So You’ve Decided to Build a Killer Robot…

For those of you who attended BrickCan 2018, you probably spent some time watching a big plexiglass case with LEGO robots battling each other built by WilF.  If you saw it and thought this looks like fun, and want to build your own for BrickCan 2019, then read on….

The rules are posted on Facebook: … 549021114/



This is going to be a comprehensive guide to beginning your adventure into destroying other people’s Lego by means of robotic combat. Here, I will be going over the basics of design and thought process, as well as a little of what I’ve learned over the past year.

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The Controller:

Let’s start with the brains of your robot and their effectiveness. To build a competitive machine you will need a micro controller that is capable of performing the tasks you want it to do. Let’s go over some of your options:

-Lego IR receiver: Lego’s previous generation controller for their Power Functions peripherals. It uses infrared to communicate with the user. It is capable of performing basic tasks but is susceptible to interference given off by fluorescent lights. It is also held back by a limited number of channels and the receiver must be visible to the user’s handheld control at all times. Its range is also limited to 15-25 feet and or even less in convention settings.

-Lego Powered Up: Lego’s new generation controller platform. At this point in time, Powered Up shows promise for the future of Lego robotics. Powered Up uses Bluetooth to communicate with the user’s controller or smartphone. It is compact, has an on-board power source and is not hampered by range or interference, unlike Lego’s previous generation IR controller. However, the only motor available for Powered Up is a motor equivalent to Power Function’s M Motor. Powered Up also only has two slots for peripherals which makes Powered Up useless for building a robot with two drive motors and a weapon motor. Powered Up-compatible motors also have new plugs which cannot be stacked on a single socket, unlike the old Power Function motors. Until Lego releases a socket splitter, then Powered Up is all but useless.

-Third party controller, “SBrick:”


The Sbrick is an extremely capable Bluetooth controller. It communicates to the user by smartphone app. It is Power Functions compatible. It receives power via a PF battery box or any power source that is PF compatible. It has four plug sockets on top and one power socket on the bottom. The Sbrick’s circuits are limited to approximately 11.6 volts at 2 amps.


The app is an extremely customizable way of building a control scheme for your machine. You may build your custom control scheme via their website or choose from a variety of premade control profiles. Follow the jist of these steps to get things working
1) Log in or sign up to
2) choose the aspect ratio of your phone screen that your control profile will be used upon.
3) place your sliders, joysticks, etc and save when done.
4) log onto the sbrick app on your phone, add your controller and then assign the appropriate SBrick motor sockets to your sliders, joysticks, etc.

Pro-tip: If you want to use the joystick to controller a tank drive, rotate the joystick placement in the designer phase by 45 degrees.

It is also possible to control SBrick with a game controller … gaming-pad

-Third party controller, “BuWizz:”


BuWizz is a polarizing controller among the community. It is a fairly recent addition to third party Lego controls. BuWizz has a lot of bugs to iron out, assuming they’ll ever iron them out. Its control interface is clunky. Customization is shallow and not nearly as in-depth as that of the SBrick. For instance, there is no way for you to be able to efficiently control tank drive by joystick through means of interface customization. The price point is also a massive downfall. At $200CAD, it’s a large financial investment to put down on a toy controller.

That being said, the devs behind the BuWizz have a clear set of intentions that are quite frankly, insane. Let’s run some bare numbers about the capability of this thing. The BuWizz has an on-board power supply that is a god damned 12 volt Lithium Ion battery. Its maximum output is 4 Amps of current. For those of you questioning whether or not that is a lot of power, yes. Yes it is.


To put into perspective, a Power Functions battery box runs somewhere in the neighbourhood of 7.4-7.8 volts with NiMH batteries, 9 volts with NiCd batteries. The Power Functions LiPo box runs at about 7.4 volts. All PF battery boxes have current limited to approximately .8 amps before thermal overload protection trips. We should also consider that Lego rates their motors to safely run between .5-.7 amps, and should not exceed 1 amp of current. So when you’re dumping that much current into Lego’s motors, well, you’re gonna do things with Lego that it may not have been specifically designed for, such as getting a weighted disk to whip around at a couple thousand RPM, moving from the category of “children’s toy” and more towards “potentially dangerous weapon.”


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There are two things to consider when investing in your controller.

The first one is price. These things can be heavy financial investments. An $80 SBrick costs a little bit less than a $200+ BuWizz. While I only mentioned these two as hardware recommendations, there are other third party controllers out there that may be cheaper. You may even go the route of buying an RC controller or an Arduino. It’s only through personal experience and ease of setup that I recommend the SBrick and BuWizz. I know the Pfx Brick is a preference for some, but I haven’t used it because I don’t believe it suits my needs.

Secondly, consider what sort of robot you want to build. You may find that what you want to design is limited by the controller you’ve bought. Do you want to build a robot that has a passive weapon or an active weapon(a weapon that is only used at the user’s discretion, versus a weapon that needs to be constantly turned on to be effective)? Do you want to design a robot whose strategy is centered around driving/maneuvering or kinetic energy? A robot that uses a clamp to grapple an opponent may use less electrical power than a robot that uses a spinning blade, and may require a controller that gives the user a superior control interface rather than sheer explosive energy.


This section I will be going over some of the strengths and weaknesses of Lego Motors to the best of my knowledge. I am going to focus on the Power Functions line of motors because they are the most easily accessible and because I am most experienced with the PFs. If you are looking for extremely in-depth charts and power tests on the motors, I’d direct you to this website:

Have a look over the page. It’s an extremely useful resource for everything past and (nearly) present for all things Lego motors. In fact, check out the whole webpage

-MOTOR 5292 Buggy Motor:


Okay, I did say I’d be focusing on PF motors, but 5292 is the supposed Power Overwhelming of all motors that Lego has ever produced.

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This thing is so power hungry that the modern standard power sources cannot even adequately feed it the juice that it needs to run at peak efficiency. At its base output, it runs at 1000rpm+, compared to say, the PF motors that run base in the low to mid hundreds. I myself have zero experience with this thing, so I cannot personally verify the claims that those on the interwebs have said about 5292. I also cannot personally speak for its speed to torque ratio, either. What I do know is that I cannot be bothered to put out $90+ for a used, approaching twenty years old motor that does not have any sort of overload protection and might cook itself in an instant if put in the wrong situation. If you can manage to get a hold of one of these motors, cherish it. Its notoriety as an unprecedented and legendary Lego part makes it more of a collectors item rather than something you’d want to dump into a scenario where you risk destroying it. On the off hand that you are considering using it, consider the following points:

Advantages of 5292 Buggy Motor:
-Essentially God Mode
– ∞ RPMs
-Will tear hole in space-time
-Underpowered if used with standard, currently available Lego Power Sources. Third party power sources required.
-$90-$130CAD for a used one
-16 years old
-No built-in thermal/current protection
-Unverifiable statistics to tell if it’s a viable motor in robot combat

-MOTOR PF Medium:

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Something you need to consider when designing a fighting robot is its weight as a finite resource. In all robot fighting competitions, classes are limited by weight. Because of this, you should think about how you’re attributing weight to your robot’s subsystems. How strong do you want your drive and weapon subsystems to be respectively? If you want to build a control robot where you are focused on outdriving your opponent, you may want to add bigger and more powerful motors to your robot’s drive. On the other hand, if you want to make an extremely powerful weapon, you need to dump more weight into the weapon drive.

This is where the M motor comes into play. It is the lightest out of the three PF motors at 31g, but it is also the weakest. Ungeared, it delivers the most rpm in the PF line, but is also susceptible to being overworked quickly and cannot move heavy loads without gearing it down.

Advantages of the M motor:
-lightest at 31 grams
-physically takes up the least volume/smallest footprint
-highest direct rpm
-lowest current draw
-Lego stud mounting base
-Susceptible to overheating and dying during overusage
-somewhat underpowered. Useful only in specific applications.
-Only 4 Technic mounting points

-MOTOR PF Large:


I’ve found the L motor to be a decent balance between torque, speed and weight. Additionally, it also has 14 mounting points–the most out of any of the PF motors.

Advantages of the L motor:
-significantly increased performance in every way over the PF M
-14 Technic mounting points
-42 grams
-Not good enough to be used for kinetic energy weapons
-Can be a power suck. If this motor stalls, you risk tripping the thermal overload on your battery box.
-For some reason this motor costs more than the XL motor



It is possible to mistake the XL motor as the weakest because its rpm is the slowest. This is not the case. The XL motor is by far the strongest of the PF line and quite possibly the best motor Lego has produced. This motor needs to be geared in order to be used properly due to its rather low RPM. A single XL Motor can be geared up to 1:7.5 to give you an excess of 1000rpm+ with a weighted load. For instance, Lego Nightmare is geared to 1:7.5 while pulling a 180 gram, 20 stud wide disk with ease at approximately 1350 rpm at 4 amps. I have tested an M and an L motor with the same 1:7.5 gear configuration. Both the M and L struggle with that load compared to the XL.

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If you combine two XL Motors, you can gear them to 1:15.At that point you start moving into the physically dangerous weapons territory of things.

Kinetic energy weapons are not the only application XL motor can be used for. I use one on a 1:1 gear ratio on a lifter and 2 XL Motors on a 1:4 gear ratio to power an overhead swinging hammer. If you can manage to allocate weight and space into your robot design, then the XL is for you.

Advantages of the XL motor:
-Most versatile motor and has multiple applications
-Highest amount of torque out of all three PF motors
-69 grams. One of the heaviest Lego motors and the heaviest PF motor
-Very bulky. It’s nearly as wide as it is tall. Its overall shape and placement of mounting points makes it hard to place into a machine.
-Gearing this motor to fit your application is going to take up additional space
-So power hungry you can only attach two to a single modern Lego battery box at once
This concludes the primer to basic electronics in regards to their usage in Lego robot combat. In the next part, I’ll go over the thought process on designing your fighting machine from the ground up.


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