Lego Mindstorms

Hi. I do a lot of work with Mindstorms (outside of FIRST) and have a axle, connect directly via an axle extender to a wormgear in a gearbox, driving a 24tooth gear.

Does anyone know how many rpm’s LEGO’s 9 volt moter runs at?


–Ben Mitchell

Which motor the geared or ungeared?


I used the pregeared 9V motor that comes with the mindstorms kit. I have it hooked via axle extnder through a worm gear in a gearbox, driving a 24 tooth slip gear (the wierd white one) I also have a rotational senser hooked up on the same axle as the worm gear.

I don’t know if that will slow the motor down. its doing a heavy amount of stuff, but I figure the sensor woulds be most accurate with as many rpm’s as possible.

You might wonder why. I built a model of last year’s robot with mindstorms. the moter in question is driving a long shaft of toothed plates, and a claw which opens as closes using rubber bands and a wedge.

Thanks for any information.

In my experimentaion with the mindstorms roataion sensor the slower you can get it the better, i think it may have to do with the RCX not checking as fast as it needs to or sumthing like that. Im not sure on the RPMS maybe, unless you need to calculate anything with legos the best way to get a program to work is get some idae of what to do and tweak the programming til you get it right, due to the fact that even if your motor goes crazy and your creation breaks its always repairable.


I actually made a robot for my computer science project in my last year of high school using exactly the setup you described, except with the higher-speed (lower power) early-version 9V motors. I had no problems with efficiency (as long as the shaft lines up well; it’s often a good idea not to attach the sensor too rigidly, so that it doesn’t jam on the shaft). I also found it be extremely accurate, and I read somewhere that the RCX monitors the sensor more than fast enough to keep up with even ungeared, unloaded motors.

-Ian Mackenzie
Woburn Robotics
Team 188

When it comes to being a rookie, just look here.
So, here’s my quesiton: What is “Mindstorm”?
Sounds interesting.


LEGO Mindstorms ( are robots you build and program yourself, using legos, an a programming language (there are several)

FIRST does a Lego League competition, kind of a junior robotics session, but I although i’m not currently involved with an FLL team, I find them interesting.

I’ve made quasi-strafing hal-tracks, tanks, light-seekers/

but the grandest of all is a model of last years team 303 robot.

It uses three motors, has a claw that opens and closes, moves forward and back along a shaft, and has 4 wheel drive, using lego chains.

There is so much you can do with Mindstorms! I got hooked immediatly. they’re not cheap (200$) but well worth it. Check it out at the web site. there’s a lot to see.

–Ben Mitchell
–team 303