Mini MAZ! - 1:43 scale (~9 inch long) MAZ 537 8x8 scratch build

[B_Honeydew]

(Moderators - feel free to move this thread to Multi-axle if you think that is more appropriate)

Hey everyone -
First real build post here. A little background...

As far as scale RC trucks and crawlers, I have built an RC4WD BeastII and modified a Barrage with servo motor drivetrain to make it crawl real slooow. This idea is a blending of those 2 ideas, in the form of a MAZ-537. So the concept is a really small (works out to about 1:43 scale, about 9 inches long), reasonably scale version of a proper ugly Russian prime mover that I think is pretty cool.

<The Build>
Since the concept is small, I started with the parts that would be hardest to build on my own - the wheels/tires and the differentials. I found a set of 39mm OD tires with somewhat scale tread/sidewall:

Those tires basically set the scale for the build, which is results in the slightly odd 1:43 scale. From there, I needed to find some small differentials. I wanted actual diffs (not spools) since this thing is an 8x8 and I wanted it to actually be able to turn. I also wanted to have the drivetrain/suspension similar to the full-scale truck, so the diffs needed to be ring and pinion style, and the suspension needed to be independent wishbones. I ended up finding what I needed in a 1/28 scale drift car from Atomic RC:
ATOMIC R/C Products Official Web Site

This stuff is tiny. After a while, you start thinking 2mm is pretty big.
Here is a pic of the ball diff:

I was really surprised at the quality of these kits, and it would have been impossible to piece together the diffs, suspension, hardware, etc for less than what I paid for these kits. Too bad I had to cut them all apart.

Once I had these basic pieces in my hands, I could measure them up and start laying things out in CAD. Turns out the suspension and diffs allowed me to keep the scale width/length very close to the actual truck - I was really surprised.
From a layout viewpoint, my MAZ is basically 2 of the Atomic RC cars, with extremely short wheelbases, joined by a central homemade transfer case, with a set of homemade final drives between the #1/#2 and #3/#4 axles.

The CAD exercise was really challenging. Although I was using small components, I was trying to fit those components into a small space. It turns out each millimeter was important. There were a lot of small tweaks to get everything to package, and when you zoomed in on CAD you thought you had lots of space when in reality you only had a millimeter or so.
Finding the right set of gears for the transfer/final drives that allowed for proper packaging of the driveshafts and the layout of the steering proved particularly difficult.
Once I was somewhat satisfied with the CAD, I sent the Cab, transfer cases, final drives and wheel covers out for 3D printing. The other parts I will make by hand. The 3D parts are back now but I save that and some other build details for another post.
Thanks for reading/watching!

 

[Topher Builds]

Wow, this is a really cool concept and plan you have here. Looking forward to seeing it come along.

 

[ScaleLifeNewbie]

Subbed.

This is very unique, can’t wait to see how it all comes together! [emoji106]




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One lonely TRX4....

 

[B_Honeydew]

Building the frame

While the parts were out for 3D printing, I started work on the frame.

The actual MAZ frame has a basic C-channel with an angled flat section below it where the suspension mounts and the drive shafts exit.

I wanted to keep a similar scheme for my model, except I couldn't keep the angle because the diffs would not fit. That means the sides of the frame are vertical, which works better for the AMZ suspension bits I will be using anyway.

One of the nice things about making a mini-sized crawler is that I can print out drawings using regular 8.5x11 paper. This helped me get angles and hole centers right.

The construction is soldered brass using some flat plate, C-channel and some 90 angles. It took a few tries but I finally got something that I was happy with.

The next step was to turn some fittings for the suspension mounts and then solder them on. The biggest holes in this picture are 2mm.

Here I am using a shaft that runs the length of the frame to keep the lower suspension points straight and level as they get soldered.

I learned a bit about soldering during the process. Here I am using wet paper towels to keep previously soldered points from loosening up while I solder a mount for one of the tie rods.

Here are the frame halves, with the suspension points soldered. Axles 1 and 2 use a torsion bar on the actual truck, so I will try that as well. I made a prototype of it and it seems to work well (more in another post). Axles 3 and 4 are a walking beam, which isn't really good for crawling but I chose to match the actual truck. The extra mounts are for the walking beam and the tie-rod links.

There is a lot of internal debate about whether to bolt the halves together or solder them. The only way to get the diffs out of the chassis is to either bolt the halves together or, cut the bottom of the frame under each drive shaft hole to allow clearance and then solder the halves together. I left it bolt together now while I figure out how to fit everything else in but I like the idea of eventually soldering it together.

 

[ScaleLifeNewbie]

I would nut and bolt it together just for accessibility. Looking good so far!




_________________
SCX10 ii
TRX4

 

[nick_a]

This is looking very impressive, anxious to see how you get on.

Potential source of parts at roughly your scale: https://modelsshop.eu/catalogsearch/result/?q=maz+537

particularly this item with a metal body: https://modelsshop.eu/1353avd

 

[B_Honeydew]

Thanks guys!

@ Nick_a - thanks for the link. I wish I had known about that before I started. Amazing that the scale that I arrived at and those parts are the same.


I have been working on making all the pieces fit and work together. It seems like I have put this thing together and taken it apart about a million times now.

The front/rear drives are basically symmetrical. The front has the added complication of trying to package the steering system for the #1 and #2 axles. In the CAD work, I knew it was going to be difficult to pack all of this stuff in. The reality is even harder.

The final drives are based on a set of 3D printed cases, with the distances between the shaft centers being set by the gear and bearing size. The bearings are 5mm x 2mm (really tiny). The final drive fits between the 2 diffs from the AMZ kit, and uses that kit's ring/pinion setup.

The gears are plastic press-fit and epoxied onto the shafts (gulp!). Maybe I can get away with this in micro-scale? I later discovered some brass gears that I could probably solder but I am willing to give this setup a try.
The small brass rings keep the gears space off the bearings.

Here is the final drive between the diffs, with the covers off

As I mentioned, the front set of diffs needs to package the steering. The servo mounts at the very front, with a push-rod system (from a micro RC airplane) running under/through the diffs to allow for axle #2 steering. The flexible push-rod was necessary to clear the ring gears on the diffs.
Here it is without the diffs:

And with diffs:

Here is a "taste" of where it stands now, with the parts roughly mocked into place. I will cover the transfer case, motors, and shafts in another post.

It has been a challenging build so far but I am starting to see it come together now.

 

[Shape_Shifter]

Outstanding! I love actual modelling!

 

[nick_a]

That is a tight clearance when you have to grind into the brass to clear the ring gear... Really impressive work, cant wait for the next update.

 

[moerdogg]

Great craftmanship! Eagerly following this.

 

[BIGW0RM]

Gnarly cool!!! "thumbsup"

 

[SurlyBurly]

works out to about 1:43 scale

God damn thats small.

about 9 inches long

.. thats actually pretty big. With all the brasswork and custom gearboxes, this is practically clockmaker level crafting.

 

[Gula]

Looks great! You must have steady hands, pretty good with tweezers, and a magnifying lens/light. I applaud you for creating something that small. I couldn't even imagine trying myself. How do you solder the pieces together?

 

[B_Honeydew]

Thanks everyone! There are times when I really want to put this thing on the shelf and forget about it for a while but your encouragement keeps me at the workbench.

@GULA:
"How do you solder the pieces together?"
Nothing really special. I use a small butane torch. Most of the time I get the parts held together with a clamp or pins and place small "dots" of solder around the joint. A few seconds of heat and usually things solder together pretty well.
Here's the torch, solder and flux:

Here's an example of the parts clamped together. If you look close, you can see the small "dots" of solder around the part. When heat is applied, they tend to ball up, then once the joint gets hot enough, they flow into the joint.

The wet paper towels next to the part keep previously soldered parts from coming undone.

Progress:
I mentioned the transfer case in my previous post. Here is a pic:

It is pretty much the same tiny construction as the final drives. I had to use a three-shaft setup in order to get the driveshafts to layout the way I needed. Even with the three-shaft setup, I had to clearance the top of the #2 and #3 diff cases to clear the shafts.

These are the wheels I wanted to use:

They use a round shape with a couple of half circles to attach to the half-shafts. The half-shafts from the AMZ kit I am using use a couple of flats machined into the half-shaft to attach the wheel. I decided to machine (poorly) the wheels so that they had the corresponding flats by widening the hole in one axis. It also required machining away some extra material (again-poorly) on the wheel to keep them from interfering with the hub.

After and Before:

Machined to accept the half shaft:

I also needed to lengthen the half shafts from the AMZ kit, so I machined some brass extensions, cut the original shafts (gulp) and glued them together with JB weld (gulp). This slow-speed micro stuff allows me to get away with cheats like this. We'll see how well the hold up.

A simple jig to hold things together while drying:

The rear suspension on the real truck is a walking beam. I wanted to duplicate that on the model, so I pieced this together. It's pretty lousy as far as suspensions go but I suppose it works for hauling a heavy load. On the model, the beam is a control rod thing from RC airplanes that allows you to harness two servos together. I needed a beam looking thing with a ball joint in the middle, so this did the trick. I then trimmed the ends off to accept some small RC ball joints. The ball joints then attach to the upper arms. I think I got lucky that all this stuff works together. I will dress it up some point in the future.

I am missing pictures of the front suspension now. That will have to wait for another post.
With some more random odds and ends and taking it apart about 1 million times, I finally got the chassis together:

Here is a shot next to its "big" brother, my 1/24 Barrage chassis:

The Barrage donated its RX/ESC for a test run:

I have to admit, it isn't very exciting and there is a lot of fine tuning to do. It crawls along at the speed I expected it to. The open diffs that I worked so hard to source and package are kinda sad for crawling over stuff, and the turning circle that the opens diffs should help is still pretty big. The steering needs some tuning. The suspension has about 5mm of travel, and the rear is a walking beam, so it isn't very compliant. I suppose all of these aspects are pretty scale-like. The actual truck is a prime-mover, not an offroad beast, so I have to keep that perspective. I did a test drive for my wife, and she said "THAT's what you have been working on for the last few months?". I sheepishly said "yes". I have to keep in mind it is somewhere between a scale model and a crawler, and then I don't feel so bad. Ha!

I also got around to messing with the body work. The cab is 3D printed from a CAD model I made. The winch housing and bed are made from simple styrene. Here are some teaser starter mock-up pics:

Again, next to "big" bro 1/24 Barrage (the truck that started me down this rabbit hole):

I am now onto finishing, details, painting, etc...

 

[Shape_Shifter]

Outstanding! Don't let it seem anticlimactic to you because, as you said, it's a prime mover, not a rock crawler. This is an excellent project from conception all the way through.

Im supersized that little motor moves it....

 

[Marasaiii]

Yeah this is amazing! I agree that you shouldn't look at it as a crawler, it's more of like a trail truck. I mean you've built a working 8 wheel drive 1:43rd scale model largely from scratch! I've seen a lot of different kinds of RC, and this is really impressive. Looking forward to seeing more.

 

[B_Honeydew]

Finished?

Well it has been a while but I think I can finally call this project finished (mostly). Here are a bunch of pics.

I worked on a simplified interior. The MAZ faithful will point out that the actual MAZ does not have a center console, but I had to make one to fit the steering servo. I also had to split it in half to install it to the cab.

I also needed a comrade to drive this thing, so I made "Sergei". A plastic body with a no-sew uniform. I had to make him twice because the first attempt was a little too big in scale. I also ended up amputating his left foot to fit him in the cab with the headlights. He didn't complain.

The headlights are some tiny LEDs with turned brass bezels and some plastic reflectors. I made a simple battery holder. I think they give off a proper yellow glow.

Then there was a whole bunch of painting and touch-up and fiddling.
Here is my "kit":

Here it is in it's (mostly) finished form:

If it ever stops raining around here, I will get outside for some better photos and a good test drive.

 

[durok]

Damn, that's excellent work!

A real utilitarian beauty!

(and SO tiny..."thumbsup")

 

[HumboldtEF]

very well done! I hope it drives as good as it looks "thumbsup"

I built the Cross RC version of the Maz 537 and its pretty darn similar to what you came up with (drivetrain wise).

 

[SurlyBurly]

Man, don't be disheartened that it's not some super crawler. The fact that it looks that good and works, at all, and doesn't spit half shafts and little smoky melted bits on the ground when you turn it on, is a huge success in my opinion. Well done.