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Microdrive Machines

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Thank You Cole, Chad, Albert, & Herbie!

The first three photos, of an Otis Microdrive machine, were provided by Cole Haston of Kansas City, Missouri, U.S.A.
The last twelve photos were provided by Chad Weinberger and Albert Pritchard of the John Deere Company in Horicon, Wisconsin, U.S.A.
There is also a photo of a microdrive winding-drum machine provided by Herbie T. Mann - a frequent contributor to this web site!

With these three photos and four additional images I would like to attempt an explanation of the Microdrive machine. I have never seen a Microdrive machine in operation. I have heard these rotating brakes described as "widow makers" and I can see why! I had always wondered how the entire brake assembly could rotate and still function as a brake...now I know. I think the following explanations and images will clear up a few questions about these interesting machines.

These explanations are "culled, quoted, and paraphrased" from these three excellent books as well as Cole's first person observations.

ELECTRIC ELEVATORS by Fred Hymans which can be purchased at elevatorbooks.com.
ELEVATORS by Frederick A. Annett which can be purchased at elevatorbooks.com.
ELEVATORS by John H. Jallings which can be purchased at elevatorbooks.com.

From ELECTRIC ELEVATORS by Fred Hymans:

"Micro-drive machines are designed for service with elevators that require the car to be stopped in exact register with the landings. They have been furnished for passenger service, but their particular field of application is with heavy freight elevators where the loads are handled on trucks. They compromise a main machine for the hoisting operations between floors and an auxiliary machine to which the load is transferred shortly before the stop, and which brings the car to the landing at slow speed. It is the slow speed of the auxiliary machine and its control by a leveling switch that enable the micro-drive machine to make its exceedingly accurate stop."

Microdrive Machine
Image 1 (1 of 3)
The majority of the driving machines, brakes, gear boxes, and controller can be seen here.
The guards for the rotating brake have been removed and are on the floor next to the drive sheave.
This arrangement is similar in design to Drawing 3
Image provided by: Cole Haston
I know more!

Microdrive Machine
Image 2 (2 of 3)
A view of the main machine motor, the smaller auxiliary machine motor as well as both brake assemblies.
As you will see in Image 4 the main machine might also be gearless.
These motors appear to be of the AC type, however, the main machine seems
to have either a commutator or slip rings on the rotating element.
Both brake assemblies are of the AC type and the coils are submerged in oil.
Image provided by: Cole Haston
I know more!

Microdrive Machine
Image 3 (3 of 3)
A close-up of the "widow maker!"
Image provided by: Cole Haston
I know more!

Microdrive Machine
Image 4
The main machine might also be gearless...
This image was "borrowed" from the excellent book ELEVATORS
by Frederick A. Annett which can be purchased at elevatorbooks.com.
I know more!

Microdrive Machine
Image 5
Or the machine might be geared with a winding-drum...
Tennessee Coal & Iron's Ensley Works - Birmingham, Alabama, U.S.A.
(We think this is a microdrive unit...it sure looks like it.)
I would guess that the chain running from the drum shaft to the controller is used to
operate the "machine final limits" as required by most codes. (See A17.1S-2005 - 2.25.3.3.2)
Image provided by: Herbie T. Mann
I know more!

Geared Traction Machine
Image 6
American Canning Company in Simcoe, Ontario, Canada
Another one...
Image provided by: Clark Monsieur
I know more!

Nothing Runs Like A DeereTM

Microdrive Machine

...but this 1929 Otis microdrive machine gave John Deere a run for his money!

The following 12 images are from the John Deere Plant in Horicon, Wisconsin, U.S.A.
Chad Weinberger & Albert Pritchard were kind enough to send in these photos of a hard working Otis elevator.
The main machine motor was recently rewound and a few other items were reconditioned as well.

Microdrive Machine
Image 7 (1 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 8 (2 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 9 (3 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 10 (4 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 11 (5 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 12 (6 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 13 (7 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 14 (8 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 15 (9 of 12)
What could be in here?
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 16 (10 of 12)
Tools and what appear to be "resistors grids?"
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 17 (11 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine
Image 18 (12 of 12)
The John Deere Plant in Horicon, Wisconsin, U.S.A.
Image provided by: Chad Weinberger & Albert Pritchard
I know more!

Microdrive Machine Drawing
Drawing 1
This is a vertical section through the auxiliary machine and rotating brake.
Drawings 1 and 2 will be used to explain the operation of the rotating brake.
This drawing was "borrowed" from the excellent book ELECTRIC ELEVATORS
by Fred Hymans which can be purchased at elevatorbooks.com.
I know more!

This makes sense to me...

The rotating brake should be thought of as a coupling between the auxiliary and main machines. The main machine does not have a traditional brake but relies upon the service brake on the auxiliary machine, through the rotating brake, to hold the car and counterweight at rest.

Most of what you see in Drawing 1 is mounted on the auxiliary machine. Brake pulley c is connected to the main machine motor shaft b and is the interface between the two machines. (A section of Diagram 1 is displayed below for your convenience.)

The auxiliary machine is released from the main machine as follows:

When the brake coil m is energized, brake lever n rotates counterclockwise and slides shaft o to the right.
Shaft o passes through what we would normally call the sheave shaft d , if it were a conventional geared machine, on the auxiliary machine.
Shaft o presses against two bellcranks k which pivot at point l causing the brake shoes i to lift off the brake pulley c .

Microdrive Machine Drawing

As you can see if the brake shoes i are applied to the brake pulley c and the auxilary machine is energized - the entire brake assembly rotates and moves the main machine at leveling speed.

I know more!

Microdrive Machine Drawing
Drawing 2
Spring j is used to adjust the brake shoe i tension against the brake pulley c .
This drawing was "borrowed" from the excellent book ELECTRIC ELEVATORS
by Fred Hymans which can be purchased at elevatorbooks.com.
I know more!

Microdrive Machine Drawing
Drawing 3
This drawing was "borrowed" from the excellent book ELECTRIC ELEVATORS
by Fred Hymans which can be purchased at elevatorbooks.com.
I know more!

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