Alt-BEAM Archive
Message #01385
To: "Steven Bolt" sbolt@xs4all.nl, "Ian Bernstein" ian@beam-online.com
From: "The Mesiti Family" mesiti@pbq.com.au
Date: Mon, 8 Mar 1999 18:33:58 +1100
Subject: [alt-beam] Re: Improved SunEater WAS: Advanced?
How much are those super caps?? Where can I get them from ??
Thanks!!
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| From: Steven Bolt
| To: Ian Bernstein
| Cc: beam@corp.sgi.com
| Subject: Improved SunEater WAS: Advanced?
| Date: Friday, March 05, 1999 7:26 PM
|
| 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.
|
| ----------------------------------------------------------------------
| # sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
| ----------------------------------------------------------------------
|
|
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