Battery screwdrivers are great because they often have a torque
release on them.
Cedric

> On Jul 3, 2007, at 3:31 AM, Russell McMahon wrote:
>
> Here's a simple but reportedly effective way of producing a low cost
> electrically operated valve.
>
> He uses a standard hydraulic valve, driven by what he says is an
> electrically operated pepper mill to provide the actuation. I've not
> seen such a mill here but an electrically operated coffee grinder
> would probably do the same job (and just may be what this is)(but
> probably isn't).
>
> An electric battery  powered screwdriver would also be suitable. Such
> have 2 or 3 stages of epicyclic gearboxes to allow a relatively
> modestly sized electric motor to produce the very substantial torque
> required to turn screws. Actuation speed will depend on gearing and
> voltage used.
>
> Performance is not mentioned on the web site but in an email to the
> ARocket list he says:
>
>> The 1/4" valve opens, at 50 bar, in 2/10 sec, on 9V.
>
> That's reasonably impressive.
> It may give the potato cannon people some ideas :-) - if they haven't
> been doing this sort of thing for years without me noticing.
>
>
>             Russell
>
>
>
> _________________
>
> On the site he says:
>
> This valve is the most recent I made. It's also the easiest to
> operate, probably the most reliable, and even though the cheapest.
> It's a 1/4" BSP hydraulic valve, connected to the mechanism of a cheap
> electric pepper mill (the kind you can buy at < $5). I made an
> aluminium frame that holds the two parts together; the torque is
> transmitted via a custom-made piece also. There is a small on/off
> switch that stops the motor when it has made a quarter of turn (not
> visible on the picture, it wasn't installed yet). One can probably
> replace it with a magnetic position sensor and thus get a throttleable
> valve.
>
> This and a pyro and servo operated vales described here:
>
>         http://www.student.montefiore.ulg.ac.be/~teney/ 
> h2o2propulsion_actuatedvalves.htm
>
> Picture here:
>
>         http://www.student.montefiore.ulg.ac.be/~teney/ 
> h2o2propulsion/electroactuatedvalve.jpg
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