One of the great myths of high power rocketry is that you do not save any money making your own motors and reloads. The truth is that the savings are there starting with the “G” class motor and the savings become more dramatic as you move up in motor class. The best way to show this is to actually cost out a particular case.
Initial Equipment Cost
First, there are a couple of items that you will need to buy on a one time only basis regardless of what size motor or how many you plan to make. The first item is a good laboratory balance. A mechanical triple beam balance with extra weights can be bought for about $125 new. There are a few electronic balances with adequate accuracy for the same amount or a little more. The second item you will want is an electric mixer. While you can mix the propellant by hand, it is really nice to use an electric mixer for propellant batches a half pound or more. A simple “egg beater” type mixer will work, but the best mixer is the low end Kitchen Aid type mixer. Its mixing action gives the best quality propellant. For our example, we bought a lab balance for $125 and a Kitchen Aid mixer on sale for $180. A total one-time cost for initial equipment = $305.
Propellant Cost
The cost of the propellant is about $8 per pound plus or minus $2 depending on what formula you use. Now, lets look at a typical “J” motor, such as the 54mm Aerotech J90W. It sells for $93.99 (Price on Nov. 6, 2021). It contains 0.861 lbs of propellant. The kit also includes nozzles, o-rings, sleeves, etc.
You could make a J motor out of 2″ PVC pipe and fittings where you cast the propellant into 1.5″ PVC pipe cartridges that slide into the 2″ PVC pipe chamber. The motor cost is as follows:
- Propellant cost ($8/lb * 0.861) = $6.89
- PVC fittings = $2.5
- PVC pipe for chamber = $2
- PVC pipe for propellant cartridges = $2
- Water putty for nozzle = $0.75
- Phenolic insert for nozzle = $0.75
- Glue and primer consumed = $0.5
- Silicone rubber consumed = $0.25
- Total Cost of Homemade Motor = $15.64
You Saved $70.35 By Making Your Own J90 Motor Rather Than Buying A Reload Kit!!!
But what about the cost of the mixer and balance? Well, after you’ve made only five J90 motors instead of buying them commercially, you’ve saved enough to cover the cost of the mixer and balance. From that point on, the savings are yours to fly more or to spend on other things.
If you want to make your own reload, the cost will be about $20 higher as you have to buy OEM parts from RCS motor parts. In this case, it will take about six homemade reloads to cover the cost of the balance and mixer.
