LEGO Technic 8421: Mobile Crane

Technic Lego lost its way over the past years and this set marks a return to form. I think it is one of the best sets ever produced.

The model is made in 2 sections: the main body and the crane itself. The body is packed with features including 6-wheel steering, working outriggers and a V6 engine. The steering geometry is perfect and allows for tight turning circles. The crane features a motorised boom that telescopes twice, utilising the longest technic axle ever produced. A clutch mechanism from the old supercar series allows the motor to extend the boom and drop the crane hook, or operate the hook independantly. The motor is from the now discontinued indoor radio control sets and seems to be the standard technic motor, having seen the 2006 sets. Two pneumatic cylinders in series lift the crane boom.

The instructions are clear to follow, taking up two sizeable books but I made several mistakes with the crane boom before I got it right. The string tends to tangle in the crane body if the crane is operated under no load, and the pneumatics drop the boom too abruptly- a minor modicifation is necessary to stop this happening.

Overall this is an extraordinary set and deserves a top rating.

This has been listed at 200 pounds for a long time on Amazon via resellers - however you can buy it for 100 pounds direct via mail order from the Lego store at lego.com. So don't waste your money...

I'd seen this set in a toy shop in Gibraltar in '06. It was priced at £64.00 & I'd toyed with the idea of shipping it back to the UK, but at a shipping weight of almost 4kg the cost was too high. I managed to find one in a discontinued sale for £85.00 delivered, so the kids bought it for me for Xmas.

I spent a couple of four hour sessions on it, then possibly another couple on tweeks. The sheer size of the thing is daunting, with bags of yellow & grey everywhere - 1884 pieces in all. You need to be organised, have a large, clear workspace & don't try to do much in one go - I recommend plenty of coffee.

There are quite a few repetitive sections, but once you've done the first, they're easy. The completed set is impressive - it's about 18" long, the boom extends over 2' & it weighs over 2kg. The boom extension is motorised & by moving a toggle switch, the hook raises/lowers using the same motor. There are three steerable axles which are turned by a flywheel at the back. Another flywheel raises/lowers the outriggers. The boom angle is controlled by a pneumatic (toggle)switch, which also lowers the boom.

Overall its a very sturdy build (my eight year old son is Autistic & regularly plays with it. So far nothing has come adrift apart from the string holding the hook becoming entangling around the winch)

However, there are couple of niggles. The turntable is turned by hand, it would have been good to have had a turnwheel to do this. But the biggest issue is the the pneumatics working the boom. I actually have two problems with it. The first is that the air leaks out of the system over time so you cannot display the model with the boom in an upright position - over a period of hours, the boom will descend. The second is that when you release the air from the boom via the toggle switch, the boom comes crashing down - there is no way of a gradual descent. There are a few mods of varying complexity which can reduce or correct this issue. They range from adding another pneumatic switch & connecting it into the system, locking the boom in a raised position, fitting double pneumatics or, as I have seen on one forum, fitting a direct motor drive to the bottom of the boom. Check out technicbricks.com & eurobricks.com - there are quite a few ideas there.

It's not perfect, but it's one of the more interesting builds in terms of complexity & functions. Try & pick one up second-hand if you can