Payload 2015 Class 1 By Jeff Dunker 5/12/2019 2014 Beginner Payload

Altimeters Altimeters come in two flavors, barometric or accelerometer based. Barometric altimeters work by measuring changes in atmospheric pressure using a barometric cell. As you go up in altitude the pressure exerted by the atmosphere drops. The amount that the atmospheric pressure drops with increased altitude is well characterized. 5/12/2019 2014 Beginner Payload

Barometric altimeters You can measure when an altimeter starts rising and stops rising, to measure the apogee. Most barometric altimeters are activated by a quick change in pressure equivalent to anywhere from 100' - 300' of altitude change. Typical ranges for barometric altimeters are from sea level up to 15,000' - 25,000' of altitude. Some special models claim to be readable up to 50,000'. Barometric altimeters are quite versatile, but they have two drawbacks: They need to be in a chamber that is sealed off from any ejection charge gases (which are corrosive and can foul the altimeter), but is vented to the outside so that changes in atmospheric pressure can be detected 2) As a rocket passes through the sound barrier (Mach) a shock wave forms at the tip of the nosecone and travels down the airframe. When the shock wave passes over the vent ports for the altimeter chamber, the pressure fluctuation it causes can fool the altimeter into believing the rocket has reached apogee and is started back down to the ground. 5/12/2019 2014 Beginner Payload

Accelerometer based altimeters Accelerometer based altimeters use a small horizontal pendulum rated to measure anywhere from +/- 25 G’s of acceleration to +/- 100 G’s (a G is one gravity or 9.8 meters/second/ second of acceleration). The acceleration sensor in the altimeter must be in the proper orientation to measure the acceleration, orientation of these accelerometers is critical to the proper operation of the altimeter. Because of this, all accelerometer based altimeters need to have markings on the altimeter to indicate “this end up”, ensuring, if installed in that orientation, that the sensor is properly oriented with respect to the (intended) direction of flight. 5/12/2019 2014 Beginner Payload

Determination of apogee with Accelerometers Determination of apogee is made by monitoring the accelerometer and integrating the signal to determine the point at which the rocket stops rising. Is this a true apogee? Not always, but it’s usually close enough. Altitude measurements derived in this manner are seldom accurate as the accelerometer integrates acceleration versus time (which yields velocity) and then integrates velocity vs. time to obtain distance traveled. The main problem with this approach is that the distance traveled is only equal to altitude if the rocket flies a perfectly vertical trajectory - no weather-cocking, no arcing over, no deviation from a vertical flight, period. If the rockets flight path is anything other than vertical the actual altitude attained will be less than the distance traveled by the rocket to reach apogee. 5/12/2019 2014 Beginner Payload

Two significant advantages over the barometric altimeter In spite of this measurement problem with altitude, an accelerometer-based altimeter does have two significant advantages over the barometric altimeter. These advantages are that the accelerometer requires no venting of the electronics bay in order to work That the accelerometer is not sensitive to pressure differentials caused by supersonic flight. One significant negative for accelerometers is that a single axis accelerometer of the type most often used in rocket electronics cannot measure how high the rocket is following apogee. Why? This limitation could be gotten around by employing a full three axis accelerometer suite and a more powerful microprocessor, but that would raise costs. 5/12/2019 2014 Beginner Payload

5/12/2019 2014 Beginner Payload

5/12/2019 2014 Beginner Payload

5/12/2019 2014 Beginner Payload

What is a electric circuit? A circuit involves a source of electrical power and a PATH for the current to flow from between both connections. A DC circuit is a loop allowing current to flow between the positive to the negative connection That is the proper definition even though we now know that the electrons flow from the negative terminal to the positive. All the equations work just fine with either definition but you must be consistent with what you are doing, everything must use the same definition in all your math. 5/12/2019 2014 Beginner Payload

The Electronic Terms 5/12/2019 2014 Beginner Payload

Ohms Law Current = V / R Current also called Ampere (Amp’s) using the same analogy as before is the amount of water that comes out in the same unit of time. The circuits we are working with have both low voltage and low current - this also makes it safe to work with High Current Medium Current Low Current 5/12/2019 2014 Beginner Payload

Ohms Law Voltage = I * R Voltage is similar to water pressure in a can the more pressure the more voltage High pressure – high voltage Medium pressure – Medium Voltage Low Pressure – Low Voltage 5/12/2019 2014 Beginner Payload

DEMO 1 - What is electricity Can you have Voltage without Current? What is the difference? Touch the glass of the bulb what happens? Now I need a volunteer for the current version. What happened? Why the difference? Two demo’s help show the differences and relationships What is a conductor? What is an insulator? Bring shock box and electric field ball 5/12/2019 2014 Beginner Payload

Hardware Communication The means to communicate a hardware circuit connectivity is called a schematic. We will look at individual components what they do and their symbols and how this is used to define our circuits. 5/12/2019 2014 Beginner Payload

General Circuit items Digital symbols Bring poster board of parts 5/12/2019 2014 Beginner Payload

More Schematic symbols and parts See how many you can find on the Parts Board 5/12/2019 2014 Beginner Payload

Any combination of electronics components DEMO 2 - A Circuit + - Any combination of electronics components Our first part, the switch Some sort Of power source Almost every electronic device will use one or more switches, the first And most basic is the power switch, notice how it opens and can close the loop making an operation circuit. We’ll use a lamp. What happens When the switch is closed? Yes we just made your basic flashlight!! 5/12/2019 2014 Beginner Payload

5/12/2019 2014 Beginner Payload

We usually use them to measure Voltages Note the sensitivity of the answer to the Meters internal resistance Ideal meter answer Note: my multi-meter has 30K/V rating and I get a reading of 4.25 volts 5/12/2019 2014 Beginner Payload

DEMO 3 Circuit voltage DVM Let’s use a DVM to measure the voltage, we’ll also change the DVM connections And look across the lamp. What is the voltage about 12 Volts 5/12/2019 2014 Beginner Payload

DEMO 4 Circuit current DVM Now let use the DVM to measure the current, again we’ll change Battery sizes notice the lamp again. What is the current about 0.08 Amps 5/12/2019 2014 Beginner Payload

Power or Watts Also usually means heat This is simply the measure of the amount of work that can be done. W = V * I or Watts is equal to the Voltage time the current Think of how hard each of the example before would push a water wheel is the flow of the water stream. 5/12/2019 2014 Beginner Payload

DEMO 5 Circuit watts Anyone have any idea why I am using an Incandescent lamp? DVM Volts DVM Amps Now let use the DVM to measure the current, again we’ll change Battery sizes notice the lamp again. So what is the power? About 12 X .08 = 1 W 5/12/2019 2014 Beginner Payload