MOTOR MAKING INTRODUCTION

If you want to learn to make rocket motors to save money – forget it. There is a financial undertaking you must commit to before you even start. Equipment must be bought and chemicals must be purchased. In today’s rocketry community it seems everyone is making motors. This is not the case. Everyone is getting motors from those that are making them. If you are serious about making large motors it could balance out after a year or two. If you are looking to make motors 38mm or smaller – don’t waste your time and dollars. If you’re determined to get involved in this part of the rocket hobby please continue.

The first thing you want to do when learning how to make your own motors is to obtain a copy of Prof.Terry McCreary’s book EXPERIMENTAL COMPOSITE PROPELLANT. This will be your bible. It is written for P-Ban motors however, change the word P-Ban to HTPB and everything will apply – except for P-Ban based formulas, which the book contains. The main difference between HTPB and P-Ban is P-Ban can be mixed without a mixer, thus minimizing major degassing. And, P-Ban requires a specific curing time, where HTPB can be used the afternoon it is mixed. Very few people use P-Ban in larger rocket motors – just not practical. To get a copy of EXPERIMENTAL COMPOSITE PROPELLANT visit our MERCHANDISE page by clicking HERE

Obtain a copy of a computer program called BURNSIM. This is a program that assists with designing and analyzing rocket motors and their performance. It is a very inexpensive purchase but its value to the motor maker is extremely great. There is a free download which lets you see and learn how it operates however don’t be cheap, buy the full version. You’ll end up buying it anyway – you’ll need it. To get a copy of BURNSIM got to: http://www.burnsim.com

The next item you need is a mixer. A good beginner’s mixer is a Kitchen-Aid; available just about anywhere kitchen stuff is sold. Make sure it is at least a 6qt and 325watts. Anything smaller will have the motor burn up in a VERY short time. There are other counter top mixers on the market but the Kitchen-Aids seem to be the most popular and longest lasting.

A Scale is required. Find one that will measure at least 10 lbs. It has to be able to do both Lbs and Grams. It must be able to accurately measure at the least a single gram. Anything else is a waste of money.

You will also need to invest in a vacuum pump. This is where things get iffy. It needs to pull at least 29 inches of Mercury and hold it for several minutes. Many will not pull the required 29 inches and if they do they cannot hold it for an extended period of time. You'll also need hoses and fittings and probably have to build a vacuum plate that fits your mixing bowl to seal it for degassing.

You need to purchase Liners & Casters. These are the tubes to hold the mixed propellant. The Caster tubes actual hold the propellant and the Liner tubes separate the Caster tubes from the motor case as a form of insulation. You will also need to make bases to hold the Casters while “casting” the mixed propellant.

Along with Casters & Liners, Chemicals will be your biggest repeatable expense. You will find that your investment in chemicals is major since you can’t buy just what you need for one or two motors. You need to buy quantities, not only for the price break but also to save on shipping. Be forewarned most of the time Hazmat shipping costs rival the item being shipped.

In addition you will be purchasing a bunch of small items such as containers of various sizes, paper measuring bowls, spatulas, scrapers, etc$$$

Once you’re making motors it will become obvious that despite all the formulas you have collected, and all you think you know, you actually have no idea in the world just what motor you’ve made. The best rules of thumb really fall short – or over. What good is it making great motors that you really have no idea what they are. Now you need testing equipment.

A test stand is an item that you literally need to build yourself. None come ready made. And if you do find one chances are the price is tremendous. Besides the actual stand to hold the motor for firing, you’ll need a load cell, computer, a device called an A to D board, probably a pressure transducer and a few other items. Then you need the software to collect and process your firing data. All of these can get pricey.

And all along you thought you were going to save money!!

The last thing you will need, if you plan to enter the vast and expensive field of rocket motor making, is discipline. You must be aware at all times as to what you are doing, who is around, what is happening and what you are going to do when the big one occurs. Safety must always be in your mind. Never take for granted that all is well or that a short cut can be made. Redundancy (you’ve made a bunch of these) is the leading cause of complacency. Whether it’s your first motor, or your 100 th motor, never take anything as SAFE. A big bite is always lurking.

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