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SuperFly 2018.10.07 12:14 PM

Timing bridge aperture question
 
I'm in the process of building a sensor bridge for an I-Lap decoder/transponder system, and I'm curious if anyone has done any testing or has any knowledge about how deep/wide the bridge channel should be.

I'm not an engineer (ha!), so I don't have the terminology to describe the distances, ratios and angles, but I think this drawing describes the question.

The sensors themselves are 1" wide, so that is the minimum interior width. I'm hoping to pick up some off-the-shelf U-channel of some sort, and just wondering about what size will work. TIA!


http://www.grymttr.com/greg/bridge.png

EMU 2018.10.07 12:47 PM

I-lap is usually very good at providing information. Shoot them an email, and see what they recommend.

arch2b 2018.10.07 07:14 PM

This is the design I made long ago.

In the end, I ended up lowering the bridge height and using only 2 pick up sensors.

SuperFly 2018.10.07 08:20 PM

Quote:

Originally Posted by arch2b (Post 466335)
This is the design I made long ago.

In the end, I ended up lowering the bridge height and using only 2 pick up sensors.

I'm going with two sensors as well. I've been scouring that thread, and the thing I'm trying to figure out, as much for mental exercise as practical application, if the problem you solved by lowering the bridge could be solved by narrowing the beam. I imagine there's a threshold somewhere when the aperture is too narrow and you start missing real signals. Obviously if it's too wide, it picks up everything, but I also feel like the lower the bridge is, the more visually disruptive it is, so I was trying to find the sweet spot between high enough off the track that you don't visually lose your car behind it, but that the sensor zone is still focused and accurate.

arch2b 2018.10.07 10:12 PM

Correct. Too low and you run the risk of greater inaccuracy due to limited pickup zone/time and it does become more of a visual distraction as well. Especially if you have opaque legs. Despite mine being a 2” U channel, painted black and almost visually imperceptible legs, it’s no issue at all. I’ve built 3 with this template.

I would recommend staying between 12-16”. We actually mapped the functional pickup zone with much practical testing to get a happy medium. Sadly I do not have the physical mapping data anymore. I should have digitized it on the blueprint but didn’t. I didn’t want to go any larger than a 2” channel as it becomes disruptive visually. At 2”, you also have space to fine tune the pickup by fabricating cones or aperatures for each sensor without it being seen. It leaves you some practical working room in other words. Just make sure you use Velcro to attach the sensors so you can easily tweak placement.

arch2b 2018.10.08 09:05 AM

If you find a source for plastic U channel, please let me know. I had to order aluminum channel online as it wasn't available at typical hardware stores either.

TPDazzle 2018.10.08 12:16 PM

Quote:

Originally Posted by arch2b (Post 466338)
If you find a source for plastic U channel, please let me know. I had to order aluminum channel online as it wasn't available at typical hardware stores either.

That was going to be my question. I 3d printed towers to give a bit more scale appearance, but I haven't been able to make the bridge. I bought a sheet of styrene and heated and folded it, but I couldn't get a clean enough fold, we are still using a cheesy pvc ziptied to plywood bridge.


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