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Old 05-19-2012, 03:09 AM #22
General Cole
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Depending on differences of the ball, yes. I was a EE, you might shooting me some info on it? I have a bunch in various stages of building based on eye type chronographs sitting around. If you wouldn't mind shooting me what you've got, I'll shoot what I have to you and we can get something even better going.
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Old 05-21-2012, 10:22 PM #23
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has some ghetto characteristics, but i like it! Did it cost more to make than a regular chrono?
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Old 05-22-2012, 11:27 AM #24
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Quote:
Originally Posted by General Cole View Post
Depending on differences of the ball, yes. I was a EE, you might shooting me some info on it? I have a bunch in various stages of building based on eye type chronographs sitting around. If you wouldn't mind shooting me what you've got, I'll shoot what I have to you and we can get something even better going.
i've got pretty much everything down except the physical packaging.
I haven't made much progress in the past month since ive been busy with other stuff, including my barrel condom stuff which pays for my paintball
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Old 05-22-2012, 11:29 AM #25
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has some ghetto characteristics, but i like it! Did it cost more to make than a regular chrono?
if you count the programmer, then yes it cost more,
if you count the time it took to build, then yes it cost more,
if you count the time it took to debug, then yes it cost more.


if you just count raw materials, it's somewhere ~$10 right now.


but it's all a learning process and i really enjoyed using my college education for the hobby i love. how many people get to say that
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Old 05-22-2012, 12:52 PM #26
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haha! not alot. college education helping your hobby-never! but very nice. im sure it was a blast to build!
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Old 05-28-2012, 12:15 PM #27
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Know what you could do? Sell kits! Gather up all the not-so-common components like the phototransistors, LED readout, and microcontroller. Then flash the chip with your code, throw it all in a bag with some sort of basic schematic and leave all the tedious mounting/soldering to the customer. Only thing is you would need some easy way of calibrating it.
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Old 05-28-2012, 12:38 PM #28
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two. spaced a known distance.
one would be a little tricky and probably inaccurate.
So you have them spaced the distance and then record the time difference between when the ball passes between the first and second, then calculate the speed from that? Neat.

Did something similar for a science project in high school but without actually building the gates myself.
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Old 05-28-2012, 01:28 PM #29
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Yea, you just have to be SUPER precise about it.
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Old 05-29-2012, 10:51 AM #30
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Know what you could do? Sell kits! Gather up all the not-so-common components like the phototransistors, LED readout, and microcontroller. Then flash the chip with your code, throw it all in a bag with some sort of basic schematic and leave all the tedious mounting/soldering to the customer. Only thing is you would need some easy way of calibrating it.
Yes I did briefly consider that, but what if the chrono doesn't work? who's fault, responsibility is that? I'd probably have to have a bunch of support for those that are less electronically inclined. I'm not sure if i'd want to deal with angry customers..
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Old 05-29-2012, 10:52 AM #31
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Yea, you just have to be SUPER precise about it.
yep. fortunately there are a few ways to calibrate so if someone puts the holes 3.00001" instead of 3" apart they don't have to start over.
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Old 05-29-2012, 10:54 AM #32
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So you have them spaced the distance and then record the time difference between when the ball passes between the first and second, then calculate the speed from that? Neat.

Did something similar for a science project in high school but without actually building the gates myself.
yep. the concept is exactly that.
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Old 05-29-2012, 12:23 PM #33
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Yea, that should be coded into your controller. Have you calibrated against a different chrono? And are some plans available? I have a housing design ready for a chrono that I think I can fit this one into.
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Old 05-31-2012, 10:12 PM #34
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parts list and a schematic.
people would pay. so many people would pay...
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Old 06-01-2012, 11:57 AM #35
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yep. fortunately there are a few ways to calibrate so if someone puts the holes 3.00001" instead of 3" apart they don't have to start over.
Can you speak a little more about the issue of calibration? How precise did you get it, and how precise does it need to be? I remember doing some rough calculations years ago when someone else was looking into building the same thing, but I never got any further than that. If your microcontroller is fast enough then you might be able to use one set of eyes. I'd be curious to see how that works out.

Anyway, nice to see someone go through with it, it's a very simple concept but seems kinda painful to tune. To avoid having to reprogram, add two push buttons which allow you to do software tuning. Multiply the time you measure by 1 to start, and have the buttons increment/decrement that weightage by a very small amount. You'd have to figure out how to save that variable when you power down but that's doable. If you wanted to deal with the calibration outside of software, I can imagine having slots (rather than holes) to keep each set of eyes in place. The user could then fine-tune the system by actually moving the sets of eyes. That would be really elegant but would require a really good casing design.

Well, I'm just rambling now. It's a cool project! I think you could sell kits if you clean it up more, get casings and PCBs made, and maybe a better user interface (use an LCD instead?).
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Old 06-01-2012, 12:08 PM #36
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Can you speak a little more about the issue of calibration? How precise did you get it, and how precise does it need to be? I remember doing some rough calculations years ago when someone else was looking into building the same thing, but I never got any further than that. If your microcontroller is fast enough then you might be able to use one set of eyes. I'd be curious to see how that works out.

Anyway, nice to see someone go through with it, it's a very simple concept but seems kinda painful to tune. To avoid having to reprogram, add two push buttons which allow you to do software tuning. Multiply the time you measure by 1 to start, and have the buttons increment/decrement that weightage by a very small amount. You'd have to figure out how to save that variable when you power down but that's doable. If you wanted to deal with the calibration outside of software, I can imagine having slots (rather than holes) to keep each set of eyes in place. The user could then fine-tune the system by actually moving the sets of eyes. That would be really elegant but would require a really good casing design.

Well, I'm just rambling now. It's a cool project! I think you could sell kits if you clean it up more, get casings and PCBs made, and maybe a better user interface (use an LCD instead?).


i suppose this isn't a huge trade secret that I'm giving away so I don't feel uncomfortable sharing. I can (haven't actually implemented this yet) use a potentiometer to calibrate it to within +/-1 fps of a commercial chrono.
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Old 06-01-2012, 12:09 PM #37
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people would pay. so many people would pay...
haha I know I know. I've just been slow and lazy. other things in life taking priority. like watching the playoffs
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Old 06-01-2012, 01:04 PM #38
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i suppose this isn't a huge trade secret that I'm giving away so I don't feel uncomfortable sharing. I can (haven't actually implemented this yet) use a potentiometer to calibrate it to within +/-1 fps of a commercial chrono.
Right, that works. I'm always leery of using pots for tuning though. If you get a trimpot you won't have to worry as much about accidentally changing the value by touching it, those are the kind you need for something like tuning. When you use cheap ones they can be really finicky. I'd try the software compensation if you can, but a trimpot certainly works.
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Old 06-01-2012, 04:46 PM #39
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it's simple enough that anyone who can program a microcontroller should figure out how to make one without looking at my schematic just by knowing it's a phototransistor sensor.
Two break beam eyes and a known distance would do it yeah?

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Can you speak a little more about the issue of calibration?
IMHO, what I would do is apply a scale factor to the programming which will allow you to raise/lower the velocity using a separate chrony as a baseline.

I did some research on Doppler Radar style chronies. Spoke with Chuck Hendsch on the subject a while back.
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Old 06-01-2012, 06:12 PM #40
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Two break beam eyes and a known distance would do it yeah?



IMHO, what I would do is apply a scale factor to the programming which will allow you to raise/lower the velocity using a separate chrony as a baseline.

I did some research on Doppler Radar style chronies. Spoke with Chuck Hendsch on the subject a while back.


two break beams yes.

and yes, you can adjust the scaling. you could use software or hardware.
doppler radars are a bit trickier and more expensive.
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Old 06-01-2012, 06:14 PM #41
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Two break beam eyes and a known distance would do it yeah?

IMHO, what I would do is apply a scale factor to the programming which will allow you to raise/lower the velocity using a separate chrony as a baseline.
I just assumed this is what he did, not sure if he said it explicitly though. But it's the simplest way. I think maybe you could get away with one set of eyes but that would only be better for the sake of simplicity.

As for tuning, yeah, that's what I suggested above. Except you don't want to have to reprogram the board every time to change the scale factor. Instead, you start it off at a nominal value and allow the user to change it on the fly by pressing an "up" or "down" button which slightly tweaks that scale factor in the program. That way, you can calibrate to any chrono without having to change anything in the code. All these boards have some memory capacity so you should be able to save that scale factor after powering down. If it turns out to be slightly off the next time you have access to another chrono, you just recalibrate a bit.
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Old 06-01-2012, 06:41 PM #42
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You wouldn't want it to be something the user could monkey with. Set it and forget it, really.

A potentiometer has a tendency to be able to get knocked if the user treats his/her equipment badly. There are surface mount ones that would work in an enclosure.

Ideally if you were to place one in a molded plastic enclosure you would still have to assume a certain amount of play in tolerance, problems with calibration after cleaning (as the nature of paint).

This is why shooting chronies and doppler chronies are really preferrable. Doppler chronies take up to ten samples per shot. They are quite remarkable devices.
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