Earthing a truck

This is entirely hypothetical of course! Let's say you had a large petrol powered truck that had to drive along railway lines, and you wanted to earth the truck to the lines. The truck has rubber tyres. Perhaps a small four steel-wheeled wagon that is dragged along under the truck. That's the easy part. When driving the truck, how can you see where the wagon is, so that the truck doesn't derail the wagon? The truck would be 100 times heavier than the wagon, so can't really be connected directly to it except by a towbar and a wire. Possibly a CCTV camera. Yes, that would do. Any other brilliant ideas?
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On 03/08/2013 05:17, Matty F wrote:

Sliding shoe contacts like third-rail electric railway systems - but, obviously, to the running rails rather than the (non-existent) third rail.
--
Rod

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On Saturday, August 3, 2013 7:26:37 PM UTC+12, polygonum wrote:

railway lines, and you wanted to earth the truck to the lines. The truck ha s rubber tyres.

e truck.

wagon is, so that the truck doesn't derail the wagon? The truck would be 1 00 times heavier than the wagon, so can't really be connected directly to i t except by a towbar and a wire.

.

OK, I looked up sliding shoe contacts. They don't go over gaps and points v ery well. I think I like four wheels better. I don't want to see sparks!
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On 03/08/2013 08:48, Matty F wrote:

Why is the earthing so important?
The sparking of UK third-rail is reduced by having more than one fitted so that, most of the time, at least one is in full contact. And you only get spectacular lightning when the train is using a significant amount of traction current. If you are only earthing the truck for low current, the sparking would be insignificant in most cases.
--
Rod

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polygonum wrote:

If track occupancy detection is involved, then a low resistance connection between the rails is vital. On occasion, with track that's not regularly used, it can miss a single truck. In some places, I've seen a bead of weld run along the rail surface to ensure that any rust is removed as soon as the first axle travels along the section.
Another possibility as the OP specifically mentions petrol power, maybe he's worried about sparks igniting fuel vapour. Or he's trying to arc weld....
--
Tciao for Now!

John.
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On 03/08/2013 08:48, Matty F wrote:

Given that an earth conductor should not normally be current carrying, there ought not be any even if the contact is not always perfect.
--
Cheers,

John.
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On 03/08/2013 08:48, Matty F wrote:

I don't see why not? The limited circumference of a wheel would pass over points with more undulation. I also don't see why you will get less parking. The unsprung weight will exacerbate contact issues.
A shoe with radiused ends is the typical method of conduction on the underground.
An example shoe though not sure where this type of shoe is used:
http://www.railway-technical.com/shoe-02.jpg
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On 03/08/2013 08:48, Matty F wrote:

If you're passing a lot of current through this setup, surely you'll get arcing across the wheel bearings. They won't take kindly to that. At least shoes can be made to take the punishment.
Cheers,
Colin.
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On Sunday, August 4, 2013 12:12:45 AM UTC+12, Colin Stamp wrote:

Not that this is anything to do with trams, but trams have a solid axle that the motor rests on via solid bronze bearings. So I could connect the wire to bronze bearings.
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Just how are you going the keep the rubber tyred wheels on a rail Matty?..
Road-rail vehicles do exist they normally have a separate set of wheels that can be put up or down as required...
--
Tony Sayer


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On Saturday, August 3, 2013 9:42:26 PM UTC+12, tony sayer wrote:

Very carefully! The ground is paved on either side of the rails. We already drive ordinary trucks along that.
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On 03/08/2013 05:17, Matty F wrote:

You have seen those trucks with railway wheels on swing arms that actually drive using the tracks rather than the rough track beds?
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On Saturday, August 3, 2013 7:26:38 PM UTC+12, dennis@home wrote:

railway lines, and you wanted to earth the truck to the lines. The truck ha s rubber tyres.

e truck.

wagon is, so that the truck doesn't derail the wagon? The truck would be 1 00 times heavier than the wagon, so can't really be connected directly to i t except by a towbar and a wire.

Yes, but we will have to use the existing rubber tyres. No rough track beds around here :)
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Matty F wrote:

The wheels on the swing arms are only for guidance and some weight transfer, traction is still through the normal road tyres. You may have a problem with the width of the vehicle not matching the gauge of the line, and with double tyres as used on larger trucks , it would be rather embarassing if the rails were to coincide with the gap between the pair of tyres on each wheel.
What is the vehicle type? If it's a Land Rover, then the tyres are the right distance apart already.
Also, have you thought about the difficulty of steering the thing exactly enough to keep it on the rails? It's not possible at anything above a very slow speed, and even then, the odds are you'll fall off the rails onto the track bed within yards.
--
Tciao for Now!

John.
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Matty F wrote:

Possibly something along the lines of a T shaped metal thing with L shaped brackets on each end, and attached to a towball on the truck would be the simplest. Just make sure that it's always at the trailing end to avoid it catching in the joints.
On the other hand, if this also has to trigger the type of track occupation sensors that most railway lines in this country use, it needs to guarantee a continuous low resistance from one rail to the other to work safely. This implies a good, guaranteed contact to both rails.
What most people in these circumstances do is install a hydraulically controlled bogie with metal rail wheels fore and aft, which carries some of the weight, guides the rubber-tyred vehicle, and guarantees track occupation circuitry triggering.
--
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John.
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On Saturday, August 3, 2013 7:48:52 PM UTC+12, John Williamson wrote:

railway lines, and you wanted to earth the truck to the lines. The truck ha s rubber tyres.

e truck.

wagon is, so that the truck doesn't derail the wagon? The truck would be 1 00 times heavier than the wagon, so can't really be connected directly to i t except by a towbar and a wire.



There is no track occupation circuitry to worry about. The surface around t he track is nice an smooth. The trolley will need to be under the truck so that people can't touch it.
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Matty F wrote:

How about giving us a hint as to why you need to earth the truck. Then we may know of a working solution. Working under tram wires, for instance, needs a different answer to running a high power transmitter in the truck. Which needs a different solution to earthing out a lightning strike.
--
Tciao for Now!

John.
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On Saturday, August 3, 2013 8:51:37 PM UTC+12, John Williamson wrote:

g railway lines, and you wanted to earth the truck to the lines. The truck has rubber tyres.

the truck.

he wagon is, so that the truck doesn't derail the wagon? The truck would be 100 times heavier than the wagon, so can't really be connected directly to it except by a towbar and a wire.

?


ds



me


nd the track is nice an smooth. The trolley will need to be under the truck so that people can't touch it.

Well OK, it will be running under an overhead wire at 600V DC, and needing an earth return. There are several devices that need power, e.g. a welder o r large motors. It will be driven very carefully along the rails. Really I just want any other ideas for how to know where the trolley is und er the truck. I have a spare CCTV camera. Otherwise some kind of indicator to show how central the trolley is.
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On 03/08/2013 11:10, Matty F wrote:

A pair of parking sensors either side that sense distance to the trolley?
--
Cheers,

John.
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Matty F wrote:

And *still* you avoid the T word.... <Grin>
Put the trolley on a towbar with a swivel at each end and drag it behind, or use clips to attach an earth lead when you stop. If you're working under a live overhead line, you'll want an exclusion zone round the truck anyway, so the public tripping over it won't be a problem. Even if you're not working live, it's good discipline to stop and earth the truck before working under overhead wiring anyway. Any time you save by doing it the way you seem to want it will be more than cancelled out by not complying with safety requirements. Also, if you have a tower on the truck, it must be dropped before you move near overhead cables anyway, to keep things safe.
And that's ignoring the risk of working on an earthed platform at height under live wiring. At 600V, if nothing can get within a foot or two of the wire, you don't need the earth anyway.
If you're worried about damaging an earth clip or its cable, connect it via a plug and socket, so if you drive away, it just pulls out.
You seem to be making life both overcomplicated and less safe for yourself.
If you insist on working live, take professional advice.
--
Tciao for Now!

John.
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