Power Functions™ presentation
Article written in collaboration with Didier Enjary

July 2008 update: Brian Davis opened a XL motor, his photos details the dual stage planetary gear reduction.

January 2008 update: LEGO has released the infra-red protocol used by Power Functions.
Here is the notice accompanying the document:

Last year we introduced a range of products using our new electronic building system: LEGO Power Functions. This new electronic building system will open up a lot of possibilities now and in the future. One of the new things we offer now is modular remote control. In the process of designing the Power Functions RC system we did a mapping of different RC functionalities. This mapping formed the basis of the Power Functions RC protocol and most of this is built into the Power Functions RC Receiver. The RC Handset launched now provides direct 'bang-bang' control, but the RC Receiver supports much more functionality like PWM speed control and single pin operation. Now that the Power Functions elements are available at the LEGO Shop online we have decided to release the Power Functions RC protocol as open source. Please feel free to use any information from the protocol document for personal, non-commercial use only, provided you keep intact copyright, trademarks and other proprietary rights of the LEGO Company - have fun. Gaute Munch Technology Product Manager LEGO Company

LEGO Power Functions RC Version 1.0 (PDF, 400kb)

 

Power Functions is the new electric building system by the LEGO company released in 2007 in TECHNIC and Creator sets. The Power Functions family is composed of remote control (RC) elements, motors and a brand new type of electrical plug and wire. Let us introduce the family members.
	The battery box powers the system. A green light indicate that the power is on. The orange control switch can be pushed in either side driving a motor in either direction. In the middle position power is turned off. The plug is of female type and in the whole system, female plugs are the feeding plugs just like the domestic AC plugs are. The battery box needs to be filled with 6 AA-size batteries.
The motors are internally highly geared down, turning slowly and delivering high torque. See the technical measurements in the second part of this presentation, and in the 9V motors comparison page. They receive power through an attached cable. There are two types of motors : a medium one and an XL one.
	The medium motor fits both studded and studless elements as shown in the illustration. It is 6L long and 3L wide and tall.
	The XL motor is studless only and its diameter is 5L wide.
The RC handset and receiver work together, the handset sending IR signals to the receiver. The RC system has 4 channels and you will find channel selectors on both the remote and receiver. They need to be set on the same channel. If needed you can control several receivers from a single handset by moving channel selector.
	The receiver has two outputs, red and blue coded, corresponding to the two control buttons on the handset. This way you can independently control up to 8 different functions in your models. Just like the motors, the receiver is powered through a cable. As the battery box, the outputs plugs are of the female type.
	The RC handset also include two small black direction switches on each side of the channel selector, below each control buttons. They allow you to flip the direction of the corresponding output. The handset has to be filled with 3 AAA-size batteries.
	The Power Functions plug is of a new type. It has 4 connections giving new possibilities for the future. An extension wire (available early 2008) gives to Power Functions compatibility with the existing 9V electrical system and with NXT.

Power Functions LDraw and LeoCAD parts

I have modelled all 2007 Power Functions devices. Files necessary to model your constructions are available here below.

Warning: These parts are not yet official, parts number, origin, orientation might change when these parts become official, so use this at your own risk! Check often LDraw Parts Tracker for improved versions.

Working with Stone Gray colors

The Power Functions parts use several gray colors that are relatively new. Older LDraw software programs either need some configuration or do not support them at all. Here is a few tips and tricks.

Color definition:

Color name	LDraw color number	RGB value	Approaching old color name	LDraw color number	RGB value
Stone_Gray	71	#A3A2A4	Gray	7	#C1C2C1
Dark_Stone_Gray	72	#635F61	Dark_Gray	8	#635F52
Light_Stone	151	#E5E4DE	Light_Gray	503	#E6E3DA

These colors are defined in ldconfig.ldr (more details here). Make sure that the latest version of this file is present in your LDraw folder. Hopefully all LDraw programs should use this file as color definition, unfortunately many older programs do not.

MLCad:
MLCad needs some configuration to use Stone Gray colors. To do so, load this file in MLCad, select a brick and click on the "M" button of the color bar. Press the "Save as default colors" and you will be able to use Stone Gray colors. MLCad will save these colors in the header of all files you create after that.

LDView: LDView will display Stone Gray colors as soon as ldconfig.ldr file is present in your LDraw folder.

LDGlite: Place this file in the folder containing LDGlite program.

L3P (and also L3PAO and LPub that use it): L3P doesn't accept directly the Stone Gray colors. The only way is to convert your file to use 24 bit color codes (or to directly use custom 24 bit colors when you create your model, but that's tedious at best). This conversion can be automated thanks to Jim Devona's PreL3P utility.

Download LDraw parts

I have created 3 versions of the LDraw Power Functions parts kit for your convenience, choose the one that best fits your needs. In addition if for some reason you need the old mockup parts they are still available here (try not to mix up these old part with the newer ones as there are a few dimension and position discrepancies).

• LDraw Stone Colors version: This contains the parts present on LDraw Parts Tracker, parts are coded with stone gray LDraw colors 71 and 72. This version is not recommended if you use L3P/L3PAO/LPub.
   
• 24 bits Stone Colors version: Parts were color coded using direct 24 bit codes. This should work fine with all programs listed above.
   
• Old Gray Colors version: All Stone colors were changed to their older equivalent (7 and 8). You may use this version if you don't want to mess up with any configuration, or if you use programs that don't work with 24 bit colors. The price to pay is that colors obtained are not exact (especially the old Dark Gray has a distinct yellowish shade).
  

Usage:

• Unzip the kit in your LDraw folder.
• Launch MLCad
• Do a File/Scan parts and accept when prompted for file list write.

Download Unofficial LeoCAD parts for Power Functions (150k).
Usage:

• Unzip leocadpf.zip somewhere
• Start from a fresh LeoCAD 0.75 installation
• Launch LeoCAD
• Launch File > Pieces library manager
• In this window, File > Load update, and select cleanuppf.lup you just unzipped (this will remove the old Power Functions parts if needed, avoids to get them twice)
• then File > Load update, and select updatpf.lup
• When update is complete, close and re-launch LeoCAD.
  

All Power Functions parts should now be available.

Power Functions gallery

Images courtesy of The LEGO Company.

Power Functions working

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The backbone of PF is a 4-wire cable ended by a new stackable connector. This connector is keyed so it is always plugged the right way.   Signal name Description +9V Power supply 0V (Ground) C1 Control signals C2 Power lines carry supply voltage from the battery box to all devices that need it, such as the remote control receiver. Note that since all devices that have input and output plug pass through power lines, devices can be daisy chained. Control signals may be outputs (the remote receiver creates C1/C2 according to IR commands) or inputs (the motor takes power from C1/C2 and turns according to their state).

The table and diagram below show the how the system works.

Power Functions motors compared to old 9V motor

We compare here PF motors only with regular 9V mini-motor in its two versions: the 71427 produced from 1997 to 2002 and the 43362 motor produced from 2002 to 2006. Externally identical these motors differ mainly in the weight, 43362 motor is much lighter.

All the tests below are performed with motors directly connected to a laboratory power supply.

Conclusions are clear: PF motors outperform their elders (sometimes with huge difference) in all respects except energy efficiency.
 

PF motors power curves when connected to IR remote receiver

Since motor driver inside remote receiver has some dropout and current limitation, charts above don’t tell the whole story. The two curves below show the mechanical power of PF motors driven by the remote receiver. These characteristics were measured at 9V (alkaline batteries voltage) and 7.2V (NiMH rechargeable batteries voltage).