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Unformatted text preview: ENES 100 Introduction to Engineering Design Spring 2011 Problem Set #6
Due: In Class March 14 (M) or March 15(Tu) Reading: Chapter 6 and 7 of the course text: Programming Problems: 1. You have a circular disk‐shaped hovercraft with a radius of 200mm and a mass of 1.5kg. You have two thrust fans that have a maximum thrust each of F=2N. They are capable of operating in either the plus or minus direction as shown. The distance sensor indicates that the edge of the hovercraft is 0.5m from the wall. The both fans turn on 100% forward. Assume Ffriction=0. If your hovercraft is accidentally rotated 10⁰ off center towards the wall:
a. How long in seconds until you bump the wall? b. If you needed a second to decide and react before you bump the wall: i. What is the largest angle off center you can have at full force? ii. What percentage of fan max will allow you have a 30⁰ misalignment? Xbump = d/sinѲ X = Xo+vot+½at2 xo=vo=0 a = 2F/m Xbump = d/sinѲ = Ft2/m a) Solve for t 1.47 seconds b) i> solve for theta at 1 second 22.02⁰ c) ii> solve for F/2N (percentage) at 1 second and 30⁰. 75% See spreadsheet below ENES 100 Introduction to Engineering Design m= 1.5 v/t 2.666667 m/s dist theta F timetil hit wall 0.5 10 2 1.47 0.5 22.02 2 1.00 0.5 30 1.50 1.00 75% Spring 2011 ENES 100 Introduction to Engineering Design Spring 2011 2. The pseudo‐code flow diagram is as shown for the above hovercraft. Assume the hovercraft is initially perfectly straight and static friction has been overcome. If FanPower=75% and pulse=3 seconds: How far does the hovercraft travel until it stops and how long does it take stop? a. If Friction Force is = 0.5N and acts at the centroid. b. If Friction Force is = 1.3N and acts at the centroid. c. If Friction Force is = 2.6N and acts at the centroid. Set Fan1=FanPower
Set Fan2=FanPower
Wait t=pulse Set Fan1=0
Set Fan2=0 Equations: a= Fnet/m = [2(FanPower)F – Ffriction] / m x = xo+vot+½at2 v = vo + at Start: t = 0 xo=vo=0 t = 0 until t=pulse = 3 seconds x3 = +½a(3)2 v3 = a(3) where a= Fnet/m = [2(FanPower)F – Ffriction] / m t=3 until stop xstop = x3+v3t‐½(Ffriction/m)(tstop)2 vstop = v3 ‐ (Ffriction/m) tstop solve for tstop where vstop = 0 tstop= v3m/Ffriction Plug into solve for xstop ENES 100 Introduction to Engineering Design m=
Ff
step 1.5
75% (F/m)*t
Fnet
vf
3
2.50 5.00 15
(0.50)
‐ Spring 2011 0.5
t elapse
0
1 Ff
step 1.3
t elapse
0
1 Ff
step 3
3.923077
2.6
t elapse 0
1 75% (F/m)*t
vf
1.70 3.40 (1.30)
‐ Fnet 3
0.461538 75% (F/m)*t
vf
0.40 0.80 (2.60)
‐ Fnet 7.50 x=xo+vot+.5at^2
x
0
7.50 45.00 5.10 x=xo+vot+.5at^2
x
0
5.10 11.77 1.20 x=xo+vot+.5at^2
x
0
1.20 1.38 xo xo xo a> tstop = 15seconds, x = 45.0m b> tstop = 3.9 seconds, x = 11.8 m c> tstop = 0.46 seconds, x = 1.38m ...
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This note was uploaded on 04/03/2012 for the course ENES 100 taught by Professor Jacob during the Spring '08 term at Maryland.
 Spring '08
 JACOB

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