Basic Strobe Motors
WARNING AND DISCLAIMER: If you are underage, then consult with your parents or guardians before attempting any of this. You are on your own - I'm not responsible for your actions or harm you may bring to others because of your actions. Making the items described below can result in injury or death to you or people in your vicinity. Some things mentioned here may be illegal to make in your city, county, state, or country so check the laws that apply to you before you attempt anything described here. These notes are not complete on purpose. If you are reading them and new to pyrotechnics, then you are making a mistake. Stop now - this page is not for you. Get a beginning book on fireworks (see Skylighter or American Fireworks News (very quick shipping) for a start) and read up. You can't make any of this work without more information so read up or join a club or ask someone to help you.
Strobe rockets are unique skyrockets that require a good deal of configuration and tuning. They consist of an initial grain of fast whistle mix, followed by a longer grain of strobe mix. There are commercial strobe tool kits on the market and they work fine. However, even a BP spindle can be used to make a strobe rocket. Whatever spindle is used, follow the guidelines for the whistle increment - seen in the picture below. The strobe mix is NOT going to cause CATOs on launch - if CATOs are encountered, they will almost always be caused by a bad whistle grain/configuration.
Strobe mix is one of the most dangerous of mixes. It burns slowly but it will detonate easily. That makes it quite deceiving - be careful when using it. We've shot 150 grams of strobe mix with a rifle before and the resulting explosion was much bigger than an equivalent 500 gram whistle detonation. They really go "Boom!" ONLY PRESS STROBE MIX - NEVER TAMP IT.
Here is a two pound strobe rocket. Notice the distinctive sound. It used a 5" spindle. The first 1.75 inches were whistle and the rest was pressed strobe mix. Click on the picture below to see and hear it.
Getting the strobe to strobe usually requires a bit of work. The variable factors are the mesh size of the metals and the quality of the barium sulfate. Some barium sulfates simply will not work. Contact me if you want a current name of a good BaSO4 provider. Here is a known good formula for me - but your chemicals might need adjusting! There are other, slightly varying, formulas in the compositions section on this website.
Ammonium Perchlorate 60
Magnalium -325 mesh 13
Magnalium -100-200 mesh 10
Barium Sulfate 15
Potassium Dichromate (debatable need if using MgAl) 5
Vaseline 2 (dissolved in lacquer thinner - put baggy with Vaseline and lacquer thinner in hot water to get it to dissolve - put in strobe mix and blend)
Dry the mix after it is well blended. Usually you don't need to screen it since it is quite soft. Bag it. BE CAREFUL - THIS MIX IS QUITE SENSITIVE TO SHOCK!
Put in the whistle increment and then put in the strobe increment to about 1/4" above the spindle. Put in a delay grain of some sort. The one in the movie above was 1.375 inches of green mix made with 80 mesh charcoal.
Press to about 8000 on the whistle and about 4000-5000 on the strobe. You can get away with a range of pressures but these pressures seem to make a more lasting rocket motor. However, I usually don't store these motors. I press them and fly them.
The following file was made by Steve La Duke and was reposted here with his permission. This is a reprint of a PDF - print it out in landscape and you should be able to read it better. The only change is that the 3/4" spindle is now 3" long. Note that longer spindles and different diameter spindles can be used. Longer spindles will use the same whistle increment. Different diameter spindles may need tuning with the whistle mix to get it right. You can always start with 10% less than you guess and see if it works.