Alt-BEAM Archive

Message #05266



To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Mon, 12 Jul 1999 13:02:47 -0700
Subject: [alt-beam] Re: Nu(tating) Motor


Hi Bruce,

you wrote

>Unfortunately, these parts are plastic (delrin, I suspect), and so
will
>not be able to handle a lot of torque.

Note the point about the large number of teeth between the inner and outer
gear that are engaged greatly increasing the maximum torque rating of
plastic gears.

Nutating gear technology is primarily used in pumps and meters. Some of the
latter use Nutating discs (ratio of circumferences) and at least one
company uses this to make an infinitely variable gear box. There are 3
different types of Nutating gears: one I described earlier using 2 conical
gears, one type you described using the concentric gears with the rotation
of the inner gear fixed but wobbling inside the outer gear using an
eccentric drive point, and the other type uses a flexible oval gear.

Remember that I described a Nutating motor which has one other interesting
feature: The gears disengage to freewheel the output shaft when the motor
power is removed. I guess a similar arrangement could be (and probably
already has been) used on solar rollers to increase the rolling distance by
disengaging the motor when decelerating.

regards

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411

> -----Original Message-----
> From: Bruce Robinson [SMTP:Bruce_Robinson@bc.sympatico.ca]
> Sent: Sunday, July 11, 1999 8:53 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: Nu(tating) Motor
>
> Wilf Rigter wrote:
> >
> > I mentioned Nutating gears earlier so here something to wrap you head
> > around...
>
> > ... When the magnetic force has moved through 360', the rotor will have
> > advanced one tooth since it has one more tooth than the torroid gear.
>
> A couple of years ago I picked up 5 surplus Allis Chalmers engine hour
> meters for less than $3.00 each, thinking they would make useful
> mechanical counters. However, turning the input shaft didn't seem to do
> anything. Mounting it in my lathe and running it at 2000 RPM didn't seem
> to do anything either, so I dismantled one -- 1,920,000 to one
> reduction, in 4 stages!! And that was just to drive the first digit in a
> 5 digit meter.
>
> The principle is very similar to the one described. In this case a
> 40-tooth outer gear (with the teeth moving inward), and a 39-tooth inner
> gear meshing with it. The inner gear is prevented from rotating but is
> otherwise free to move. This gear is instead revolved around the
> centerpoint of the outer gear. One revolution of the inner gear produces
> 1/40 revolution of the outer gear. In a tiny volume, they have stacked 3
> - 40:1 and 1 - 30:1 reduction.
>
> Unfortunately, these parts are plastic (delrin, I suspect), and so will
> not be able to handle a lot of torque. However, with a little mechanical
> skill you could probably dismantle a unit and build yourself a nice,
> compact reduction unit for light duty work.
>
> For those of you in Canada, I picked mine up from Princess Auto, and
> last I looked these were still in the catalogue.
>
> I'd be interested in hearing from anyone who adapts one of these units
> to make a walker.
>
> Regards,
> Bruce

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