[dorkbotpdx-blabber] where to get and learn about solenoids
Donald Delmar Davis
ddelmardavis at gmail.com
Wed Dec 3 19:31:33 EST 2008
Actually as an experiment (I was at powells technical) I looked up
solenoids in Dan Osullivan's "Physical Computing: Sensing and
Controlling the Physical World with Computers" and sure enough there
was a great overview from a hardware and software perspective with all
of the relevant points made here in it.
Everyone on this list should own that book. http://powells.com/biblio/4-9781592003464-2
So just it on your christmas wish list NOW.
Don.
On Dec 3, 2008, at 12:40 PM, douglas repetto wrote:
>
> There are push/pull soleniods that can both push and pull the shaft
> (when power polarity is reversed), but they're rare. They work by
> using a magnet as the shaft, rather than a piece of plain steel.
> That way the polarity of the electromagnet (set by the polarity of
> the power supply hookup) _does_ matter, since there will be an
> attraction/repulsion relationship between the poles of the shaft
> magnet and the poles of the electromagnet.
>
> But for most purposes that's not necessary and a spring/gravity
> return is sufficient.
>
> douglas
>
> Greg Grunest wrote:
>> Yes. That's exactly how a linear solenoid works! Once the
>> electromagnet
>> (coil) pushes (or pulls) the shaft, a spring returns it to the
>> original
>> position when the coil is deenergized.
>> On a rotary solenoid, it's usually a spring and some gears and a
>> little cam
>> type device.
>> - Greg
>> -----Original Message-----
>> From: dorkbotpdx-blabber-bounces at dorkbot.org
>> [mailto:dorkbotpdx-blabber-bounces at dorkbot.org] On Behalf Of John
>> Brown
>> Sent: Wednesday, December 03, 2008 12:26 PM
>> To: A discussion list for dorkbot-pdx (portland, or)
>> Subject: Re: [dorkbotpdx-blabber] where to get and learn about
>> solenoids
>> Thanks Douglas! That's a great page.
>> If I may ask a quick question, though, does a solenoid work is the
>> same way as a coil gun, in that the induction of current into the
>> wire
>> draws in the metal shaft? Is that what gives it the binary action?
>> And
>> then when current is stopped, what pulls the shaft back out of the
>> coil?
>> I hope I am understanding it correctly.
>> -John Brown
>> On Wed, Dec 3, 2008 at 10:58 AM, douglas repetto
>> <douglas at music.columbia.edu> wrote:
>>> FWIW, I have a website that I teach lots of workshops from that
>>> covers the
>>> basics of different kinds of motors/solenoids/relays/etc. By
>>> basics I mean
>>> basics, but with the goal of providing the vocabulary so that you
>>> can go
>> out
>>> and do web searches for more specific info once you actually know
>>> what you
>>> want to learn about. It's here:
>>>
>>> http://music.columbia.edu/~douglas/classes/motor_mania/
>>>
>>>
>>> best,
>>> douglas
>>>
>>>
>>> Greg Grunest wrote:
>>>> Greg,
>>>>
>>>> Solenoids come in all different varieties. Typically, you find
>>>> the 12 V,
>>>> linear, push or pull solenoids in everyday consumer electronics
>>>> (disk
>>>> drives, hard drives, tape players, that old and now useless
>>>> Zip-100 drive
>>>> has a really cool 6v one in it but it's *really* hard to get it
>>>> out,
>>>> etc...)
>>>> but every so often you can find surplus rotary solenoids too.
>>>> For moving
>>>> the drumsticks, a rotary solenoid might be the thing. They
>>>> typically
>> move
>>>> through a 90 degree arc when energized and then return to where
>>>> they
>>>> started
>>>> when power is removed. However I've had some before that sort of
>>>> ratchet
>>>> through 15-30 degree increments each time power is applied
>>>> eventually
>>>> spinning all the way around. They were connected to a little
>>>> mechanical
>>>> counter and appeared to do nothing more than count how many times
>>>> this
>>>> thing
>>>> had fired.
>>>>
>>>> The pros:
>>>> They're cool!
>>>> They typically work forever - millions of cycles.
>>>> You can do things with an $8.00 solenoid that you could
>>>> otherwise
>>>> spend hundreds of dollars trying to replicate. (I once built a
>>>> remote
>>>> controlled golf cart and used Ford starter solenoids ($8.00 from
>>>> Napa) to
>>>> switch the 600 Amp battery connections to the motor. I used a $3
>>>> optoisolator to drive the solenoids and an 8051 to drive the
>> optoisolator.
>>>> Controlling 600Amps from a microprocessor for $11 - Woot!)
>>>> You can get feedback from them by measuring how much
>>>> current they
>>>> draw (voltage drop across an in-line resistor) and tell if they are
>>>> hitting
>>>> anything. They tend to draw a lot of current (like a stalled
>>>> electric
>>>> motor) if you hold them against their will.
>>>>
>>>> The cons:
>>>> They suck current like mad and therefore are not good for
>>>> battery
>>>> driven applications.
>>>> It's basically a coil so you have to worry about re-
>>>> induction when
>>>> the magnetic field around the coil collapses so you don't blow up
>>>> sensitive
>>>> circuitry (like the Arduino or a transistor).
>>>> They are typically not driven by any control signal that is
>>>> easy
>> to
>>>> generate in a microprocessor world, 9-50V, 500ma-2A.
>>>> (Because of these two drawbacks, I highly recommend a
>>>> simple 8 pin
>>>> optoisolator to drive them. It's cheap and completely protects the
>>>> Arduino.)
>>>> You can't control how fast they move like you can with a
>>>> servo.
>>>> They are either in or out, turned or not. In fact, if you try to
>>>> slow
>>>> them
>>>> down by limiting the voltage they draw a LOT of current.
>>>> They are entirely digital - On or off, in or out.
>>>>
>>>> And the number one drawback is........ can you say "latch
>>>> up"?
>>>> (sometimes they stick in the "energized" state.)
>>>>
>>>> Just my 2 cents.
>>>>
>>>> BTW: If you're interested, I think I have a couple of the 90
>>>> degree
>>>> rotary
>>>> ones left. Enough for you to play with and try the drums anyway.
>>>>
>>>> - Greg Grunest
>>>> greg at grunest.com
>>>>
>>>> _______________________________________________
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>>>> dorkbotpdx-blabber at dorkbot.org
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>>>>
>>> --
>>> ............................................... http://artbots.org
>>> .....douglas.....irving........................ http://dorkbot.org
>>> .......................... http://music.columbia.edu/cmc/music-dsp
>>> .......... repetto............. http://music.columbia.edu/organism
>>> ............................... http://music.columbia.edu/~douglas
>>>
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> .....douglas.....irving........................ http://dorkbot.org
> .......................... http://music.columbia.edu/cmc/music-dsp
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>
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