For some reason I'm seeing someone hacking up an old Garrard automatic
turntable. Let's see:

12 inch diameter platter. check.
33 to 78 RPM. check.
Sector gear with engagement tooth. check.
Sine wave. Mount a pin on the platter and have a slotted slide above.
check.

Your way would probably be better.=20

Cheerful regards,

Bob


On Wed, 01 Dec 2010 17:20:23 -0500, "Dave Tweed"=20
> I have a client who wants to do some experiments involving deliberate
> antenna
> motion in a GPS-based system. He's done some simulations and likes what
> he
> sees, so now it's my job to set up an actual prototype so we can see how
> well
> it works in practice.
>=20
> We have a small box of electronics that includes the GPS antenna and
> receiver
> that masses a total of about 0.5 kg. We want to move this box along a
> horizontal linear track that's about 300 mm long, with a sinewave motion
> that
> has a period on the order of 1.0 seconds. This means that we need to be
> able
> to generate a peak velocity of about 0.95 m/s and a peak acceleration of
> about 6.0 m/s/s (and a force of about 3 Newtons).
>=20
> We also need to know with fairly good timing precision (on the order of
> 0.5
> to 1.0 ms and 0.5 to 1.0 mm) where the box is in its motion cycle. In
> case it
> matters, the motion will likely not be continuous -- instead, the box
> will sit
> most of the time at one end of the track, and on command, will make one
> trip
> to the far end and back.
>=20
> I've never put together a motion control system before, but based on some
> preliminary Googling, I would guess that given these speeds and loads,
> that
> a belt-driven stage powered by a stepper motor would be the type of thing
> I
> should be looking for, along with a high-level motion controller that can
> be
> programmed with the sinewave profile.
>=20
> Secondary considerations are that the unit should be relatively compact
> --
> our box of electronics is about 50 x 50 x 125 mm and we don't want
> something
> that completely dwarfs this. We don't want to spend more than about $1K
> to $2K
> on this, but we want to buy as much of it off-the-shelf as possible. This
> is
> just a one-off for now, but if it works out, we'll want a cost-optimized
> solution for a production design. The control interface would preferably
> be
> RS-232 (with a separate hardware sync signal?), but we can adapt as
> needed.
>=20
> Does anyone have any recommendations for vendors for this sort of thing,
> or
> any other pertinent advice? Thanks in advance.
>=20
> -- Dave Tweed


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