What is a LEGO GBC (Great Ball Contraption)? Review Time-lapse Fire Rescue First Responder to GBC 34

What is a LEGO GBC (Great Ball Contraption)? Here we review LEGO Fire Rescue First Responder set 42075 and see it converted to a Great Ball Contraption module. This is done through FREE instructions produced by PV-Productions: “GBC 34 Tilt Lift Workshop Module”.


A time-lapse is shown of the breakdown and build of this GBC module. I also have a subtle design tweak which I think improves the module.

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Transcript from the show:

G’day Everyone, Matt Elder here and today I’m going to review turning this Fire Rescue First Responder Lego set, 42075, into this Great Ball Contraption module. The second part of this video has a time-lapse breakdown and build of this.

What is a LEGO GBC?

First you might be wondering, “What exactly is this I’m looking at, and what does it do”?

This is a single unit which has an entry point for these little balls, and then moves them along to an exit point. You join a number of these modules together, so it forms a continuous loop. Thus, balls move along the system in perpetual motion.

This is a sub-genre of LEGO building called the GREAT BALL CONTRAPTION, or GBC for short. My apologies to any purists out there, I’ve only just discovered this so might be butchering any explanation.

Online Instructions

I was looking around on the internet and discovered PV-productions.com . They happened to have free instructions on how to convert this First Responder set to a single module. My son only recently got the set and thought this would be an easy entry point, he was also very excited at the idea.

We have some of the larger technic sets PV-productions make into more elaborate GBCs so thought this would be a good  chance to see the quality of their instructions. Their instructions were reasonably easy to follow, although a couple of steps weren’t super clear. The build is probably a medium Technic challenge.

Rather than constantly having to feed balls in, you can bring this boom piece across. Thus, the motion will continue with a set number of balls in it, and is quite rhythmic to watch.


Now for the time-lapse on how the model was broken down and built.

First up we must break down the Fire Rescue First Responder vehicle. I have a trades screw box and some plastic bowls off to the side to sort pieces into. This just helps when building the model to find pieces rapidly, as this isn’t exactly coming in the standard numbered bags out of the box.

I’m always amazed how people can come up with the alternative MOC models with the fixed number of pieces in a given set. I would love to know the thought process or what critical elements of the build get done first. This even manages to use the engine blocks and pistons. Very cool.

Wheel Positions

One of the things to appreciate with this build is the wheels don’t actually rotate. One set of wheels also need to have enough clearance so can slide up beside part of the frame. This was a little hazy in the instructions and can be difficult to tell where exactly the wheels should sit.

I found the more angle you could get on the moving ramp, by adjusting the wheel height, the more likely the ball would be pushed along to the exit point.


You can hand crank the ramp, but you really do need a separate power functions motor, which we had but doesn’t come with the First Responder set. As at time of recording, November 2019, you can still get these motors but believe in a couple of months, they will be retiring the motor.

As our first attempt at a Great Ball Contraption module, we think this came out rather well. The kids spent a fair bit of time tinkering around with it and they have been asking questions around gears and seeing the inner workings.

Also being kids, they have been sticking their fingers into the gears, and finding out the gears that will hurt. They have loved loading up the balls … and sometimes chasing them around the room when they overloaded.

Thoughts on Instructions

The PV-productions instructions are pretty good in the main but you really do need to watch the orientation of the build as you go. Having made some of my own instructions for builds, I know how fiddly it can be to make instructions.

There are around 70 steps in the instructions and will take a solid couple of hours to build. They even include a little piece to build, to put on your power functions on/off switch. This blocks the switch being turned to the wrong direction. The gears can go in both directions, but only 1 really works to get the ramp action working correctly.

Design Tweak

There is one design tweak I would make. There is a gap here where balls can get stuck. Looking at PV-productions promo video, they have balls that get stuck in there too. It just creates a little pocket where balls can sit and restrict the general flow across the module.

I discovered you can just roll this piece over here on either side, and it creates enough of a barrier, balls can’t get stuck in there anymore.

PV-Productions also password lock the PDF file. While I get this in terms of protecting their IP and the time and effort that goes into these, when every page has your email address on it, it is a little annoying. I also found my Chrome downloader manager corrupted the PDF so had to download the file normally – first time I’ve run into that problem.


This was fun to do and really got the kids excited and engaged. Will be checking out more of PV-Productions instructions and more of these Great Ball Contraption modules.

That’s it for another video and please give a like if you found useful. Here are some other videos that you might find interesting. You’d be a superstar if you subscribed or share this video, as it helps us keep producing more videos. Happy building until next time when we talk about all things LEGO.

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