Source of copper tipped sprung contact fingers?

[PippinParticipant @phillspowart84010]

Something I’ve been working on, which I could do with some advice on. This is a 1/5 scale model of a controller for a battery mining loco, which I’ve been working on for a while. So far I’ve designed and prototyped the case and handle/star wheels/reverser and interlock mechanisms, which now work. The controller will be just like the original, 5 speed series-parallel with a box of resistors elsewhere on the loco, controlling two cheap electric scooter motors off ebay.

I’m about to start figuring out the barrel and finger mechanism. The fingers will be some form of spring strip with a copper contact on the end, approx 5mm wide by 30mm long. A photo of a totally different roller barrel type controller is included to give some idea (The green one). Before I go design and make a load from scratch, can anyone thing of such an item that is available off the shelf? It seems like the sort of thing you’d get in switch gear, but everything I can find online is either too big or too small. I bet there’s a mass produced switch somewhere that has the perfect part buried inside it, but I don’t fancy buying the whole CEF catalogue to pull to bits to find out.

 

[bernard towersParticipant @bernardtowers37738]

Wouldn’t you be better off using a modern controller hidden in the box?

[PippinParticipant @phillspowart84010]

Maybe, in the same way that a steam outline model with a battery and motor in the tender is easier to build and run than live steam. I want the equivalent of a live steam model, in that it doesn’t just look like the real thing buts works like the real thing too. Though I have drawn the line at making my own motors with field windings.

[Peter Cook 6Participant @petercook6]

Don’t know if they have anything that would suit , but you could try these people in the US. They do say they will ship to the UK, and have a fairly large variety of contact styles.

[BazyleParticipant @bazyle]

One of the sources of this type of thing used to be post office relays.

[Robert Atkinson 2Participant @robertatkinson2]

Your best option would be to look at relay contacts. They will have different contact material (like the green unit) but that is a good thing.
What size contact (length and width) are you looking for?

Robert.

[PippinParticipant @phillspowart84010]

Around 5mm wide x 30mm long, thankyou. I looked at PCB contacts, but they are too small. I have at least found that half round copper wire is something you can buy, which would simply making contacts from scratch.

[Martin Johnson 1Participant @martinjohnson1]

I get what you are trying to do.  Turning a pot on a modern controller is just not the same as driving on old tram (for example).

As to sources, old equipment such as switchgear or relays would be good.  For model use I wonder if plain BeCu strip without the copper contact blocks would be good enough?  How many thousand hours of operation per year are you planning?

There was a series in ME on making pneumatic relay motor contollers for a model electric loco.  Obviously the business end of the pneumatic relays would be good inspiration.  They had the full monty of knuckling contacts, arc blow out chutes etc.  There was also a tram building series in the seventies by ?? Jackson-Stevens (IIRC) which had details of the classic rotary controller.

Hope that helps,

Martin

[peak4Participant @peak4]

Try a search for “Strowger 3000 type relay” & variations around that, and see where it leads you.
Contacts for a GPO ringer would also work well and may be heavier duty.

How many do you need?

Bill

[PippinParticipant @phillspowart84010]

Thankyou again for the replies. I need 26. I am hoping I might get the loco design published in some way though, so I’m hoping to find something available off the shelf.

Here’s two views from Alibre. Done from works drawings, with versions in 3.5″ and 5″ gauge representing 18″ and 2ft.

[BazyleParticipant @bazyle]

Half round copper wire will not be springy. You need phosphor bronze strip with a separate contact rivetted on (solder heat might destroy the spring  temper).
For the larger parts you seem to want an old fashioned electric bell might be the source if you can find a load of them at car-boots or a flee market. Also a dewhurst drum reversing switch – a kind of cannibalism.

[PippinParticipant @phillspowart84010]

Sorry, that would have made much more sense if I’d finished writing that thought. If I do make fingers from scratch, I’m thinking BeCu strip with half round copper contacts-again following the real thing. The availability of half round copper wire means I don’t need to mill down round bar stock.

[Andrew TinsleyParticipant @andrewtinsley63637]

I am unsure if copper contacts are a good idea. I would be tempted to use tungsten contacts. But then I am not really cognizant of your requirements.

Andrew.

[PippinParticipant @phillspowart84010]

Copper contact tips on copper barrel segments are how the real thing works. Lubricated with vaseline originally, though better switch grease is available now.

[duncan webster 1Participant @duncanwebster1]

12 position rotary switch with a chain of resistors would give the feel of an old controller but match up to a modern PWM controller

[Speedy Builder5Participant @speedybuilder5]

car distributer sprung contact strips.?

[John HaineParticipant @johnhaine32865]

I have a quantity of BeCu 50 x 0.1 mm shim which grossly exceeds my likely lifetime requirement, you are welcome to a few inches if that would help.  It strikes me that you need to generously dimension the contacts as the motors are likely to draw a LOT of current when starting, the likes if PO3000 relay contacts (even if you could find them) wouldn’t do.

[PippinParticipant @phillspowart84010]

Thankyou for that offer, I might be in touch. Though I think 0,1mm might be a bit thin. You need a bit of pressure on the contact tip so it doesn’t rattle and arc.

[MichaelRParticipant @michaelr]

If you feel like spending a bit of money see Ride on Railways shows a nice controller.

https://www.rideonrailways.co.uk/accessories/index.html

[PippinParticipant @phillspowart84010]

Much as I appreciate the suggestions to steer me away from going mad trying to make this thing, I really am determined to make this as close to prototype as I can. Think along the lines of those incredible people who make working Westinghouse compressors or Stones generators, yes there’s easier things to do but where’s the fun in that?

I may regret saying that of course 😉

[Chuck TaperParticipant @chucktaper]

Disembowel a Myford Dewhurst Forward/Reverse Drum Switch – possibly?

 

[Ian PParticipant @ianp]

That might get expensive!

Phil wants 25 fingers, can’t be that many in a Dewhurst surely.

Ian P

[Ian PParticipant @ianp]

I’m not into models, but I am confused about your statements like make this as close to prototype as I can, 5 speed series-parallel with a box of resistors and box of resistors elsewhere on the loco.

I am all for making accurate scale models but its not practical to scale absolutely everything, you’ve already accepted the motors and that choice alone means that the look and feel will not relate to the original. I’m not sure that scooter motors (permanent magnet type?) will be amenable to control via a series parallel arrangement and a bunch of resistors. If I remember correctly ‘series parallel’ refers to the field and armature windings so not relevant to brushed PM motors anyway.

I definitely endorse making the controller drum switch as you have prototyped but I would suggest that you only use its contacts to handle low current. If you did make scale copies of the original contact fingers they would be unlikely to carry the current anyway and if you beefed them up you would be departing from the originality goal. I think it should be a scale copy externally and have the correct notched detent feel.

Replicating the originals loco’s response (acceleration, deceleration) to its controls using electronic speed controllers, in conjunction with your custom drum switch is pretty straightforward stuff these days (one could even add sound). I don’t think any of this takes away any of the authenticity of your model, rather it enhances it.

Just my two penneth

Ian P

 

[PippinParticipant @phillspowart84010]

Motors are ZY6812 cheap chinese ebay specials. Permenant magnet and brushed, so should cope OK. Obviously this wouldn’t work with modern brushless motors.

Series-parallel refers to the arrangement of the two motors, so will work fine with these. (Some single DC motor vehicles had two sets of field windings that were ran series-parallel, which might be what you’re thinking?). See diagram attached.

The innards aren’t remotely scale, the PM motors mean I need half the contacts of the original (11 main barrel 12 fwd/rev vs 6 main barrel 4 fwd/rev). This means I can make the contacts much wider, current design is 6mm wide (scale would be 2mm :O). I had a good stare at the original wiring diagram and managed to remove 3 contacts on the main barrel today, which was nice.

It might not work, but it’ll be interesting to try.

[old martParticipant @oldmart]

You can get small sheets of berylium copper in various thicknesses on ebay and if tips for wiping contact were required then making them from electric motor brushes, which are sintered copper with graphite. If you decide onthe BeCu, then take care not to breathe in any dust produced while making the parts, and wash your hands before eating.

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