[TriEmbed] Rocket derby help

[Rodney Radford]

This is a nice writeup of testing of various igniters showing the current
profile during a launch cycle.

Skip forward to figure 11 and it shows a peak current of 12.39 amps with a
12v source:

https://publicmissiles.com/IgnitersWhitePaperbyG-Wiz.pdf

While this article shows the initial fire current is 2.0 amps, but it is 3x
this value (6.0 amps) to burn the igniter through.

So if you really have 1.2 ohms between the battery and the launch box, the
voltage drop on the wire will be too high to ignite the wire.

I agree with Tad's suggestion of putting the launch battery at the launch
box, and then use a smaller battery in the control just to trigger relays,
which then supply high current through shorter wires. This is how the high
power guys do it that have much higher current requirements, and would also
be useful even with low power clustering systems.




On Mon, Jan 30, 2017 at 10:48 PM, Shane Trent via TriEmbed <
triembed at triembed.org> wrote:

> Estes reports that 90% of engine ignition problems are caused by the
> ignitor not touching the propellant. It seems they recommend a plug to hold
> the igniter. That is new to me, I haven't launched a rocket in 30 years!
>
> http://www2.estesrockets.com/pdf/Model%20Rocket%20Engines%
> 20&%20Igniters.pdf
>
> Shane
>
> On Mon, Jan 30, 2017 at 10:39 PM Shane Trent <shanedtrent at gmail.com>
> wrote:
>
>> Craig,
>>
>> I suggest changing to a 12V battery. A small SLA should fit the bill and
>> offer plenty of launches per charge.
>>
>> Shane
>>
>> On Mon, Jan 30, 2017 at 10:25 PM John Vaughters via TriEmbed <
>> triembed at triembed.org> wrote:
>>
>> Craig,
>>
>> I do not know what it takes to light the fuse, but right off the bat,
>> your currents seem tiny. Are you sure you got the scale right? Also, cat 5
>> cable does not transmit alot of current, but it may be enough. I just do
>> not know how much current you need. I also do not have the specs on the
>> igniter and what voltage/current is proper. I think you need to start with
>> the specs for the igniter, look that up first. Then consider upping the
>> voltage at the button box to get the proper voltage at the igniter. If it
>> worked before then it may be as simple as verifying the specs of the
>> igniter and the provided voltage, but be careful if it is truly only cat 5
>> cable. It is very low current cable.
>>
>> Did I miss the email about the car race results and solution? If not,
>> please let us know how it went.
>>
>> Thanks,
>>
>> John Vaughters
>>
>>
>> On Monday, January 30, 2017 9:43 PM, Craig Cook via TriEmbed <
>> triembed at triembed.org> wrote:
>>
>>
>> Now that Pinewood derby is over, onto my next challenge.
>>
>> Last year I was launch master for our Cub Pack.  We have been having
>> problems with our rocket launch system.  6V large square battery powers the
>> system.  There is a rotary switch where you can select from position 1,2,3
>> or 4.  This box is connected via 45 feet of cat 5e wire to junction box
>> (DB9 serial connectors attach from the launch box to cable, and another one
>> to the junction box).  The junction box is split out to 4 sets of wire with
>> alligator clips.  These clips attach to the rocket fuse (1,2,3 or 4).  The
>> Cub presses a button on the launch box, energy is dumped into the fuse and
>> the rocket should take off.
>>
>> The last few years we have had problems with the fuse not getting enough
>> energy to burn fast enough and launch the rocket, result is an unhappy Cub.
>>
>> I cut off and re-soldered the alligator clips thinking that would solve
>> the problem.  It didn't.  I checked and I have 0 resistance from the
>> junction box to alligator clips, so I think my soldering was ok.
>>
>> I measure 1.2 ohms of resistance from the launch box to the junction box
>> going over the 45 feet of wire.
>>
>> Battery has 6.5 Volts, at the junction box I measure 4.19 Volts.
>>
>> Battery has 0.005 Amps, at the junction box I have 0.003 Amps.
>>
>> Is there a way to store energy at the junction box, then have it released
>> when a switch is pushed?  I think that is what a capacitor is for, but not
>> sure.
>>
>>
>> I was considering replacing the cat 5e wire and DB9 connectors with RJ45
>> ones.  Would that help?
>>
>> No idea how old the batteries are, are the Amps too low?
>>
>> Whoever made this setup knew what they were doing.  It has been well put
>> together.
>>
>>
>> Thanks
>>
>> Craig
>>
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