[TC20] 8460/8431/8438-B Truck with Knuckleboom Crane

[Wiseman_2]

It's been a long time since I've entered a contest here, but when the theme was announced I just couldn't resist giving it a try. The model I've chosen is something I've wanted to remake for some time and this contest was a great reason to push it up my project list. I did briefly give some consideration to other sets (notably 8414, which was the first Technic set I ever got), but in the end I decided to go 8460/8431/8438-B - the first appearance (as far as I am aware!) of a knuckleboom crane in a Technic set. Trucks with cranes are a staple of Technic, but there have only ever been two folding knuckleboom cranes as far as I am aware (I'm sure somebody will correct me if I'm wrong), and the original is one of my favourite B-Models.

While I would have liked to get this topic going to show WIP earlier, I honestly had no idea if I would find the time to finish it (working in a hospital in the middle of a pandemic will do that for you). The model is now pretty much complete though, so here are a few preliminary photos. I will hopefully get some more cleaned up photos ready for entry (emphasis on 'hopefully').

I decided to go with the new tractor tires for this as they fit perfectly with the model's aesthetic. They are slightly larger than the originals, but I managed to keep the scale more or less the same because the tires on the original actually feel a little small.

The model's functions are identical to the original, including in their geometry (which was a real pain to get done because there a half-stud offsets everywhere):

• Front wheels steered via the roof light
• Individually controlled left and right side stabilizers
• Crane rotation via gear on left side
• Two stage crane, with pneumatic switches on the left side, with the pump mounted horizontally between the rear axles and activated by a lever at the back of the truck

And one additional function that is pretty much standard on every truck these days:

• Mini piston engine and spinning fan driven by dual rear differentials

The original model does include an engine of sorts, but it is non-functional and only for display.

The pump was particularly annoying to fit in, since in the original it goes right between the two rear axles. Here, it is mounted above them to allow space for the differentials, but this meant there was less space for the lever that would move the pump. It therefore uses a linkage to allow for the full pump stroke in a more compact space.

I was not sure whether to go with panels or not. The rear bed would definitely use them were it to be built today, and there really isn't any way to replicate the brick-built sides of the original in a clean way using studless building; I've therefore added doors and a hood to the engine, which I think completes the looks a bit better.

Some comparisons with the original model:

I tried (successfully I think) to retain the aesthetic of the original engine, while also making it fully functional in the same space as the original.

 

 

There have been some really great entries so far (as there always seems to be). I'll try get a few more photos up and get it entered.

 

 

Edited July 27, 2021 by Wiseman_2

[Maaboo the Witch]

Oh, this is simply amazing! A faithful update of the original and it looks so cool! 

[GerritvdG]

Yes, this is very well done! Extra special because it was one of my chilhood sets.

I'm curious about the pump-solution... the original solution was already very smart, a photo of the bottom of the truck would be nice! Also the mini piston engine is a nice extra, would love to see a video of all the function.

Just enter the contest with these images! 

[howitzer]

Very nice and faithful to the original by the looks of it. Some WIP photos or photos of the internals would be nice, as just seeing the completed build hides a lot of the more technical aspects.

[Erik Leppen]

This is a great model! A real contender, and maybe the best use of those new wheels I've seen so far :) Super recognizable model of one my personal favorite set (at least of its B model) :) I think the way you did the paneling is really nice: not too much but it has panels where it needs to. I like how simple it looks - it's a sign of good design if it looks simple.

One thing that always bothered me about the original is the slanted roof; your model fixed that :)

The outriggers are maybe a bit too similar, but they're effective, so yeah :) Also I'm not so sure about those cams in the middle of the crane arm - it doesn't look too strong there. As far as extra functiones goes, a tilting bed would have been a nice extra. But it's plenty functional as it is. The addition of an engine is a nice feature, but as others, I'd really like to see more of the internals. How did you route all the functions, how did you make the pump work, etc. Maybe a shot from below is the easiest way of showing a bit of the functionality.

[Wiseman_2]

Thanks for your comments everyone :)

I didn't take many photos of WIP for this one as I normally would, because I'm a pretty slow builder at the best of times (my last project took 18 months and I still haven't shared it yet), so I wanted to focus on the build in the little time I had. The only photos I did take in progress were before I made substantial changes, so I would know what to revert to if the change didn't work... so the only WIP photos I really have are of elements that didn't actually make it into the final model.

Fortunately the bed is easy to lift up, so here are a couple of shots to show how the pump is connected. You can also see on the left the worm gear mechanisms for the stabilizers and the turntable rotation, and the blue hose that connects to the pneumatic switches:

The yellow 1x4 liftarms are connected to the top of the pump, while the grey beams are then connected to the lever at the back. The white beams then stick out at an angle from the back of the bed as the lever that you press. I would have liked them to remain flat but the only way to get this to work and keep the pump beneath the bed was to have the switch at an angle (I tried a lot of different things and was very close to just having the pump sit upright in the cab). This side-on shot shows how the linkage is connected:

It was a rather tight squeeze and there's exactly enough room for the swing of the pump that it doesn't touch the 20T gears connecting the differentials.

The pneumatic hoses are routed under the turntable in pretty much the same way they are in the original, and like the original, there's really very little room (I always underestimate how much space is needed for pneumatic hoses) - unfortunately the structure almost completely blocks any view from outside, but there isn't much to really show inside other than the hoses anyway:

And as requested, here is a shot from below:

This probably doesn't show as much of the internals as you might have hoped, because there are frames from front to back. I had thought when making the studless conversion I would have used 6 to 7 studs for the center of the chassis, but the new tires were too wide, and so it's actually 6 to 5 studs (at least at the axles) and consequently relies on beams running across the top and bottom of those frames for structural stability. At the front you can see the 20T gear that drives the engine; it is mounted just in front of the axle as placing it at the front of the vehicle (like most sets) would have extended the whole front grill and subsequently looked a bit out of proportion.

18 hours ago, Erik Leppen said:

Also I'm not so sure about those cams in the middle of the crane arm - it doesn't look too strong there.

Yes, I did try a few different methods here, but the cams are necessary as the beam in the original is 10.5 studs long, and those cams were the best way of achieving that here. They are sturdier than they actually look and are well braced; maybe it wouldn't be sufficient on a more heavy-duty build but they are more than sufficient here. I think if I had more time I would have tried to find a solution that would allow it to fold without the half-stud offset.

[Pattspatt]

Wow - well done! I wasn’t aware of this B-model until your post, but it’s a great choice. The linkage that you found for the pump is superb. Thank you for walking us through the internals!