Speed Measure Car

[medusa]

Hi,

 

the discussion about Hall sensors made me posting this... actually, it was my first model railway project after wiping the dust off my only left 40 years old loco. Did that in 2015, sorry for the bad photo quality. At that time I was not yet familiar with the camera.

The idea is not mine, actually someone earlier made something like this in a Z scale car. Basically, it uses a Hall sensor and a tiny supermagnet glued to a wheel (or axis) to generate a pulse chain. The latter is sent via some cheap 2.45 GHz sender/receiver pair (think they made these for electronic keys and the like). The pulse chain from the Hall sensor finally ends in an auxillary tachometer as sold for bicycles and motorbikes, and here it is converted in some more or less fancy speed display.

 

 

This image may be most interesting for Hall sensor fans. It shows the sensor glued into the bogie and two 1mm supermagnet cubes forming a rotating magnet bar sticking to the axis. A little bit challenging was to get electrical connections since all usual wires were way too stiff. I ended up making my own copper spirals, bent with help of a sewing needle.

 

 

Electric schematic is quite simple. I decided to power the measure/sender unit via batteries in a second car. (Some time later people in the german forum found tiny step-up converters starting to generate 12V from only 3V track voltage on.)

The Hall sensor's output is biased by a pullup resistor and fed directly into the sender unit. A LED display shows battery voltage (it's a remain from an earlier stage of the project). The battery (3 x 3V lithium cell) is housed in a second car. (second scematic)

The receiver unit (first schematic) feeds the signal (which is of course noisy) through an RC-filter into a Schmitt trigger network to restore the original rectangular shape of the pulses. The motorbike tachometer (of type "MC 10") has its own internal battery so it is kept insulated by a small signal relais separating it from the receiver circuit.

 

 

About the model - it's the kind of car which German Railways used for traction tests of locomotives, speed tests of cars and the like. For track measurements different cars were used. Until the 1990s these cars were painted plain yellow. Often a pair was in service, one car did the measurements and the other kept spare parts and tools. A panto could be used to power the instruments independently of the loco under test.

I modded a restaurant car with panto for the measure car and a baggage car for the tool car (taking the batteries here).

 

Due to the battery powered model the car set can take speed measures from zero speed on (so, for zero track voltage). Some fun was to find out how fast my old loco could drive... you see it on the last photo with 327 kph. Well, not quite like in real world. The E 03 was limited to 200 kph in regular service even if one unit with special gear sets did test drives up to 280 kph at that time.

 

 

 

EDIT: removed a bunch of typos

Edited December 15, 2016 by medusa

[cteno4]

Quite brilliant medusa! Love it! Now you can make some kits and sell them! Kudos!

 

Thanks,

 

Jeff

[NXCALE]

What a great project!

Thank you for sharing (also the diagrams).

 

I checked my spare parts and I found these RF modules.

 

To be honest I haven't use them or check much information about these.

One day I will give it a go to see what happens.

 

Cheers,

 

[warnerj01]

Could I see a bigger side shot of the digital speed display?

[medusa]

nxscale,

 

these things become cheaper and cheaper. I paid about 1.50 Euro for my 2.45 GHz pair and the next people who tried to build something like this got modules about half the size.

At that price, however, you can't expect much quality control so I recommend to order more of them (say, 3 or 5 pairs) and select the best-working one.

So don't worry about the RF modules if you can't find the spec any more... ;)

 

 

warner,

 

which one? The red LED display in the car is some cheap digital voltmeter for battery checks. Do you mean the LCD type Sigma MC-10 bike tachometer? I have no better photo of it, but here you can see it in the web:

http://sigmasport.com/de/images/sigma_website/produkte/slider/slider_mc10/slider/03_mc10.jpg

[NXCALE]

Thanks for the extra info.

 

I agree on having/ordering extra modules/spare parts when starting a project.

It saves time and reduces the risk of unnecessary frustration (i.e. you are doing all well but just the component does not work  - and you just found it out later).

 

Cheers,

[warnerj01]

nxscale,

 

these things become cheaper and cheaper. I paid about 1.50 Euro for my 2.45 GHz pair and the next people who tried to build something like this got modules about half the size.

At that price, however, you can't expect much quality control so I recommend to order more of them (say, 3 or 5 pairs) and select the best-working one.

So don't worry about the RF modules if you can't find the spec any more... ;)

 

 

warner,

 

which one? The red LED display in the car is some cheap digital voltmeter for battery checks. Do you mean the LCD type Sigma MC-10 bike tachometer? I have no better photo of it, but here you can see it in the web:

http://sigmasport.com/de/images/sigma_website/produkte/slider/slider_mc10/slider/03_mc10.jpg

 

I was just hoping to see a better sideshot of the car that has the red LED display.

[medusa]

Hi warner,

 

I digged through the old photo data and can show you one detail from the photo above and another from the early construction stage which shows the LCD fitted inside.

 

 

If you're interested in detail about the car model finish, I have still some other photos with better resolution.

[gavino200]

This is incredible!!! Amazing!!