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Date: Wed, 22 Jan 2014 23:03:48 -0500
Message-ID: <CACPio-5jYucCB+q1=5jnjcYbZUUgEPdk8dvxJXg=hM4cZCaHJw@mail.gmail.com>
Subject: Re: [geda-user] Best way to measure RPMs
From: Nathan Stewart <therealnathanstewart AT gmail DOT com>
To: "geda-user AT delorie DOT com" <geda-user AT delorie DOT com>
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I dunno about arm bikes, but a regular road bike IIRC they preach 90RPM as
your target spin rate.  60rpm is one rev/second, which sounds on the
leisurely side of average to me - still it' gets you close enough to get
started. Electromagnetic can be really low power if you have a permanent
magnet involved. But, since 50/60Hz is probably smack dab in the region of
interest, you need to be prepared to deal with power line noise if you go
electromagnetic.  I started sketching a reflective sensor guitar pickup a
few months ago, but I quickly realized anything  with a battery powered
emitter is going to eat batteries compared to anything merely sensing a
disturbance (assuming it's battery powered). Reflective is more power
hungry than direct/interrupter systems. This is one cool aspect of the
guitar pickup type sensor - fixed permanent magnet, sensing disturbance in
the field, you can get the power draw down to minuscule levels.  Also, if
you need resolution (or simply getting your tick count away from power line
noise), if you're sensing gear teeth, you automatically get a multiplier of
40-50ish.


On Wed, Jan 22, 2014 at 6:06 PM, Kai-Martin Knaak <knaak AT iqo DOT uni-hannover DOT de
> wrote:

> Rob Butts wrote:
>
> > The application is an arm bicycle where the spinning shaft is connected
> > to a handle on each end so with no gearing the rpms will not be too
> > high.  I don't have any encoder yet and I can attach anything to the
> > shaft.
>
> There is a spinning top experiment in the physics lab at my day job. We
> attach a little magnet to the wheel and put a pick-up coil from an
> electrical guitar in the sensor. A comparator turns the signal from the
> coil into TTL compatible form. This gets fed to a digital multimeter with
> frequency input.
>
> The set-up works nicely from up to 3 cm distance. And it proved to be
> student safe since 3 semesters :-)
>
> ---<)kaimartin(>---
>
>
>

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<div dir=3D"ltr">I dunno about arm bikes, but a regular road bike IIRC they=
 preach 90RPM as your target spin rate.=A0 60rpm is one rev/second, which s=
ounds on the leisurely side of average to me - still it&#39; gets you close=
 enough to get started. Electromagnetic can be really low power if you have=
 a permanent magnet involved. But, since 50/60Hz is probably smack dab in t=
he region of interest, you need to be prepared to deal with power line nois=
e if you go electromagnetic.=A0 I started sketching a reflective sensor gui=
tar pickup a few months ago, but I quickly realized anything=A0 with a batt=
ery powered emitter is going to eat batteries compared to anything merely s=
ensing a disturbance (assuming it&#39;s battery powered). Reflective is mor=
e power hungry than direct/interrupter systems. This is one cool aspect of =
the guitar pickup type sensor - fixed permanent magnet, sensing disturbance=
 in the field, you can get the power draw down to minuscule levels.=A0 Also=
, if you need resolution (or simply getting your tick count away from power=
 line noise), if you&#39;re sensing gear teeth, you automatically get a mul=
tiplier of 40-50ish.<br>
</div><div class=3D"gmail_extra"><br><br><div class=3D"gmail_quote">On Wed,=
 Jan 22, 2014 at 6:06 PM, Kai-Martin Knaak <span dir=3D"ltr">&lt;<a href=3D=
"mailto:knaak AT iqo DOT uni-hannover DOT de" target=3D"_blank">knaak AT iqo DOT uni-hannover=
.de</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div class=3D"im">Rob Butts wrote:<br>
<br>
&gt; The application is an arm bicycle where the spinning shaft is connecte=
d<br>
&gt; to a handle on each end so with no gearing the rpms will not be too<br=
>
&gt; high. =A0I don&#39;t have any encoder yet and I can attach anything to=
 the<br>
&gt; shaft.<br>
<br>
</div>There is a spinning top experiment in the physics lab at my day job. =
We<br>
attach a little magnet to the wheel and put a pick-up coil from an<br>
electrical guitar in the sensor. A comparator turns the signal from the<br>
coil into TTL compatible form. This gets fed to a digital multimeter with<b=
r>
frequency input.<br>
<br>
The set-up works nicely from up to 3 cm distance. And it proved to be<br>
student safe since 3 semesters :-)<br>
<br>
---&lt;)kaimartin(&gt;---<br>
<br>
<br>
</blockquote></div><br></div>

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