canisters are made up from plastic pipe, wire, medical tape and thin copper sheet

 

 

I spent some more time working on the side armour for the left hand side sorting out the leaf springs and rivets

 

 

and a little work on the stowage bags at the back, I fabbed up a second bag in copper sheet, but decided that this metal would be too stiff for the top and chose to use the thin lead sheet instead, can anyone recommend an appropriate glue for this, I have used superglue for now but I don't know if it will last. (Given this was 7 years ago, I think the answer is yes)

 

 

I did a test fit into the stowage frame, I noticed afterward that I put it on back to front!

 

 

On to the turret and with the help of the Meng model I came up with this..

 

 

 

 

So I had the late summer break and then cut out the base of the turret, so I couldn’t leave it lying around as a bit of flat plate, which meant I had to get the blow torch out again.
Unfortunately I do not have the equipment or skill for tig welding, so I have been using a aluminium braising rod instead. It is tricky to get the hang of and I am not convinced of the strength so I have used rivets as well. All in all, it turned out well.

The whole thing would not have been possible without the super accurate Meng Models Merkava 3d kit to scale from, so I have Michael Mass to thank for that!

I should really learn CAD and prototype in card beforehand, but I am ever so lazy and give that this was done ‘old school’ I only had on error along the way that could not be resolved with a little filler. Not to be sniffed at in my book.

 

 

Whilst I wanted to get on with the fabrication of the turret, I realized that a lot would hinge (No pun intended) on the positioning of the main gun, so I collected a few components from work and spent an afternoon putting it all together.
To begin with I chose to use some HDPE pipe as the main barrel in order to keep the weight down. This has an aluminium inner lining to thicken the barrels bore and make it more realistic.
The heat shroud is curved and folded 1mm aluminium in two pieces (Upper and lower) with a folded overlap. I was surprised that I managed to get it right on only my second attempt.
I ended up using cable ties for the securing straps and with a bit of filler and trimming, I should be able make them look realistic. If anyone can suggest a better way I would be interested in hearing it.

 

 

The vacuum extractor is more plastic but towards the back I switch to a polished steel rod and a linear bearing, courtesy of VX Bearings ( http://www.vxb.com/ ). This has been sitting in my box of supplies for two years up till now! The nice part of the bearing is that it has mounting holes pre drilled.

 

 

 

 

 

 

 

 

 

 

 

[jdflute]

So that is where I got to, before I moved to New Zealand and there it has sat in the corner of my workshop whilst I have been elsewhere engaged, a very sorry state of affairs.

 

 

But I have been busy learning new skills over the last five years and as a result I realised that I could use two of them to great effect, CAD and 3d Printing and so the Merkava rises again 

 

 

 

 

So this will take some time to detail, but given the complex geometry of the Merkava's turret, the hard work is out of the way.

 

I suspect that I will revisit a lot of my previous work at some point down the line with a view to righting some of the wrongs that comes with scratch building.

 

Jd

 

 

 

Edited January 29, 2020 by jdflute

[Bandsaw Steve]

That’s obviously an awe-inspiring bit of work but unfortunately I have only been able to view a handful of the photos. It might be my internet connection. Is anyone else having problems seeing the photos?

[Corsairfoxfouruncle]

6 hours ago, Bandsaw Steve said:

It might be my internet connection. Is anyone else having problems seeing the photos?

Hmmm In North America and I have no issues here ? I wonder if anyone else is having problems ? 

[Foxbat]

Think I've seen them all up here in Durham, and they were well worth seeing

 

Andy

[Bandsaw Steve]

Ok - I am on another wi-fi now and can see all of the photos just fine. Sorry about the false alert. The project is looking incredible. 👍

[Pete in Lincs]

You can colour me impressed too. 

[jdflute]

Just a little update with the CAD work, 

 

 

 

 

I have been working my way around the turret adding detail and fixing geometry. There are the back and right hand sides still to complete before I can cut it open and slice it for printing.

Once I have the base structure printed, I can think about adding the finer details.

 

Jd

[npb748r]

amazing skill to make this. 

[jdflute]

Bit of an update, I am 95% complete with the base structure design so I decided now was the time to slice the model into printable sections and run a test print. 

The piece is the rear middle panel which is purple in colour

 

 

And in real life it tested the limit of my print bed to it's maximum

 

 

 

 

For those of you interested in the details of 3d printing, I used adaptive layer height of 300 microns for the bulk of the print, switching to 150 microns for the upper layers requiring detail. The top layer isn't perfect as I should have doubled the number of solid top layers to account for the change in layer height. However, as a test print, using old filament, the detail is there and I am more than happy with the results.

I am planning on picking up some carbon fibre PLA for the final print for added strength.

 

The next stage is hollowing out and providing mechanical fixing points, 

 

 

As you can see in the above cut out, I am using m5 bolts to added extra strength to the glued joints and I also need to provide a pivot point for the main gun.

 

 

Jd

[BeeKay]

JD I am more than impressed with your build skills thus far and cannot wait to see this turret and ultimately the full vehicle come together. One amazing and inspiring scratch-build project.

 

Thanks for sharing 

 

Brian

[jdflute]

I have been away from home for a little while and ended up in isolation, but this has given me the opportunity to work on the turret and print the pieces, it is finally starting to come together.

For those of you with 3d printers, I am using a modified Anycubic i3 Mega and am printing PETG filament at 0.3mm layer height and 80mm/s speed. This equates to between an average print time of between 10 to 15hrs for each piece of the puzzle. What is also interesting is that I am orientating the prints 'end on" ie with the back of the turret and the bottom which allows me far better print resolution than you would normally see at such a layer height.

 

 

I fitted the linear bearing as a pivot point for the main gun which will allow for gun elevation and recoil.

 

 

 

And whilst the big prints have been going, I have had time to work on some of the details such as the hatches

 

 

This test print was at 0.15mm resolution and took 4hrs to print

 

 

 

 

Jd

 

Edited April 4, 2020 by jdflute