Sharp GP2D12

Archiver

I'm interested in using the Sharp GP2D12 analog distance measuring sensor.

Since it is making a continuous measurement, would it possibly measure
something rotating?

In my case I want a rough measurement of a set of rotor blades.
I would be about 2 ft from the center of rotation. Each blade is about 8"
in width, and turn from 100 to 500 RPM.

Would I see a pulse train with the two voltage levels. One corresponding to
the distance of the a rotor blade, and the other being 0.6V (>80cm) as the
sensor is pointing up...

Any help appreciated.
Bill Heacock

Archiver

Yes but need some considerations. The GP2D12 does not takes mesurements
contimuously but at several times each second . 38ms per reading that
means a 26.31 Hz. To have reliable sample readings your system should
work at maximum of 13 Hz (Nyquist). This will depend of how many blades
you have rotating.If you have one blade rotating a 500 RPM this means
500/60 = 8.3 Hz. But if you have 2 blades will be 16.6 Hz. 3 blades
will be 25 Hz.
ACJacques


William Heacock wrote:
>
> I'm interested in using the Sharp GP2D12 analog distance measuring sensor.
>
> Since it is making a continuous measurement, would it possibly measure
> something rotating?
>
> In my case I want a rough measurement of a set of rotor blades.
> I would be about 2 ft from the center of rotation. Each blade is about 8"
> in width, and turn from 100 to 500 RPM.
>
> Would I see a pulse train with the two voltage levels. One corresponding to
> the distance of the a rotor blade, and the other being 0.6V (>80cm) as the
> sensor is pointing up...
>
> Any help appreciated.
> Bill Heacock

Archiver

Thanks,
Where did you find the 38ms per reading?
I did find a 2 page data sheet on it, but it did not mention this. My
project will be two blade design so it would become marginal above 390 RPM.
Bill Heacock


At 10:09 PM 5/29/2000 -0300, you wrote:
>Yes but need some considerations. The GP2D12 does not takes mesurements
>contimuously but at several times each second . 38ms per reading that
>means a 26.31 Hz. To have reliable sample readings your system should
>work at maximum of 13 Hz (Nyquist). This will depend of how many blades
>you have rotating.If you have one blade rotating a 500 RPM this means
>500/60 = 8.3 Hz. But if you have 2 blades will be 16.6 Hz. 3 blades
>will be 25 Hz.
>ACJacques
>
>
>William Heacock wrote:
>>
>> I'm interested in using the Sharp GP2D12 analog distance measuring sensor.
>>
>> Since it is making a continuous measurement, would it possibly measure
>> something rotating?
>>
>> In my case I want a rough measurement of a set of rotor blades.
>> I would be about 2 ft from the center of rotation. Each blade is about 8"
>> in width, and turn from 100 to 500 RPM.
>>
>> Would I see a pulse train with the two voltage levels. One corresponding to
>> the distance of the a rotor blade, and the other being 0.6V (>80cm) as the
>> sensor is pointing up...
>>
>> Any help appreciated.
>> Bill Heacock
>
>
>
>
>

Archiver

Look:
http://www.acroname.com/robotics/info/articles/sharp/sharp.html
In the booklet supplied by Acroname for GP2D12 buyers they said
that measurements are updated about about 32ms.I dont now who is
correct, but this figure is a litle better in your case. With readings
at 31.2 Hz you become marginal at around 450 rpm.
ACJacques

William Heacock wrote:
>
> Thanks,
> Where did you find the 38ms per reading?
> I did find a 2 page data sheet on it, but it did not mention this. My
> project will be two blade design so it would become marginal above 390 RPM.
> Bill Heacock
>
> At 10:09 PM 5/29/2000 -0300, you wrote:
> >Yes but need some considerations. The GP2D12 does not takes mesurements
> >contimuously but at several times each second . 38ms per reading that
> >means a 26.31 Hz. To have reliable sample readings your system should
> >work at maximum of 13 Hz (Nyquist). This will depend of how many blades
> >you have rotating.If you have one blade rotating a 500 RPM this means
> >500/60 = 8.3 Hz. But if you have 2 blades will be 16.6 Hz. 3 blades
> >will be 25 Hz.
> >ACJacques
> >
> >
> >William Heacock wrote:
> >>
> >> I'm interested in using the Sharp GP2D12 analog distance measuring sensor.
> >>
> >> Since it is making a continuous measurement, would it possibly measure
> >> something rotating?
> >>
> >> In my case I want a rough measurement of a set of rotor blades.
> >> I would be about 2 ft from the center of rotation. Each blade is about 8"
> >> in width, and turn from 100 to 500 RPM.
> >>
> >> Would I see a pulse train with the two voltage levels. One corresponding to
> >> the distance of the a rotor blade, and the other being 0.6V (>80cm) as the
> >> sensor is pointing up...
> >>
> >> Any help appreciated.
> >> Bill Heacock
> >
> >
> >
> >
> >

Archiver

for your rotor blade measurment can you use the hand held digital rpm
indicators made for model airplanes and helicopters? they can measure 2,3 or
4 blades. An 8" blade sounds like a full size helicopter to me <S>
Sincerely
Kerry
http://Mntnweb.Com
WWW hosting and Authoring
Admin@M...

Archiver

It's actually a full size Gyrocopter. My challenge is measuring the angle
of the rotor while in flight. On a gyro, the two-bladed rotor is mounted on
a teetering hinge that allows the rotor disc to seek its own angle of
attack (AOA) relative to the airframe and oncoming wind.
My intention is to measure the distance at 18" from the center hub and
calculate the angle. I'm using another IR sensor and the Stamp's pulsin
command to make the RPM measurement.
I think my answer may be to use the RPM pulse to sync the measurement for
the most reliable measurement.
Bill Heacock

At 10:34 PM 5/30/2000 -0400, you wrote:
>for your rotor blade measurment can you use the hand held digital rpm
>indicators made for model airplanes and helicopters? they can measure 2,3 or
>4 blades. An 8" blade sounds like a full size helicopter to me <S>
>Sincerely
>Kerry
>http://Mntnweb.Com
>WWW hosting and Authoring
>Admin@M...
>
>
>
>
>
>
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