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[DPRG] Pittman GM87XX Homebrew

Subject: [DPRG] Pittman GM87XX Homebrew
From: Dan Creagan dcreagan at bellevue.edu
Date: Tue Aug 28 15:32:37 CDT 2001

Well.... using a combination of ideas from the list, and a morning or two, I
managed to get the encoder to work on the back of an 8712.  I tried to make
something that could be put together without any special tools.  For a few
bucks, some super glue, epoxy, and a tap, you can make it.

See: http://academic1.bellevue.edu/robots/tanner/

Dan
-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org]On Behalf
Of David P. Anderson
Sent: Tuesday, August 28, 2001 12:43 PM
To: robologist at yahoo.com
Cc: dprglist at dprg.org
Subject: Re: [DPRG] Pittman GM87XX Homebrew


Howdy RoboDave,

The gearhead and the rear shaft and brushes are keyed so that
you can't really put them back together wrong!

regards,
dpa

>
> Heh, coool, motor guts. Dave, this is some great info, good
> stuff for making encoders. I had to open up one of the
> gearboxs here to look around, hope it's back together right.
> Are they difficult to align or any problems with that? You
> and Eric and Kip and Barry and Eds stuff can make a really
> great example on a website for developing a robot platform.
> Oh, one point, think Pittman specs these as 60.5 to 1, maybe
> how the weird count of gear teeth came up.
> David P
>
> ----- Original Message -----
> From: "David P. Anderson" <dpa at io.isem.smu.edu>
> To: <dprglist at dprg.org>
> Cc: <seattlerobotics at yahoogroups.com>
> Sent: Monday, August 27, 2001 7:16 PM
> Subject: [DPRG] Pittman GM87XX Homebrew
>
>
> > Howdy
> >
> > I took the Pittman GM8712 motors from Tanner's out to
> visit Michael Hamilton,
> > designer extraordinare for Traxxus et al, and we took one
> apart and played
> > with it.  He pronounced it "first rate stuff."  Not bad
> for $11.00!!
> >
> > Here are some pictures of it disassembled:
> >
> >
> ftp://www.geology.smu.edu/pub/users/dpa/robo/pittman/pittman
> _gm8712.jpg
> >
> > It is a seven pole motor, which accounts for the high
> torque at low rpm
> > and for it's extremely quiet operation, always a plus for
> hobby robots.
> > Notice in the upper right-hand image that the seven poles
> are wound
> > with lots of extremely fine wire (we measured 12 ohms).
> The poles are
> > also "skewed" helically.  Michael tells me this provides
> for smoother
> > operation, as the poles "overlap" each other.
> >
> > The gearhead has 4 stages.  We counted the teeth and the
> last three
> > stages have 32 tooth spur gears driven by 10 tooth
> pinions, 3.2:1
> > per stage.  The first stage has slightly smaller teeth and
> we were
> > not able to count them.  However, they must provide about
> 1.8:1 ratio
> > for a final ratio of 60:1.  All gears are "high quality"
> metal gears
> > with steel axles riding in bronze bushings.
> >
> > He is of the opinion that we should probably NOT mount
> wheels directly
> > on the output shaft because of the small diameter of the
> rear pin and
> > bushing.  I told him we were thinking of a 5 to 10 pound
> platform.
> >
> > I have gathered together the parts for a simple home-brew
> encoder for
> > these motors as discussed previously.  This consists of a
> paper encoder
> > wheel, Hamammatsu emitter/detector, black plastic film
> canister, and
> > a cable tie.
> >
> > Here is a picture of the pieces:
> >
> >
> ftp://www.geology.smu.edu/pub/users/dpa/robo/pittman/home_br
> ew_enc_01.jpg
> >
> > I'm using a 28 division encoder wheel as a starting place.
> The wheel is
> > super-glued to the rear of the motor shaft.  The
> Hamammatsu is mounted
> > on a small piece of perfboard with a couple of other
> components.  This
> > will probably change.  The perfboard is glued into the
> back of the film
> > canister with the leads exiting through a slot in the
> side.  The canister
> > was cut down with an xacto knife and slotted to clear the
> motor wires.
> >
> > Here is a picture of the assembled encoder.  The cable tie
> allows the
> > film canister to slide in and out to adjust the exact
> distance for the
> > Hammamatsu sensor.  Then it is tightened to hold it in
> place.
> >
> >
> ftp://www.geology.smu.edu/pub/users/dpa/robo/pittman/home_br
> ew_enc_02.jpg
> >
> > I haven't had a chance to test it yet, so more
> improvements will no doubt
> > come along the way.  This home-brew encoder requires no
> machining and
> > can be assembled with simple hand tools.  It represents an
> improvement
> > over our previous encoders in that it is adjustable and
> also has a
> > light shield and protective cover over the encoder wheel.
> >
> > More to come!
> >
> > cheers,
> > dpa
> >
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>
>
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