LEGO 51515 Robot Inventor vs. SPIKE Prime set 45678

| | ,

LEGO has four robotics sets on the market: Boost, SPIKE Prime, EV3, and Robot Inventor. I compared EV3 to Robot Inventor in a previous article. In this article, we’ll look at SPIKE Prime vs. 51515 Robot Inventor. The comparison is interesting because both sets have very similar hardware, and you can get them for about the same price. I’ve seen both boxes retail at a price between EUR 340 and EUR 380. Here’s a buying guide for your next MINDSTORMS.

LEGO 51515 vs. SPIKE Prime hubs
LEGO MINDSTORMS Robot Inventor vs. SPIKE Prime: side by side comparison

The concept: LEGO 51515 Robot Inventor vs. SPIKE Prime

SPIKE Prime is for educators

LEGO targeted SPIKE Prime at educators. You can’t even get it in official LEGO shops and most retail stores. The only official way to get it is through a LEGO Education supplier, although some online stores sell it to everyone. The idea behind SPIKE Prime is to give teachers a tool for exploring robotics with their class. It is colorful, easy to use, and full of 1-hour activities. The models are small and straightforward. SPIKE Prime aims to teach about concepts like programming, entrepreneurship, robotics, and the environment. In my opinion, SPIKE appeals to ages 8-12. There are exceptions: some adults do crazy stuff like making a trapeze artist swing 360’s

MINDSTORMS 51515 for the family

LEGO MINDSTORMS 51515 Robot Inventor is a so-called ‘retail’ set. With that set, LEGO aims for kids who want to have fun and be creative. There is little to no educational content in the app. It’s mostly fun activities. The models are much larger, so the building fun lasts longer. 

It’s interesting how the MINDSTORMS brand has left the classroom. Seymour Papert – who originally coined the term – was creating material for school kids. He found out that kids will learn and explore if you create inspiring worlds around math, language, or programming. Exploring these worlds gave kids Mindstorms. Adults enjoy their Mindstorms too. Some take up meditation, while others just buy a box of LEGO MINDSTORMS. I’d say Robot Inventor appeals to kids in the age range of 10 to 100 years old.

The LEGO SPIKE box vs. the LEGO 51515 box

As an educator’s tool, SPIKE Prime has a solid plastic educator’s sorting box. LEGO designed SPIKE Prime to be assembled and taken apart daily. The boxes stack neatly for storage at school. The lid snaps on to prevent the loss of bricks.

LEGO 51515 vs. SPIKE Prime boxes
Box of 5151 Robot Inventor vs. SPIKE Prime storage container

To give you more plastic to build with, LEGO Robot Inventor comes in a cheaper cardboard box. It still is a better box than the average LEGO box because it has a lid and you can reclose it. Most other LEGO boxes tear open from the side and end up in the paper bin. It does not feature sorting trays, however, or a large format print of the part list. This style of box is practical at home, but it is terrible in the classroom.

LEGO 51515 electronics vs. SPIKE Prime electronics

The electronics inside both sets have a lot of commonalities. They both have the new 6-port hub, albeit in a different color. Both have the new medium motor, light sensor, and ultrasonic sensor. This is where the similarities end.

SPIKE Prime features a Force Sensor and the Large Motor

SPIKE Prime features two particular electronic parts over MINDSTORMS Robot Inventor. The force sensor is an upgrade from the EV3 touch sensor because – as the name suggests – it can sense the gradual force applied. The EV3 touch sensor could only sense pressed or not pressed. Force sensing is excellent in classrooms where you learn about springs, newtons, mass, and weight. When building cool robots, there is less use for such a sensor. 

The Large Motor has a larger torque than the medium motor, but also a more inconvenient form factor. Even though it has more pin holes, I find it more complex to build with. So for I never had a lack of torque on the medium motors. Maybe they are useful in large robot arms?

LEGO 51515 vs. SPIKE Prime sensors
LEGO MINDSTORMS 51515 sensors vs. SPIKE Prime sensor range: the force sensor makes the difference.

LEGO MINDSTORMS Robot Inventor has better robot electronics

What Robot Inventor lacks in variety, it makes up for in quantity. There are no less than four medium motors in the set. They come in a practical shade of grey that is easy to combine with other colors. When I build robots, I will always choose an extra degree of movement over a force sensor. It is the more practical set in the daily life of a Technic robot builder.

LEGO 51515 vs. SPIKE Prime motors
Motors in the 5151 Robot Inventor set vs. motors in the SPIKE Prime set

SPIKE Prime plastic parts vs. Robot Inventor parts

The first thing you notice when comparing both sets is the volume. SPIKE Prime has a meager 520 parts. 51515 Robot Inventor almost doubles that with nearly 1000 parts included. Having less LEGO bricks is acceptable in the classroom. The more bricks you have, the more bricks you can lose. That being said, SPIKE Prime has some interesting pieces of plastic that are not present in the Robot Inventor set.

The Technic 28 tooth gear

The 28t gear is the newest addition to the lineup of angled gears. In my video about gear meshing, you can see just how useful it is. When I first started building with it, it felt like a long lost link in the gear collection. SPIKE Prime has two of them, while LEGO Robot Inventor sadly has none. If I didn’t have a box of SPIKE Prime, I’d buy them on Bricklink or get myself a Liebherr R 9800 for using it with MINDSTORMS.

Caster wheel

SPIKE Prime has a single caster wheel, ball-and-cup style. The get a second one, you need the SPIKE Prime expansion pack. Most medium robots need 4 points of contact with the floor. Usually, that’s two caster wheels and two powered wheels. To build this, 51515 Robot Inventor has hard plastic 18mm sphere wheels. They might have a little more friction but work perfectly fine.

LEGO 51515 vs. SPIKE Prime caster wheels
LEGO MINDSTORMS 51515 caster wheels vs. SPIKE Prime caster wheel

Kjeld bricks

SPIKE Prime was the first set to feature 2×4 bricks with axle holes inside. They are called Kjeld bricks because Kjeld Kirk Kristiansen – LEGO’s owner – was directly involved in the design. They allow you to add studded LEGO to your Technic studless robots. I am personally more of a Technic builder, and I believe you should be able to drop robots or run them into a wall without parts falling off. That’s why I usually avoid studded LEGO. There is one exception: I did have fun with the Kjeld bricks when I was making a remix of the LEGO Super Mario set with SPIKE Prime.

Use of the Kjeld bricks in this SPIKE Prime + SPIKE Prime expansion + Mario remix

Robot Inventor software vs. SPIKE Prime software

You can try both LEGO Robot Inventor and SPIKE Prime software for yourself. There is no need to buy the sets yet. If you compare both, you will see that they are very similar. Both provide a series of activities and building instructions. Scratch and Python coding is very similar. There is one big difference: LEGO MINDSTORMS Robot Inventor software has options for remote controlling your robot. 

LEGO Robot Inventor 51515 hub vs. SPIKE Prime
MINDSTORMS Robot Inventor hub vs. SPIKE Prime hub

If you buy either set, you can use either piece of software because the hubs are almost identical. So the differences in the software are not a significant factor in the buying decision. 

SPIKE Prime Expansion vs. LEGO MINDSTORMS 51515 Expansion

I love the challenge of one-kit builds. Making do with what’s in the box is an intriguing puzzle for me. I enjoyed building a swinging monkey with only a SPIKE Prime base kit or a race car with only LEGO MINDSTORMS EV3. 

However, LEGO being LEGO, you will ultimately want to expand and combine with other sets. When I see kids build, they seem to have a total disregard for color combinations. That screams creativity, but it also hurts my designer’s eye. Building models with a coherent color palette pleases me. Colorwise, expanding 51515 Robot Inventor with LEGO Technic sets is more flexible than expanding SPIKE Prime with all its screaming colors. Robot Inventor has grey motors, black wheels, and black-and-white sensors. Only the teal hub could prove to be a challenge to combine with regular Technic.


If you are not an educator, get Robot Inventor 51515. You will find it has much more value for money. There is more plastic in the box, and it has a better selection of electronic parts. This to overall more play value in the set. The colors make it somewhat easier to combine with your other Technic sets. Teachers will enjoy the clarity and speed of LEGO SPIKE Prime prime. The lessons in the software are easy to integrate into regular classes. 


EV3 vs Robot Inventor: LEGO 51515 and 31313 sets compared

2 thoughts on “LEGO 51515 Robot Inventor vs. SPIKE Prime set 45678”

  1. Great article, thanks. If I buy the Mindstorms set, would the touch sensor from Spike. a prime be compatible with the Mindstorms software/hardware?

    • The hardware is compatible. The MINDSTORMS software, however, has no Scratch block for the touch sensor. You need to use Python or flash the SPIKE Firmware on it.


Leave a Reply

%d bloggers like this: