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| Simple Motors |
| Intro |
This tutorial explains the construction of a very small motor. It is a very good low
power motor, and if you're launching small rockets it is ideal. You will have to use
your own recovery system, or experiment and add one onto this motor. You also
have the choice of a paper or pvc casing. Go for the pvc, it is much more reliable,
and easier to get. I use paper casings only because i find discarded paper tubes
from mortar packets, which come from the neighbor's fireworks. These work great,
but still are not as reliable as pvc. You need to be much more precise and
consistent with paper. Also, if using PVC, use a pressure rating of at least 315 psi.
Trust me, it is not worth somebody's life to be lazy, get the highest pressure rating
you can find. Also, please always static test your motors todetermine their safety,
and don't fly them until you know they are safe.
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| Ingredients |
-Durham's Rock Hard Water Putty
-3/4 in. pressure rated pvc or paper casing cut at 3 in. in length
-Kno3 (potassium nitrate, or saltpetr)
-sucrose (table sugar)
-7/64 in. drill bit
-~7/64 in. diameter nail
-two part epoxy
-3/4 in. dowel
-paper wadding (toilet paper is fine)
-cardboard (optional)
-screwdriver or countersink at 90 degree angle |
Nozzle
The nozzle is constructed from casted Durham's Rock Hard Water Putty. Mix the
water putty according to its directions, and fill the casing up about 3/4 in. Try not to
get excess on the inside of the casing walls; if you do, try to scrape it off, for it will
cause difficulties later and lower motor performance. Let it dry for 1 full day, then
drill a 7/64 in. hole straight through the middle of it (MAKE SURE IT IS STREIGHT
AND IN THE MIDDLE, a drill press is helpful). This is your nozzle throat.
Countersink the outside end of this hole with a screwdriver at about a 90-degree
angle. Let it dry for another two days. While it is drying, you will need to make some
tools.
Packing Tools
The packing tools you will make will be a tamp and a coring mandrel. They pack the
propellant, while forming a core. To make the mandrel, take the 7/64 in. diameter nail
and nail it through a very thin piece of wood. The motor should be able to slide onto
it after it dries, with the nail sliding up through the nozzle- it may be a tight fit, but twist
it and work it all the way on. You will also make a tamp. This is very simple. Take
the ¾ in. dowel, and drill slightly larger than a 7/64 in. hole up into it. It should be
able to slide into the motor, with the nail fitting into the hole that you drilled. You may
have to work with it to get everything to fit together.
Propellant
The propellant is the kno3 sucrose prop. Because of the simplicity of these motors,
the propellant can be hard packed rather than casted. Larger motors require casting
of the propellant. This propellant has a core to raise burn surface area to volume
ratio. Mix it in a ratio by weight of 65% kno3, 35% sucrose. Put the mixture in an
airtight jar and shake vigorously for 3 min. or more. Wait for the dust to settle in the
jar, and fill the motor with it. The motor should already be on the mandrel by now.
Then use the tamp to pack it down. Continue to do this until you can't see the nail any
longer. Then put the paper wadding in, and pack that as well. Finally, mix the two
part epoxy and pour it about 1/5 cm. deep onto that. Put a circular piece of
cardboard on top of that (optional). Let it dry in a warm place, and you have a
motor!
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