My Lego Clocks
This page is not in affiliation with The Lego Group. Lego
is their
trademark.
I love clocks. I have always been interested in clocks, and I have
always wanted to build one. I have also always loved Lego, and I
started getting back into Lego building when the Mindstorms Robotics
kit first came out. I had been mulling over the idea of building a
clock out of Lego for a while, and I was inspired to try when I came
up with an idea for a simple escapement. Later, I found out that a
number of people before me had also built clocks, so I created an
index to their inventions as well.
Clock Design
A clock needs a few basic components. The heart of the clock is the
regulator. This is a device that makes the gearwork of the clock run at a
constant (and very slow) pace. One way to regulate a clock is with a
pendulum escapement. A mechanism is devised that allows a single tooth of
a gear to pass with each swing of a pendulum. The escapement must also
provide power to the pendulum, to prevent it from running down due to
friction. This is the method that I have been using.
A second component is a power supply. This can simply be an electric
motor, which provides relentless power on demand, or a falling
weight. With the falling weight, a huge gear reduction must be used, since
the weight needs to power the clock for hours on end. The friction in this
geartrain is critical. It is very difficult to overcome the friction by
simply adding more weight, since the gears can only stand a very modest
amount of pressure, and the plastic Lego beams will bend under too great a
load. To build a clock that uses a reasonable
amount of weight (a few pounds), and a small amount of string (around a
yard), requires a very efficient design. Efficiency can be measured in
units of hrs/(ft lb), or hrs/(kg m) if you are metric. Most Lego clock
designs can only run for a few hours per winding.
The third component is the time indicator. This can be a simple dial, or
it can be a complicated system of chimes. I have designs for both. The
striking works for a chime are a challenging design problem, since they
need to strike 156 times a day. Power, regulation, and all the other
problems for clock design need to be addressed in the striking works as
well.
Two issues you should also not ignore are providing a means for the clock
to be rewound and set. This can be accomplished with one-way ratchet
systems. The
drive axle clicks open while the spool is rewound, and the clock hands are
disconnected from the power if the setting crown is turned forward or if
you rewind the clock. Without this feature, the time needs to be set every
time you wind the clock.
Below, in reverse order, I will post my designs as I finish them.
Clock #3
This was my breakthrough, and the last of my clock projects. I finally
succeded in getting a lego clock to keep good time for 24 hours without
rewinding. It was 15 minutes slow by the
end of this period, but the pendulum had only been adjusted once before
the run, and I think it could be much improved with a little more
adjusting.
It can run on 2 lbs, with a great efficiency of 3.5
hr/ftlb, but it is more reliable if it is run with 3 lbs. My big breakthrough
was to use turntables as large gears, which allows a gear ratio of
571.7:1. For the 24 hour run, I used a three-pulley system for the
weights, so they had 4 strands, and I used 5 lbs of weight. I lubricated
the spool and the primary gear shafts with teflon grease, and the upper
gear shafts with WD-40. The efficiency drops off with weight, because the
friction goes up. I've found that 5 lbs is pretty much a maximum load. Beyond
that, I start breaking things. Gears shed their teeth, and axles bend and break.
Large Gear
This was my last clock for a while. I was driving my wife nutty with my
mountains of Lego mess, so I packed it up. Later, I worked on trying to use the
old-style lego cogs as an escape wheel, but my design would only run
intermittently. Chris Daniel came up with a design that works, and it is similar
to the dual paddle arrangement I used, but I think it could be more efficient
than my design, since it needs fewer turns per minute.
Clock #2
Clock #2 is the first striking clock made of Lego, as far as I know. It
uses a variation of the locking-plate striker that was invented in the
14th century. In my version, I use chain links instead of a locking
plate. The chain has a mix of narrow links and wide links. The chain feeds
over a gear (the locking gear), and a fork drops down over the top of the
gear. The fork jams
the gear whenever a large link feeds through. The spacing between the
large links corresponds to the number of hours between 1 and 12. The
locking gear drives a second gear that trips a hammer with a pin (the pin
gear). For example, when it is 10 o'clock, the fork is momentarily lifted
by the hour
wheel. The locking gear is freed, and it starts to turn. Its speed is
regulated by an escapement. It turns the pin gear, and the bell is
struck. It continues to turn until the bell is struck ten times. At that
point, the next large link is fed through, and it jams the locking
gear.
Above is the striking mechanism by itself. In this version, I didn't have
the escapement and I used a fan to regulate the ringging to some extent,
but it rang much too fast. With the escapement, it rings at a nice stately
pace. I have a avi movie of the striker in
action, so you can see how it
works.
Clock #1
Clock #1 was a 2 lb clock with an efficiency of
around
2 hrs/ftlb. On my desk with 24 inches of string play, it could run
for around 8 hours. Adding more weight hurts the efficiency, since
the additional weight requires taller gearing (which means more
gears, generally). This adds friction, and kills the efficiency. I
worked on getting to 24 hrs with taller gears and more weight, but this
brute force method isn't a very good way to get more run time.
It uses a 1.6 sec pendulum period. The drive train is:
Spool-> 24:8 -> 40:8 -> 40:8 -> 40:8 - 1/6 per swing escapement (12
teeth)
= 2250 periods per spool rotation
1.6 seconds per period = 1 spool rotation per hour
But somewhere I made a miscalculation, and clock #1 ran about 25% too
fast.
It ran strongly however. After adjusting, it
could possibly
run for 12 hours in this configuration.
I came up with a really simple drive for the hands. It uses two parallel
shafts, conected together by 24:24 gears. One has a worm that drives a 12
bevel, which runs the hour hand. The other runs a 12 bevel which drives
another 12 bevel to run the minutes, by way of a 16 gear meshing with a 16
idler. The worm shaft can be pressed down to disengage the clock mechanism
from the input, and then it can be turned to set the time (much like the
crown knob on a watch).
It is like:
1 turn/hour input -> 1:12 (worm to bevel) -> Hours
-> 24:24 -> 12:12 -> 16:16 -> Minutes
This clock can be rewound by turning a key. To wind it, I have a tiny
ratchet-axle that uses the type-2 gearbox. It locks for power
transmission, so it doesn't add any friction to the system. The ratchet
clicks open while you rewind the clock, so it only makes friction in the
rewind direction. The whole gizmo turns with the shaft when it is under
power, so no gears are meshing.
Clock #0
This isn't really a time-telling clock, but it is the idea for the
escapement. This version could run over night, so I was excited about the
prospects for turning it into a clock.
This is the first working model of the escapement.
My later designs use a pair of 3-bladed rotors on each end. This
requires a better pallet. My later clocks use pallets that are adjustable
in 3 dimensions. To make a working version of this, be very
careful with gear alignment, and be sure no gears are pinched at
all.
The pendulum must hang perfectly straight. If the pendulum
stops after running for a while, see which rotor has jammed. Shim the
opposite side of the clock a little and run it again.
I have another escapement design I have been working on, a modified gravity
escapement. It runs very well.
Here are some diagrams: Modified
Gravity Escapement
.
Here is a big 11MB movie of it: Movie
