Alt-BEAM Archive
Message #01118
To: beam@corp.sgi.com
From: Steven Bolt sbolt@xs4all.nl
Date: Mon, 1 Mar 1999 21:20:09 +0100 (CET)
Subject: [alt-beam] Re: pocket motor-tester / BEAM multi-meter
On Tue, 2 Mar 1999, Justin wrote:
---8<---[ all sorts of interesting ideas ]---8<---
> Hmmm, I think it might be a much better idea to use a suneater or
> suneaterII circuit as this would allow you to add a dial which sets the
> trigger voltage. Yes, that would be very useful.
Note that the adjustable resistor(s) on SunEater_II/III give just
enough range to get from one extra diode in the voltage trigger
chain to the next. The first SunEater_III had servo motors and
needed three diodes; the second, using small recorder motors was
eventually judged to be better off with two diodes (and the
adjustables almost in the other corner).
> A more far-fetched idea would be to put a little gear-box in the unit,
> with some sort of rubber grommet or something such that you could just
> poke the motor shaft into it to run the gearbox, which goes through a
> few worm gears (yes - they do have a use :) and rotates a dial on the
> front panel. With it geared down sufficiently, a 4700uF discharge would
> get you about a 270 degree revolution on a good motor,
Note that the same amount of energy can be put in small and large
caps - its the combination of farads and volts that counts. The
small solar panels limit us to low voltages, but it does make a
difference whether you charge a cap to 2V or 2.5V. The latter takes
longer, unless you use a smaller cap.
A higher voltage in a smaller cap tends to be harder to convert
into acceleration from stop than a lower voltage in a larger cap,
given the usual motors. But to make a valid comparison, you'd have
to change both cap and voltage to match the individual motor, while
keeping the charge time constant. Using a solar cell, you won't be
entirely honest, because that will give the advantage to the lower
voltage. You need a current source.
> thus giving you a visual guide and comparison to how many
> revolutions a prospective motor gets from the charge, and thus
> presumably, how efficient it is. Except this doesn't measure
> torque,
The mass of a motor is also important, but exactly how important
depends on the mass of the total `bot. Small recorder motors are
rather heavy, but their combination of torque and efficiency at low
rpm tends to compensate pretty well for that disadvantage. It's
seriously hard to be really scientific about all this...
Best,
Steve
----------------------------------------------------------------------
# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
----------------------------------------------------------------------
------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/list/alt-beam
Free Web-based e-mail groups by eGroups.com
Home