Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 1

Hi All,

I take great pleasure in introducing Howard’s outline article to build a horizontal traverse unit for the

standard 7051 Märklin crane which is controlled by joysticks for easy control. Howard first posted some

photos to the Marklin-users.net forum and I liked his ideas and asked him if he could write an article (this

article) for my web pages. My thanks to Howard for contributing to my Tips page.

Howard explained to me he has no formal engineering or electronics background so I’m impressed with the

high standard of his project. As the project was developed on his work bench documentation wasn’t a first

priority so Howard supplied the outline text and photos which I have edited and combined into the supplied

text in the format presented.

Howard’s Article Below

General Notes

This article describes a method of adding horizontal movement to a 7051 Märklin crane. The article is

intended to provide a basis for a project and is not a formal blueprint for construction.

Demonstration Video 2:10 time

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 2

Problems and Solutions

The hurdle to overcome is the need to provide power to the moving crane as the crane motors are mounted

on the base and move with the crane. The crane needs a minimum of six wires to control movement and

magnet function if a lifting magnet is to be used. The wires can be simply dragged along behind the crane as

it moves, or a ribbon cable could be used to flex back and forth. Neither of these would be pleasing to the

eye and could induce wire fatigue. A concertina of cable suspended behind the crane as in prototype cranes

would not work in HO scale.

To avoid using wires, an alternative method is described here. It depends on current pick up from copper

contacts by carbon brushes. The brushes are mounted on a foot that is attached to the moving platform on

which the crane rests. The movement is attained from a linear screw slide and saddle which was sourced

from eBay (part# 152685072601 ) and is a 300mm version. Shorter and longer versions are available, but

remember, with the crane boom rotated to the direction of travel, the hook will extend well beyond the limit

of travel in each direction.

The slide I used came with an attached NEMA 42 stepper motor but to avoid using a stepper controller, I

replaced it with a Canon 12 Volt DC gear motor sourced from an old ECG machine. Any small motor would

work but it should be geared down to allow slow movement, and the lead screw can provide further

reduction. The stepper that is initially attached directly to the lead screw provided the bearing for that end so

a new bearing and housing is required if the motor is exchanged. Use a bearing with a 5mm internal shaft

size, mounted in a circular holder which in turn presses into the hole in the end support where the stepper

had been attached. An adapter shaft is required to attach to the end of the lead screw coupler and should

reduce from 8mm to 5mm and pass through the bearing. On the end

of this shaft fit a toothed cog to allow the motor to drive it via a

toothed belt. This offsets the motor from the shaft and allows a bit of

lateral movement of the motor to tension the belt. Fit a small thrust

bearing between the toothed cog and the end bearing to minimise any

end play. This is recommended as the lead screw is a loose fit in the

bearing at the other end and

the natural tendency is for

the lead screw to move fore

and aft in the bearings as the

motor drives the screw to

move the saddle.

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 3

Each side of the aluminium extrusion moving saddle is blanked off by a plastic insert. It is necessary to use a

drift and tap the “back” one out (the “front” side will be where the moving foot is to be located). The lead

screw can be completely removed from the assembly and the saddle held in a vice to implement this. Four

large loose nuts in the saddle channels can be removed at this stage as they are not needed.

Two pieces of aluminium U

section are required to fit into the

channels in the saddle with the

sides facing down. Cut these to

length with no overhang. A

tapped hole of 2mm is made

about 10mm in from each end.

Screw a 2mm screw cut to the

correct length into each and when

they bottom, the U channel is forced up and locked in place. In the mid line of these U sections above the

lead screw, fit a threaded piece of brass tube which ultimately will pass through holes in the upper moving

wooden platform. In the very centre of the saddle tap a 3mm hole and screw in a piece of threaded brass tube.

This will allow internal wires to pass up to the wooden table above. Three pieces of brass tube now project

upwards in the line of the lead screw, two to move the platform and one to convey wires up from below.

Mount the slide to a wooden base by four countersunk

machine screws from below. Loosely attach nuts to the

screws and then bring the slide in from the end to allow

the nuts to engage channels in the bottom of the slide. To

allow this, the mounting plate at each end of the slide

must first be removed. Once tightened up, the slide is

firmly held to its wooden base and the end mounts can be

replaced. This sub assembly is mounted onto a large

wooden plinth which is needed to attach the rest of the

project. Attach wooden ends with wood screws and also

cut pieces of pine for the top section to act as a base on

which the travelling platform will run. Mount the two platform pieces 5mm apart onto the right hand

wooden end and their other end to the left hand motor mount. Mount another two shorter pieces from the left

hand end and marry the two platforms by a piece of thin MDF screwed with Märklin K track screws. The

height of the platform should be arranged so that the moving aluminium saddle has a clearance of a few mm.

The 5mm slot allows the three brass tubes to run the length of the table.

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 4

Electrical Wiring

I fashioned the moving foot from a piece of 3mm aluminium plate screwed to the side of the aluminium

saddle. Attach a right angle bracket to this with slotted holes to allow up and down adjustment of the brush

holder. The brush holder is a two piece arrangement with a 3mm plastic forefoot to carry the brushes and a

Vero board rear section to mount the terminal block and in line connectors. The terminal block affords the

best way to mount the brush spring wires and allows wires to be attached to the Vero board. This avoids the

impossible task of connecting wires to the steel spring brush tension holders. Six 3mm holes must be placed

precisely in the forefoot to line up with the copper strips below. The Vero board spacing (every second hole)

is useful to achieve this and separates the spring wires

nicely. Mill the holes for exact 3mm (Märklin

brushes about 2.9mm). They could be drilled as long

as an accurate drill press is used. Bend the tension

springs to shape by hand with long nosed pliers.

Next six wires from the rear of the foot are routed up

the footplate and into a small hole in the front face of

the moving saddle. Then manipulate them from the

back of the saddle with forceps to pass up through the

centre brass tube and leave them long enough to

attach flat edge connectors later. Keep the wires taut

to prevent any interference with the lead screw. Place

intermediate edge connectors in the wires so the

structure can be disassembled easily should the need arise. Make a wooden platform just a little larger than

the crane base with side wheels, and drill holes in the upper surface in a line to accept the three brass tubes

from below. I milled aluminium rails for the wheels to run in from flat bar, but these are not essential. This

gave me a moving wooden platform running on wheels and being propelled by two brass tubes connected to

the moving saddle below the baseboard. Tap the two tubes internally to a 2 mm thread and countersink their

holes a little to accept a compression spring over the tubes and force them down by a screw in the threaded

end of the tube. This gives a measure of force downwards to keep the platform steady and prevent accidental

lifting up. The wires emerging from the base of the crane are connected to two small edge connectors and

mated to corresponding flat sockets on the wires emerging from the central brass tube. The crane base is

recessed enough to cover these nicely when it is screwed down to the wooden platform.

The current to the crane is provided by six wires from the

controller. I soldered these to the piece of PCB used to

create the six long contact strips. This is the tricky bit

because I used a bench mill to mill the copper out

between the strips. It could be done by etching the copper

or by using three side by side 2 track copper conductors,

as seen behind the PCB in a few photos. This is available

online and can be glued to the baseboard carefully. Any

flat pieces of copper or brass strip could also be used side

by side, screwed to the base board at each end. Fit a

micro switch to each end to prevent accidental overrun,

noting the moving foot would impinge on the face rather than tangentially. A micro switch with 3-4 mm

actuation play is best for this, and the slow speed will ensure the foot doesn't jam home. (See note about the

micro switch wiring later).

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 5

The wiring from the controller is brought in via a 10 pin panel plug

and socket. (Six wires to the crane, two to the LED strip (optional)

and two power wires to the transfer motor). I used edge connectors

again to allow easy disassembly if required. (Once completed and

working, the complete unit was taken apart to sand the wood and

apply three coats of clear polyurethane).

Joystick Control

I have used joysticks to control my other

Märklin crane and the Heljan container crane

for a few years and would recommend them. I

found a small pair of joysticks on eBay

(part # 282789119685) which were perfect for

this job. These are digital in action, not

analogue, meaning they are simply micro

switches arranged around the central control

arm. To use an analogue type to control speed

as well as direction of the crane and transfer

motor would be nice but adds another layer of

complexity. A micro switch is a single pole change over type and this can't be used to reverse the direction of

a DC motor as that requires DPDT action (or half wave AC with diodes). Forward and reverse relays solve

this problem and the joystick controls their actuation. The relays output a common pair of wires to the

transfer motor but one is the reverse polarity of the other. One of the pairs is selected by the joystick for

direction control. For the overrun micro switches to function, a pair of reversed diodes is required to control

the power, and the diagram shows the connections for this. Note there are two distinct power routes, one

provides 15V AC to the crane motors and magnet, and the other provides about 22V DC to be regulated

down via the variable regulators. One regulator is set for 12 VDC to supply the relays, another is arranged to

provide variable voltage to the transfer motor and another to provide 9VDC for the LED lighting strip. The

variable speed to the transfer motor could be set internally in the control box and left alone once a suitable

speed is found, and the LED lighting is optional. This would simplify construction a bit.

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 6

To enable the magnet to hold on, a 12 VDC latching relay is interposed so that a touch of the right joystick

backwards will hold it on and a touch forward will release it. This is preferable to holding the joystick on.

The power supply is a 15VAC transformer rated at 1 amp. This is sufficient to give good control of the crane

motors and magnet, and is capable of supplying enough DC current to activate the relay coils, transfer motor

and LED lighting. The control unit comprises a small rectifier board, 3 regulators, a reversing relay board

and a connector board with latching relay, to facilitate connection of the various wires. The speed control pot

is mounted on the front panel and replaces the multi turn pot on the transfer regulator board (this is optional

as mentioned). Mount the two joysticks as left side for crane rotation and hook lift and right side for transfer

motor and magnet activation. An on/off switch and separate switch for the LED lighting are included. If the

unit was to be mounted on a layout it could be set up as a crane for a barge or scrap yard below it, or

mounted under the layout with the layout table becoming the base for the transfer table and crane to run on.

A suitable 5mm slot would be needed in the layout baseboard for the three brass tubes to run back and forth.

This was planned and built as a standalone project, and a piece of 3mm clear acrylic was added to slide into

each side for viewing.

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 7

Electrical Diagrams Outline

Parts sourced from Jaycar

Electronics

Tranformer (part # MM2002)

Voltage regulators (part # XC4514)

Latching relays (part # SY4060)

Tip: 7051 Märklin Crane with Horizontal Traverse Upgrade

By Howard Ryan Date: 18-07-2018

http://members.ozemail.com.au/~rossstew/rms/marklin.html 8

I hope this project acts as a catalyst for lateral thinkers to improve upon.

Once again Howard thank you for this concept outline of the traverse upgrade for the Märklin 7051 crane.

As always enjoy your model trains