[MOC] LEGO RC Car with GearBox

[SimplyLegoTechnic]

Hello!

Here's my MOC RC Car with GearBox. I picked a roadster body since it's light and doesn't need many parts. This keeps the chassis fast, maneuverable, and the gearbox working smoothly. It's a rear-wheel drive car. Like in my other MOCs (https://reb.li/m/186485, https://reb.li/m/186574), I didn’t focus on detailing non-functional stuff like fake engines or steering. The main goal is functionality, playability, and reliability.
 

Free instruction: https://reb.li/m/190094 .

A short video with the bilding and testing of the gearbox and the entire model.
 

https://youtu.be/8Zy2hgXiuh4

The model uses 4 PU LEGO L-motors:

• 2 paired motors to drive the wheels,
• 1 for shifting gears,
• 1 for steering.

It uses a standard PU LEGO Hub. Since there's no clutch, the model needs to be under 1.5 kg for the gearbox to work properly while moving (my MOC is about 1.2 kg). This build isn't perfect and might have its quirks, but it works great if you stick to the recommended specs.

 

Gearbox details:

• 1st gear: 5/9 (9 motor turns in give 5 turns out),
• 2nd gear: 1/1 (5 motor turns in give 5 turns out),
• 3rd gear: 5/3 (3 motor turns in give 5 turns out)

This gives gear ratios of 0.56, 1.00, and 1.67. The speed difference between 1st and 3rd gear is three times. So, it can move pretty fast on flat surfaces, and the low gear has enough power for any incline with good traction. Low gears are also great for slow, precise maneuvers.

The suspension is quite stiff since it has low ground clearance, meant for smooth surfaces. The front wheel camber and toe are set for max maneuverability and easy turning. The turning radius is small, and the different angles for inner and outer front wheels make sense. The rear axle and suspension are complex but reliable.

No clutch means you shouldn't shift gears while reversing under heavy loads. It's just how it's designed.

You control the model using the Controlz app on your smartphone, which is free on the AppStore and GooglePlay. There are detailed step-by-step instructions for setting up the control profile.

Thank you for your attention! I'd be happy to answer your questions, share details about this MOC, and discuss the specifics of how the LEGO gearbox works while the model is moving.

And sorry for the many pictures and renders.

Edited July 20, 2024 by SimplyLegoTechnic

[Paul B Technic]

Very nice and I love the level of detail in your post.

[SimplyLegoTechnic]

https://reb.li/m/190094

Rebrickable approved the instructions.

They are now completely free to access.

Maybe there was no point in making these instructions since they use a very rare part: the red 24-tooth gear for the gearbox...

[Berthil]

I haven't looked into the model in detail but very good of you to make your work available for free!

The red 24t red gear can be purchased at the LEGO Pick a Brick for 96ct so isn't rare.

On the programming topic, you could also consider using Pybricks to control the model, that way you can share the code via Rebrickable. But maybe another builder will make it when building your model.

Edited July 20, 2024 by Berthil
Pybricks remark added.

[SimplyLegoTechnic]

2 hours ago, Berthil said:

I haven't looked into the model in detail but very good of you to make your work available for free!

The red 24t red gear can be purchased at the LEGO Pick a Brick for 96ct so isn't rare.

On the programming topic, you could also consider using Pybricks to control the model, that way you can share the code via Rebrickable. But maybe another builder will make it when building your model.

Thank you for your response!

I don't see much point in making paid instructions, because my MOCs are quite complex, and are not copy models and do not have a stunning appearance. It's not a mass product to try to make money on it. Paybricks is interesting, but so far I prefer a minimum of third-party devices.

[Paul B Technic]

Well done for sharing your instructions for free.