Simplest latch imaginable

[MTB]

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

Rgds,

/\/\

 

[Fred Bloggs]

MTB wrote:

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

Rgds,

/\/\

Please view in a fixed-width font such as Courier.


7V
R1= ---------------
ignitor ignitor current

+----o~~~~o------+------/\/\--------+----+
| | R1 | |
| | | /
| | | 10K
| | | /
| / e \
| 100K \| |
| / 2n2907 |--+
--- \ /| |
- 9V | c |
| | | c
| | / 470 | |/
| +----o o---/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+----------------+------------------+----+

 

[Active8]

On 24 Apr 2004 01:59:59 -0700, MTB wrote:

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

Rgds,

/\/\

Is the deceleration going to be enough to cause that heavy mercury
to move all the way to the end of the bulb? I'm thinking of the
switches found in home heater themostats.

Maybe using the switch to trigger an SCR would be best. The igniter
in the anode circuit, once blown, would reset the SCR. This is
really unneccessary since the open circuit won't be drawing any
current anyway.
--
Best Regards,
Mike

 

[Fred Bloggs]

Fred Bloggs wrote:

MTB wrote:

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

Rgds,

/\/\


Please view in a fixed-width font such as Courier.


7V
R1= ---------------
ignitor ignitor current

+----o~~~~o------+------/\/\--------+----+
| | R1 | |
| | | /
| | | 10K
| | | /
| / e \
| 100K \| |
| / 2n2907 |--+
--- \ /| |
- 9V | c |
| | | c
| | / 470 | |/
| +----o o---/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+----------------+------------------+----+

I suppose it would help to make allowance for arming the thing- this
uses a two pole shunt- move to ARM position after battery voltage is
thrown ON:
Please view in a fixed-width font such as Courier.

7V
SHUNT R1= ---------------
ignitor current
+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K ignitor | R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------------------+---------------------+----+

 

[Fred Bloggs]

Please view in a fixed-width font such as Courier.



Make that:



7V - ignitor voltage
R1= ---------------------
ignitor current


SHUNT

+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K | ignitor R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------------------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------+---------------------------------+----+

 

[Richard Rasker]

On Sat, 24 Apr 2004 01:59:59 -0700, MTB wrote:

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

First of all: don't use real mercury switches in rockets - they're bound
to break and spill their toxic content in the environment. Electrolytical
types are OK though.

Second: I'm not sure whether a liquid tilt switch in general is the best
solution for the problem. Consider what happens:
1. First stage fires -> acceleration, G-forces -> all liquid stays in
the bottom of the switch (where it was in the first place).
2. First stage stops -> free fall = zero-G condition -> liquid doesn't
move in any particular direction, maybe doesn't even close the contacts
for several seconds.
I'd say this is rather unreliable - when you're out of luck, the second
stage fires only when the nose already points downward (or has reached
the ground, in extreme cases). Then again, when the rocket makes a sudden
movement sideways for whatever reason, the liquid might slosh up and close
the contact prematurely.

So what you actually need, is some sort of crude acceleration measuring
device, which fires the second stage when zero-G occurs. I'd choose one of
those levered microswitches, with the lever weighed down sufficiently to
keep the lever pushed well down at 1G (in rest).
Only during zero G will the lever come up and activate the switch. And the
best thing is: this situation will persist until the rocket accelerates
again, so you don't need any extra electronics to keep the current flowing.


Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/

 

[Fred Bloggs]

This is getting ridiculous, scratch this:

Fred Bloggs wrote:

Please view in a fixed-width font such as Courier.



Make that:



7V - ignitor voltage
R1= ---------------------
ignitor current


SHUNT

+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K | ignitor R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------------------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------+---------------------------------+----+

Use this:
Please view in a fixed-width font such as Courier.



Make that:



7V - ignitor voltage
R1= ---------------------
ignitor current


SHUNT

+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K ignitor | R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------------------+---------------------+----+

 

[Dan Charette]

You know... since you're doing a multistage rocket, I'm assuming that
you are wanting to go higher and faster with the second stage. So,
why detect when the rocket slows and then fire a stage stage at that
point? And, carrying an extra ciruit to detect this would just
increase the payload. Why not take a simpler approach by taking your
first stage motors and time the burn cycle in a test on the ground to
see how long they go. Then, instead of carrying a relatively heavy 9V
battery, why not use an old fashioned fuse that has a specific burn
rate that you cut to length based on your measurement of the burn
cycle on the first stage. I know this isn't all that hip and circuit
driven, but if you are going for distance and speed, don't let the
rocket decelerate and then have to use another motor to regain your
momentum.
If a little payload weight isn't of concern, then instead of a fuse,
design a smaller timer circuit that is started when the first stage
ignitor is triggered. The timer then counts until the first stage
comes into about 95% of it's burn. Then, the timer would trigger a
switch to hit the ignitor for the second stage so it can take over and
pick up with the first stage burns out. You may even just use a large
RC circuit tied to a comparator to do the timing and the triggering of
the second stage turn on. Just find a combination of high R and a
good sized electrolytic that will give you a few seconds of time to
get that first stage burned almost all the way through.

Have fun!
Dan Charette {dan@thesonicfrogFUZZ.com}
Remove the "FUZZ"
from my e-mail address
to contact me.

"I may not always be right, but I'm never wrong."

 

[mike]

Fred Bloggs wrote:

Fred Bloggs wrote:



MTB wrote:

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

Rgds,

/\/\



Please view in a fixed-width font such as Courier.


7V
R1= ---------------
ignitor ignitor current

+----o~~~~o------+------/\/\--------+----+
| | R1 | |
| | | /
| | | 10K
| | | /
| / e \
| 100K \| |
| / 2n2907 |--+
--- \ /| |
- 9V | c |
| | | c
| | / 470 | |/
| +----o o---/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+----------------+------------------+----+


I suppose it would help to make allowance for arming the thing- this
uses a two pole shunt- move to ARM position after battery voltage is
thrown ON:
Please view in a fixed-width font such as Courier.

7V
SHUNT R1= ---------------
ignitor current
+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K ignitor | R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------------------+---------------------+----+

This is a disaster waiting to happen.
Add a fail-safe to make absotively, posilutely CERTAIN that the
second stage cannot ignite before the first stage.
Pressure switch, conductor that the first stage burns thru...
anyhting to keep the second stage from firing when you
bump it.

SCR does the same thing, saves the weight of a transistor.
Don't know how much energy the ignitor takes, but charging
that cap might be dangerous.

I prefer switches that fail safe when a wire breaks loose.

This one requires that the ignitor shunt work.

Having said all that, aren't there commercial solutions for two-stage
rockets? Dedicated newsgroups? Check there. Your MUCH better off
with recommendations from people who are currently doing successfully
the exact same thing. Solutions from a bunch of engineers with no clue
as to the gotchas in model rocketry may not be optimum...or safe.
Be careful that you quest for minimum weight doesn't lead you to
maximum blindness when it goes up in your face. Safety first!!

mike

--
Return address is VALID.
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX
Yaesu FTV901R Transverter, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Ben Bradley]

In sci.electronics.design, mtbrecyclebin@hotmail.com (MTB) wrote:

Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch

I agree with everyone else, don't do that. Put the mercury switch
in a 'dangerous items from the past' museum.

to detect the deceleration of the first stage motor stopping.

I suspect you wouldn't want to wait that long (if it makes any
difference), you'd probably want to fire the second engine when the
acceleration drops below one gee.

My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

You can do quite a lot with electronics nowadays that weighs a lot
less than a standard 9 volt battery. IMHO, the 9V is too heavy, I'd
make something that runs on a couple of AAA's or watch batteries (the
minumum that could provide enough power to the fuse, even if three
volts goes through a swithching supply to get to 9 volts). I presume
you would prefer to minimize weight over a battery that lasts through
hundreds of launches.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small.

That's good, surface mount components are small...

I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

The lightest is not neccesarily the simplest or best.

Any experts out there care to help?

If you knew what you can do with electronics nowadays, it might
motivate you to learn more about it.

For this app, I would use a microcontroller and a MEMS
accelerometer chip (as used in automobiles to trigger air bags in an
accident). The microcontroller would fire both (or all) stages. I'm
sure many here would have reservations about using a microcontroller
in such an application, but it can be made a lot more reliable than
the negative-gee-activated switch idea, especially with the problem
others addressed of accidentially firing the engine prematurely.
A serial connection (contacts on the bottom of the rocket laying on
contacts on the launchpad) to a handheld controller sending a
CRC-checked command sequence would tell the processor to go, which
would immediately fire the first engine. I presume these have some
minimum and maximum running specs, say five to ten seconds. After
(let's say) three seconds the processor would look for acceleration to
drop to 1 gee, meaning the first stage is down to just keeping up with
Earth's gravity and no longer applying an increase in speed to the
rocket. It's at this point the processor should ignite the second
engine.

ISTR an article several years back, I think it was in "High Powered
Rocketry" magazine or some such for 'serious' rocketry enthusiasts (I
didn't buy it, I just read this on the newsstand - I really am
interested in model rocktry, but I already have enough
techno-hobbies). It described a microcontroller/accelerometer/EEPROM
device which was mounted inside a rocket and measured acceleration
throughout the flight.

As for construction, you could make it with old-fashioned
through-hole parts and sockets, and have it weigh no more and not be
too much larger than a 9-volt battery. But without much trouble you
can go surface mount and make a smaller board and use less solder
(which being about 50 percent lead, you want to minimize to keep
weight down).

Rgds,

/\/\

 

[MTB]

On Sat, 24 Apr 2004 17:11:44 +0100, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Aubrey McIntosh <mcintosh@spam04.v
ima.austin.tx.us> wrote (in <4782640f.0404240657.604e08ce@posting.google
.com&gt about 'Simplest latch imaginable', on Sat, 24 Apr 2004:
mtbrecyclebin@hotmail.com (MTB) wrote in message news:<9da81cc6.0404240059.59401
33@posting.google.com>...
Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.

Some people are *very* afraid of mercury. There are many reports of
using evacuations and "Moon Suits" to clean up after broken
thermometers.

Yes, well, it runs after you to kill you, if you run away downhill. (;-)

Guys, When I were a boy, they used to hand the stuff out in chemistry
classes and let you play with it. Apart from wearing glasses I have no
visible side effects, but then who knows what tomorrow will bring. Too
much scottish salmon can reputedly have a greater effect......

 

[MTB]

On Sat, 24 Apr 2004 12:08:38 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

This is getting ridiculous, scratch this:

Fred Bloggs wrote:
Please view in a fixed-width font such as Courier.



Make that:



7V - ignitor voltage
R1= ---------------------
ignitor current


SHUNT

+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K | ignitor R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------------------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------+---------------------------------+----+



Use this:
Please view in a fixed-width font such as Courier.



Make that:



7V - ignitor voltage
R1= ---------------------
ignitor current


SHUNT

+--o ARM o SAFE o---+
| | |
+-+--/\/\---+---o~~~~o--+---------/\/\--------+----+
| 100K ignitor | R1 | |
| | | /
| | | 10K
| | | /
| | e \
| | \| |
| | 2n2907 |--+
--- | /| |
- 9V | c |
| | | c
| | / 470 | |/
| +------o o----/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+-----------------------+---------------------+----+

Fred,

Looks good AND I can understand it. Thanks for that.

As mentioned elsewhere in the thread, a mercury switch may not be the
ideal, but it is relatively simple. Solid state pressure sensors and
decelerometers can also be used, but the complication for this bear of
little brain far outweigh their elegance from a design point of view.
I'm afraid that KISS wins the day.

Thanks again.

/\/\

 

[MTB]

On Sat, 24 Apr 2004 10:24:05 -0500, "Garrett Mace"
<g.ryan@macetech.com> wrote:

"MTB" <mtbrecyclebin@hotmail.com> wrote in message
news:9da81cc6.0404240059.5940133@posting.google.com...
Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.
My elementary knowledge of electronics seems to indicate some sort of
"latch" since the switching action of the mercury switch may only be
"on" for a few milliseconds. This latch would have to turn on as soon
as the mercury switch did and then remain on. The "load" in the
circuit would be the second stage igniter (essentially a fuse) which,
when it blew, would turn the circuit off again.
Whole thing would be powered by a small 9V battery.

Since the last electronics I did was when discrete transistors were
the norm, my abilities are small. I seem to remember though that a
monostable might serve this purpose?

Question is, what is the simplest (and therefore the lightest) circuit
to achieve this?

Any experts out there care to help?

Rgds,

/\/\


Don't do this, for the following reasons:

1. Mercury switches will probably slosh up and trigger right when the rocket
is initally fired
2. Mechanical switches might do the same
3. Neither switch will sense the deceleration when the rocket motor burns
out: rockets coast for quite a while
4. If the switch is sensitive enough, then it will trigger on the launch pad
if you bump or tilt the rocket the wrong way: very unsafe!

Multistage model rockets use a primary engine designed for that purpose,
without an ejection charge in the top. The fuel burns to the top, and a jet
of flame goes up and ignites the second rocket. This accomplishes the task
very simply and well.

This link shows how to ignite the second engine if it is far away from the
first engine; up to about ten inches:
http://www.apogeerockets.com/education/how_to_multi-stage.asp In addition to
running a narrow tube from the first to the second rocket, you need to
provide vents at the top so that the hot exhaust reaches the second engine.

Garrett,

The narrow tube method is notoriously unreliable, hence the search for
something that is "guaranteed" to set off the second stage motor.
Trouble is, its almost never possible to guarantee it! The idea of a
timer seems OK to me, but doesn't allow for ease of alteration when a
different first stage motor is experimented with. Deceleration should
occur in any configuration!

Rgds,

/\/\

 

[Garrett Mace]

The narrow tube method is notoriously unreliable, hence the search for
something that is "guaranteed" to set off the second stage motor.
Trouble is, its almost never possible to guarantee it! The idea of a
timer seems OK to me, but doesn't allow for ease of alteration when a
different first stage motor is experimented with. Deceleration should
occur in any configuration!

Instead of a chargeless motor for multistage rockets, use a standard one
with ejection charge. Then use the pressure from the ejection charge to
activate a switch.

However, the batteries you will need to successfully ignite the next engine
will be heavy. The weight of the batteries will probably negate the
advantage of having a multistage rocket. Plus, the concentrated weight above
the thrust point of your first engine may seriously affect the stability of
the rocket, causing it to point nose-first within a few seconds.

 

[Aubrey McIntosh]

John Larkin <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in message news:<8k2l80hfq0ggcbp7g34d074u6h6nuupvop@4ax.com>...

On Sat, 24 Apr 2004 08:22:16 -0700, Jim Thompson
thegreatone@example.com> wrote:


I have a friend who, in High School, decided that boiling mercury
would make a dandy temperature reference.

Landed him in the hospital and gave him *permanent* near death
sensitivity to more mercury.

Very nasty stuff for the nervous system.

...Jim Thompson

Is the liquid stuff that bad? It's fairly non-reactive, and the vapor
pressure is very low.

I did handle the liquid as a kid in the 50s, but don't have much
exposure now. The way chemists treat several chemicals has undergone
significant change in the past 30 years, and mercury is on the cusp of
change right now.

The rumor I hear is that old chemists tend to accumulate beakers with
broken thermometer parts in odd corners of their offices. With poor
ventilation and long term exposure, the do have symptoms, particularly
if they happen to set the beaker on the radiator in the summer, pile
stuff in front of it, and forget what they have done. The consensus I
hear, without references, is that it is vapor of the 0 oxidation state
and that the entry is through the lungs. All of this is rumor, and I
don't now of case histories or references. I have had the question as
to whether the 0 oxidation state is getting a bad rap because of the
toxicity of the organomercury compounds and name similarity. Jim's
story is the first story that I would call "traceable" and "credible"
for +0 oxidation state.

This is different from many organomercury compounds, which are much
faster acting and which are dangerous beyond all question.

This is very parallel to stories of osmium. Most chemists accept as
fact the idea that osmium vapor causes blindness and is lethal. This
is paradoxical, because the vapor pressure is presumably very low.
However, the excretion pathways are very slow. Again, no literature
references, just person to person rumor in the hallways.

 

[Bill Sloman]

John Larkin <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in message news:<8k2l80hfq0ggcbp7g34d074u6h6nuupvop@4ax.com>...

On Sat, 24 Apr 2004 08:22:16 -0700, Jim Thompson
thegreatone@example.com> wrote:

On 24 Apr 2004 07:57:24 -0700, mcintosh@spam04.vima.austin.tx.us
(Aubrey McIntosh) wrote:

mtbrecyclebin@hotmail.com (MTB) wrote in message news:<9da81cc6.0404240059.5940133@posting.google.com>...
Hi,

I want to ignite the second stage of a model rocket by using a mercury
switch to detect the deceleration of the first stage motor stopping.

Some people are *very* afraid of mercury. There are many reports of
using evacuations and "Moon Suits" to clean up after broken
thermometers.

I have a friend who, in High School, decided that boiling mercury
would make a dandy temperature reference.

Landed him in the hospital and gave him *permanent* near death
sensitivity to more mercury.

Very nasty stuff for the nervous system.

...Jim Thompson

Is the liquid stuff that bad? It's fairly non-reactive, and the vapor
pressure is very low.

The mercury vapour pressure above a clean liquid mercury surface at
room temperature is dangerous. An undisturbed mercury surface rapidly
becomes dirty - probably coated with some mercury sulphur compound -
and the vapour pressure drops by a factor of two hundred or so, to a
level which isn't dangerous.

As a chemist working with a vacuum line, evacuated by a mercury vapour
pump and monitored by a mercury barometer and a mercury-filled
rotating McLeod gauge, I read and cited Stock's book "Hydrides of
Boron and Silicon" Cornell University Press, Ithica, New York (1933)
which is the Old Testament for people who work with vacuum lines.

In the book Stock describes how he got mercury poisoning from exposure
to continuously refreshed mercury surfaces, and lists his symptoms.

In the 1950's we did no more than scatter finely divided sulphur over
the residues from minor mercury spills, and the regular tests for
mercury vapour with a mercury resonance lamp indicated that this
worked well enough to keep us out of danger.

------
Bill Sloman, Nijmegen

 

[Richard Rasker]

On Sat, 24 Apr 2004 19:03:37 -0500, Garrett Mace wrote:

The narrow tube method is notoriously unreliable, hence the search for
something that is "guaranteed" to set off the second stage motor.
Trouble is, its almost never possible to guarantee it! The idea of a
timer seems OK to me, but doesn't allow for ease of alteration when a
different first stage motor is experimented with. Deceleration should
occur in any configuration!


Instead of a chargeless motor for multistage rockets, use a standard one
with ejection charge. Then use the pressure from the ejection charge to
activate a switch.

However, the batteries you will need to successfully ignite the next
engine will be heavy. The weight of the batteries will probably negate
the advantage of having a multistage rocket.

Perhaps a flat lithium battery might be the answer? And I still think that
a weight-loaded switch is the best way to reliably ignite the second stage
upon zero gravity (when the first engine cuts out).

Plus, the concentrated weight above the thrust point of your first
engine may seriously affect the stability of the rocket, causing it to
point nose-first within a few seconds.

I've experimented quite a lot with home-brew rockets (including fuel
rods based on cellulose, i.e. toilet paper , and I can assure you that
the flight stability of a rocket improves with a higher center of gravity.
The lower the center of gravity, the bigger the stabilizer fins will have
to be to prevent your rocket from going anywhere but up.
It's actually quite easy to understand. Suppose the center of gravity is
found at one third of the height, measured from the bottom. This means
that two thirds of the body surface is located above the c.o.g., and one
third below it. This causes even the smallest air flow with a horizontal
component to push the rocket further off its course - unless this surface
ratio is compensated by the surface of the fins at the bottom. With the
c.o.g. in the top half of the rocket, the rocket will automatically point
its nose in the direction of the air flow. With a sufficiently high
c.o.g., one doesn't even need stabilizer fins (like with those firework
rockets, which only have a long, lightweight tailstick at the bottom).


Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/

 

[Garrett Mace]

I've experimented quite a lot with home-brew rockets (including fuel
rods based on cellulose, i.e. toilet paper , and I can assure you that
the flight stability of a rocket improves with a higher center of gravity.
The lower the center of gravity, the bigger the stabilizer fins will have
to be to prevent your rocket from going anywhere but up.
It's actually quite easy to understand. Suppose the center of gravity is
found at one third of the height, measured from the bottom. This means
that two thirds of the body surface is located above the c.o.g., and one
third below it. This causes even the smallest air flow with a horizontal
component to push the rocket further off its course - unless this surface
ratio is compensated by the surface of the fins at the bottom. With the
c.o.g. in the top half of the rocket, the rocket will automatically point
its nose in the direction of the air flow. With a sufficiently high
c.o.g., one doesn't even need stabilizer fins (like with those firework
rockets, which only have a long, lightweight tailstick at the bottom).

But that only works up to a certain weight...and usually with the weight
distributed evenly. During the initial boost, there isn't enough airflow to
stabilize the rocket; you are depending on rotational inertia and the launch
rod to keep the rocket stable at the beginning. If you have a very heavy
object up front, the rotational inertia of the rocket is very low, while the
force due to acceleration is very high. The slightest disturbance will cause
the thrust end of the rocket to kick out.

Well, I'm probably thinking of the batteries as being a bit too heavy, a
significant portion of the rest of the rocket's mass. If he can get the
special low-current igniters, then it might have a chance of working with a
small battery.

 

[Winfield Hill]

Ken Smith wrote...

Fred Bloggs <nospam@nospam.com> wrote:

+----o~~~~o------+------/\/\--------+----+
| | R1 | |
| | | /
| | | 10K
| | | /
| / e \
| 100K \| |
| / 2n2907 |--+
--- \ /| |
- 9V | c |
| | | c
| | / 470 | |/
| +----o o---/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+----------------+------------------+----+


Why build an SCR when they can be bought in a TO-92 package?

Indeed, e.g., 2n5062, 16 cents each. X0202MA, 52 cents each.

Depending on the value of R1 above, the current through the
made-up-SCR may be rather high, and much of it goes through
the two transistor's bases. While a BJT base can take higher
current than one might imagine, this is not a good situation.

Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)

 

[John Larkin]

On 25 Apr 2004 11:20:35 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

Ken Smith wrote...

Fred Bloggs <nospam@nospam.com> wrote:

+----o~~~~o------+------/\/\--------+----+
| | R1 | |
| | | /
| | | 10K
| | | /
| / e \
| 100K \| |
| / 2n2907 |--+
--- \ /| |
- 9V | c |
| | | c
| | / 470 | |/
| +----o o---/\/\---+--| 2n2222
| | sw | |\
| | / e
| === 10K |
| |0.47u / |
| |metal film \ |
| | | |
+----------------+------------------+----+


Why build an SCR when they can be bought in a TO-92 package?

Indeed, e.g., 2n5062, 16 cents each. X0202MA, 52 cents each.

Depending on the value of R1 above, the current through the
made-up-SCR may be rather high, and much of it goes through
the two transistor's bases. While a BJT base can take higher
current than one might imagine, this is not a good situation.

Thanks,
- Win

whill_at_picovolt-dot-com (use hill_at_rowland-dot-org for now)

The '5062 might pop a wire bond firing a squib, too, but probably not
if powered by a regular 9-volt battery. But it's a sensitive-gate
thingie, and a little static could fire it.

Oh, just last week I was playing with a 20-amp TO-220 triac. It had
about a 100 ohm resistance gate to cathode (I refuse to use the silly
MT1-MT2 nomenclature) and that resistance has a very nice positive
(hmmm... I think it was positive... gotta check) TC. There must be a
use for that fact somewhere.

John