Need to Know When Vehicle is Moving

GPS?

I don't think that GPS will be accurate enough.

The car is self propelled and is typically stationary. Sometimes it is moved but it is done at a very slow speed, roughly 1 mph.

This system is for safety, to detect if the car moves without being told to. Something bumping into it or pushing it.

My problem with an accelerometer is that this is located on a trestle and it vibrates quite a bit.

I was hoping to use something that could detect the rotation of the wheel on the truck of the car. The other problem is that this is a very dusty/dirty area.

Accelerometers ?

Mk.1 eyeball?

I think I may have just found the answer by using a rotary encoder. Now I just need to find the right one.

A photoeye and a can of spray paint will do the trick.

You can make a non-contact encoder like function by simply applying some sort of reflective and light absorbing surface to the wheel.

Then you will need to determine when the photoeye changes state because you never know if the wheel will stop on reflective or non-reflective surface (a "1" or a "0").

Or you could just glue some reflective strips on if you didn't want to use paint.

Another way to "skin this cat" (sorry Del!) is to use a sensor that detects reflected light from the ground. When it is stationary, the output will be fixed. When motion is involved, the output will change. Resolution and lighting are the problems using this method. You will need to provide a consistent light source. I would use LEDs.

Only problem with that is this is an industrial area and very very dusty. I'm thinking magnetic rotary encoder is going to be the way to go. I'm looking at some on Mouser now.

I would look at the type of encoders that are used with Anti-Lock brake systems on automobiles. They have the "detector" mounted in close proximity to a cogged wheel mounted on the hub of the wheel to sense rotation.

Tom D.

You could adapt the design of an optical mouse to make it more robust or use 3, 5, 7, 9 . . . mercury switches mounted on the wheel , any change in state may indicate movement.

There is an American system now used in the UK. (Don't ask me what it's called).

Under the loco a Doppler system measures the speed of the loco's travel in relation to the track bed. This information is combined with the speed feed back from the driving wheels to allow up to 15% slip, each wheel set is individually controlled. This came about after the old accepted theory of molecular adhesion of rail wheels was disproved.

If I recall correctly class 66 loco's use this system

There is no real track bed here. It's a dump system for a conveyor belt located over 50' in the air on a trestle. So no doppler system.

You can also approach like this.Modify the design.

This what i did ,In one of my engineering project .This design is having advantage

1) detect motion

2) speed.

The Thickness of the metal disc attached to the wheel should decrease uniformly to some value.

Inductive sensor detect the change in value, when the wheel starts to move.

Sorry for the poor drawing.

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Correct me if i am WRONG .......

I think I'm going to do something really similar. I'm looking at a couple of products from Electro-Sensors (.com). Specifically the SS110 Slow-Speed Switch and the SCP1000 Presettable Speed Switch.

They both look like they will work and both are suitable for the dusty environment.

Not exotic enough.

Measure the resistance through the car couplings. A car cant move unless its being pulled and when it is, the coupings are tighter, right?

If the cars are moving without being pulled, Id guess theres a much BIGGER problem...

Any good engineering solution has some complex, whacky circuit, and at least one laser. Im not sure where a laser fits that system, but there HAS to be one....maybe to blind the graffiti artists? ANY good system design causes the observer to ask "what was he smoking..."

Seriously, such a system could also PREDICT movement before it happens as the slack has to be taken up before the car can move.

This is self propelled and does not even have couplings. So, no fancy exotic resistance measurement. Lasers are definitely a must though. If your going to design it, you've got to incorporate a laser somehow.

use a motion sensor