General > General high-speed discussion

Measuring Speed

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wilheldp:
Is there a proper name for the backing board that you can place behind a fast-moving subject to measure its speed?  The Mythbusters used them all the time, and I've seen them on some ping pong cannon videos too.  Basically, it is black and white lines of known width (inch/foot, or metric markings).  If you know the frame rate of the camera and playback frame rate, you can measure the exact distance that an object moves between frames, and calculate its speed.

I'd like to do some of those experiments with my Chronos.  I can probably make one, but if they are relatively cheap to buy, I'd rather go that route.  I don't have a lot of spare time at the moment, and I'd be worth it to me to just buy such a board unless they are exorbitantly expensive.  As of yet, I've failed to find a string of search terms on Google or Amazon that gets me what I want.

NoDak:
That is a good question. I know exactly what you are talking about, but have no idea what they are called.

I don't think something like that has a high enough volume to be ecenomic to mass produce. The high speed market is small and everyone will need different sizes and graduations for their particular project.

I made one out of a yardstick and tape years ago. My camera at the time wasn't up to the task so I never got far with it.

tesla500:
I've been calling those things a "Scale" or "Scale sheet". For small ones, you can just print something out on a printer, calibrated to whatever your favorite unit is, 1cm wide lines work well for something that fits on a normal printer. It's really easy to draw out the scale lines in Paint or a similar program, then you need to figure out the print scaling, this usually requires a few test prints and measuring the size that actually came out.

For bigger ones, the best option is to mark out and mask off a piece of wood with masking tape, and paint the stripes on.

wilheldp:
Yeah, I'm starting to think that nobody sells them commercially.  The NHTSA website references "inch tape" with alternating yellow and black, 1" bands, but I couldn't find anybody selling that.  I found some photo scales on forensic supply websites, but the biggest ones I could find are 1-1/4" wide and 12 inches long.  I guess I'm going to have to make my own.  I really hate painting.

NoDak:
Just measure it and use duct tape. That's what Mythbusters and company have done on occasion. Nobody says it has to be cable TV grade. Just mark at one foot intervals and put the edge of the tape on that line. Then you'll have 12", 10", and 2" intervals. (Assuming you use 2" duct tape.)

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