Building a tiltrotor aircraft using Circuit Cubes [Review]

We’ve occasionally reviewed non-LEGO products on The Brothers Brick, by BrickArms, BrickForge or Citizen Brick for instance; companies that provide accessories for LEGO builds. A new kid on the block is Circuit Cubes. Instead of (accessories for) minifigures they make LEGO-compatible building sets and components, such as electric motors, aimed at teaching STEM subjects to children. They got in touch with me after reading my article on building a remote-controlled vehicle with LEGO Power Functions. They sent me several of their products in return for providing them with feedback. The sets themselves don’t interest me all that much. However, I would like to know how the Circuit Cubes components can be used to enhance my LEGO models. And this may interest those of you who want to motorize your own models too. So, this is not a traditional set review. Instead, I’m going to tell you about Circuit Cubes and how I used them in my own custom LEGO model: an XV-15 tiltrotor aircraft.

A tiltrotor is an unusual flying machine, but the basic idea is simple: with its rotors facing up it can take off and land like a helicopter; with them rotated facing forward they serve as propellers, with the aircraft’s wings providing lift. So, unlike a normal fixed-wing aircraft, a tiltrotor can land in tight spots or on small ships, but in forward flight, it is faster and more efficient than a helicopter. In practice getting this concept to work was difficult, but the Bell XV-15 TiltRotor Research Aircraft first flew in the late seventies and demonstrated that a practical and controllable tiltrotor was viable.

The challenge when building my RC vehicle was hiding the LEGO motors, battery box, Power Functions IR receiver, and what seemed like 2 meters of wiring. I could only fit them inside by building a van with quite a lot of space inside. Because of this experience, two of the Circuit Cubes immediately caught my attention: the Bluetooth Cube and the Cubit. The former is a rechargeable battery pack and Bluetooth controller in one. It has three outputs, remotely controlled via an app (available for Apple and Android). It is rechargeable using a USB cable. The Cubit is an electric motor. What makes these parts interesting is their small size. The Bluetooth Cube has a 4 x 4 stud top and is only two bricks tall. The Cubit has a 2 x 4 stud top and is also two bricks tall. This is much smaller than anything similar made by LEGO, with the exception of old 9V Micromotors.

Like many of my recent aircraft builds, the scale of my tiltrotor model is 1/40, suitable for minifigures. The real XV-15 is quite small, though, and space inside my model is at a premium. There’s enough room in the cockpit for a single minifigure. The Bluetooth Cube sits in the forward fuselage, just behind the cockpit. There the fuselage is slightly taller than it is wide and I could only fit the Cube inside by mounting it vertically. Its on/off switch can be reached by removing a panel at the top of the fuselage. The recharging port sits in the Cube’s side, which is why attaching the recharging cable requires partially disassembling the cockpit canopy and removing the pilot.

Each of the two engine nacelles houses a Cubit that drives the proprotor. The wires that connect the motors to the Bluetooth Cube run through narrow channels inside the wings and down into the fuselage. Allowing the nacelles to tilt required a little bit of slack in the wires, but one of the nice features of the Cubits is that they have ports for the wires on three sides, which meant I didn’t have to loop the wires to reach them. The wires and their connectors are a bit fiddly, but they take up little space. A drawback of having a motor in each nacelle is that the proprotors run at slightly different speeds. They too are driven using rubber bands and tend to go out of phase. On real tiltrotor aircraft a shaft connects the proprotors, to synchronize them, but there is no space for that in my model.

A third Cubit sits inside the aft fuselage, just behind the main wheels. This drives a worm gear via a rubber band and pulleys. The worm gear in turn drives a shaft inside the wing that tilts the nacelles and proprotors. I am not a complete novice when it comes to Technic building, but coming up with this mechanism required a fair bit of trial and error. I also had a video chat with some of my collaborators for BrickFair Virginia. This is something we’ve been doing every month or so during the pandemic. Their advice was invaluable and the mechanism works flawlessly. The rubber band prevents the motor from stalling or the mechanism from tearing itself to pieces when the nacelles reach their extreme positions.

Installing the Circuit Bricks app on my iPhone and getting it to connect to the Bluetooth Cube was very easy. The app has a “tinker” mode, in which you can control the speed and direction of the individual motors separately. Controlling two motors together, which is what I want for the proprotors, is possible using a “gamepad” controller in the app, but this does have the drawback that letting go of the control stops the motors. I have yet to explore all of the options, though. For instance, apparently, it can also be set up to switch motors on and off at predetermined times. The Cubits are small, but they work really well in this model. Spinning the proprotors doesn’t unduly tax them. The use of the worm gear lightens the load on the Cubit that powers the tilt mechanism. Circuit Cubes also provided me with two larger Cubes with motors. One of these has the same motor as the Cubit, but its larger housing includes a gearbox, to increase its torque. The other motor itself is larger, which suggests it is a bit more powerful. I intend to find out what they can do in future models.

I didn’t have to compromise too much on the model’s looks to include the functions. The nacelles are a bit too large and I could have given it thinner wings if I wouldn’t have had to include space for the wires. But everything fits and works. Using non-LEGO elements isn’t everyone’s cup of tea, of course. However, the Circuit Bricks allowed me to motorize a much smaller model than could be done using  LEGO elements. And thanks to this, my tiny tiltrotor is a much cooler model.

The Bluetooth Cube, two Cubits, the wires to connect them, and a USB recharging cable are included in Circuit Cubes’ Bluetooth Upgrade Kit.

Circuit Cubes sent The Brothers Brick examples of their products for review. Providing TBB with products for review guarantees neither coverage nor positive reviews. Circuit Cubes is an advertising partner of The Brothers Brick. Advertisers have no influence over editorial content.

5 comments on “Building a tiltrotor aircraft using Circuit Cubes [Review]

  1. Eugene

    I wish they (circuit cubes) had a hand-held stand-alone controller. It’s interesting info otherwise.

    What’s the range of the bluetooth receiver in the kit? If I build a car with this kit, will it be out of range when it’s 20 feet away?

  2. Mad physicist

    I didn’t check the range when I was building the model. However, I did a wholly unscientific test in my house this evening and with a direct line of sight to the model, it was still responding to commands from about 20 ft away. I actually had to go down two flights of stairs and was walking to the diagonally opposite corner of my house when the app indicated that it had lost communication. That’s at least 30 ft in a straight line through two concrete floors.

    Obviously the range will depend on the signal strength of the phone and on the surroundings. Lots of other devices nearby that are using Bluetooth will probably decrease it.

  3. Eugene

    @Mad physicist. Thank you for checking. I think I will get the kit… Jayson of JK Brickworks recently built a nice monorail using Circuit cubes:

  4. Mad physicist

    I know circuit cubes has reached out to a number of builders, many of whom are far more accomplished than I am at including motorization in their builds.

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