LEGO – Fluid Drive Bus #6683 – It’s Alive!

So after several months of painstaking development and experimentation, my first (and hopefully not last?) fluid drive LEGO vehicle is now complete! I wasn’t certain whether or not I’d achieve this feat, of building a successfully, genuine, model of hydro-dynamic awesome-ness (if I may say so myself), but it seems I’ve done it and here it is!

For those interested in the ‘journey’ I’ve taken to get to this point, I’ve posted photos of the progress below, most of which you probably haven’t seen before. Unfortunately the earliest photo of the development I have, is from the 12 April 2014. It really is amazing how quickly things have moved, even though it has taken me about 6 months to complete this project. I can still remember the prototype chassis frame I ran through the house with a very early fluid coupling iteration. I wish I took photos back then! Oh well.

Of course, also included in this post are photos of the completed bus as it stands today.

‘In Progress’ Photo Gallery (Circa April-May 2014)

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‘Complete’ Photo Gallery!

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PDF Operator’s Manual:

Click here to access the PDF Operator’s Manual

Next steps

So where to from here? Aside from the mountain-load of plastic model kit boxes which currently await me in my hobby room, I think the ‘LEGO bug’ has well and truly bitten (for better or worse!). Sooo…I’m thinking that next on the agenda may well be another LEGO bus! Whether to utilise the wonders of fluid-drive or not for next time remains yet to be seen however.

One example of a bus I am eyeing-off at the moment is the famous Greyhound/GMC Scenicruiser. The very earliest (prototype?) version of this bus had TWO engines, driving through a fluid coupling to a 3-speed transmission with a 2-speed auxiliary transmission behind that, offering 6 speeds in total. Building this in LEGO would certainly be my next challenge…and if I chose to model the prototype, I’d be putting in two LEGO motors and probably TWO fluid couplings to ensure I extract the maximum power from those motors. Or, I could choose to model the later, more prevalent models of the Scenicruiser which had a standard clutch and transmission. Boring?? Haha. Time will tell…but I will be sure to keep you all posted here on this blog! I will close with a photo of a real-life Scenicruiser…


Sweet Sixteen! ‘Vintage’ LEGO Sees Light of Day

Here’s a blast from the past…!

I grew up in a coastal town here in Australia and one of the things I remember fondly in my teens, was a great old derelict truck that was abandoned on an empty lot not far from my regular cycling route.

Being a young, inquisitive lad, I spent quite a bit of climbing over this truck. At the time, I knew relatively little about how it got to be where it was – but needless to say, I was fascinated by the vehicle all the same (what little boy wouldn’t be?!). So it wasn’t long until I started building a LEGO rendition of this truck. A period of time after, I noticed that the truck disappeared, and the empty lot on which it had sat was re-developed – I remember feeling a bit saddened at the time – I had feared the worst, that the truck was taken away to be dismantled or wrecked.  This was about 16 years ago now – I would have been just 15.

Fast forward to today however, and this LEGO truck is a survivor and is still in (mostly) one-piece, albeit quite dusty and dirty…but rough and ready all the same – sitting lonely on my shelf. And as it turns out, the real-world counterpart is also a survivor as you’ll read below.

In reading about this LEGO model of mine and viewing the pictures below, please bear in mind that I was only a teenager when I built this model and there’s probably quite a few things I could have done better in building this truck but hey, it is what it is…a time capsule – a tangible record of my memories and LEGO-building skills back in 1998.


Before I go too much further, here’s a bit of back-story on the history of this truck (the real-world counterpart) that you might find interesting. It turns the truck I had been so obsessed with all those years ago was actually quite rare indeed – being one of only two in Australia.

As a bit of history, these trucks were known as Rotinoff Viscounts and were specially-built by Rotinoff of London. Only two (I believe) of the Viscount models were shipped to Australia (having been purchased by the Vestey Brothers organisation) and they spent their days transporting cattle to Vestey’s-own Dewhurst butchers all over the country. The trucks were hard-working, pulling several cattle trailers at once and were powered by mighty Rolls Royce engines.

The two Viscounts which entered Oz were named ‘Julie’ and ‘Jackie’. I seem to remember the faded-out name ‘Jackie’ on the example I climbed-over in my youth. It turns out that Julie has ended-up in the National Transport Hall Of Fame at Alice Springs, Northern Territory here in Oz, fully restored and by all accounts looking great. Unfortunately, Jackie, now also in the NT (having joined her sister) is still sitting derelict. Could be worse I guess.

I’m going to refrain from posting actual images of the real-world Viscount trucks directly in this post (to avoid any Copyright issues), however a simple Google search on “Rotinoff Viscount” should yield a reasonable amount of information (including photos) if you’re interested in finding out more. I’ve also placed just a few links at the bottom of this post.

 So what’s under the hood??

I’ve listed below, the features that my Rotinoff Viscount LEGO truck sports. Again, nothing too fancy mind – I was only 15! Some parts of the truck had been upgraded shortly following the initial build (and this build is actually “series 4″ – so I had clearly gone through a few iterations at the time also). Upgrades include the wheels and tyres for example, which were purchased some period after to replace the original wheels. Most of the running gear and body work however, is still present in its original, worn, pitted, chipped and dust-ridden glory (as you will notice in the pictures)!

It also worth mentioning that at the time, there was no ‘Power Functions’ LEGO motors or IR controllers (apart from the standard LEGO 9V motors and controls one could acquire – which was a little out of the budget for this then-15 year-old – I was lucky to have enough money and means to replace the worn axle shafts!). Thus, I resorted to pulling-apart old radio-controlled vehicles and raided them for their motors and other such parts of interest. This is why you’ll notice that this LEGO vehicle has been fitted with an electric motor that is perhaps a little too big for it! Nonetheless, it furnished the power requirements just fine, even if it was only powered by four 1.5 (or 1.2) volt batteries!

To furnish the requirements of remote-control, I fashioned a length of suitable-diameter PVC pipe, into which I fitted metal contacts and wires. The batteries would then be inserted into this pipe which would then serve as the hand controller – touch the wire to the end of the series of batteries and away you go! I do remember quite a few instances where I shorted-out the circuits/overloaded the motor and ended up with a slightly-singed fingertip where the wire I was pressing down heated up. :o Fun times indeed.

You’ll also see evidence of plastic tape wrapped around most of the rotating parts, the transmission and drive shafts for example – at the time (due to my very limited budget) I was quite worried about wear and tear and aimed to reduce this as far as possible. Buying new parts meant mail-order catalogue and a cumbersome money-order. These days, I generally just smear a very light coating of silicon oil on my LEGO models’ running gear to minimise wear – and I have BrickLink (and not to mention a reasonably-endowed PayPal account!) to satisfy my craving for spare or replacement LEGO parts!


  • Remote-controlled electric motor (from memory – a Mabuchi RS-540 running at approximately 5 VDC)
  • Two-speed sliding mesh manual transmission (gear lever located in truck cab)
  • Realistic ladder-frame LEGO Technic chassis frame
  • Solid front and rear axles
  • Realistic truck tires with ‘dualies’ fitted at the rear
  • Combination of Technic and ‘conventional’ LEGO brick styling
  • Novelty RPM gauge (runs off the vibration forces from the drive belt)

Keen observers will note that I have not included a tandem axle setup on the rear end, and the front end may not be a 100% (or even 90%) accurate rendition of the real-world Viscount counterpart. I had taken some artistic license in these respects, mostly because these features and accuracies proved just a little too impractical from a LEGO standpoint – back then (and I do emphasize back then).

This vehicle also does not have a functional steering system, and so basically the vehicle only runs straight ahead or backwards (if you flip the hand controller upside down to expel the batteries and re-insert them with opposite polarity that is!). Furthermore, the power level for the motor is not controllable, it’s either off or on. So, quite a simple little vehicle, but powered nonetheless.

Next steps

You’re probably thinking that this vehicle would be GREAT to revisit and revamp, but before I start looking at perhaps reconditioning some of the parts or even retrofitting a power functions kit (with steering perhaps?), I will first focus on getting the thing running!! At the moment the drive belt which attaches the motor to the transmission pulley is perished as you’ll see in the gallery below. My past-self was handy enough to place some spare belts on the rear of the cab, and depending on how kind time (and UV rays) has been to those spare belts, I will look at replacing the belt soon to get this vehicle up and going.

Following that, who knows…there may be a revival of sorts on the cards for this oldie! But part of me aches to see this model get revamped all the same; there is a certain charm to it at the moment…and some of that ‘vintage-ness’ (not a word I’m sure) would certainly be lost if I started upgrading or restoring it. Perhaps, like its real-world counterpart, ‘Jackie’, its fate is to live out its days in its original (somewhat derelict) shape after all…

I’ll close here with links to the real-world counterpart, followed by an image gallery of my LEGO vehicle. Once I get it up and running I will make a video perhaps of it in action!

PLUS: Also included below is a scanned-rendition of the tattered ‘Operator’s Instructions’ document which my 15-year-old self wrote, dated 30 August 1998 – which still survives to this day. As you can tell, I was big into writing even back then! ;) I’m sure I even wrote a detailed ‘shop manual’ about this model as well, however the Operator’s Instructions is all that it appears that I’ve managed to salvage.


Images of the scanned manual from 30/08/1998:

Cover Page Page 1 Page 2 Page 3








Links to the real-world counterpart(s):

Image Gallery of the LEGO model:

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LEGO Pneumatic Tractor Mk1

So here it is finally!

Over a year ago, I managed to build myself a prototype pneumatic engine out of LEGO, after viewing some examples on the Internet. I was quite chuffed that my initial version worked so well, that I even posted a video about it. Then it seems, nothing happened for a while. Well really, it did, I just neglected to blog about it!! :( So, here it is, the main model which resulted from my dismantling the LEGO Unimog kit I had blogged about a while back.


So what exactly is a pneumatic engine you might ask? Well, a long time ago, Lego came up with the idea of incorporating pneumatic cylinders into their kits. These are basically cylindrical rams powered by low-level compressed air and were designed to operate kits with crane arms and other such creations. It seems however, that Lego builders around the world (me included) will always find ways to re-purpose these parts and thus, the pneumatic engine is born. Looking on the Internet, there are quite a few different types of these engines, some operating at crazy-high, Lego part-melting RPMs. Others (such as mine), operating at more ‘reasonable’ levels of speed, and boasting steam-engine-like levels of torque. In this post I’ll give a ‘teaser-like’ overview of the main points of the tractor, but I do hope that related documentation and assets, such as the video at the end of the post and also the images will be able to do some of the talking too.

Also, be sure to check out the detailed Operator’s Manual which I’ve written for this tractor!! (link at the bottom of this post also)

How the pneumatic engine works

I have, as aforementioned, already written a very in-depth operator’s manual regarding this tractor, and so here’s an excerpt from the manual, which I think describes the principles of the pneumatic engine best:

The engine operates because a flow of compressed air is directed to each of the two cylinders in a predetermined sequence. Once compressed air reaches the inside of the cylinder, it is directed to push against a piston, as it has nowhere else to go. Each piston in a cylinder is connected to the engine’s crankshaft, which is forced to revolve as the pistons move up and down. Finally, the crankshaft is connected to the Tractor’s transmission.
The engine can continue to run as compressed air flow to a given cylinder alternates as the piston in that cylinder moves up and down.

As the piston reaches the bottom of a cylinder, compressed air is routed to the bottom of the cylinder to push the piston upwards.
When the piston reaches the top of the cylinder, the compressed air is routed to the top of the cylinder, pushing the piston down, and the cycle repeats as long as compressed air is supplied.
This is referred to as the ‘double-acting’ or ‘double-action’ process.

The result is a continuous rotation of the engine crankshaft, which is directed to the transmission, which then feeds power to the rear wheels.

Other components and systems

I saw fit to load this tractor with as many systems and components as I could, being that I had quite a lot of parts left-over from the dismantling of the Unimog. So, here’s a short list of the systems and features of this tractor, in addition to the pneumatic engine (I’ll mention the engine again anyway ;)):

  • Two-cylinder double-acting, non-reversible, pneumatic engine – runs on air alone
  • Two-speed forward and one-speed reverse constant mesh gearbox
  • Automatic pneumatic parking brake featuring twin-brake shoe design
  • Drag link steering system
  • Rear differential
  • Rear pneumatic-operated ram (actuates various accessories)

The Operator’s Manual I’ve written describes these systems (and more) in much greater – almost exhaustive – detail. Be sure to check it out (link at the end of this post)!


Here’s some pictures of the tractor as well as a video and a link to the very detailed Operator’s Manual. Enjoy!!

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Link to the Operator’s Manual PDF

Where to now?

So what’s next at the Harman Motor Works? I am currently working on a remote-controlled Lego bus, to be based loosely off an AEC Regal MkIV single-decker. This Lego bus is fitted with my latest prototypical fluid drive coupling, of which I’ve also recently blogged about. I’m currently at a reasonably-advanced level of completion of this vehicle, having got the rolling chassis and box frame mostly complete. There is however still quite of bit of work to go. I will post an update or two on this blog over the coming weeks!

Here’s a sneak-peak at what the Harman Motor Works work-bench looks like at the moment:


LEGO – Fluid Drive Madness

So…ever since I was a wee lad, I dreamt of building one of these little contraptions, and yet, here it is, achieved, it seems. I should be over the moon right?? Well, I am. :)

So, here it is…the big reveal…a LEGO Fluid Drive Coupling…which actually works!!


I’m actually surprised how quickly I got to this point…but as you’ll see from the video at the bottom of this post, the darn thing works!


What on earth could I use such a coupling for you may ask? Well…the venerable London Routemaster bus used one successfully, as did many vehicles of the Chrysler Corporation all those years ago. And let’s not forget, today’s far-advanced cousin, the torque converter –  as seen in countless automatic transmissions – no doubt owes its very existence to the humble fluid coupling.

The advantage this coupling offers over a conventional dry plate friction clutch is smoothness – to the extreme. And you will see this touted no doubt in many old-time promotional materials and videos concerning fluid drives…smooth this, smooth that, no jerks in the drive-line, less wear and tear, etc, etc.

I actually got the idea whilst building my Revell Routemaster London Bus plastic model kit (yes that’s right, I’ve started building a model kit and haven’t yet blogged about it – naughty me!). So now much of my energy is being spent refining this fluid coupling of mine.

So let’s delve further into the technical details of this shall we?

How It Works

The basic principle of a fluid coupling is as follows: you have two elements opposing each other…the input and the output elements. These elements are NOT physically connected in any way whatsoever. The input element is the “driving” element – or pump – which is powered by an engine or motor. The output element is connected to the transmission and thus to the wheels (for example) of a vehicle and serves as the “driven” element – or turbine. The key component in a fluid drive is, as the name states, FLUID. Without fluid, the coupling would not function. It’s hard to imagine that such a flighty liquid could actually transmit torque and driving force, but this is in effect what is exactly happening in a fluid drive. There is of course bound to be a certain degree of slippage in the unit as a matter of principle, but after seeing this thing work “in real”, in LEGO form, I am utterly convinced that I can use this coupling to power my next LEGO model vehicle.

The old-time image below illustrates the principle of operation of the fluid couple. Here it is likened to two electric fans opposing each other. One plugged-in and running, the other stationary and off. The running fan produces airflow which is directed towards the opposing stationary fan, which actually causes it to rotate also. The principle of a fluid drive is the same, however instead of air, a fluid medium is employed (fluid, being much less compressible, can impart a greater amount of force and influence than air ever could).


So, the LEGO fluid coupling I have doesn’t actually need too much oil, it’s actually kept about a quarter-full which is just as well, because having it too full would mean greater incidence of oil leakage. The rear output shaft seal on my prototype isn’t that great you see, and so I have to play things cautiously.

What is great is the ‘welds’ I’ve achieved around the coupling case you may have noticed in the pictures so far. Crude as they may seem, they are actually quite sturdy and serve the hold the two halves of the casing together even while it spins around at great speed, with the centrifugal force of the oil pressing ever outwards against the join.

If you haven’t already gathered, the coupling case – in the prototype version at least – is simply two bottle-caps joined together, permanently (or semi-permanently) sealing the LEGO components in an (almost) leak-proof casing. The input shaft is actually bonded to the couple casing, so that the unit spins as one. As it does, oil inside gets flung about with great force, significantly influencing the rotation of the output shaft turbine, which is free-wheeling. It works surprisingly well in practice (it’s greatly exceeded my expectations) and I’m quite excited about it all.

I won’ t go too far into the technicalities here and unfortunately I don’t have pictures of the unit disassembled, but the video at the end of this post will hopefully help to show and explain just how this thing works.

Suffice to say, it works, and I’ll be doing my best to implement it into a vehicle and get it off the test bed.


As always, here’s a gallery with images and video to do the rest of the talking. Enjoy, and stay tuned for more (hopefully).

Additional Links

Lego Unimog U400 Kit – Modified by Harman Motor Works

This post has been a while coming, but I thought it was high-time I did post it, as the Unimog might not be around for much longer! :o

You may be aware from one of my previous blog posts, that I received the Lego Unimog kit as a gift a while back. At the time, I mentioned that I would kit-out the model with my own custom modifications in order to get more out of it and ‘make it mine’. Well, fast forward several months, and that has been achieved. Keep reading to see the details on just what it is I did to the truck…

Mod #1: Power to the people

One of the first things that I wanted to do with this model was make it powered. I figure that it came with a very capable all-wheel-drive system out of the box, so why not make proper use of it? So, I promptly ditched the fake piston engine provided by Lego in lieu of an M-motor, coupled to a hi/low range gearbox, to drive all four wheels. The result was certainly worthy of the effort.

Mod #2: High/low range gearbox

As I briefly mentioned above, I also added in a compact two-speed gearbox just behind the motor, to enable speed and torque to be adjusted to the conditions. In low-range, this thing really develops some decent torque given that it’s one heavy truck powered by only an M-motor. In high-range, the vehicle picks up some good speed as well. The gearbox ranges can be controlled via a lever which protrudes up into the cab beside the driver’s seat.

Mod #3: Air suspension (rear) & air tank

The next thing I did was add in an air tank to the truck’s chassis. I managed to neatly tuck it in within the chassis frame…it just turns out that there was a perfectly-designed ‘nook’ just waiting for the tank to make its new home. Cool! The air tank not only extends the capacity of the pneumatic circuit, it also means the electric motor which drives the air compressor (on-board) doesn’t have to run constantly when operating the air-driven devices.

Another thing I did while I was at it, was to replace the main drive gear from the compressor motor, with a gear which has a safety clutch it its hub; this basically means the clutch will kick-in when the air pressure in the pneumatic system reaches its upper limits, and prevent the motor and the related pneumatic components from strain and damage.

With the air tank fitted, I decided to ditch the rear springs and replace them with two pneumatic cylinders, which act as adjustable height air springs. The great thing about these things is that the ride height can be adjusted to suit no matter what type of load is carried on the rear of the truck, so no more spring-sag when carrying heavy items. The rear air springs are controlled via a pneumatic switch in the cab.

Mod #4: Auxiliary manual air pump

My efforts to cram as much as I could onto this model resulted in this next mod: a manual hand pump/crank system to drive the onboard air compressor when battery power was unavailable. I figured that now I have the rear air springs, it would be handy to be able to pump them up whenever I chose even if there was no electric power available. The system works well, and the manual pump handle is stowed away in a specially-made storage compartment by yours truly.

Mod #5: Lower-ratio raised hubs

This was actually one of the earlier mods I did the vehicle, and not major by any means, but necessary all the same, if I was to effectively motorise the truck. This mod involved removing the 1:1 gear ratio at each raised-hub, and replacing it with a set of gears offering 3:1 gear reduction. The result was perfect to give that M-motor the extra torque it needs to power such a large and heavy model. Combined with the low-range gearing, this truck seems to easily tackle most obstacles.


So that’s basically it for now. Unfortunately I may have to dismantle this model soon; I have a hankering to use its many parts on some new models of entirely my own design, and it pains me to see that I have several hundred Lego parts sitting on the shelf locked-up in this kit, that I could otherwise be using for my own creations. I do seem to enjoy building my own models from scratch moreso than building Lego kits to the letter. With that said however, I did thoroughly enjoy custom-modifying this kit, and even stock out-of-the-box, it certainly was an impressive kit to build. It’s just a shame that I did not get to add remote-control capability to this kit. Maybe next time.

I’ve included some pics below and also a link to a video of the truck on my YouTube channel, Harmanmotor.


Christmas Comes Early – Unimog Style

This latest news comes courtesy of my “enabling wife” (her words not mine). An overly-large parcel arriving in the mail, and uneasy looks from her eyes when pressed as to the contents, I guess I should have known something was up…but no, I was caught completely off-guard by this; and what a pleasant surprise it was too.

Do you have anything smaller?

This has got to be, by far, the largest Technic kit that LEGO has ever produced. I don’t pretend to possess detailed information on every single kit ever made, and I’m not normally one to go for the biggest and baddest kits either, but this one is simply massive and comes in at over 2,000 pieces!

Not only is it big, it’s also licensed by one of the world’s most respected automobile manufacturers…Mercedes Benz.

Ladies and Gentlemen, I give to you…the Mercedes Benz U400 Unimog….

Devil in the details

Of course being the type of blog that this…blog…is, I couldn’t go without detailing some of the cool features that this kit promises to offer. As I type this, the massive box sits beside me, beckoning me, and luring me in. Deep within the box are the makings of some pretty cool systems just waiting to be built; things like pneumatics, raised hubs, electrics, tilting cabs, steering, cranes, winches, 4×4, and much more.

As I alluded to above, this kit comes with pneumatics. This will be the first time I’ve ever built with such systems and I cannot wait to get started. The pneumatics will power a fully articulated crane system which will sit on the rear of the vehicle, and there also seems to be an electric motor which can “charge” the pneumatics with the aid of a piston air-pump. What is missing is LEGO’s air tank system which is on my list of things to add to this vehicle as part of my grand (re)engineering plans (more on that below).

The vehicle also comes with a 4×4 system which features Mercedes Benz’ patented (I think?) ‘raised hubs’ design, referred to here as the “gear block”. This is basically a vertical gear-set which sits just inboard of each wheel and serves to greatly increase overall vehicle ground clearance while still providing drive. I’d known about this system in real life since forever (I remember looking at the real thing on the Unimogs at car shows in the past). Very neat.

A little more about the 4×4 system though: it appears that LEGO has again done what they seem to be doing a lot with their Technic kits…the drivetrain is not powered in any way shape or form by a motor or otherwise. There is, what appears to be, a fully-fledged full-time 4×4 system under there, with no less than three differentials, but not a driving motor in sight. This is definitely where I think I will come in…

There are just too many little awesome little features in this kit for me to mention here, and it’s getting harder to continue typing this with the box so close to me, so I will have to wrap this post up (pun not intended) shortly, but not before giving you a taste of what you can expect from me once I finish this vehicle in its “stock” form…

(Re)engineered madness

As awesome as this vehicle will be once built, I can see (already) that there will be heaps of room for improvement (and also to see how many additional systems and features I can cram onto this platform). I haven’t even started building this kit yet and already here’s my list of ‘to-dos’ or even, my ‘wish-list’ for this vehicle – some of the things may not be possible but that doesn’t mean I won’t try ;)

  • Add additional motor to drive…the drivetrain (believe it or not, this vehicle does not move under its own steam out-of-the-box). A fully-fledged 4×4 system is just waiting to be driven with this kit. I may also look at incorporating high/low range gearing controlled pneumatically if at all possible…
  • Customised pneumatics system (add an air tank for increased pneumatic capacity and add a manual pneumatic charging system option in addition to motorised compressor)
  • Possible remote control system utilising LEGO’s IR remote systems
  • Tilting flat bed using pneumatics
  • Steering using pneumatic assist (“power steering”)

Many of these things might have been nigh on impossible if this kit was any smaller (and who knows, may still be impossible), but the sheer size of the vehicle makes it an excellent platform to start trialling out these extra systems and it will really make it easy(ier) to let the imagination run wild and see just what can be achieved.

I guess it’s a good idea to mention that now this kit has arrived, my doomed Technic half-track project has stalled even further! Before I close, I will leave you with a pile of pics of what this kit looks like at this moment (see if you can “Where’s Wally” the little LEGO man in the pics below…just to give you a sense of the scale of this kit…).

The next few weeks are bound to be quite interesting…

Merry Christmas all! (hehe)

Making Tracks

A quick blog post which may hint at my next big kit that I will be building (along with a hint from the end of my previous LEGO post here – can you guess?).

My dastardly-evil (just kidding) other half gave me this recently: kit 8259 with the chain-link treads which I was after (nyuh nyuh how did she know!?).

I rarely if ever build LEGO kits “to the letter”, preferring instead to dump the bits into my collection and go DIY (the most fun!), but I thought I’d give it a go this time around and here’s some quick pics of how that turned out.

Of course, the main thing of interest (for me at least) in this kit is the treads which will be used in my next big build.

There’s still more parts to acquire before I can truly get started, but stay tuned for more on that front soon! In the meantime, enjoy…

Two kits in one!
This is what I came for!
Misc parts
The shovel can be raised and lowered
Didn't take long for the Gorilla Suit Guy...

Blood, Sweat and Gears (Mk2!)


Here’s the follow-up post to my LEGO Technic Custom Flat-bed Truck, Mk1 of which I blogged about a few days earlier.

What you’ll see here is the latest and greatest iteration of this truck of mine – and probably the last one at that – alas, I’m looking for bigger fish to fry. More on that later though, let’s start by getting down and dirty with all the changes and upgrades which have happened to this vehicle since Mk1 back in 2009…

Point me in the right direction

One of the things I could have done better with the design of the Mk1 was that of the steering system; the steering gear ratio didn’t deliver as much steering torque as I would have liked. I solved this by adding an additional gear-set to which increased the gear reduction by another 3:1. This means more turns of the steering wheel is required to get the same amount of steering action, but with it comes a welcome increase in steering force and realism.

I’ll let the following video do the rest of the talking…

Chain me up (again)

Another new feature with Mk2 is the addition of a “chain brake”. This is basically a form of “handbrake” which serves to hold the vehicle stationary and stop it rolling away, or off a table onto the floor for example. :o

Normally the gearbox serves as a sufficient braking mechanism when either 1st or 2nd gear is selected and the motor stopped, however if the gearbox should slip into neutral, the vehicle has the tendency to let gravity take over…

The chain brake operates by sliding a “friction gear” into mesh with the gearbox final drive gear. The friction gear is keyed to a stationary shaft which cannot rotate, meaning that once in mesh with the gearbox, it resists movement of the drivetrain and thus, the rear wheels. The only disadvantage of this system is that if one rear wheel (or both, somehow) are off the ground, the vehicle can still roll even with the chain brake engaged due to the action of the rear differential.

The picture below highlights the location of the chain brake and its associated linkage system and lever (red). Keen observers may also notice the chain tension gear I’ve added to the rear chain which helps avoid the chain jumping links and slipping over the rear differential crown gear under load:

Chain brake

Trippin’ on LSD

That somewhat controversial heading is somewhat (fully?) matched by the sheer innovative genius that could only describe the limited slip differential (LSD) that has made its appearance with Mk2. /brag

A bit of background…

The design of this LSD is purely my own and took a bit of experimentation and tweaking to get right, but I must say, it works quite swimmingly in its current form. For those who aren’t quite familiar with what an LSD is in “vehicle-speak” (you’re still reading this?? just kidding!), it’s a differential system which attempts to overcome a traditional differential’s one major short-coming: the tendency to transfer ALL torque to the driving wheel with the LEAST amount of traction.

Let’s step back one step further: the purpose of a differential is to allow one wheel on a common axle to turn faster than the wheel on the opposite side during a corner. This ensures effective steering action and reduced tyre wear. I won’t go too far into this, as there are a lot of articles and info on this on the Internet already (see the end of this post).

“Most” cars and vehicles are fitted with what’s known as an “open” or “standard” differential. This works fine around corners and during general operation on stable, high-grip surfaces where both wheels on the axle have equal amounts of grip. However, if one should venture into a loose surface, and one of the wheels connected to the differential should slip, or become raised off the ground by a bump, etc, all torque is immediately transferred to that wheel. Meanwhile, the wheel on the ground on the other side of the axle (in most cases with all the traction) sits motionless – when it could be driving and moving the vehicle.

An LSD works by re-routing the torque that normally takes the “path of least resistance” and transferring it to the wheel which actually has traction, i.e, the “loaded wheel”. Thus how the system earned its titled “limited slip”. A good measure of how well an LSD works, is to raise one driving wheel off the ground, and seeing how much torque gets transferred to the “loaded” wheel on the other side (an “open” differential in such a situation would spin the lifted wheel uselessly and move the vehicle nowhere). You’ll see me perform this test in my LSD test video below shortly.

How it works!

So we finally get to the nitty-gritty; just how the LSD system on the Mk2 functions. Originally, I was going to trial a geared version but belts and bands have always intrigued me for their smoothness in operation and the fact that they are generally more forgiving under load and perhaps even more variable in setting than straight-up gears.

So…I went with a “dual-band” setup for the Mk2’s LSD system. I’ll do what I always do and attempt to explain in text, follow with a vague pic, and finally show you a video. :)

On each half-shaft of the differential, I’ve mounted a large pulley. Now these two pulleys on their own don’t achieve anything special, but to these pulleys I’ve added a “band” each, which then connects to a “common shaft”. This common shaft is mounted upon an adjustable mechanism which moves the shaft back and forth (adjustable by the user using the “torque wheel”) so that it’s either closer-to or further-from the pulleys and thus band tension can be almost infinitely adjusted.

Here’s that pic:

LSD close-up

Increasing band tension has the effect of making the common shaft “connect” both of the large pulleys (and the two halves of the differential) together as a single unit. What this ultimately achieves is making the differential unit behave less like an “open” differential and more like a solid axle. This naturally means that when the LSD is set to its maximum torque transfer setting (maximum band tension), differential action (allowing one wheel to turn faster than the other around corners for example) is limited, but this is where the magic of using bands rather than solid gears comes into play: no matter how tight the band setting, there is always a little bit of “give” in the system.

Time for a video…

Some additional notes…

Band wear

As mentioned earlier, the use of bands rather than “solid” meshing gears gives this system its own  type of “elegance”.

With this so-called elegance however comes one disadvantage over the use of traditional gears: band wear. It must be said however that under “normal” operation on solid ground and with minimum tension, the bands experience almost no wear as the pulleys go about spinning by their own free will. It’s only when the bands are tightened and the differential subjected to prolonged slip condition (where one wheel turns faster than the other), band wear starts becoming evident as they try to rotate the common shaft and transfer torque (band wear is generally visible in the form of bits of rubber residue along the bands). Having said all that, I’ve gotten several hours worth of LSD operation out of the bands currently fitted to the truck, and they haven’t let go…yet!

Slip ratio

Now slip ratios are not an easy thing to determine with a band-drive LSD system as there are many factors and variables which could affect it, such as band wear, band tension and perhaps ground surface type.

From my observations so far though, I’ve noticed that under full band tension, the LSD unit comes reasonably close to achieving a 1:1 slip ratio…meaning that the loaded wheel in a slip condition almost turns as fast as the wheel up in the air (doing nothing). Obviously getting as close to 1:1 as possible (or even over-driving) is desirable, but with a band system, it’s not as easy to achieve this (as compared to a geared setup). I’d hazard a guess and say that under band tension, this LSD transfers around 50% to 75% of the torque to the loaded wheel, which is not a bad effort indeed and as you can see in the video above, seems to work quite well in practice.


One of the other major advantages I’ve seen with this LSD system is the fact that the system is very compact and hardly takes up any more space than the standard differential unit. The large pulleys mounted on the differential half-shafts hardly protrude from the vehicle and the common shaft is tucked neatly up into the chassis of the vehicle too.

Me likey.


Differential article (Wikipedia)

Other stuff in Mk2

Some of the other additional features I’ve added to Mk2 that I thought worth mentioning (but not exactly worth their own heading) are as follows:

  • Rear flat-bed-mounted hoist (adjustable for tilt via linear “hydraulic” system)
  • Headlights! (yes, that actually work)
  • Various miscellaneous chassis strengthening tweaks


Here’s a bit of an image gallery showcasing the Mk2…

Mk2 Showcase
Chain brake
Underside 1
Underside 2
LSD adjustment wheel ("torque wheel")

Final thoughts…

I’m quite happy with the way Mk2 turned-out in the end. It’s certainly come a long way since I laid out the bare chassis rails on my building bench and started dreaming for the first time. I would have loved to add an RC system to this truck and maybe even a PTO (Power Take-Off) unit to the rear-end, but alas, some things just weren’t meant to be it seems.

Where to now? Onwards and upwards onto bigger and better things! My next model could be a U.S. Army Half-track, or a robot. Who knows?

LEGO Mini Figures – Episode 1 – “Enter The Gorilla Suit Guy”

The Samurai Warrior takes in the scenery...
Space Villain: "HALT! I am the Space Villain and I will now villain-ise you!"
Gorilla Suit Guy: "Not so fast Space Dude! This is a hold-up!"
Gorilla Suit Guy: "You'd better believe it!"
*Suspenseful music*
Samurai Warrior: "UTSUKE!!!" ("Idiot!")
Samurai Warrior: "Shinpai gomuyou?" ("Are you okay?")
Alas...the Space Villain was not okay...and Gorilla Suit Guy was about to do his big reveal...
Should have seen this coming from a mile away...

This episode was brought to you by Lego Mini Figures (Series 2) and me, of course.

Special thanks goes to “How to Talk Like a Samurai“.

I hope you enjoyed this “just for fun” post. Stay tuned for more LEGO posts in the near future – including an update on the latest development of my LEGO Technic Custom Flat Bed Truck I blogged about earlier.

LEGO! “Technic” To Be Exact


This is the first post in my blog where I talk about the custom LEGO Technic  Custom Flatbed Truck that I’ve had since about May 2009 when I started to get back into building LEGO Technic models. This model truck (purely my own design if I may say so) has gone through quite a few iterations since May ’09 and I’m still working on putting the finishing touches to the latest version as I type this.

Let’s take a step back though; this first post will introduce you to the development (from scratch) of the prototype truck and the subsequent (initial) MkI “release” (I’ll leave the latest-and-greatest version for a future post).

Prototype me!


When starting any new LEGO Technic vehicle project, I tend to start off by getting the basics down-pat first: the chassis frame “rails”. The chassis will form almost the back-bone of the vehicle and will function as the main component which everything else bolts onto (much like real-world trucks). I normally go through a few design “phases” before I settle upon the length and width of the chassis unit. It can be difficult to envision just how long and high I want the vehicle to be, so I try to get the chassis as close to “perfect” as I can before I move on (because changes to the chassis rails can become very hard once everything else is attached to it!).

Rolling gear

Once the chassis is sorted, I start thinking about the next most important thing: the wheels! Obviously the wheels and their mounting system will form an integral part of the chassis unit and are obviously an essential part of the truck. Considerations such as wheel-base, wheel-track, steering and ground clearance start coming to the forefront of my thoughts.

Once I’ve got all these considerations sorted and perhaps after experimenting for a little while, I’ll normally end up with what you see below – a rolling chassis!

Not much to look at...yet

Wait a sec!!??

Ok so I cheated a bit here. What you see above is actually (believe it or not) the truck at a slightly more “advanced” stage of completion. You may (or may not) notice a longitudinally-mounted electric motor connected to a 2-speed gearbox, so let me fill you in those components now.

Electric motor

The electric motor I settled-on for this project was one of LEGO’s own: the “M-motor”. One thing I’ve noticed with most of LEGO’s motors, is that they mostly come with their own integrated gear-reduction. This is helpful as it means I don’t need to worry about tweaking the overall gear ratios too much before the power hits the ground. For this truck however, I still opted to build a gearbox of my own design…

Box of gears anyone?

For this project, I decided to custom-make my own LEGO gearbox from scratch. The gearbox offers 2-speeds: LOW and HIGH, plus a “neutral” range (which obviously transmits no power to the wheels).

The actual design of this ‘box is one which I’ve used for ages in my LEGO models now…it utilises an “input” shaft which connects to the electric motor, and from there, transmits power down to a “layshaft”. Finally, the power reaches the rear-end of the gearbox where I generally mount a drive shaft to the rear wheels, or in this case, a “final drive” unit which will run a chain/sprocket drive on the rear axle. If I’ve lost you several lines back, here’s a pic:

Gearbox explained...maybe

Selection of gear ratios is obtained by sliding the lower half of the gearbox (the layshaft)  back and forth so that it engages LOW, neutral, or HIGH. It’s a relatively simple design but one that works admirably. As any gear head will tell you though, only one gear ratio must be able to be selected at a time, otherwise (as expected) the gearbox cannot rotate and will lock-up, so I ensured that the gears were aligned sufficiently to avoid any issues.

Here’s a YouTube video of the gearbox in action…you’ll also get to see the rolling chassis in this video (incidentally, the proposed “RC” [radio-control] feature never materialised – at least not yet anyway):

Gear ratio-wise, LOW gear offers 3:1 reduction, while HIGH gear doesn’t change the ratio at all, offering a true 1:1 ratio (direct) drive straight through the gearbox. That’s not the end of the gear reduction though; at the rear end of the gearbox, the final drive reduces the ratio (no matter what gear is selected) by 3:1 again. In other words, the trucks enjoys some fairly serious gear reduction with LOW gear engaged, to the point where the motor can easily break the rear rubber tyres loose on slippery surfaces.

Chain me up

Eventually, I hooked up a chain drive from the rear-end of the gearbox down to the rear axle of the truck (which incidentally added another 1.5:1 worth of gear reduction!). The rear axle features a fully-functioning differential unit with three spider gears. I won’t bore you too much with the details, but some of the pics you’ll find at the end of this post should hopefully tide you tech-heads over.


OK, so I’m speeding things along a little bit here (mostly for the sake of readability)…to talk about the other major component and consideration for the vehicle. The frame! Otherwise known as the body or cabin or “cab”.

Here’s one of the earliest iterations of the framework which I came up with for the truck (note the battery box mounted immediately behind the cab, which takes 6x AA batteries):

First version of frame/cab

But alas the angles in the front pillars drove me crazy from a geometrical perspective (they could never seem to line-up 100%), so I scrapped that design and went for something a little more rigid (and at more sane right-angles!):

Final frame - awaiting gearbox

Once the frame was mostly settled-on, I could focus on getting the interior sorted and other somewhat minor details such as hooking up a gear lever and linkage so that the gears could be selected from the cab (as you’ll see in videos further down this post). But there was still one of vital component remaining…a steering system!!


Steering systems are always a challenge to build. On the one hand you have two giant front tyres which need room to be turned about their steering axis (this is where you need to make sure your chassis rails are narrow enough at the front end to allow this!), and on the other hand, you need to devise a way with which you’ll get the motion of the steering wheel inside the cab all the way down to the front axle to do the actual turning of the wheels (read: a pile of linkages!). On top of this, all these linkages must clear the rest of the vehicle, the motor, etc and everything else as they move back and forth, to and fro, to steer the wheels.

The system I ended-up using for the truck could perhaps be considered a type of “drag link” and you can see a bit of how it works in the YouTube video at the end of this post. The steering system you see in action here, while satisfactory, didn’t make me as happy as I could be – the steering gear ratio was too high – so after MkI, I lowered the ratio significantly. I’ll fill you in on this in future posts.

Mk1 ready!

So I eventually got the truck built to a level of my satisfaction and thought I was done. Hah! Unfortunately (or fortunately), in LEGO land, things are never finished…there’s always something more to be added, adjusted, broken-down and re-made or just plain changed. I will save all that subsequent development for future posts though, and instead leave you with pictures of how MkI turned-out. Enjoy!

Rear 3/4 view
Heli view
Front 3/4 view
Belly of the beast
Chain drive to rear differential
Looking down into cab...
Rear end

Mk1 videos