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Bucket Wheel Excavator

(Author: Niels Gottlob)

Transcribed from typed document with photos

Buckel-wheel excavaor built by N. Gottlob in the years 1971-73.  Its three main dimensions are: length 4 metres, height 1.8 metre, and number of nuts and bolts about 7000.  The real reason for building this model was to solve mechanically the problem that the lower delivery conveyor must be totally independent of the rest of the machine, free to move lengthwise and free to turn in a full circle.  And still it should be possible to slew the superstructure, also, of course, through a full circle.

Bucket wheel

The large bucket-wheel has ten buckets.  The circumference is made of ten 4½" strips forming a ten-sided polygon transformed into a 20-sided polygon by adding ten 2½" strips.  Unlisted 2" narrow strips have a good effect on the built-up braced girder.  The "gallows" seen in the background (and also on some of the following pictures) fixes the end of the first conveyor directly above the second conveyor regardless of the position of the circular baffle shield.

The other side of the bucket-wheel.  The two driving motors are housed in the framework supporting the circular baffle shield, which determines at which point of the circumference the earth is to leave the buckets and fall on to the first conveyor.  The ½" pinions below this small transfer conveyor are handles for tightening the conveyor band.  To the left of the left-hand 57 teeth gear wheel you can see the screwed rod imparting movement to the circular baffle shield.  The connecting rod below activates the limit switch for the baffle shield movement.  The connecting rod is not bent, but made up from rods, a flexible rod and two rod connectors.

The driving mechanism from the baffle shield to the bucket-wheel.  Note the double spokes of the big wheel giving a tremendous rigidity, even though the spokes are simply clamped between 4" circular plates.

The first passages for the earth are more clearly shown in this picture.  In the top left corner can be seen the end of the cabin containing the relays, which ensure that the earth moving mechanisms (bucket-wheel and conveyors) are always started and stopped in the correct order.  F. inst., the bucket-wheel must be started last and stopped first.  And if, during normal operations, say, the second conveyor is inadvertently stopped, the wheel and the first conveyor must also stop immediately, which the relays make sure they do.

Slewing mechanism

The completely encaged chain and worm drive to the two slewing pinioins.  By removing three screws all the housings can be removed.  The slewing mechanism is housed in a cabin, the bottom of which is shown at the top of this picture.

The double slewing mechanism - please excuse the not very clear picture.  The near motor is for slow slewing, the far motor for fast slewing.  The crux of the mechanism lies in the fact that the two pinions below the ½" x ½" pinion are not identical.  One has 19, the other 20 teeth.  The near rod is really two short rods each journalled in a lug on the small fork piece shown.  When the near motor is started the cage carrying the ½" x ½" pinion is spinning while the 19t pinion is at rest.  This causes a speed reduction of 20:1 betweeen the cage and the 20t pinion.  When the far motor is started the cage stands still, and the ½" x ½" pinion is just an intermediary gear between the 19t and 20t pinions.  The two short couplings opposite the large pinion are simply counterweights.

The underside of the superstructure.  Note the two slewing pinions.  The nine current collectors are mounted on a vertical rod.  To lift off the superstructure the only necessary preliminary is to turn this rod to disengage the current collectors from the current collector discs.

Two limit switches below the second conveyor.  The near switch controls the height of the bucket-wheel, the near, curved connecting strip being fixed to the cabin lift frame (see later picture).  This frame is always held in a vertical position.  The other switch controls the movement of the baffle shield.

The hoisting gear.  Driven from one motor through a differential ensuring equal pull from the two drums.  Two small equalising beams at the top of the machine ensure equal tension in each rope.  The gear wheels on the drums are of Stokys manufacture (170 teeth).  The small guide pulleys are moved automatically on screwed rods.

Undercarriage and crawlers

The undercarriage with crawlers.  The four push-buttons on the small black plate operate the two levelling motors.  There is a twin screw mechanism inside the boilers.  The lower boiler end is moved up and down for a total distance of ½".  Part of the steering mechanism can be seen.

The two steering arms for the two steering crawler assemblies.  The assembling cord of the crawler band is guided by the groove in the 2" pulleys.

One of the non-driving bogies seen from below and showing the tensioning mechanism.  For each crawler one pair of 2" pulleys is journalled in the long holes in 2" slotted strips (see number two picture before this - extreme left).  The tension in effected by two screwed rods in threaded couplings.

All bogies are completely equalised.  If you lift one bogie you lift one twelfth part of the excavator's total weight; if you only lift one end of a bogie you lift only one twentyfourth part of the weight.  Current to the travelling motors are supplied through wires inside pieces of spring code, as can be seen on several of the other pictures.

Central roller bearings

The loose, intermediate ring with the bottom of the central hopper and pivoted guides for the delivery conveyor visible in the aperture.  This large ring is completely free to turn (through as many full circles as you like) quite independent of the undercarriage and the superstructure.  As can be seen, there is no centre axle, no "king pin".  The mechanical solution of the working of this ring was actually what challenged me into building this monster machine.

The top of the central hopper.  The material first drops into a delivery chute, and below this the hopper can be very vaguely discerned.  The horns with connecting rods attached are part of a stabilizing equipment to keep the lift rails for the driver's cabins always vertical.

The mechanical solution to the loose ring involves three almost identical roller bearings of which this is the topmost.

The two upper bearings are removed (you can see them on the table in the background) and the central hopper is clearly shown.  There are 9 current collector discs (only eight were in use because of a reconstruction of the wiring diagram during the erection of the model) at the top, and 7 pointing downwards into the undercarriage, there are two relays at the near end of the undercarriage; they operate the 6 driving motors, because these motors carried so much current that you had to take it directly at the current inlet terminals to avoid resistance losses in long wires and a number of contact points.

The lower roller bearing, and part of the driving mechanism to the levelling mechanism inside the boilers.

Part of the undercarriage seen from below.  Most of the steering mechanism including its limit switch is shown.  Also some more of the levelling mechanism.  Inside the boiler you can see the thrust ball bearings for the levelling screws (3/16" balls in chimney adaptors).  Actually, those four ball bearings carry 2/3 of the total weight of the machine which goes up to something like 150lbs.  Limit switches are also incorporated in the levelling mechanism.

The two driver's cabins seen from the rear.  When one goes up the other goes down.  The frame is always held vertical by long tie rods connected to the centre of the superstructure.

One of the cabins showing the layout of the handles and switches.  For a driver seated in the comfortable swivelling chair the handles to the left are (front to back): bucket-wheel height, baffle shield position, travelling, and steering, and finally eight start and stop push-buttons for bucket-wheel and three conveyors.  Right behind the back-rest a push-button cancelling the travelling limit switches, activated by the delivery conveyor.  To the driver's right is a hand-wheel for slewing and a lever for slow and fast slewing.  Behind the hand-wheel a lever for the cabin lift movement.

Electrical systems

Main switch, fuses, and distributor panel for the machine.

The complex wiring to the bottom of the cabin.  The heavy cable has 21 cores.  Top left: the double slewing resistance activated by the hand-wheel.  Nearly 130 yards of wire was used, and about 350 connections made.

Four relays ensure that the bucket-wheel and the three conveyors can only be started and stopped in the correct order.  You are forced to begin by starting the delivery conveyor and end up by starting the bucket-wheel.  And if any conveyor is accidentally stopped, the bucket-wheel and any intermediary conveyor will automatically stop also.  Thus you can stop the complete earth transport system simply by operating the stop button for the delivery conveyor.  The hand-wheel operates a switch that makes either one or the other cabin operable - you cannot have both cabins to function at the same time.

Service crane

The small service crane is fully electrically operated from four handles in the small cabin controlling four motors for the four movements.  The switches are spring clips brought in contact with +6 or -6 volts in bare wires laid on the underside of the dabin floor which is made of insulating strips.  The cabin housing can be quickly removed.

The motors for hoisting and trolley movement can be seen.  Three limit switches, one for hoisting and two for trolley movement, are incorporated (with the only draw-back that one of the trolley switches will also cut off the hoisting operation).

The current supply to the superstructure is effected by using a broken bush wheel and two countersunk 6BA bolts.  You can vaguely see the arrangement of the switches below the cabin floor.

A not too sharp picture of the travelling and slewing mechanisms.  As the latter is worm driven, operation of the former will not cause slewing of the superstructure.  The travelling motor is shown, while the slewing motor, positioned directly above it, is removed.

Wiring diagram

Wiring diagram for Bucket-wheel excavator

Editor's notes: This document has been transcribed from a typed document belonging to Graham Jost, with kind permission.  The headings have been added to break the document into sections, but otherwise the text is unaltered.  There was one paragraph next to each small black and white photograph.

mucgkyr      (at 4:53am, Mon 17th Dec, 12)

hule8i lrsiqnkzxctf

Baron      (at 10:49pm, Wed 12th Dec, 12)

Sharp tihkning! Thanks for the answer.

Bhanu      (at 8:37pm, Wed 12th Dec, 12)

This is a great post if you have some control of yosulerf inside Target! I've got none! I wish I could say that I would follow these great tips and maybe I could follow the one about watching as it goes down the conveyor belt and adds up beyond the budget but I swear I'm under a spell in that place!! Everything's so cute and brightly colored or advertised with such great prices and packaging. I also like the idea of staying out of certain aisles. For me that would be the wrapping paper and party stuff!! I love that stuff and always spend too much!! Thanks for the fun post! (Now I wanna go shopping!)

josephdemeyer      (at 7:04pm, Sat 28th Jan, 12)

just wanna say this is the most amazing meccano model i have seen so far!

iosilverroy      (at 1:10pm, Wed 25th Aug, 10)

this is the most biggest and most involved model crane I have ever had the privilage to see thank-you very much. All my regards Roy Malkin


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