Newsgroups: comp.robotics
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From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: Where can amateur buy cheap solenoids for robot control?
Organization: The Armory
Date: Thu, 1 Sep 1994 12:24:09 GMT
Message-ID: <CvGAGH.n1H@armory.com>
References: <33te78$ogp@search01.news.aol.com> <BDS654.94Aug30095959@aerodec.anu.edu.au> <343tgp$bc4@rc1.vub.ac.be>
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In article <343tgp$bc4@rc1.vub.ac.be>,
Jurgen Van Gorp  <jvgorp@vnet3.vub.ac.be> wrote:
>In article <33te78$ogp@search01.news.aol.com> BWHUCKABEE,
>bwhuckabee@aol.com writes:
>>Where can I buy cheap solenoids for robot control?  I'm not an engineer. 
>>Just playing around.  I want something that will move in or out when I
>>apply electricity to it.  Motors are too complicated.  I've considered a
>>car starter solenoid, but they require too much current and also cost too
>>much.  Can anybody help?
>
>Take the screen wiper motor. It`ll ask less current. If you look around,
>you should be able to find lots of smaller and bigger motors, that do not
>come from your car (maybe some long-forgotten dumped tape recorder
>somewhere ?)
>
>In article <CvBLpn.75o@armory.com> Richard Steven Walz,
>rstevew@armory.com writes:
>>Best solenoid bearing material is nylon or other slippery but hard
>plastic
>>tubes. Glass tubes have also been used. Wrap your own coils! It works
>fine!
>>We made a robot walker with nothing BUT solenoids! Used the nitinol
>walker
>>principle. All it takes is pulling the right cables or wires. And the
>pull
>>needn't be much!
>
>Could you elaborate on this, Steve ? We tried to wrap a coil for use as a
>shaker for mechanical structures.  Calculations pointed out that the
>currents needed to become even a small force would be far too big.  
>I made a coil to do some tests (2000 windings, length 3.5 cm, internal
>diameter 2 cm, wire diameter 0.3mm) : at a voltage of 60V and a current
>of 0.8A, the force applied on a steel shaft was a shitty 2.5N. 
>
>I would really be interested in the sort of coils you have been using,
>the voltages, currents and most of all the forces you got from the coils.
>
>  Jurgen VAN GORP
>+----------------------------------------------------------------------+
>! Free University of Brussels, VUB       Fax  : +(32 2) 629 28 50      !
>! Dept. ELEC - Building K, Level 6       Voice: +(32 2) 629 28 69      !
>! Pleinlaan, 2                           Email: jvgorp@vnet3.vub.ac.be !
>! B-1050 Brussels - BELGIUM                                            !
>+----------------------------------------------------------------------+
---------------------
Well, we saw one of those nitinol walkers, a friend and I, and we grabbed
some light acrylic and some coathanger wire, and followed the principle.
First we just thought of using motors with bobbins and small size long coil
springs as return, but then we happened on using a stack of small magnets
and solenoids wrapped on bobbins between them. Made two stacks of
Magnet-Bobbin-Magnet-Bobbin-Magnet, and they can pull quite well for little
current for a short distance. just enough to make a simple six legger
rocking type frame walk. Used a 9 volt large wall wart power pack, that's
all. Just tricky getting the springs right. we later thought of reversing
polarity in the bobbins we wrapped to release, but didn't bother. Look at
that stupid nitinol walker robot they sell in a kit. The motion is simple
and trivial! The current was limited to 2.5 amps at 7 volts out of a cheap
power pack. Motors can work too, and possibly better, I found out later, if
you put an armature on the shaft and use it to wind two separated cables to
pull with. Make their separation about 3/8". Then wind it a bit and load
it. You just run it till it stalls in place at low load. As for the
solenoids, I have made small solenoids for models and model railroad for a
friend for years with simple homemade construction. I don't know what your
problem is with thinking of this stuff yourselves, actually. I was building
robots that ran from DC motors and homemade solenoids when I was 8, in
1958! We just had no controllers then, and I craved microrelays that were
just coming out!!! My dad scrounged a few for me from his sample box, as he
was a mechanical engineer with electrical experience for Harris. I managed
to make a robot stop and turn autonomously at age 10! Out of erector. I
still have almost 100 pounds of old Erector Set. And now I tend to collect
tiny hi-quality relays, even though I never get to using them!!! What our
childhoods and their deprivations do to us for many decades after!!! I
STILL want to build logic with relays!!! My craving was unrequited and now
obsolete!! Hasn't anyone built open frame motors that actually had some
real torque?? We would cut out annealed steel sheet with snips for days to
make exactly the three pole motor we wanted, because we couldn't afford
one!!! We had a dragster with a huge homemade motor and boosted it with
capacitors. I'm talking 20 pounds here!!! Geared it up with belts!
As soon as I saw saran wrap I was dreaming about a light electric airplane!
Haven't got to build it yet though!
-Steve Walz  rstevew@armory.com

