Paint Shop – Wilesco D320 Steam Lorry

Further to my most recent post detailing the acquisition of my Wilesco Steam Lorry, here is a follow-up post showing some of the minor modifications (all cosmetic) that I’ve performed of-late.

I’ve decided to take to the model with a paintbrush (well, aerosol can) and spruce-up the colour scheme somewhat. I found there was a little too much brass and other ‘conflicting’ colours on board, so I set about changing some of these finishes to give the model a more ‘professional’ look.

What was (re)painted

Listed below are the items I’ve re-painted so far:

  • RC receiver/battery box (painted a more-realistic wood brown – the wood texture was already molded into the plastic!)
  • Drive chain & drive cog (painted a semi-gloss black to remove the toy-ish brass look [not to mention the cheap ‘necklace’ look of the original brass chain!!])
  • Wheels and hubs painted semi-gloss black to better balance out the colour scheme (in my opinion, this change immediately transforms the model into looking like a ‘proper’ scale Lorry)
  • Rear axle painted flat black (except for the top-most surface – I wasn’t too sure if painting it completely would hinder the radio signal range as there is a ground wire (signal wire ?) connected to it from the RC receiver box
  • RC steering rod (flat black)

What’s next (maybe!)

Whilst I don’t want to make any promises, I do intend to actually re-visit the green colour scheme on the main body panels and cab and see what else I can achieve there.

My thoughts at the moment are a more dark green (think British Racing Green) rather than the colour shade the Lorry currently has.

Once I’ve done this, I may well choose to lose the golden plaque at the front of the Lorry (jury is still out on this however) and attempt some stencil lettering and perhaps if I’m feeling ambitious, attempt some pin-striping around the cab body panels. I may also choose to darken or otherwise stain the light wooden panels around the rear cargo tray and/or attempt further stencil lettering there also.

For the time being however, I thought this post would serve well to update on you on what I’ve achieved with the Lorry so far.


IMAG0396 IMAG0397 IMAG0399 IMAG0400 IMAG0401 IMAG0404

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!!

Dsc00846 Dsc00847 Dsc00848 Dsc00849 Dsc00851 Dsc00852 Dsc00854 Dsc00855 Dsc00856 Dsc00857 Dsc00858 Dsc00859 Dsc00861 Dsc00862 Levers

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 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)

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! “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