[TriEmbed] Rocket derby help

[kschilf at yahoo.com]

Hi Craig,
We built a similar system for a YMCA event.

The igniters (they come in different sizes) require a modest amount of energy but expect the energy to be delivered quickly (several amps for 10 msecs +/-).
Most smaller alkaline batteries would be hard pressed to produce that kind of current.  One solution would be a larger battery (12v lead acid for example).  Luckily, you don't need a sustained current of several amps just a brief pulse.  As you mentioned, a capacitor bank in combination with the battery allows a much more modest battery to do the job at the expense of adding capacitors.  The goal is to slowly charge the capacitors to reduce the battery requirement but then dump the charge quickly to ensure ignition.

Having not seen the system, here are a couple of off the cuff thoughts.  The 24 AWG wire (Cat 5) has a resistance of 2.5 ohms / 100 feet plus the resistance of the intervening connectors, solder connections, etc.  You may not have much headroom starting at 6V.
Sincerely,Kevin Schilf


      From: Craig Cook via TriEmbed <triembed at triembed.org>
 To: TriEmbed <triembed at triembed.org> 
 Sent: Monday, January 30, 2017 9:42 PM
 Subject: [TriEmbed] Rocket derby help
  
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

_______________________________________________
Triangle, NC Embedded Computing mailing list
TriEmbed at triembed.org
http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
TriEmbed web site: http://TriEmbed.org


   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20170131/c91e2112/attachment.htm>