Drill Mount Description
See Safety Precautions below

I had been experimenting with LEGO propellers.
These need fast rotation in order to generate significant propulsive thrust.
I began with a single 47154 motor at 2-3000 rpm under load at 9 Volts, power 3 Watts.
I moved up to four motors, nearer 3000rpm at 9 Volts, total power 12 Watts.
The fan being rotated needed twice the speed and hence (at least) 4x the power.
The drill power rating of 135W is a lot more than the 3W of a LEGO motors.

This is a fast drill, in the range 10000 to 33000 rpm.
The idea was to run the drill at its minimum speed, which is 2-3 times as
fast as the LEGO technic motors, starting with it being geared down
3:1, so that the speed would be the same as the LEGO motors, to ensure good
running before increasing the speed.

My first experiment before mounting the drill was to fit a 3.2mm tube to the chuck to try it out.
I held the drill as prescribed in the instructions and pointed it away from me before turning it on.
A small imbalance in the tube mount caused it to bend and fly out of the chuck at high speed!
Good job I pointed it away from me to start with.  This is why safety is so important.

I decided to mount the drill securely, since I would not be holding it in the prescribed fashion.
135W mains power could cause serious injury and is not to be trifled with!

I fitted a tube and axle interface to the drill, mounted in an extension to the pictured drill frame.
The frame extension had guard pieces to catch any flying parts.
I ran the drill at minimum speed.
A small imbalance caused the beam holes and axle to wear.
The amount of power melted the axle, depositing the plastic in the slots of the cross shape.
The axle also moved axially, wearing the 8-tooth cog and bush.
Power was transmitted to a 24-tooth cog.
Unfortunately, wear of the parts was so rapid that sustained operation was not feasible.
The noise told me that further operation might have had worse consequences, so I stopped.
The experiment did not pass the "good running" test.

The experiment was useful in finding the limitations of LEGO parts.
Years ago, 4000rpm motors were discontinued in favour of 300rpm gearmotors.
This experiment shows why - high speed wears out the parts, so gearing inside a motor
can reduce the speed with a lot less friction, wasting less power too.

I will have to content myself with 4000rpm motors and a bench power supply.
The power supply can supply more current for more motors at 9 Volts.
I have run the four 47154 motors at 9 Volts with a propeller system.  The motors
pulled about 1 Amp between them.
That experiment still has potential consequences of blade detachment.

Safety Precautions
Anyone using a drill with LEGO parts must have adult supervision and
must take all possible safety precautions.
Consequences include high energy debris, which might cause serious injury
to people or serious damage to property in the vicinity.
I recommend using a polycarbonate screen between yourself and all moving parts.
Do not do this type of experiment near anything expensive or fragile such as a TV.
Isolate the drill from the mains before touching anything that could move.
Make sure the 'off' switch and socket are available to cut power to the drill.
Wear goggles to reduce the risk of any flying parts hurting your eyes.
Do not touch the model when it is moving.
This list is not exhaustive - take other appropriate safety precautions for fast drill operation.
Perform your own risk assessment before you switch on.

In the design of LEGO propellers and fans, make sure they are robust.
Design them so that blades or other parts cannot fly off.
Check the anti-blade release features before each run.

You use or make fast spinning devices and propeller and fan models entirely at your own risk.
I cannot be held liable for your own experiments or their consequences.

Mark Bellis
May 2009