Infrared Timing System....

[Blackout]

I'm revisiting an infrared timing system with a twist. This one will be installed on my pond or our club's pond during test and tune days. The display shown below has 5" tall LED digits and will be on the shore for easy driver's view. Every time a boat passes through the traps, the front chute top speed will automatically be displayed. Two boats could run at the same time as long as they were spaced out a bit. I'm using an Arduino micro controller to record elapsed times, compute mph, and send outputs to the display. The Arduino is programmed using the C language.

Any thoughts on the minimum trap distance to produce accurate speeds to 1/10th of a second? Most boat speeds will vary between 50 - 80 mph. I know the IMPBA uses 330 feet. The current program is at 150 feet. But with mph computed at the drag strips only 66 feet, I'm wondering how short I can go. A shorter distance would save a little money and maybe make setup easier. Thanks for any input.

 

[Terry Keeley]

Cool project.

I think the accuracy of the derived speed will depend on the accuracy of your timing chip. If it's good to thousandth's of a second then a short distance would do, even 50'.

If it only counts full seconds, then 1000' wouldn't be enough to minimize the error...

 

[Blackout]

It does count every .001 seconds and could be programmed to count every .000001 seconds. But how accurately it counts at those intervals, I don't know for sure. But it's a modern CPU for hobby robotic use, so it surely should accurately count at .001 second intervals.

 

[Andy Greene]

Awesome project- its only a matter of time before technology catches up to our uses and we can have an extremely accurate timing / lap counting / speed type scoring lakeside in real time. Its efforts like this that broaden the horizons IMHO .

Good stuff

 

[Terry Keeley]

It does count every .001 seconds and could be programmed to count every .000001 seconds. But how accurately it counts at those intervals, I don't know for sure. But it's a modern CPU for hobby robotic use, so it surely should accurately count at .001 second intervals.

If you want a "speed" reading I would make the trap short, like even 25' near the end of the saw. That way the average speed between the traps will be close to the maximum speed.

80 mph is about 117.3 ft/sec, so 25 ft would take just over .213 sec. If your timer was accurate to 0.001 sec, your speed would be accurate to about +/- 0.5% (at 80 mph and 25'). So you 80 mph reading could be 79.6 to 80.4, pretty good.

 

[Marty Davis]

Some people have sites that can't have a transmitter and a receiver because the pond is to wide.

How about just building a radar unit with a display to place at the end of the SAW?

 

[Blackout]

Some people have sites that can't have a transmitter and a receiver because the pond is to wide.

How about just building a radar unit with a display to place at the end of the SAW?

I have thought about buying a radar gun for many years, but a good one is expensive. This setup can be done for less money I think.

 

[Blackout]

It does count every .001 seconds and could be programmed to count every .000001 seconds. But how accurately it counts at those intervals, I don't know for sure. But it's a modern CPU for hobby robotic use, so it surely should accurately count at .001 second intervals.

If you want a "speed" reading I would make the trap short, like even 25' near the end of the saw. That way the average speed between the traps will be close to the maximum speed.

80 mph is about 117.3 ft/sec, so 25 ft would take just over .213 sec. If your timer was accurate to 0.001 sec, your speed would be accurate to about +/- 0.5% (at 80 mph and 25'). So you 80 mph reading could be 79.6 to 80.4, pretty good.

Good info, thanks Terry.