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96 Build Your Own Electric Vehicleimportant to you: high speed, long range, or a utility commuter vehicle midwaybetween the two.So step two is to design for the capability that you want. Your EV’s weight, motorand battery placement, aerodynamics, rolling resistance, handling, gearing, and safetyfeatures must also meet your needs. You now have a plan.Step three is to execute your plan—to buy the chassis that meets your needs. At itsheart this is a process no different from any other vehicle purchase you’ve ever made,except that the best solution to your needs might be a vehicle that the owner or dealercan’t wait to get rid of—one with a gas-guzzling, diesel, or otherwise polluting engine—so the tables are completely turned from a normal buying situation.Used is usually the least expensive, but don’t go for something too used. You wantto feel confident about converting the vehicle you choose before you leave the lot. If it’stoo small or cramped to fit all the electrical parts, let alone the batteries, you know youhave a problem. Or if it’s particularly dirty, greasy, or rusty, you need to think twice.Figure 5-1 gives you the quick picture. The rest of the chapter covers the details.Let’s get started.Optimize Your EVOptimizing is always step number one. Even if you go out to buy your electric vehicleready-made, you still want to know what kind of a job has been done so you can decideif you’re getting the best model for you. In all other cases, you’ll be doing theoptimizing—either by the choices you make up front in chassis selection or by yourconscious optimizing decisions later on. In this section, you’ll be looking to minimizethe following resistance factors:• Weight and climbing and acceleration• Aerodynamic drag and wind• Rolling and cornering resistance• Drivetrain systemYou’ll look at equations that define each of these factors, and construct a table of realvalues normalized for a 1,000-lb. vehicle and nine specific vehicle speeds. These valuesshould be handy regardless of what you do later—just multiply by your own EV’sweight ratio and use directly, or interpolate between the speed values.You’ll immediately see a number of values reassembled in the design section of thischapter, when a real vehicle’s torque requirements are calculated to see if the torqueavailable from the electric motor and drivetrain selected is up to the task. This designprocess can be infinitely adapted and applied to whatever EV you have.Conventions and FormulasThis book uses the U.S. automotive convention of miles, miles per hour, feet per second,pounds, pound-feet, etc., rather than the kilometers, newton-meters, etc., in commonuse overseas. Any formulas borrowed from the Bosch handbook have been convertedto U.S. units. Speaking of formulas, you will find the following 13 useful; they havebeen grouped in one section for your convenience: