EV3 vs Robot Inventor: LEGO 51515 and 31313 sets compared

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This article has an in-depth comparison of MINDSTORMS 51515 Robot Inventor vs EV3 (set 31313). Are you considering an upgrade from EV3? Or maybe you want to get into LEGO robotics, and you doubt whether to buy an EV3 set on sale or shell the full price of a shiny new Robot Inventor set. Wonder what to buy? Find out here what the differences are between EV3 and the new 51515 Robot Inventor set. 

People will be calling this LEGO set ‘teal MINDSTORMS’ or ‘MINDSTORMS 5’ or ‘MINDSTORMS 515’, which is short for the set code. Maybe the name ‘Robot Inventor’ takes hold. Time will tell. In this article, I’ll refer to the sets by their set numbers. The numbers are short and easy to remember.  

The Robot Inventor set has many improvements over the 8-year-old EV3 set, but it will be the costlier of the two. Retailers are getting rid of their EV3 stocks because it’s end-of-life. I’ve seen EV3 on sale for less than EUR 300. When I wrote this article, a quick Google search for ‘51515 Robot Inventor’ showed prices between EUR340 and EUR 380.

Robot Inventor, for its higher price, is not all sunshine and rainbows either. The set has its shortcomings. Is it worth the extra investment? As a member of Robotmak3rs, I received a preview box to evaluate. Read on to find out whether I think the new 51515 Robot Inventor set is worth it.

EV3 vs 51515 Robot Inventor: hub size
EV3 Intelligent Brick next to his smaller Robot Inventor brother

The 31313 and 51515 cardboard boxes compared

Like all LEGO boxes, the set number, set name, and suggested age is here in the top left. The age recommendation is still 10+. 

The graphics of the 51515 are very different from LEGO technic and the previous MINDSTORMS. The black and bright colors give the set a bit of an 80’s retro-cool look. The overall feel of the 51515 seems friendlier and more unisex than the more aggressive style of the EV3. Sizewise, the box is the same as the EV3 box. 

The new set doesn’t have a playmat wrapped around the box. This does not feel like a significant loss because the EV3 playmat was pretty much useless. The best use I found was cutting it up and using at as a sail for my LEGO MINDSTORMS land yacht.

The practicality of the Robot Inventor box
The Robot Inventor box is practical for storing parts and half-build models

The 51515 box has one great advantage: it opens from the top, making it reusable. You can pour your parts in and store your half-built robot ideas.

Winner of the box and packaging comparison:

51515 Robot Inventor

A usable box vs. a useless play mat. Need I say more?

The new Robot Inventor hub compared to EV3

A green SPIKE Prime hub

As you’ve seen in all of the previews, the new MINDSTORMS hub is basically a green SPIKE Prime hub. This means we get a built-in gyro and accelerometer. With the internal six-axis inertial motion unit, you can sense the orientation of the hub. It can also detect taps. You can also read out its rotational speed over 3 axes. The 51515 hub runs a different firmware than 45678 SPIKE Prime. You can recognize it by the first icon after booting. SPIKE shows a heart, MINDSTORMS shows a play icon.

The biggest improvement: smaller and lighter

The new Robot Inventor hub is quite a bit smaller than the EV3 hub. It is much lighter too! At 147g, the new hub is almost half the weight of the 284g EV3 hub. This means it will be easier to build: you don’t need to add so much plastic for a robot to support the hub. Especially for walking robots, this will be great. I remember struggling a lot to get my blue dragon walking because everything was so heavy. 

51515 Boots instantly vs. 30 seconds on EV3

Starting an EV3 brick takes 30 seconds with the official LEGO firmware. Staring it with ev3dev, the full Debian Linux takes a whopping 90 seconds! The new Robot Inventor hub goes from button press to fully usable in 7 seconds. That’s 4 times faster and it feels like instant booting. That being said, I’m very used to the slow booting of the EV3 brick, so I usually remember to power it on before getting coffee. Once it’s on, I don’t turn it off. This means the boot time doesn’t really bother me in practice.

Built-in rechargeable batteries are so much better than AA cells

Unlike the EV3 hub, this hub has a built-in battery! Yay! No more tedious charging of AA cells. It also has pinholes on ALL sides. Not just bottom, left, and right. 

Batteries for the EV3 hub and Robot Inventor hub.
No more endless charging of batteries. The new hub has micro-usb charging with a 2100mAh Li-ion battery

Drawbacks of the Robot Inventor 51515 hub

The new hub has its share of drawbacks.

  • The new hub will probably not support WiFi. There is no USB port to add a stick. The only way to add WiFi is probably through an extra CPU connected to the ultrasonic sensor.
  • Memory and processing power are minimal. David Gilday found it challenging to fit his Rubik’s cube solving Python code in the hub’s memory. He had to apply some hacks to make it work. Also, First LEGO League teams are hitting the memory limits of the new hub too!
  • The new hub does not run Linux like EV3. That is both a blessing and a curse. The absence of an OS means faster and more realtime sensor readings, in theory. The current LEGO firmware is still suboptimal and uses a lot of resources in the hub. So we don’t get much of the increased speed in practice. The cool thing about an OS like Linux is broad support for third party hardware. Ev3dev, for instance, now even features a voice synthesizer.
  • The 25-pixel display is only a tad better than the illegible EV3 display. The Robot Inventor pixel display isn’t very bright and you can’t change the pixel color.
  • There is no brick-to-brick communication. Advanced builders, who make robots with 8 or more motors, use several EV3 Intelligent Bricks chained together. Brick-to-brick is also nice for remote control. I, for instance, have built an EV3 steering wheel to control an EV3 racing car. Eric Steenstra did both in his massive remote-controlled tank, using 48 motors. This is not possible with two 51515 Robot Inventor hubs. Maybe third party firmware or an update from LEGO will fix this someday. But since this is such an advanced feature, I doubt it will be soon.

You can debate whether an on-board gyro sensor is always the best option. It was fine to make a monkey do 360 swings, but I would have been able to make Swingbot with a built-in gyro. The gyro needs to be on the wires to give usable readings for swinging.

Hub comparison winner: it depends.

The 51515 has an edge with its size and weight but is no clear winner

If you’re into the Internet of Things and like to hack with third-party hardware, the new hub is a step-down. For the average user, the new robot brain is a paragon of speed, weight, and simplicity.

EV3 motors vs. Robot Inventor motors

Compared to EV3, the new motors are much smaller, lighter, and more comfortable for building. I guess they will have less torque, but this won’t be a problem since your robots will be much lighter. Philo Hurbain’s website contains all the torque test data you need.

You get no less than four motors with the robot inventor set. I remember that with EV3, one of the first things I bought was another motor. So an extra motor is a big plus.

The new motors have an internal absolute positioning system. This means you never have to find their limits or zero positions when your robot boots. Thanks to its absolute encoder, the motor will always tell you where the little grey mark is when you start your robot.

Four motors with 51515 Robot Inventor vs. three with EV3
Four motors with Robot Inventor vs. three with EV3

The gearbox’s accuracy and internal slack for the 51515 motors are about the same as for the 31313 motors. The only problem with the new motors is that their position sensor is on the output. There is a gearbox full of slack between the electromotor and the sensor. This means you can’t hold a motor position with much force before the control loop starts oscillating. The motors are better, but they aren’t robot motor Walhalla.

Winner of the motors comparison:

51515 Robot Inventor

The new set has motors that are easier to build with. They are smaller and have an absolute positioning system.

EV3 removable cables vs. 51515 fixed cables

There has been a lot of debate about fixed cables vs. removable cables for motors and sensors. EV3 has thick removable wires with large plugs. You can create them yourself if you have the right cable shrinking tools. Robot Inventor has thin and flexible fixed wires. The plugs are a lot smaller too. If you break a line because your robot is rubbing and bending it too much, the only thing you can do is buy a new motor or sensor. 

EV3 wires and Robot Inventor wires compared
The maximum distance from the 51515 hub is comparable to the shortest EV3 cables.

Which is better? It depends. I’m personally in the fixed wires/smaller plugs camp. The reason is that I design a lot of models. Smaller electronic LEGO parts make my life easier. More flexible cables make my life easier too. They are easier to fold and hide. So far, I’ve never broken a wire, and I’ve never had to trash an electronic component. I’m cautious about limiting the stress on wires when designing robots. Only once did I have to scrap an idea because the wire lengths wouldn’t allow it. 

Furthermore, Technic Power Function 2 builders – who use the same plugs as MINDSTORMS 51515 – have been screaming for extension cables. If LEGO does not produce them, some third party will. So I’m reasonably confident that we will get extension cords at some point in time.

Winner of the cables and plugs comparison:

51515 Robot Inventor

Flexible wires and smaller components trump long, replaceable rigid cables.

EV3 IR Proximity vs. 51515 ultrasonic sensor

LEGO MINDSTORMS NXT – the white-and-orange one – used to have an ultrasonic sensor for measuring distances. In MINDSTORMS EV3, LEGO decided to swap that for an infra-red proximity sensor. With Robot Inventor, we’re back to ultrasonic measuring. I think that’s a good thing. Infra-red can’t ever give centimeter precision on distances. White surfaces seem closer than dark surfaces to the sensor. The speed of a sound wave is a more precise measurement of depth. 

EV3 proximity sensor and Robot Inventor ultrasonic sensor
EV3 IR Proximity sensor (left) and the new Robot Inventor ultrasonic sensor (right). Lights on!

Furthermore, the Robot Inventor set has four LEDs in the sensor eyes that you can control individually. That is great fun and adds a lot of character to your robots. On top of the LEDs and the increased accuracy, there’s an extra feature on the 51515 sensor: the plastic module’s shape is more comfortable to build with. It is boxier and has more versatile pin hole placement. Will you ever miss the IR beacon function on the EV3? Or the clunky IR 4-button remote? I think not.

Winner in the distance sensor comparison:

51515 Robot Inventor

The new kit has a better sensor, featuring lights and more versatile pin hole placement.

Robot Inventor Light Sensor vs EV3 Light Sensor

The EV3 light sensor could do colors, depending on its color reading mode. Red for reflected light, blue for color detection. In my blue dragon, I hacked the sensor reading mode to flicker different colors and make it look like fire breathing. The Robot Inventor sensor, like SPIKE Prime, has only one light color. It is a very nice night bright, however. You can use it as decoration or a headlight if you don’t need color sensing. The biggest advantage of the new sensor is it’s size and pin hole placement. These factors make it much more versatile.

51515 light sensor vs. 31313 light sensor
Winner in the light sensor comparison:

51515 Robot Inventor

The new kit has a more practical sensor, featuring lights and a more compact build.

EV3 touch sensor vs. Robot Inventor

The 51515 set ships without the SPIKE Prime force sensor. I don’t expect I’ll ever miss the force sensor. With EV3, I used the force sensor mostly for calibrating motor positions. If you want to make your robot interactive with buttons, remember that you can use a motor as a button. You can also tap the hub. It recognizes taps in three directions because there’s an accelerometer inside. Frankly, if I could choose a third sensor for the 51515 Robot Inventor, I’d choose one of these bright color sensors over the SPIKE force sensor anytime.

EV3 touch sensor and Robot Inventor motor with absolute encoder
One of the new Robot Inventor motors could serve as a touch sensor with some programming creativity.
Winner in the sensor pack comparison:

51515 Robot Inventor

I would choose an extra motor over a single-purpose sensor anytime, especially if it’s a small motor with an absolute encoder.

Number of frames in the 31313 set vs. frames in the 51515 set

I remember running out of 5 x 7 frames often when building with EV3. This was so frustrating that I bought the bucket wheel excavator. The reason? There was a HUGE amount of frames in that set. It seems that LEGO has listened to people like me. They have included no less than five 5 x7 frames. Not only that, that set also has the new 7 x 11 frames and the 11 x 15 frames. I like frames because you can build so quickly with them. They are pretty rigid and take parts from almost all sides. Frames are at the core of most robots.

Frames in the EV3 set (grey, left) vs. frames in the Robot Inventor set (black, right)
Winner in the frames comparison:

51515 Robot Inventor

More and larger frames are better. Hands down.

Signature parts in the Robot Inventor set vs. EV3 signature parts

The EV3 parts are pretty vanilla. Only the Bionicle swords would set EV3 robots apart. The new set has some pretty inspiring signature parts with the Duplo ball, the new differential gear, and the large white mudguards.

The 51515 MINDSTORMS is the first set to include a differential gear. Differential gears are built to improve turning performance on cars. But you can also use them to combine the output of two motors or create nifty automatic gearboxes. 

Signature parts of the Robot Inventor (left) vs. the Bionicle swords in the EV3 kit.

The Duplo ball will help kids to invent fun games. The large mudguards help give a robot character by integrating the complete robot design. Before 51515, the mudguards were only available in olive green on the 4×4 range rover. To me, they are inspiring parts. They look so lovely that you just want to build a robot around them. Could they be legs? Or maybe a mouth? Or a funnel?

Winner in the signature parts comparison:

51515 Robot Inventor

The new parts make me want to design new robots all the time.

31313 caster wheels vs. 51515 caster wheels

The MINDSTORMS 51515 set has these black beads with an axle hole for caster wheels. I feel that they will perform better than the EV3 caster wheels because you don’t run the risk of blocking any direction. If you ever used a shopping cart, you might have noticed that sometimes it doesn’t want to go where you push it because one of the wheels is turned wrong. That is OK when shopping, but it can derail your carefully crafted robot program.

Caster wheels in EV3 (left) and Robot Inventor (right) for use in a tank-steering wheeled robot.
Winner in the caster wheel comparison:

51515 Robot Inventor

Non-blocking caster wheels? Sign me up.

EV3 guns vs. Robot Inventor guns

I guess proper robots should have guns. EV3 featured Bionicle ball cannons. I liked them because they were easy to recharge, and you could extend the magazine to carry as much as six bullets. The new Robot Inventor set has Ninjago missile launchers. This part can do nothing but shoot. It doesn’t shoot very far, and I don’t like recharging them all the time.

EV3 Bionicle sphere cannon vs. Robot Inventor arrow launchers
Winner in the cannon comparison:

31313 EV3

With more ammunition and shooting larger distances, the EV3 cannon was definitely better.

Robot Inventor wheels vs. EV3 wheels

The new wheels are the same as SPIKE Prime. Luckily LEGO made these wheels black! My SPIKE Prime wheels tend to get this dirty really quickly. The light blue shows any dirt you pick up while driving.

These new wheels are just the perfect robot wheels. They are solid, so wheel diameter doesn’t change under load. This means you can drive with more accuracy. They also have a perfect diameter. Any smaller and your robot goes really slow without gearing. Any larger and the motors might not have enough torque to get your robot moving. They aren’t as wide as the EV3 wheels and have many more holes for pins. This makes them more versatile.

ev3 vs robot inventor wheels
EV3 wheel collection (left) vs. Robot Inventor wheels (right)

This box includes no less than six wheels! Mars rovers are now within your reach. Apart from the big wheels, there some small 23mm wheels for driving.

EV3 had rubber tracks. They look cool, but the stiffness of the rubber rendered them pretty useless for most robot applications. Wheels are just much more efficient and effective. The regular EV3 wheels were too soft, too small, and too wide to drive robots accurately. 

Winner in the wheels comparison:

51515 Robot Inventor

Solid rubber rounded 56mm wheels are the best LEGO robot wheels. Ever.

Comparing the generic LEGO Technic parts in Robot Inventor vs EV3

The 31313 set provided a respectable 606 parts. The robot Inventor set comes in at a whopping 946 parts! There is a lot of plastic in the box to build robots with. Below is a list with some attractive LEGO bricks in the 51515 kit.

  • The 3×3 cookie. This has long been a missing piece. I can’t believe I’ve been able to build so many years without this guy. It’s the perfect mini frame.
  • White panels. Covering your robot is simple, with so many plates. These white panels also serve as backup frames if you run out of them.
  • Turntables. Gun turrets, walkers, and segmented vehicles: all these robots use turntables. Expect AT-ST’s and other cool one-kit models with these. That part was also missing from EV3.
  • Pins. I remember running out of blue 3L pins with some EV3 builds. 51515 provides a comfortable amount of 82 blue three-length pins with friction!
Winner:

51515 Robot Inventor

With more and better parts this is an easy victory for Robot Inventor.

Build speed: Robot Inventor vs EV3

To test how quickly you can build with the new MINDSTORMS, I created a little car with a differential gear. Then I programmed it for remote control. I was impressed with the speed at which I could design and program a small remote-controlled car. In total, I was busy for less than an hour – and a big part of that hour was taken by firmware updates. The new 51515 building and programming system is way faster than EV3 because it is so intuitive. 

Watch the unboxing video below to see the RC car speed build.

After unboxing, you can see how quickly I got the first robot up and driving.
Winner in the build speed comparison

51515 Robot Inventor

Simpler, smaller, faster and easier to program.

51515 vs 31313 for remote-controlled robots

In my unboxing video, I tried designing and remote-controlling a small robot car. I was blown away by the ease of use of the 51515 software for this. The car was up and running in less than 20 minutes, including software updates and pairing devices.

But – and this is a big but – there was quite a lag between commands on the remote control and the robot car’s response. This is OK for slow vehicles, but I like to build race cars and remote-controlled sentry drones. Those types of robots need fast and accurate controls. I believe people are working on reducing the lag. I will keep you updated on this blog and on my YouTube channel if I find ways to reduce the lag on the 51515 Robot Inventor set. 

Remote control options for your LEGO MINDSTORMS robots: IR beacon and PS4 controller

EV3 has always performed admirably with remote control devices. The response is snappy, and you can connect PS3 and PS4 controllers directly to the brick, no computer in between. I’ve even been able to remote control it via a web interface through WiFi.

Winner:

Robot Inventor has a slight edge for ease of use

Ease of use is important for most applications. Realt-time controls are essential high performing robots. Maybe we’ll get software improvements in the future?

Conclusion: 51515 wins most comparisons, EV3 still has niche applications

Rechargeable batteries, less weight, 6 motors? I love it.

The rechargeable battery on the 51515 Robot Inventor is a huge plus, as is the possibility of adding 6 motors. After playing with it for some time and designing my own robots, I found that the reduced weight is the new hub’s most significant advantage. For large and complex projects, I will keep using EV3. The increased torque of the motors and Linux operating system make EV3 a keeper. For a quick and fun robot build, however, I will use the 51515 more.

Engineers should still consider EV3

Should you buy 31313 or 51515? It depends. Suppose you’re an engineer with some programming skills, and you need maximum flexibility and performance. In that case, EV3 will probably bring you more bang for the buck. 

Even kids with advanced programming and engineering skills could be interested in EV3. The extra weight, torque, and memory could help you win Robot Sumo competitions and even First LEGO League competitions. The threshold for building great robots with MINDSTORMS EV3 is higher, but the ceiling is also higher.

When comparing the price of EV3 and Robot Inventor, remember that EV3 comes without batteries. If you add the price of 6 rechargeable AA batteries and a charger plus two rechargeable AAA batteries, the sets are rather evenly priced. Buying the official 2050mAh LEGO Li-Ion battery and charger will cost you another EUR 140. If you add it all up, the price of the 51515 Robot Inventor is actually a steal with its built-in battery.

Want to have fun with robots now? Get yourself a Robot Inventor set

If you calculate the hours of fun per euro spent, 51515 Robot Inventor is the one set to rule them all.
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In the more probable case that you’re a parent and you’re buying it for your kids, 51515 is a no-brainer. Get it! LEGO will support and update the set for years and years to come. 

If you’re an Adult Fan of LEGO, just starting to explore robotics, 51515 is a sure bet. It’s comfortable, fun, easy to use, and well designed. It has hours and hours of play value. You won’t ever regret buying it. If you calculate the hours of fun per euro, 51515 Robot Inventor is the one set to rule them all. I expect no other LEGO set coming anywhere near it.

Overall winner

LEGO MINDSTORMS Robot Inventor 51515

EV3 is still a great product but it has moved into a niche. For the general public, it has been surpassed by its 2020 successor, Robot Inventor set 51515.

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Germany 31313

US 31313

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4 thoughts on “EV3 vs Robot Inventor: LEGO 51515 and 31313 sets compared”

  1. Beautiful review. Thank you very much. I have several nxt’s, several EV3 oh, and I just bought my first 51515. I now know what to expect

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