Article written in collaboration
with Didier Enjary
2009 update: Richard Forster-Pearson sent me schematics and photos of the Power Functions lights.
update: Brian Davis opened a XL motor, his photos details the dual stage planetary gear reduction.
June 2012 update: Victor
Sluiter made measurements Power Functions protocol, his findings
He is also building a
small form factor IR receiver.
January 2008: LEGO release the
infra-red protocol used by Power Functions
Here is the notice accompanying
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
October 2009: LEGO release update
1.1 of the infra-red protocol used by Power Functions
Here is the notice accompanying
The LEGO Group has released a new version of
the LEGO Power Functions RC Receiver (identified
by a short blink on the green LED when power is
connected). The new version of the RC Receiver supports
all functionality of the LPF RC protocol and we
have added a command to access the extra address
We are hereby offering you an updated
version of the LPF RC protocol documentation. 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 Group.
Gaute Munch, The LEGO Group
- The new version of the RC Receiver supports
all functionality of the LPF RC protocol including
‘single pin mode’.
- The product code is the same #8884 – the
new item number is 4566735.
- Orders through LEGO shop online for #8884
will provide the new version.
March 2010: LEGO release update
1.2 of the infra-red protocol used by Power Functions
LEGO Power Functions RC
purpose, previous 1.0 version (PDF, 400kb) and previous 1.1 version (PDF, 340kb)
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 as
LDraw official parts.
Power Functions gallery
Images courtesy of The LEGO Company.
Power Functions working
Note: in the above diagram, dotted lines are
existing, but unused wires.
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.
lines carry supply voltage from the battery box
to all devices that need it, such as the remote
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
The table and diagram
below show the how the system works.
A few facts and tips:
- Normal motors (Medium, Large and
XL) as well as Power Functions light are connected only
to C1/C2 lines. These lines carry electric power needed
to make them turn or shine.
- Power Functions servo motor
gets its power from 0/9V lines, and is controlled from the
state and PWM duty cycle of C1/C2 lines
- All devices that
have input and output plug pass through power lines, devices
can be daisy chained. 0 and 9V are available to all element
in the chain if they need them.
- The IR receiver
gets it power from 0/9V lines, and according to commands
received, delivers power to C1/C2 lines of its two outputs.
- The Power Functions battery packs
provide power to the PF system. 0/9V lines are powered as
soon as the battery pack is on, with fixed polarity. C1/C2
lines are also powered, allowing a direct connection of
a motor to the battery pack. Their polarity (hence motor
rotation direction) depends on the direction of the switch
of the battery pack. In addition, the rechargeable battery
pack has a variable speed control, and provides C1/C2 with
pulse width modulated power.
Power Functions motors compared to old 9V motor
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.
the tests below are performed with motors directly connected
to a laboratory power supply.
regular has a weight comparable to 9V motors. XL is
much more heavy, something to expect from such a powerful
of the bounding box of the motor
XL turns slowly, giving it an impressive torque. Once
again, PF regular is similar to 9V motors.
weak point of PF motors: their no-load current is high,
denoting internal friction. They are not well suited
to low power applications such as solar panel supply.
71427 was exceptionally good for that.
torque delivered by the motors (motor is blocked). PF
regular provides twice the torque of 9V motors, while
PF XL outdoes its rivals with an axle twisting torque!
torque comes with a price, current consumption. Note
that the high stalled current of XL motor exceeds maximum
current delivered by the PF remote receiver (800mA)
and of its own internal protection. Maximum torque is
only obtained with direct battery connection for a short
mechanical power is delivered when load halves its no-load
rotation speed. PF motors easily outdo their elders
with a reduced efficiency.
is the ratio between delivered mechanical power and
electrical power provided. Note that the best efficiency
is obtained when load decreases rotation speed by 1/4
of mechanical power by motor weight.
of mechanical power by motor volume.
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
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
More power curves (with other motors and pairs
of motors) are available here.