Adding knees to The LEGO NINJAGO Movie 70615 Fire Mech

Brick Fanatics takes on the project of adding knee articulation to The

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Movie 70615 Fire Mech – how does it work out?

When fans across the 

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community first got their hands on 70615 Fire Mech to review there were common themes (with the Brick Fanatics review reflecting many of them). The set is awesome, its towering height is amazing and the fact that a mech with this many parts exists is a dream come true.

The drawback being that the knees are not articulated – that mid leg rigidity was commented on time and time again, and differentiates The LEGO


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Movie mech from a lot of previous offerings. Naturally this got the team here at Brick Fanatics wondering if the set could be modified to include the missing articulation. The answer to that question is a resounding yes, and truth be told it is not even that complicated to do. However, the result quickly reveals why the LEGO Group omitted such a feature in the first place.

Fire Mech Leg MOD-5

In making this modification to the Fire Mech I chose to try and mimic the structure of the leg as included in the original set as closely as possible. This is not a requirement, more changes could be made – the only part I would consider non-negotiable is the large hinge known as the Technic Rotation Joint. In order to insert this fairly substantial piece I enlarged the leg by a length of six studs so that it could both be inserted and still maintain a full range of motion.

Upon completion of the upgrade I was initially delighted to find that it worked exactly as expected, allowing for a much more realistic range of articulation that such a vehicle would need to actually walk. However, this was quickly tempered by confirming all the reasons I am sure the LEGO designers went for static legs. Bending the knee significantly shortens the length of the articulated leg.

70615 Fire Mech, as released, is already tall with a high centre of gravity – those six studs that I added did not help in this regard. With a shorter leg there is absolutely no way to get the vehicle to stand up on its own; cool poses require constant support by a hand or other secure structure. The result is a complete elimination of any options for posing the mech. In this regard the rigid legs as designed in the official set make sense as play and posing, while not as dynamic, are actually possible.

In the end this was an interesting exercise in reverse engineering the LEGO Group’s decision making. I would not be surprised if early prototypes of this model included the articulation I added, but eventually the design process saw it removed for the reasons I discovered along the way. If anyone is able to figure out how to do this conversion while maintaining the ability for the mech to stand on its own, please get in touch! I could not figure out a solution and would love to hear if our readers can find one.

This set was provided for this feature by the LEGO Group.

70615 Fire Mech is available from You can help support Brick Fanatics’ work by using our affiliate links.

The LEGO NINJAGO Movie features:

70617 Temple of the Ultimate Ultimate Weapon – Five Connections

The LEGO NINJAGO Movie set reviews:

70607 NINJAGO City Chase

70608 Master Falls

70609 Manta Ray Bomber

70610 Flying Jelly Sub

70611 Water Strider

70612 Green Ninja Mech Dragon

70613 Garma Mecha Man

70614 Lightning Jet

70615 Fire Mech

70616 Ice Tank

70617 Temple of the Ultimate Ultimate Weapon

70618 Destiny’s Bounty

70620 NINJAGO City

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When I was 3 years old my dad bought home 6659 TV Camera Crew as a gift — he had no idea what he had just unleashed. Three decades and no dark age later, I am still going strong. My love of LEGO led me to a career in Civil Engineering and I am now raising three budding LEGO lovers with my lovely wife who is, bless her, a huge supporter of my brick addiction. When not writing for Brick Fanatics or fulfilling my duties as the U.S. Editor of Blocks Magazine I enjoy collecting, MOCing, exhibiting, as well as running, climbing and home improvement.

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