OK, so I've bought Mindstorms. What else would be useful?

This is an attempt to describe the possible add-on sets for the Lego(R) Mindstorms Robotics Invention System (abbreviated to RIS).

I've changed the format since the original version... on this page there is a brief description of controllers, actuators, sensors and generally-useful elements. Next to each item is a link ("sets") which links to a page which gives a non-exhaustive list of the retail/service/Dacta sets which contain that item.

The questions asked (and answered?!) are:

Controllers: what can I use to control my robots?

RCX #9709

The RCX has 3 inputs and 3 outputs, plus a bi-directional infra-red interface. It is a good general-purpose base for autonomous robots.(


The Cybermaster has 3? inputs and 1 output, plus a bi-directional radio interface and two built-in motors. Tachometers on the built-in motors make this a good platform for mobile robots.


The Scout has 2(?) inputs and 2(?) outputs, plus a built-in light sensor. It has a fixed number of pre-programmed behaviours, and it doesn't look (yet) like you can program it like the RCX/Cybermaster, despite looking like the same hardware...


The Micro-Scout has a built-in light sensor and a built-in motor. It has a fixed number of pre-programmed behaviours, and it doesn't look (yet) like you can program it like the RCX/Cybermaster.

Control Centre #9752

The Control Center has 3 outputs, plus a constant 9V "test" output. It has 2 "memories" which can be used to "learn" a sequence of instructions.

Interface B #9751

The Interface B has 4 passive inputs (for touch and temperature sensors), 4 active inputs (for light and angle sensors) and 8 ouputs, plus a constant 9V "test" output. It interfaces to a PC (it may be a simple RS232 serial connection, in which case it would interface to any computer?)

Battery boxes #5114/#9831 and #5391

Don't knock the battery boxes - they can be very useful for testing your robots! There are currently two styles:

#5115/#9831 is the larger of the two. It has a two buttons, for forward and backward, and takes 6 AA batteries.

#5391 is the smaller box. It has a simple on-off switch, and takes a PP3(?) (9V cuboid) battery.

Actuators: what output devices are available?

Motors #5225 and #5114

There are currently two 9V motors:

#5114 is the older style of motor. It runs pretty fast, but the speed is affected by the applied load.

#5225 is the newer style of motor. It has an internal flywheel, which I suppose makes it run at a more constant speed than the old one.

Micro motor #5119

The micro motor is good for switches, steering and other low-speed, low-power tasks.


Pneumatics are a powerful way of moving arms, grippers etc. You'll need an air tank/compressor, and a switching mechanism though, which will probably require two motors.

Light elements

There are a few light elements. Not really very exciting though.

Fibre-optic system

The fibre-optic system is a brick with a red LED inside; the LED can be rotated by an axle - normally a micro-motor is used for this. 8 bits of plastic (presumably fibre-optic cable) are attached to the brick, so that as the LED rotates, a cycling light effect is achieved. (Thanks to Mego1283@aol.com for the description)

Sound elements

The RCX can make noises, but there is also a separate sound element in the Dacta range, plus there were various sound elements in old Town/Space sets.

Sensors: what input devices are available?

Touch Sensors (various numbers!)

There are a variety of touch sensors available:

#9888 is the original Dacta sensor. It is yellow and has (I believe) the cable permanently attached.

#975? is the Mindstorms sensor. It is grey and doesn't have a permanently attached cable.

#???? (more than one number?) are the Cybermaster sensors. These are transparent, in various colours, each of which has different resistance, which allows the Cybermaster to detect which one has been pressed. I don't know if the RCX can detect this resistance though.

Light Sensor #9890/#9758

Can be used in both active (ie it illuminates the area it's looking at) or passive modes.

Rotation Sensor #9891/#9756

Counts 1/16ths of a rotation.

Temperature Sensor #9889/#975?

Measures temperatures from very cold to above the softening point of Lego plastic!

Remote Control #????

The Remote Control can control the RCX's motors directly, stop and start programs, and can also send messages (the numbers "1" to "5"). A useful device for testing.

Robo Cam

This digital camera is not yet available...

Which specialised Technic elements are useful?

Electrical connectors / plates

These are essential items for connecting electrical elements together.


More uses than I can mention here - you'll never have too many of these!


This 24 tooth gear allows a motor to slip if the gear train locks solid!

Freewheeling 16 tooth gear

Useful for gearboxes, or for simply passing a rotation across an active axle.

Universal joint

Handy if your axle needs to bend...

Flexible axle

Handy for going around corners etc, but rather too flexible if large torques are required.

Large turntable


Chain links


Conveyor belt links


Contact Details

Stuart Crawshaw
Control Laboratory
Department of Engineering
University of Cambridge
Trumpington Street
Cambridge CB2 1PZ

Telephone: (+44)-1223-339222 (office)
Fax: (+44)-1223-332662

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Engineering Department Home Page.

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This page was last modified by S. Crawshaw on 25 September 1999.