Question About Radar Gun To Measure Speed On Coaster-Type Toys

Sunday, September 17, 2006 8:31 PM
Greetings all!

I am looking to find and purchase a device that can be used to measure the speed of a Screamin' Serpant Type toy or a marble on a marble run track. The device must be portable and cheap enough (No more than $300) and able to show several points on a track at the same time (For comparissons: Lift hill, Loop, straight-away, incline) on a screen or computer monitor.

It also must be continuously monitoring, so that a student doesn't have to aim and hold a trigger when a marble or coaster car approaches the desired area.

Of course it should have no effect on the moving object.

Finally, if we would be able to take it to parks to measure the real thing, that would be a bonus.

Any idea or thoughts about where to look for something like this?

Thanks in advance for your help.

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Sunday, September 17, 2006 10:35 PM
In school we got some light censors that we put into a marble track. The first would turn on a circuit, then the other turned it off. If you time the time it is on, then take that by the distance between the two censors, you've got velocity. You might be able to find something liek this for less than $300 in science kits
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Sunday, September 17, 2006 11:45 PM
When I worked in my college's physics laboratory, we sometimes used a software program for analying motion in videos.

The idea is simple. First, video record the motion of an object (can be a toy roller coaster or the real thing at an amusment park) while the camera is at a fixed reference point. Second, load the recorded motion into the software for analysis. Third, use the software to find, position, speed, and acceleration at any point in the motion.

The only thing you need to do is have a reference dimension of known length to input to the software. For your toy roller coaster, you can have a ruler standing next to the toy in the video. For the real thing, you could input the known height of, say, the lift hill.

The software is called VideoPoint. It costs $225. http://www.lsw.com/videopoint/vp/index.html

I believe this will meet all your criteria and thensome.

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Sunday, September 17, 2006 11:59 PM
I would look on Ebay for the video point bet you can find it cheeper that 225$
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Monday, September 18, 2006 1:29 AM
You can buy a radar speed gun at Radio Shack. I saw one there a couple weeks ago.
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Monday, September 18, 2006 12:19 PM
How about a hockey puck speed radar? It would be around $120

You might be able to figure out a way to use these with the software, I don't know, just an idea.

http://www.inlinewarehouse.com/descpage.html?pcode=PSCR *** Edited 9/18/2006 4:21:55 PM UTC by BeccaRaptor***

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Monday, September 18, 2006 4:53 PM
Look at the Hot Wheels web site. They have a radar gun that can test real speed and 1/64 speed. I saw one at walmart for $30 a couple of weeks ago. I almost bought it to check speeds of my r/c cars. I think it topped out at 100 mph real speed if I remember right. *** Edited 9/18/2006 8:54:53 PM UTC by bsr241***
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Monday, September 18, 2006 9:48 PM
Thanks for all the help. You folks are amazing.
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Monday, September 18, 2006 10:22 PM
I've used the software RollerHammer mentioned in a physics lab and it works pretty well. This would probably be a good option because you could get the speed at any number of points instead of just being limited to wherever you have your sensors set up. I also think you'd get more accurate results with this than some cheapo radar gun.
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Tuesday, September 19, 2006 5:03 PM
...Or do it the cheap way with a video camera and any method that can give you single-frame playback. In NTSC, video runs at 29.97 frames per second. You don't need software to do frame-by-frame analysis.


That's the simplest way to get results. If you want to get real-time results, the light curtain technique described above is probably your best bet. Then you can measure the time between sensor triggers using any suitably equipped computer. A real-time clock would be useful, though, so while you could do it on, say, an Apple ][ via the game port (really easy!) you probably want to get results based on real time instead of machine loop cycles. :)

So if you want to "roll your own", run the optical pairs to an encoder board driven by a microcontroller and connected to a computer via parallel or USB.

--Dave Althoff, Jr.
*** Edited 9/19/2006 9:07:22 PM UTC by RideMan***

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Wednesday, September 20, 2006 10:43 AM
It's just not fair. Some people know too much. I'm telling Mommy! ;)
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