Autonomous Vehicle Design Florida Tech AIChE 1999 P. Engel, T. McKenney, M. Mensch

Reaction Selection The optimum propellant to use for the autonomous vehicle would be one that has a high thrust and a low production cost. The simplest and most obvious choice would be to use a solid rocket propellant. The rocket propellant chosen has a high burn rate and relatively clean exhaust. A high burn rate propellant will yield a very high initial thrust, this will overcome the coefficient of static friction quickly and effectively.

The Reaction NH 4 ClO 4 (s) + Mg (s) CuO MgO (s) + MgCl 2 (s) + NO (g) + H 2 O + energy NH 4 ClO 4 (ammonium perchlorate) oxidizes the metallic fuel (magnesium) in the presence of a burn-rate catalyst (copper oxide). The majority of the product formed is water vapor and magnesium chloride.

Laboratory Requirements Vacuum Chamber –Needed to remove unwanted gases formed during mixing. – Makes the composition more uniform. Mixer –Needed to obtain the desired propellant composition. –Reduces the presence of temperature gradients during heating. Heating Pad –Needed to reduce the viscosity of the propellant. –Reduces the amount of work on the mixer Process Controller –Needed to regulate the temperature within a specific range. –Keeps the heater from overheating the propellant.

Experimental Procedure 1First HTPB, the binder, is added to the bowl and heated to 55° C while mixing. 2Next magnesium, the metallic fuel, and copper oxide, the catalyst, are added appropriately and mixed until uniform. 3Finally ammonium perchlorate, the oxidizer, is added, the power is turned off, and the mixture is placed into the vacuum chamber. 4The vacuum pump is engaged, when pressure stabilizes then the power to the mixer and heater is turned on.

Experimental Procedure 5After the mixture has been in the vacuum chamber for 30 minutes, the pressure is removed slowly and diphenylmethane diisocyanate, the curing agent, is added. 6The mixing is continued until the mixture is homogenous, then the heating source and mixer are turned off. 7The propellant is then removed, placed into molds, and left to cure.

Environmental Considerations The most widely used fuel in solid propellants is aluminum because it offers a better burn. The downside of using aluminum is that after combustion it yields aluminum chloride, this then hydrolysis and produces hydrochloric acid (HCl). Hydrochloric acid will corrode metals and lower the pH of the environment in which it comes in contact with. Therefore we chose to use a magnesium fuel, which yields magnesium chloride. Magnesium chloride is found in large quantities in the ocean and does not cause any environmental problems, nor does it form an acid.

Exhaust Evaluation The propellant chosen had a very clean burn, resulting in a very low smoke content. The exhaust consists mostly of water vapor and small quantities of nitric oxide. Nitric oxide is a lung irritant, but since the reaction only produces a very small quantity of this, the hazards related to it can be neglected. Other products that may be produced are: oxygen (O 2 ), nitrogen (N 2 ), and hydrogen (H 2 ). The Earth’s atmosphere consists of nitrogen and oxygen, these two elements are stable in the diatomic form. Hydrogen is highly flammable and therefore will only add to the propulsion flame.

Explosion Safety To prevent the rocket engine from becoming a pipe bomb, an aluminum nozzle was used. Aluminum is a relatively soft metal and therefore will yield if enough pressure is applied. This became the downfall of the design. After a number of tests, the threading on the nozzle became weak and gave out. The nozzle was projected out of the back end of the engine, and rendered useless for further tests.

Nozzle Design Aluminum Metal Material –Easier to machine than steel. –Resists melting and corrosion well. –Safer to use as a nozzle than steel. Necessity of Nozzle –Controls the pressure drop through the end of the engine. –Focuses exhaust and increase exhaust escape velocity. Size of Nozzle –Nozzle throat should be 1/3 surface area of pipe –3/8” engine requires nozzle diameter of in, since this diameter could not be machined a 1/8” diameter was used.

Chassis Design Carbon Fiber Chassis –Heat and explosion resistant –High mechanical strength –Low body weight High Grip Wheels –Increases traction Flat Bed Body –Practical for carrying load

Rocket Engine Design Carbon Steel Material –High mechanical strength. –Heat and explosion resistant. Variable Length Piston –Able to use one engine for any amount of propellant. Heat Resistant Rubber Coating –Adds friction between rocket engine and chassis

Ignition Design Electrical Ignition –Ran a current through a highly conductive metal to ignite the fuel. –Safer than using a fuse. –More professional. Mounted Ignition –Allows ignition source to be placed directly in the engine. –Increases ignition success.

Vehicle Budget