[TriEmbed] Rocket derby help

Tadd Torborg tadd at mac.com
Mon Jan 30 21:05:50 CST 2017


Craig,
  If the only thing on the clip-lead end of the wire is a volt-ohm meter, there should be any noticeable voltage drop along the wire.  The resistance of the wire is 1.2 ohms but the resistance across the multimeter should be huge.  So the drop should be entirely across the multimeter.  Something doesn’t make sense here.  Are all 8 wires 1.2 ohms?  

My first thought was below:: but then I realized that there must be something else afoot.  The system must have worked once upon a time?   

  You might put a relay on each pair of wires at the clip-lead end.  Now the button at the control box closes a relay at the launch-pad.  Now put a salvaged car battery or motorcycle battery at the launch-pad and have that put power through the relay to the nichrome wire, (rocket fuse == nichrome wire?)  
  I would put a 10 watt 5 ohm resistor in the car-battery circuit.  I have one if you need it.  I work on the north end of Davis drive. 

 Before going to this trouble, figure out if the rocket-fuse does the right thing if given a car-battery’s worth of power through the fuse.  

Relay should be 6v coil (so it actuates with your battery) and have 2 amp switch capacity (limited to that by the 5 ohm resistor).  

      Tadd

Tadd Torborg 
tadd at mac.com




> On Jan 30, 2017, at 9:42 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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