Tuesday, January 1, 2013

Logging Trucks Comparison


Sorry for the (in some areas of the world) overdue post, but several factors kept me from doing this earlier... still, I felt I needed to do this for 2012.

The first semester of 2012 saw the release of the 9397 Logging Truck, a set that depicts (surprise, surprise) a logging truck. But not just any logging truck, a six-wheeler, long nose truck with a motorised yellow grabber arm. I had shot a few photos of the box, pieces and building process for a complete review, but you all should be already familiar with the model (be it through other reviews or by owning the set itself). So, here they are all, for some eye candy and the possibility of showing something you may not have seen before.

Like is surely the case for many other people, the 9397 looked familiar to me, resembling one of the most beloved LEGO Technic sets of all time: the 8868 Air Tech Claw Rig. As Blakbird puts it on his excellent Technicopedia (currently unavailable), this is a remarkable set, and an icon in the history of LEGO Technic.

It pioneered both the small pneumatic pump and the small cylinder. It took years before another set with compressor appeared, in the form of the 8049 Tractor with Log Loader (reviewed here). However, the compressor in this set is offered only as an extra for the optional motorisation. Only in 2011 a set with a properly integrated compressor appeared again: the 8110 Mercedes-Benz Unimog U400, reviewed here. With its numerous functions, the 8868 was the most complex pneumatic set until the appearance of the 8455 Backhoe in 2003 (which, by the way, is still the undisputed king of LEGO pneumatics).

Why this comparison, and why now? Well, I don't think it's a coincidence that a black, six-wheeler, long nose truck with a motorised yellow grabber arm gets released exactly 20 years after another black, six-wheeler, long nose truck with a motorised yellow grabber arm... and an important item of LEGO Technic history, at that. To make the homage complete, though, the only thing missing is a white bullbar at the front (and perhaps white chimneys and wheels, but those can be dismissed in the name of grey being more realistic). Therefore, in my opinion we have here the first case of a modern rendition of a classic Technic model, and a comparison is in order.

Putting the two models side by side, we can clearly see they have different proportions. The 8868 is shorter, although roughly as wide and tall as the 9397. It looks as if it represents a tractor unit modified to have an excavator arm instead of a fifth wheel for pulling trailers, whereas the 9397 seems purpose-built for the task of not only manipulating logs but also carrying them.

While both have approximately the same width and height, only the 8868 can accommodate techfigs inside. Try as I might, I was unable to get those little (big) fellows at the wheel of the new iteration. Speaking of wheel, unless the 8868 is able to drive itself like KITT, the would-be driver is in serious trouble... where is the steering wheel? Let's also hope the self-driving truck doesn't go too fast when cornering, or the absence of doors will make any occupants' lives quite... interesting. In this respect, the 9397 is a clear improvement on the original, as it features steering wheel (albeit non-functional) and doors. Not that techfigs can fit inside to enjoy them.

Another improvement the 9397 has over the 8868 is in the aesthetics department. The newer set has a full grille, blinkers, license plate and an overall better shape for the bonnet, while the older set only has a bullbar for rougher environments.

On the rear, whereas the 8868 is pretty bare with only a single white Technic brick for a bumper, the 9397 also has a set of tail lights (although no license plate).

Twenty years saw a veritable explosion in LEGO large tyre/wheel variety and realism, and the newer set shows it: its "shoes" are a lot more eye-catching than the 8868's.

Personally, I'm undecided about which one looks better in the roof department. The 8868 has much better-looking horns, made with dedicated elements, but its successor has some headlights for an extra taste of that American spirit.

Mechanically, the tables turn in the 8868's favour. The 9397 features outriggers (even though they're more decorative than anything else) and the claw can rotate. The 8868 tops that with fully independent functions for the arm, and claw opening placed together with the other controls; you can therefore pick up and drop stuff with the claw without touching it.

Following the tendency of modern vehicles to have smaller and more efficient engines, the 9397 features a "simple" L4 with a small fan, while its ancestor boasts a full V6 with a large fan to cool it. It has better traction too, since the engine transmits power to all four rear wheels instead of just the second axle.


While filming the video below, I noticed an important thing: the 8868 is a lot easier and more fun to control than the 9397. For the former, all you have to do is leave the compressor turned on and flick each valve to control the respective portion of the model in the direction you desire, while for the latter you have to both set the direction of the motor and the selector lever for each portion to be controlled. For moving the arm towards the log, picking it up and bringing it back to the cargo bed, I kept making mistakes in the correct sequence of actions and had to shot multiple takes. Of course, the fact that, to open and close the grabber, I had to reach out to it and actuate it, didn't help. There was another problem, related to the shape of the claw and keeping the log grabbed, but that is discussed later.


Below is a table directly comparing a few aspects of the two models. Some of them are more important than others, others depend on each person's opinion.

Light Grey
Number of wheels
Double differential
Single differential
Front wheels, HOG
Front wheels, HOG
Cabin details
Seats, doors, steering wheel
Cargo Capacity
About half a dozen logs
Everything can be controlled from the truck
Some mechanisms' controls are adjacent to them
Superstructure Rotation
~ 180º
Side stabilisers

Personally, even though the 9397 has much better looks, the 8688 wins with a comfortable margin simply because it's more fun and intuitive to play with, and also because it's a better approximation of how this kind of machines works in the real world. Plus, the sound of it working is cooler too!

Pneumatics and Linear Actuators: Yin-Yang

I end the comparison with another comparison inside, Matrioska-style. Ever since the introduction of the linear actuator in 2008, several people claimed it would mean the end of pneumatics, as the linear actuator would bring the same functionality without the disadvantages of the old system. But, with the introduction of the 8049 Tractor with Log Loader, the 9641 Pneumatics Add-On Set and the 8110 Mercedes-Benz Unimog U400, TLG disproved this theory. This is an excellent opportunity to compare both systems, as they are used for the same application, and to show each has its advantages and disadvantages.

As you can see from the video at the review of the 8069 Tractor with Log Loader, pneumatic cylinders aren't easy to get in the exact position we want: as soon as there is enough pressure to overcome the load imposed on the cylinder's rod, it tends to jump to its opposite extreme position. Still, this tends to be compensated by the slow action delivered by a modest motorised compressor. Note below how controllable the arm of the 8868 is (even though its rotation is extremely jerky), even after I accidentally roll the 9397’s log to a less optimal position. With more powerful compressors or a manual pump, this controllability goes out the window.

There is also the matter of automated control. Since a pneumatic cylinder deals with force instead of position, as soon as you provide enough pressure to move the piston, it'll tend to jump to its extreme position, without allowing you to stop midway. Just remember what happens when you open the valve on an 8421 Mobile Crane to let its boom descend: it will come crashing down instead! For fine control, either you handle the valve expertly or use a complicated mechanism like this one. If you want to have a remotely-controlled pneumatic mechanism, you're in for some fiddling! You're going to have to build a compressor, a valve actuator, and, for safety, some way to prevent excessive pressure build-up. None of those currently exists as dedicated elements (TLG, are you reading this? ;)), so they will inevitably take lots of precious space inside your model, and this is an important drawback.

The Linear Actuator system doesn't have any of those drawbacks. It is simple to hook up a motor to an LA, and you only extend and retract it as much as you want. These are two very important advantages. However, you have to be careful to turn off power when the mechanical piston is fully extended or retracted, or else you will hear that horrible noise of the internal clutch engaging. Sure, you can mount a 24T clutch gear somewhere between the motor and the LA, but that will complicate the mechanism and there's still the problem of the gear wearing down. With an automatic pressure cut-off switch, you just open a valve and let the system do the rest. Also, you can imagine the complexity of having an extra axle going through the turntable and the arm to power a hypothetical extra LA for the claw; pneumatic tubes go through awkward places and directions much easier than axles.

Finally, a mechanism like the claw in these trucks is more suited to be powered by pneumatics than LA's. When a mechanical claw closes on an object and grabs it, it maintains this position, regardless of the object being securely held or not. A pneumatic claw grabs the object and maintains pressure against it, keeping it held tight.

Thus, the conclusion is that, even though they appear similar and competing with each other - and, admittedly, their fields of applications overlap in some areas - in reality these two systems complement each other. On some occasions linear actuators are the way to go, on others pneumatics are the best choice.


TechnicBRICKs said...

Well done Alexandre!

For some reason, I was never a big fan of the old 8868 Air Tech Claw Rig...
And maybe because they were not new anymore, every time I saw one working, it was always not performing properly somehow.
Likely because of very old cylinders and rubber belts being used.

Then my preference goes for the more modern looking 9397, despite its limitations.
In this case I tend to give more value to the presence of a gearbox. :)

Allanp said...

8868 all the way! Even tho it's 20 years older it's still way better, far better playability for the kids, far more authentic mechanisms for the adults and even sounds better too, all thanks to pneumatics! The sooner TLG dump LAs the better! BTW everyone always mentions the boom on the 8421 falling too fast, the only time that ever happened to me was the very first time I lowered it. After that I learned to use a tiny (not expert!) amount of skill when operating the valve! And I always use very powerful compressors with high flowrates and my pneumatics have always been very controlable. So to TLG, scrap LAs and give me more new pneumatic parts, and you'll get more of my spending money ;)

Alex Campos said...

@Fernando Correia: actually, when I was about to shoot the videos, I noticed that the 8868's performance was extremely poor, a lot poorer than I remembered. I found out that the rubber belt on the compressor kept slipping, and, upon partial dismantling, saw that it was almost disintegrating. After a trip to my workshop to get a fresh belt, the performance jumped to what you can see in the videos. The engine still uses the original belt, and that's why the cylinders never moved. ;)

@Allanp: that's exactly the problem with pneumatics: you have to control them carefully. And, after the arm on the 8421 (or the 8868, or any other) reaches the position you desire, any change of load (for example, if the 8868 drops the log) will change that position. None of those happen with LA's. Like I always say, pneumatics and LA's have their applications and I'm glad both exist.

Unknown said...

Awesome to see this, I used to have the 8868 myself when I was a kid. Shame I can't view your vids, they're set to private :(

Alex Campos said...

For some reason, all videos I uploaded older than my latest got set to private! I've made them public now, thanks for the heads-up. :)

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