Since 2021 LEGO has released 10 small Technic monster trucks, linked to Monster Jam. LEGO generously sent us the latest pair to be released in January so we can share our own opinion on them.
Monster Trucks are unusual vehicles that you hope never to encounter on the road; they are designed to smash, jump flip and do other stunts that you do not typically want to associate with partaking in traffic. My expectation for a Monster Truck set is therefore in a similar vein; I expect this to provide some simple fun and smiles; something that triggers play.
I admit that I did not know what “Monster Jam” was (I thought a computer game) but courtesy of Wikipedia:
Monster Jam is a live motorsport event tour operated by Feld Entertainment. The series began in 1992, and is sanctioned under the umbrella of the United States Hot Rod Association. Events are primarily held in North America, with some additional events in other countries. Although individual event formats can vary greatly based on the “intermission” entertainment, the main attraction is always the racing, two-wheel skills competition, and freestyle competitions by monster trucks.
From this I deduce that the set on review today, 42219 Monster Jam™ Grave Digger™ Fire and Ice contains the ™ symbol (twice!) for a reason and relates to a real vehicle. The set comes with 263 pieces for AU$44.99/£24.99/US$34.99/€29.99.
Come have a look at what we can learn about torque, power and acceleration for a Monster Truck. Oh, and we will also have a look at what this particular LEGO set has to offer.
Torque, power and acceleration explained
This 42219 Monster Jam™ Grave Digger™ is a pull-back action car. It means that when you pull it back there is a rotation spring that winds up and stores energy to return it to the wheels when you let go.
We’ll assume that these pull back action ‘motors’ from LEGO are all built the same, so they can store the same amount of energy regardless what vehicle they are used in, meaning that with the same number of motors you can expect the same kind of behaviour. Mostly.
When a motor tries to put a car into motion (accelerate the car) it does so by turning the wheel. These wheels apply a force to the surface of the road, which allows the car to ‘push’ itself forward. Isaac Newton has given ways to calculate how things move then a force is applied. The bottom line is: If you apply more force to an object it will accelerate faster.
So what is this torque business then? Many motors, just like this pull-back motor, do not apply force in one direction. Rather, they can apply force while turning around (rotating) and that is called torque or ‘twisting force’. This is why torque is often mentioned in relation to cars: more torque means more acceleration = faster takeoff.
There is a direct relation between torque and force. Look at this animation, courtesy Wikimedia, showing force as dark blue arrow at the ball and torque a the light blue arrow at the rotating point of the bar. Give a certain amount of torque provided by a (pull back) motor, a certain amount of force can be applied at the edge of a wheel. Important to note is that the bigger the wheel, (the bigger the distance between the edge and middle of the wheel) the smaller the force will be. You can feel this by taking a technic pin and putting a wheel on it. Try holding the wheel and the axle both firmly and turn the wheel; you will struggle to keep the axle from moving. Now try turning the axle and you will not struggle to keep the wheel from turning. This sums up the equation relating Force and Torque:
Torque = Force x radius
This all is relevant in relation to this LEGO set, because the monster truck has large wheels for the size of the vehicle. Large wheels = smaller force (as we just determined) so we can expect the acceleration to be lower than when using smaller wheels.
We happen to have another pullback car available with smaller wheels for comparison, the 42169 Neom McLaren Formula E team. Now it’s worth noting that that particular car has two pullback motors, so the car can put twice as much torque on the wheels, AND it has smaller wheels so it should be able accelerate faster.
Let’s see what that looks like in a drag race:
This video illustrates that if we want to see the effect of wheel size on a vehicle, perhaps we should make sure that everything else is kept the same. As it turns out the result of this test was a little bit affected by the steering of the NEOM, crashing into the Grave Digger.
For better scientific comparison we will look for a vehicle that is similar to Grave Digger. As it happens, we have access to 42220 Monster Jam Sparkle Smash, also generously provided by LEGO. The cars are similar in size and have the same wheels and motor
This drag race shows the vehicles are very evenly matched, as we hoped. So let’s do a better comparison by replacing the rear wheels of the Grave Digger with smaller wheels and doing a drag race again. I’ll admit that the car doesn’t look quite as cool but this is for science! We’ve gone from a 56mm wheel to a 30.4mm wheel so we are expecting (56/30.4 = )1.84x more force on the edge of the wheel to accelerate the car. This should be noticeable!
We now expect the Grave Digger to accelerate much faster because it can put more force on the ground with the smaller wheels:
As expected Grave Digger takes off faster, so fast that it nearly loses control, but in the end Sparkle Smash takes away the win. Which brings us to the next topic:
Give me power!
Power is an indication of the amount of energy a motor can put out. Both cars in the last drag race has the same power, but still one of them won convincingly! What happened there is that Grave Digger, with the smaller wheels, was able to apply more force and accelerate faster at the start, using a lot of the stored power, but then was unable to keep the wheels going fast enough to gain a high top speed.
Sparkle Smash took a bit longer to get up to speed, but was able to use the stored power better to gain momentum and and achieve a higher top speed.
Momentum? What now?
Momentum is the reason why there are speed limits on public roads. Once something is in motion, it contains (kinetic) energy which is called momentum. It takes effort to change momentum (slow things down or change direction). This is where the fun of these monster trucks comes in. Give them a bit of a run-up and you can get them to go up a ramp and take some jumps.
When the run-up is short enough you can get the car to drive to the top and have enough energy stored at the top to sometimes do fun stuff, like the wheely in the video. Go out and experiment with this!
If you do not give enough run-up the car will not have any momentum and the motor will not be able to transfer the energy into movement.
Why don’t you let us know what kind of jumps you can get your monster trucks to make.
How about the set?
Oh right yes, there is a LEGO set behind all this. Apologies I got a bit distracted by, well, this set. 42219 Monster Jam™ Grave Digger™ Fire and Ice is based on a real vehicle although the livery appears specifically related to a toy line related to this car. The left side of the car is painted in ice themed images, and the right side in fire related images. The pictures are mostly applied via stickers, with a few of the parts coloured to match the stickers.
It’s a light-weight set that can easily be built in a single sitting, does not contain any surprises or any advanced Technic mechanisms, but the pull-back car is fun to play with (as you may have gathered from the lengthy text above).
Building the set
The set comes in 3 bags (not numbered), with a sticker sheet very clearly indicating what we’re in for. Four tires and the pull-back motor are loose in the bag.
All the pieces can easily be seen on the tray at once, with the red and blue wheels, and the 3×3 tiles standing out most for me.
The pull back motor is put to work almost instantly, forming an integral part of the frame of the car. The first panels with stickers appear shortly thereafter for the bonnet of the car.
Next the rear frame is built and filled out and a few coloured beams appear supporting the ‘Ice’ side of the vehicle
The Fire side follows soon after, and additions of the wheels completes the build.
If you are a seasoned Technic builder it might be fun to try to build the whole car without instructions just using the image on the box. If you are new to Technic, this is a smooth way to be introduced to the way of Technic.
I like this car. I think. I played with the car a lot more than I do with most sets. The pull-back motor has a lot to do with that; it’s just fun to wind it up and aim it at a different target. The car isn’t particularly pretty to look at, but that’s not the point, this car should be driven and smashed!
Conclusions
At $AUD44.99/ $USD34.99/ 29.99 €/ £ 24.99 42219 Monster Jam™ Grave Digger™ Fire and Ice isn’t particularly cheap, especially considering how small it is. However, it did provide me with a lot of fun, and you can’t put a price on that. The contents of the box provided exactly what I expected, but I was a bit shocked when I saw the price. I give this set an arbitrary 3 out of 5 praise units; there is so much good stuff available around this price range that it is hard to fully recommend this set.
But I will take it for another run. Or two.
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Until Next Time,
Play Well!
postscript: Grip
I can’t help myself. Observant readers may have noticed that real-world drag racers tend to have very large wheels, which seems to be counter-intuitive to what we’ve shown here. That’s because grip is the biggest challenge with drag races and larger wheels have more rubber connecting to the road so they can ‘grip’ the road more tightly to take off.
When we tried a 24mm wheel on the Grave Digger, the torque was so high that the car lost grip and spun sideways instantly. More Torque is not always better, there is an optimum based on your situation.