1:10ish Alvis Stalwart 6x6 high mobility carrier, wrongest of the wrong

[dremu]

(NB: if pictures aren't visible, you can change a setting in Chrome. See https://rctruckandconstruction.com/s...7&postcount=16 )

Bit of background: I've been building things of many sizes for years, ranging from scale models to RC vehicles to a 1.5ton ride-on backhoe with working hydraulics. I hate hydraulic fluid.

I've done a number of 1:10 builds, starting with a Cross RC kit (nice, but kinda dry and boring cuz it's just assembling parts) to a partial scratch build HEMTT/PLS and then to full-on scratch builds. Historically I do a thread here with a picture of Jeremy Clarkson saying "How hard can it be?" In this case, I knew dang well it was going to be insanely hard.

For those who don't know it -- which is likely most of y'all -- the Stalwart aka "Stolly" is, well, a uniquely British piece of machinery. From what I've read they were at once loved and hated, loved for being decidedly British and hated for being maintenance-intensive. Think an MG sports car, but amphibious. This is a vehicle designed by the people who brought us Whitworth fasteners, you know.

You can read a bit more on Wikipedia:https://en.wikipedia.org/wiki/Alvis_Stalwart

Or, as a quick teaser, here's the end result of my build:



Fans of Dinky and Matchbox type diecasts may recognize it now.

You can also watch the pilot of Firefly for this modified one appearing in the Unification War scenes (an obscure vehicle in an obscure TV show, seems apropos!)



The drivetrain is an absolute Goldbergian nightmare. I imagine some of that was by necessity, to fit the amphibious drive stuff in and around the wheel drive. For my model, I intentionally chose to avoid the amphib part and stay with just the wheels, but nonetheless, it's fiendishly complex mechanically.

Things just doesn't work the way you think they would. For instance, you have six wheels, so you'd assume that, like in any other vehicle in the known universe, the left front wheel would connect to the right front, the left center to the right center, the left rear to the right rear.

You would be wrong. All the left wheels are driven together as one, and all the right as another set.

You would also assume that, like any other vehicle in the known universe, there would be a differential between any given set of wheels.

You would again be wrong. Each set of wheels, left and right, are on a common longitudinal driveshaft with no differential. Any turning then binds up the front wheels vs the rear. Apparently when driving on the highway, SOP was to pull over periodically and run over railroad ties to allow the drivetrain to unbind. (Alternately, the crews would drive over bollards in "car parks", as they call them.) You'll see Stollies with stripes painted across the hubs so that the crew could quickly determine when the hubs were out of sync and bound up.

At least there's a center differential at the transmission, though as we'll see later there's it's a tight fit.

Finally, the thing has independent suspension, which is essentially required because there's no frame. Each wheel/tire is hung from the hull, which was welded like a boat. This as actually much like today's mine-resistant vehicles, which are made with V-hulls to direct the blast from mines and IED's away from the vehicle's occupants.

Here's a cut-away of the thing where you can see all the bazillion parts:

[dremu]

So the first step was to throw together a CAD mockup to get an idea of size, sort out what tires would work for scale, etc:



Was actually difficult to find tires with the right NDT pattern, didn't want the modern tread. RC4WD has a set for DUKW's that worked out about right.



Totally jumping ahead there in pix, but for whatever reason I really like tires & wheels to be as accurate as possible. The wheel isn't quite right, didn't have enough room to get all of the bolt heads in, but the hub does actually come off to get a a nutdriver down there.

Next up was sorting out what all that crap in the cutaway did. Like the drive, the steering is per-side:



Highlighted is one side only. Steering rack turns a longitudinal shaft which pushes an L-shaped steering arm which has a linkage to the knuckle on the first axle. The arm is bent to clear the suspension, which we'll get to momentarily. That first axle's knuckle has a linkage to an intermediate arm, which in turn has a linkage to the knuckle on the center axle. That intermediate arm doesn't hinge at the center, but is hinged at an offset of about 2:1, so that the center axle turns about 1/2 as far as the front one.

I've seen a coupla RC builds that used straight axles and had separate steering servos for the front and center axles. Where's the fun in that? It's easy and simple and it works! For my build I really wanted to replicate the 1:1 in mechanical function (or lack thereof) =))

One part of the suspension that drove me crazy for quite some time is the torsion bar springs, because they're *also* longitudinal. I did torsion bars for my M1 Abrams, but that's easy; they're located *laterally* and couple to the arms that hold up the road wheels.



Highlighted blue is the spring for the center axle. I finally sorted it, with much arm-waving and looking at pictures. The upper control arm is hard-mounted to an outer tube. Inside that tube is the spring proper. The spring is affixed to the tube at one end, the front/left in this picture. The aft end of the tube is open; the spring passes through and has an adjuster which pushes against the hull. I used 1mm (or maybe 1.2mm, I forget) music wire, also sold as spring steel. It is resistant to being twisted and is, well, springy The outer tube is just your basic K&S brass; they're soldered together at the one end and then the adjuster is a 3D printed piece with a threaded brass insert and a bolt through that.

I've grown to love those inserts, call 'em "threadserts" for short. They come in a couple flavors and a bazillion sizes. I get the ones that are straight knurled on the sides, so I can just 3D print a hole in my part that's slightly smaller than the threadsert, and then draw the thing in with a fender washer and a bolt from the far end.



There's a baggie of the threadserts and a front knuckle, which has I think eight of them (you can see two on the left side.) Back to the suspension insanity, here's an early CAD of the setup, looking from below (front to the left, the two grey boxes being the steering servos)



The torsion bars are somewhat more visible, ie in the upper right with the upper control arm (red) U-shaped around it, the capped end at the left and the adjuster (blue-green) and its bolt at the far right.

Also had difficulty finding shocks to fit. Once again the 1:1 is annoying: the front axle's shocks mount under the cab and go to the upper control arm, but those for the center and rear axle mount to the water drive box and go to the *lower* control arm, passing by the half-shaft. There's also the matter of the 1:1 using 1960's technology (or lack thereof) so as you see in the cutaway there's four shocks (actually, IIRC, two oil shocks and two rubber rebound dampers.) In the interest of actually getting working shocks at scale, I had to limit myself to two, and even then it's a very close fit.

[dremu]

The local plastic shop was limiting their days and hours due to COVID, so I 3D printed a bunch of parts for which I'd usually just go buy styrene sheet. In retrospect this was not ideal, but ..shrug.. At the least I could design for the odd shapes and cutouts, but I shoulda made the panels thicker. Also had to split into pieces as even my big printer couldn't do them in one go, and that made the thing even more challenging to glue together.



Had leftover neon colors from other projects, and if it's gonna get painted anyway, doesn't matter, right? Still hurts the eyes though.



That's the v-hull upside down with the (rear) water drive sections to the left, and huh, that looks like a teaser of a WWII half-track in the back.



This is where you see how ridiculously skinny the hull is, and the drivetrain is supposed to fit in there? Ugh.



His Royal Highness Duke Leto Atreides II watches carefully to monitor progress.



This is the front left wheel station, with the torsion spring fairly visible.



I found that scraps of very thin styrene sheet worked nicely to bond around the weird angles of the cab.



At some point I discovered the intermediate steering arm needed not only to rotate left and right, but also up and down as the steering axles moved. Racked my brain for a while to find a ball joint to go into the middle of the arm, and eventually cut up a shock ball.

[dremu]

The next engineering challenge was slipshafts at each wheelstation. I needed a really short driveshaft (CV joint, whatever you wanna call it) with just a bit of slip, but of course the RC driveshafts are all waaaay too long. I briefly considered printing the parts, but even at high infill, they're just too small to do in plastic with enough strength, so I had to mix off-the-shelf parts with printed and fabricated to make it all fly. Err, roll.

U-joints are available in a bazillion sizes, but I needed something into which I could fit a collapsible shape which could still transmit rotational force. That is, something like square tube, in matching sizes so that the outside of the one fits just into the inside of the other and it telescopes.



Finally, there is NO extra space whatsoever in there, so the U-joint had to fit *inside* a bearing on each end. There wasn't enough length to have the bearing at the end of each U-joint.



Took forever, but eventually found U-joints that are big enough to fit the slip mechanism inside, AND matching bearings. Curiously, the U-joints are metric and the bearings are inch, but it works. Left side has a bevel gear to come off the drive shaft, right side is a 12mm hex for the wheel drive. See what I mean about short? There's all of ~2mm of slip, just enough that I couldn't have used a solid shaft or it woulda broken over time

The slip shafts have printed bushings with a hole through for the setscrew to hold down the square tube. The outer ends are sized to fit one of those brass threadserts, filed on one side for the set screw:





Fiddly to get the threadsert flat enough that the setscrew would hold it, but still leave room for the bolt to the thread into it. Also had to find fairly short setscrews so that whole thing could fit inside the bearing.

Then, in testing, discovered that the U-joints like to shift back and forth a bit in the bearing. Didn't want to glue them in, too permanent, so opted for another solution. Cleaned the chrome-ish stuff off the surface, then soldered a ring around them to prevent slipping through the bearing.





Not my prettiest work -- I'm used to electronic soldering -- but they're structurally sound.

Then onto assembling the suspension. Sooo many fasteners, so much lather, rinse, repeat:

[dremu]

This shows the longitudinal square driveshafts passing through bevel gears and held up on pillow blocks with bearings, and then the bevel gears at each wheel station and their pillow blocks. There's also a center drive section with straight-cut gears I'll get to in a minute.



You'll note that the gears on one side are forward of the side bevel, and aft of them on the other side. This makes it so that the drive shafts turn the same direction to turn the wheels, so that the center drive section need only be one gear; as you can see, there just isn't room to fit a second set of anything in there to reverse direction or the like. I spent a bunch of time rotating my fingers around in circles in the air saying "This one goes clockwise so this one goes anticlockwise..."

The center drive is also an amalgam of printed and off-the-shelf parts. While gears can be printed, fairly strong even, doing them SMALL enough to make a diff was ... well, ugly. When you can get a metal one on Aliexpress for pocket change, it's just not worth the hassle. The drive gears on the end of it are still printed, and oddly, the coupler from the pinion gear to the motor is also printed, as I couldn't find a shaft coupler of the right dimensions.



And it starts to take shape and look like a thing, save the Dr Seuss colors. Really looked forward to even just primering the thing!



Can't see the gear drive, but the silver thing is the motor. It's a gear-reduction motor rather than your typical RC type motor as I needed something in the hundreds of RPM, rather than thousands. Also needed a right angle drive as the bed goes RIGHT above this, and trying to fit a regular RC motor-transmission inline with the driveshafts just wasn't in the cards.

Again, HRH Duke Leto presides. You'll also note I finally painted just for my eyeballs' sake.

Despite my best efforts to design the steering in CAD, I only managed to get it close. Once the suspension has weight on it, the thing settled more than I had modeled and all the steering angles went to crap. Also, not having the sides coupled (remember, left is separate from right!) is hairy. I cheated a smidge there by having two servos mirrored, but it still took some trial and error:



There's several variations of the steering arm, to see what geometry worked best.

[dremu]

Speaking of trial and error in geometry, the crane was another pain point. I've done a crane before on my PLS (HEMTT, whatever), but this one is shaped differently. I also wanted to try and stay as close visually to the 1:1 as possible. The end result isn't quite right, mostly limited by the actuators available, but it has lots of range and strength.

The most annoying part is the junction between the main arm and the jib. Rather than being a simple single-point hinge, it's a compound one. See where the actuator doesn't actually push on the upper arm, but on part of the hinge? This allows greater travel at the expense of complexity and hair loss for me =))











See how that by the end of the cylinder's travel, the thing has folded in itself like it's double-jointed. Sorting out Just The Right Lengths of those components was time consuming, plus determining which part went outside and which inside.

[dremu]

Also jumping around a bit, doing detail work, namely lights and shackles and such on the cab, and a winch because they're fun and cheap. That's the back end of the PLS up there, it gets its own shelf because it's so bloody huge.



Rather than my usual Arduino-heavy setup, this one has very simple lights, just switched on and off with one of those MOSFET gizmos that runs off an aux channel on the RX. Didn't cost more to run the ten channel RX than the six, so simple was appealing. No turn signals or strobes or anything this time. Here's a little power distro board, then, for all the lights:



More outputs than I needed, but I wasn't quite sure how many I'd be able to combine, whether the rears would be 1 or 2 or 4, so ..shrug.. do a bunch and figure I'm covered.

The bedside panels and rear are a curious louvered pattern. Rather than try and fab it, I opted to print this and then glue to a backing of flat styrene:



Each section has a tab for the hinge, and then much glue, so clamp:

[dremu]

That's about it for photos of the build. Here's some of the final CAD work, split up into various sections:

[dremu]

And then various money shots of playing with it (err, I mean, verifying functionality)



Unlike the PLS, where the crane can only reach about half of the cargo area, this one has enough reach to get most loads into any part of the bed.



We don't talk about wire management; they were tidied slightly before the cab went on. At the very least they're held up out of the way of the winch and driveshafts so nothing will get shorted whilst in use.



As with the 1:1, the crane jib also has a manual extension, so it can reach down to the ground, but that's something you'd use to maneuver a load external to the vehicle, put it onto another vehicle or trailer. The arm gets so long you can't put anything into the bed.



The box in the back has a ton of room for a battery, and snaps closed with magnets (as do the bedsides.) I should prolly do up some exhaust stacks and toolboxes and such for the back corners like the 1:1's, get to that someday.

[dremu]

Hard to get good photos of lights on, at least with a cheap camera, but you get the idea.

[dremu]

The crane also rotates around 360*, reaches over the cab





And has interoperability with my PLS trailers.

The 1:1's were also used to shift loads out of other vehicles, pull the power pack out of a tank, stuff like that., and this one has the reach to do that.

Finally, coupla detail shots of the suspension because (1) I'm proud of it and (2) I don't ever want to do it again:



front right, with steering arm elbowed around torsion tube



rear right, with torsion tube visible upper left. Sooo many locknuts. Sooo much Loc-tite. Shudder.

-- A

[kerst]

This looks like a very interesting built, but I don't see any pictures. Is it me or??

Kerst

[dremu]

Originally Posted by kerst

This looks like a very interesting built, but I don't see any pictures. Is it me or??

Kerst

Read first line There's a change you can make to Chrome to allow the pix.

-- A

[jerry56]

WOW...just WOW
You are right... that is a complex machine.... beautifully done...

[dremu]

Originally Posted by jerry56

WOW...just WOW
You are right... that is a complex machine.... beautifully done...

Heh, thanks! It's not perfect by any means, flubbed a couple bits, and some I had to take liberties with. The crane, particularly, isn't exact, but like I said the cylinders (actuators) only come in specific sizes.

I tell you though, I sure breathed as sigh of relief when the thing moved under its own power the first time. 3D printing gears is tricky at best, but there's no way I was gonna find off-the-shelf gears to work... so if mine didn't work, I'd put a bunch of time and effort into nothing.

Thinking of that, here's a bit I forgot... the innermost gears on the slipshafts, wasn't enough clearance to get a regular socket cap screw or even a button head on there as they were rubbing up against the longitudinal drive shafts. Ended up cutting space into the gear for a hex head:



and then loc-tite the snot out of that to stay bound to the shaft. As long as it's only turning one direction of course it stays tight, but the left shafts turn opposite from the right, never mind backing the vehicle up. I do NOT want to disassemble this thing to get to those shafts.

Anyway, point being this is the kind of customization you can only get with 3D printing, unless you happen to have an amazing micro machine shop at hand.

Also, thinking of it, the longitudinal drive shafts are also brass square tube, right, I should buy stock in K&S. But the 4mm was not only twisting along the length but starting to deflect under load Ended up sleeving the 4mm with a piece of 3mm inside, soldered up one end to keep them together. I suppose I could have used solid stock, but (1) I had the two sizes on hand, and (2) I swear I remember from materials engineering that tube can be stronger than solid. That may not be true for rotational loads, maybe only for bending, now that I think about it, but ..shrug.. the combined shafts don't deflect and carry the rotation load. If I run the truck into, say, a chair, the gears skip, but you figure something has to be a "fuse", and I'd rather it be the plastic gears that I can reprint than the pinion or those dang slipshafts.

-- A

[jerry56]

They are never "perfect" in the builders eyes.... Pretty ingenious way to get it to move. I'm just learning how to use my 3D printer. Mostly remaking parts, but have made a couple basic things for a build I'm working on. I haven't tried gears yet but would love to figure out how to make lead screw threads....
Really a great build....

[dremu]

Originally Posted by jerry56

They are never "perfect" in the builders eyes.... Pretty ingenious way to get it to move. I'm just learning how to use my 3D printer. Mostly remaking parts, but have made a couple basic things for a build I'm working on. I haven't tried gears yet but would love to figure out how to make lead screw threads....
Really a great build....

Well, I can't take credit for the design since it's semi-accurate to the original. I don't envy the crazy people who have Stollies now, though. Keeping my Fiero running is nothing in comparison!

Anyway, as for leadscrews, what are you using to draw, or at the least, are you hip to / have you played with OpenSCAD?

I have a pretty good library for gears I got off github or someplace, the joy of opensource means you don't have to write it yourself. I also had an interest in leadscrews, was looking at doing my own actuator-linear movement thing, but the geometry made my head spin. I did find a library or two where it's been done and didn't get any farther, but can scrounge up the links if they'd be useful.

-- A

[kerst]

Originally Posted by dremu

Read first line There's a change you can make to Chrome to allow the pix.

-- A

Got it!
Impressive project!

Kerst

[jerry56]

I'm new to CAD, currently using TinkerCad. It seems pretty basic to me but it matches my limited skills. I just wanted to make some bed lift assemblies for various conversions and lift rams for loader conversions. I've found some lead screw files that I can remix and make work, just kind of wanted to know how it was done....And after seeing your use of printed gears now has me thinking of other "geewiz" kind of stuff...