Tach-like Sensor

[BillyJ]

We want to make a sensor that can measure our shooting wheel speed. Reading threads it seems like there was a "Banner" sensor that could measure white tape on a wheel, but I haven't been able to find that at digi-key.

One of my friends told me about this, would this work?
http://rocky.digikey.com/WebLib/Opte...OPB715,716.pdf

Thanks

[6600gt]

Originally Posted by BillyJ

We want to make a sensor that can measure our shooting wheel speed. Reading threads it seems like there was a "Banner" sensor that could measure white tape on a wheel, but I haven't been able to find that at digi-key.

One of my friends told me about this, would this work?
http://rocky.digikey.com/WebLib/Opte...OPB715,716.pdf

Thanks

It might, but you can only calculate the theoretical speed. You can also try the gear tooth sensor.

You might be able to use a decent powered led and a phototransistor. The ball will pass in between them and cut the light to the phototransistor. Set the interrupts to fire on the falling edge(when it reads 0). Then recored the time at that point of a timer and set the pin to fire on high next and when it fires again on high record the time again. The ball is usually a constant 7 inches, so using that and the time you can calculate the velocity. Go to radioshack and ask them.
It is more complicated but I think it will be much more accurate.
Sorry, I haven't tired it, so I can't prove it.

[Tom Bottiglieri]

Originally Posted by 6600gt

It might, but you can only calculate the theoretical speed. You can also try the gear tooth sensor.

You might be able to use a decent powered led and a phototransistor. Put the ball will pass in between them and cut the light to the phototransistor. Set the interrupts to fire on the falling edge(when it reads 0). Then recored the time at that point of a timer and set the pin to fire on high next and when it fires again on high record the time again. The ball is usually a constant 7 inches, so using that and the time you can calculate the velocity. Go to radioshack and ask them.
It is more complicated but I think it will be much more accurate.
Sorry, I haven't tired it, so I can't prove it.

He wants to measure the shooting wheel speed, not the actual velocity of the ball.

Yes, that sensor will work fine. You could also use the IR sensors that came in the kit this year.

[Matt Krass]

You can also use any leftover kit motors as a DC tachometer, see below.

http://www.chiefdelphi.com/forums/sh...ght=tachometer

Wire it up to an analog input, make sure its geared so it doesn't ouput more than 5V though, or you might damage the RC.

[6600gt]

Sorry I missed that part, but the gear tooth sensor can easily do it.
I don't know about the IR sensor in the kit because on the data sheet it says 500ms response time(it is a switch so it takes time to trigger it).

[BillyJ]

Thanks for the quick replys and options. I think we're pretty much set on using the tape on the wheel since it would be the easiest to implement at this point.

Could anybody recommend something that would be better then what I had before?

[Dale(294engr]]

Originally Posted by BillyJ

Thanks for the quick replys and options. I think we're pretty much set on using the tape on the wheel since it would be the easiest to implement at this point.

Could anybody recommend something that would be better then what I had before?

Team 294 is using the KOP VISIBLE Banner sensor to measure shooting wheel speed 20% black on white (checked out with margin at 100 rps = 6000rpm)

Team 294 is using the KOP IR Banner sensor(s) to measure ball exit velocity (IR reflected from exiting ball), one IR sensor at wheel exit, one at 1m (up to ~1' away detection range) using any BUT black half balls (blue/green, purple/green, anything but half black which absorbs IR). This (& pulsewidth below) method have proven very accurate & reliable and the sensors are well up to the speeds. (not close to limit)

We are viewing the pulse waveforms on an oscilloscope.
A 'C' program could be written to do the job of recording the data and results.

83 mS (.08333s) between 1 meter spaced sensors is 12m/s (1/.08333s)
or use exit sensor leading to training edge pulsewidth and factor in number 7" ball width in a meter.

Vexit_m/s = 1/((39.37"/m / 7"/poof ball = ~5.624) * pulsewidth)

12 m/s
83.3 mS / 5.624 = 14.8mS pulsewidth_7"ball, expected

Dale (294engr]