Alt-BEAM Archive
Message #01313
To: Ian Bernstein ian@beam-online.com
From: Steven Bolt sbolt@xs4all.nl
Date: Fri, 5 Mar 1999 09:26:54 +0100 (CET)
Subject: [alt-beam] Improved SunEater WAS: Advanced?
On Thu, 4 Mar 1999, Ian Bernstein wrote:
> When I said advanced I meant....
>
> - more complex than whats already on the net
> - at the point where you want to start designing your own circuits
> - projects that require a LOT more skill to build than just a solaroller
>
> Did this clarify everything? or just start a whole new thread =)
A couple of months ago I received two very small pager motors, much
smaller than the usual size. They seem ideal for an SMT project like
`Son of Photovore'. But the snag was obvious: SMT reduces the size of
everything except the storage cap.
As you know, photovores are at their best when they take small steps
toward the light. With a good SE, that makes them `pop' every few
seconds, even in ordinary daylight (as opposed to a direct noon sun).
But this requires a cap of a couple of thousand uF. Make it larger,
and you get boringly long charge times. Make it smaller, and the
`pop' causes insufficient motion. That saddles you with a rather
large ordinary electrolytic cap - you can't use a physically smaller
SuperCap, because it has too much capacitance.
Obviously, the problem is caused by having the SE switch on and off
at voltage levels. So I modified SunEater_II to have a switch-on
level and a switch-off *time*. It turns out to be a significant
improvement. Not only can I use the smallest SuperCap (47000uF,
13mm x 7mm), but the motor bursts have more torque at a lower
voltage. This is caused by the voltage not tapering off during the
burst. The drop is just 0.1V or so, giving the accelerating motor
much more follow-through.
The result is a considerably more efficient SE, which can be built
quite small and light. Expect a very tiny SunEater_III type `bot in
the not so far future.
Is SunEater_IV (http://www.xs4all.nl/~sbolt/Other/SunEater_IV.gif)
`advanced' by Ian's definition? I've seen more complex schematics on
the Web. It requires no special skill to build. So perhaps not. But
it did give me a kick to see it work so well :)
Best,
Steve
Btw: The schematic mentions a burst time of .15s or less. That may
look short, but even the large and heavy SunEater_III gets a 1cm
`step' from a burst of only 0.1s. And longer bursts are no problem,
just increase the value of the 220N cap. The high internal
resistance of the SuperCap is not as much of a problem as it used
to be, because the trigger now allows the downward voltage peak at
switch-on to be more than 1V. Of course it still helps to use good
motors.
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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