Let's Make Robots!

Raspberry Pi Lego car

Hello all,

I'm making my first robot using Raspberry Pi. My robot looks like a car with three wheels. Two of them are in front and have connection to motors, The third one is behind and it's no connection to motors.

I'm planning to use 2 simple motors (for each front wheel one). For now my robot weight 260g, and i have to add two motors and battery and i little of more constuction for holding motors and battery. I'm already found which type of motor should i use:

Motraxx MOTOR X-FLY 400 or Moteaxx MOTOR X-FLY 280.

First is stronger with 37.7 W. and second provide 13.8 W. Because I don't want to have very fast robot I've made some kind of transfer to power:



So...do you think X-FLY 280 will be enough or I shoud buy X-FLY 400. Remember left wheel will have motor and right wheel will have its own motor. So 2 motors on board.


Thank you for your opinion!

Have a nice day,


Image of my robot


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Hi, thank you for your replay. I've made new torque system, Motor has to do 33 round for one round wheel. Do you think this will be enought ?

Short answer is "no."  The reduction is marginal and that might work, but if you are still using the LEGO gears they aren't made for 10000+ RPMs.  I really don't think you can build a proper gear box for a 10000+ RPM motor with LEGO gears.  They are designed to be used with LEGO motors, which are already geared down to something like a couple hundred rpm.

Either of those motors would probably be powerful enough, but they turn too fast for the gears you have.  The gear boxes you have built give about a 1:4 gear ratio and the x400 motor turns at up to 15000 rpm.  That means your wheels would be turning at close to 4000 rpm.  That is WAY too fast and will not give you enough torque to move the bot.  Also, those LEGO gears probably will destroy themselves at that kind of speed.  Not to mention how you will attach the motor shaft to the gearbox.  You should buy motors that have gearboxes attached, with an output speed of around 100 to 200 rpm.  There are a lot of small gearmotors available on ebay and from other suppliers that are well suited.