Lift-span Bridge

This is my first modelling project. I am 63 y.o. and hoping that my skills set will see me through.

A while ago our local maritime museum acquired an antiquated lift-span bridge console (1964-1995). They wanted to know if it could be used somehow as an interactive display. A friend, who knows my background in avionics (RAAF 1980-86), and works at the museum, asked me to examine the console. After a brief discussion, with the curator and president, I got roped into converting the console to operate a working model of the lift-span bridge come diorama. Nobody there had the skills to build the model, or do the electronics, To do both projects (console and bridge) I became a volunteer worker. Gratefully, they left me alone to do the whole lot (no bosses).

Actually, the whole museum is run by volunteers. It is a non-profit organisation, so it has limited funding. This project is going to be built with minimum expense. The museum workshop has few tools and space to build this display. So I am building it in my lounge room (I have no garage). Besides a Dremel drill press with a bent spindle, and a few electronic instruments, everything is built by using basic hand tools. So please accept my methods as I use them.

The lift-span bridge is at Wardell, NSW, Australia. The museum is in Ballina, the next town downstream on the Richmond River.

Here is the console as photographed when it arrived at the museum:

I was unable to get any schematics for the console, so I have to reverse engineer it to understand how the switches work. Also, the bridge plans were not available for the public, or any information on how to operate the bridge (a security caveat). Instead, I got as many photos I could from the Internet about the Wardell bridge, and measured the span length and the width of the bridge road. From these two I was able to extrapolate the rest of the measurements from the photos (I snapped many photos as well).

As to the bridge operations, I interviewed the current operator. I was informed that he cannot tell me how to operate it. However, he was able to tell me what each switch and button did (though he has never seen the control panel before). From this, and many hours of deciphering the information, I was able to work out the operating sequence. It is not a simple matter of raising and lowering the span. In a nutshell, there is much safety precautions, and both road and vessel traffic conditions need to be controlled.

The curator wanted the model bridge to fit across a display area of 2400 x 1200 mm (8 x 4 feet). From my measurements, a 1/72 scale would fit the bridge nicely into the 8 foot length. I made plan drawings for the model to that scale. Later I discovered that a 1/76 scale would have been better due to the resources available for that scale, being OO model railway gauge.

to be continued:

That looks a great project, Peter

I look forward to reading your story.

MichaelG.

Fascinating!

Thank you Michael and Neil for your interest.

To make my life easier,I quickly made a layout drawing of the control panel for a visual reference.

.

Took the front panel off to access the internals. Many wires were simply cut at the base for quick removal of the console. I disconnected them from the terminal boards. The two main switches, Control Switch and Navigation Lights switch are custom made. I used the iPhone for both lighting and taking photographs. After a close examination, I realised that it would be best to strip rewire the whole control panel to suit the requirements of a model.

Examined each switch connections and made schematic drawings of them.

Now I have a better idea of how to use these switches for my purpose.

Here is the layout I have proposed to the museum with their approval.

It took me several weeks to draw up the plans for building the display table, control box (under the table), a 1/72 scale drawing of the bridge, and a circuit design and schematic diagram for its DC Power Supply Unit (PSU).

Here is a collage of some of those drawings (all done with the standard Microsoft paint program.

This drawing is to give you an idea of how both the lift-span and boat become mobilized. I am using two DC motors with 148:1 gear reduction (donated) together with their pulley-cable system.

By the way - MERRY CHRISTMAS to all the members of Model Engineering.

I have been over that bridge ! It is also very similar to the bridge over the clyde river at batemans bay on the nsw south coast . Unfortunately i have never seen either in action !

Guess what? I too have never seen a lift-span bridge in action!

Thanks for info on the Clyde River Bridge. It looks similar to the Harwood Bridge near Grafton, which the Wardell Bridge is considered its smaller brother. The differences is that the Harwood and Clyde have extended trusses on either side for added strength. The Wardell, in compensation, has long multi fingered piers deeply embedded into the river bed.

Hi Peter, Great work so far on a very interesting project.

One item I noticed on the "boat drive" pulleys/winch/motor in your schematic was that the ropes are entering the winch on opposite sides. If this is done, when the motor rotates one way it will tighten the boat drive string until it snaps, and the other way, will unwind it all off the winch. If the ropes both enter the winch on same side, your boat will move back and forth as intended.

One further idea - to tension your ropes an easy way is to tie loops at each end and join them with a small extension spring.

The bridge drive winch looks like it will work fine, both sets of cables either side of the deck need to either raise or lower at the same time.

Keep us posted on your progress, again you've made a great start.

Edited By Jeff Dayman on 25/12/2017 15:04:48

Thank you Jeff Dayman for the boat pulley correction. I now amended the drawing as such:

In regards to having the cable extended from the other side of the span I had decided to leave them out. The reason being is that the counterweights are only for appearances and will be made from balsa with aluminium clamps. I am going to rely on the span weight of about a kilogram or more to keep the cable tension.

In regards to spring tension, I have already been collecting springs from cannibalizing DVD players and TV sets for parts. I am hoping to only use them for the boat system. I will attach them to the boat vane that goes through the gap in the display table.

Thanks again. Please feel free to point out any discrepancies. Though I am limited by funding, I often improvise where I can.

Edited By Peter Hausamann on 25/12/2017 19:07:29

Wish to give you all a...

After the timber arrived I marked out all the pieces, cut them out, and assembled it like a kit. I was pleased that there were no hiccups. All the tabletop screws were countersunk, filled with wood putty, and sanded back. The line across the table is the 3 mm gap for guiding the boat vane.

A control box was built for under the display table. It will contain the motors, pulley-cable systems, and various electronics. The box has two access doors.

Edited By Peter Hausamann on 31/12/2017 22:00:58

First requirements for the console was to build a DC Power Supply Unit (PSU). Voltages required are 24, 12, and 5. Each capable of handling 2 amperes.

Edited By Peter Hausamann on 02/01/2018 00:25:53

wow........ wish I had the time.........nice to see a blue sky.........u lucky people.........hahaha......

all the best to u lot down there, from the frozen north.......hahaha.........clogs.........

Hello clogs, thanks for dropping in. It is nice to get a visit now and again.

While you have a heater going, I got a fan blowing. It will be the other way around in due course. At least Spring and Autumn are similar... my favourite seasons.

Building the bridge foundations required me to first located exactly where the centres of the footings will go. Then drill them to insert 3 mm bamboo skewer sticks for doweling. The from scrap board I cut and filed into shape the footings. Drilled their centres and glued them over the doweling into place.

Then used wood putty to fill any gaps between footings and water (table top). Drilled the piers, glued and positioned them into place. Bracing was also added. Each set of piers has its own length for the bridge is slightly arched over the river.

Then the girders were added. The loose board is the span base plate. The boxed area at one end is for allowing Bridge Street to pass under the bridge,

Fender Piers

Throughout the project I have been scavenging parts from unserviceable electrical appliances, TVs, PCs, etc. The heatsinks used on the Power Supply Unit (PSU) were from PC PSUs.
I needed a small pair of speakers for certain sound effects (alarm bell, boat engine, and perhaps a fog horn). Found a good pair of speakers from an old analogue TV set. However, the diaphragm was exposed and I had to make a mounting bracket so the diaphragm would not touch anything (or it would muffle the sound).

While I was at the museum to cut out speaker holes, etc., out of the console, there was talk about showing photographs of the console interior as part of the display. Then I opened my big mouth and said why not replace the front panel with a sheet of thick clear Perspex. So now the console will also be a diorama of sorts _ a wiring diorama. This means that the interior needs to be cleaned up, painted, and revamped. Though the control panel will also be revamped its antiquated looking exterior is to remain as is.

Thanks for sharing Peter. Top marks for interest, planning, build quality, and innovation. Plus I'm astonished by the speed at which you and other forum members work. In my workshop it takes an hour or two to find a screwdriver and then I have to have a tea-break!

Dave

Hello Dave.

Sorry to give you that impression.

I am currently half-way through the project. I came to this forum late. So I am posting photos of progress in piecemeal so not to inundate everybody with a sudden dose of 100 photographs. Hope you don't mind.

Progessing well (and rapidly).

Neil