Lego 4x4 X-treme Off-roader 42099

This Lego set looked to be a lot of fun. A remote control off-road crawler. It's part of the new Bluetooth based Technic Control+ motors / servos. Currently, it's an closed system where only certain model Lego sets (three to be specific) are supported, but it's my understanding that in the future, Lego will expand Control+ to be programmable. In the meantime, it's not so bad because we know what we get will work 100% out of the box. Note that we were not super early adopters, and that the firmware on the control / battery module updated upon first running the smartphone app. The app is available on Android and Apple.

Here's a video of the build and some offroading. Note that we changed the gears slightly for to trade off top speed for more torque. The truck is kind of neat because it's actually a great teaching tool for real 4x4 off-roading (we have a Jeep Wrangler in RL): traction, approaching obstacles, ground clearance, gearing, locking differentials, limited slip (the Lego doesn't have a limited slip or locking differentials), etc.

 

Here's rundown of the smartphone app:

This is the set selection screen. There are only three sets supported at this time: this truck, a rally car, and a massive excavator.


The Bluetooth connectivity has been excellent. Never a glitch and always connected with 100% success rate. We've tried on two Android phones, an iPad, an iPhone, and a Samsung tablet. In the screencap below is a rendering of the Bluetooth control unit. It acts as a receiver, controller for the motors, and battery pack. It's the brains and power source of Control+


Here's the control interface on my phone. Note the angle indicators, just like on the latest Wranglers. They will turn red if we go past "safe" limits. Don't want to roll the truck over! It would have been nice if Lego offered a physical controller. Maybe in the future.

 

The construction is similar to an RC car. There a shell that is put on top of the frame. The shell is secured by three Lego pins. The construction of the frame is quite sturdy. Lots of parts reinforced upon each other. In our time playing with it, maybe two L pieces got loose around the front suspension near the steering rack. Yes, there's rack and pinion steering with linkages just like on a real car.


In addition, there is independent front and rear suspension. I would have preferred a solid axle for maybe more ground clearance at the front.


In addition the the independent suspension (which has limited movement), the frame has a swivel joint in the middle that allows the front and the back parts to twist in relation to each other, allowing for more flexibility over obstacles.


This the Control+ Smart Hub as Lego calls it. I'm hoping an official rechargeable battery pack with USB charging is offered in the future. For now, I'm using NiMH rechargeable AA cells.

 

With the modified gearing, obstacles like this are no problem at all.


The front suspension could use better clearance. The back is better, so I usually go backwards over tough obstacles.

 

For obstacles or "crawler" mode, I changed the gearing around by swapped gears. The speed does diminish quite a bit but the torque increases.

This is the speed with the gearing change. It's slow, but it's not any different than trying to drive over obstacles with the Wrangler in low gear in RL. Going over obstacles fast isn't going to work, the suspension won't react fast enough.

Go to 3:50 in the video above

The truck goes over obstacles like the one seen above (the big resistor) with ease. Generally, traction can be an issue at times. I figure maybe more weight can be added. The lack of locking differentials can get you into a rut, per the video above at 3:57 with one wheel just spinning freely and the other with no power, where we needed to reverse and attack the logs from a slightly different angle.

 

The gear swap is easy.

This is for the front motor:



This is for the back motor:


STOCK: large beige on top, small black on bottom
MODIFIED (low gearing): small black on top, beige gear on bottom

This applies for both front and back motors.