Lego Technic Automatic Motor Shutoff and Alarm


Hi everyone. I’d like to present my
Lego Automatic Motor Shutoff and Alarm System. I’ll start by giving you a quick demonstration. On the left we have a motor
and on the right we have an output. When I turn the battery on
you can see that the output spins. However if I apply load to the output you can see the motor turns off
and the alarm system turns on. The alarm system is built using the
older nine volt (9v) Light and Sound bricks. And for the moment I’ll turn the siren off. To reset the system I can move the
switches back to their original position. And I can also manually turn the
system off by moving the switches. The battery box feeds power
into the switches in the middle and the switch on the left powers the motor,
whereas the switch on the right powers the alarm. The two switches are joined together
with a linkage in the middle so that only one switch
can be turned on at a time. So either the motor is spinning,
or the alarm system is on, but not both. The motor feeds power
through to the output via an axle. However in the middle of
that axle there is a clutch. The clutch is constructed
using a pin connector and into that is inserted
two (2) axle pins with friction and then two (2) axle joiners. This will want to spin as one unit. However if you apply enough force on
one side compared to the other then it overcomes the
friction in the middle and then they can spin independently. And this creates our clutch. On the left we have a set of gears
which is two (2) x 24-tooth crown gears. Because they have the same number of teeth
this is a one-to-one gear ratio. On the right we have
a set of three (3) x 16-tooth gears. And again, because these have the same
number of teeth, this is a one-to-one gear ratio. However, because there’s two (2) gears on the left
and three (3) gears on the right it means that they
spin in opposite directions. These two (2) sub-axles then feed into the
differential cage in the middle but because they’ve got the same speed,
but in opposite directions the differential itself does not spin
but the spider gears do spin. You can see that in action here. When you apply a load to the output
it slows down this half of the system. When that slows down it causes a
difference in speed from the left side to the right side and that difference in speed
causes the differential to spin. When the differential spins
it causes an axle down the bottom to spin and that’s connected to this yellow linkage and then the yellow linkage is
connected to the switches. I’ll run it through it a few times
so you can see this in action. Watch the differential cage
and you’ll see that it moves just a little bit. Next, watch the yellow linkage and you’ll see that
it also moves just a little bit when I apply a load. And then finally, watch the position of the switches
and you’ll see that moves as I apply a load. For a vehicle the loads typically change a little bit
as you go over an incline or over a bump so this system is probably
not very good for that. However for systems where the load is constant,
such as a Great Ball Contraption this system will allow it to automatically shut off if the
Great Ball Contraption encounters a jam somewhere. When the motor shuts off,
the alarm system turns on notifying the operator
that there’s an issue and then they can come and fix that,
and reset the system. If you have any questions
please leave them in the comments to this video. And thank you for watching.

21 thoughts on “Lego Technic Automatic Motor Shutoff and Alarm

  1. I've watched a few of your videos so far and you're really good with explaining your creations, just as the creations are great themselves!

  2. Considering the way its built, you could alternatively turn the output by hamd wjen the system is halted to move the switch to turn the motor back on. That could be useful if the load is based on a moving vehicle that still has momentum to overcome a false halt in the system.

  3. One flaw, now you can’t use the motor for anything that requires even a minimal amount of load…

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