Human Electric Trike Thesis

Design of an electrically assisted human powered trike

Archive for the ‘Theory’ Category

CFD Velocity plots

Posted by Bob Dold on Monday, October 23, 2006 11:32 PM

Plot of velocity profiles at several different locations:

Posted in Theory | 2 Comments »

CFD Analysis

Posted by Bob Dold on Monday, October 9, 2006 8:50 PM

To get an idea of the aero drag on the trike with a rider I built a FloWorks model of it to study the drag loads and flowline around the trike. My first model is a crude model withhalf of the trike and rider modeled to take advantage of symmetry to allow the model to run faster. The picture below shows the simplified trike model used in the analysis.

For this analysis I used an external air flow speed of 25 MPH, ground effects and spinning effects of the wheels and pedals were ignored. From this run, the solution converged after 44 iterations at about 2.4# for half the trike, or 4.8# total. The plot below shows the pressure on the rider and trike at 25 MPH:

 

To compute the Cd of the rider and trike, the drag is divided by 1/2 the density times the frontal area times the velocity squared.

Cd = Drag / (.5 * density * A * V^2)

Published values for the Cd of a traditional bike and rider vary from .70 to 1.1, a fully enclosed trike with an aero shell similar to the GoOne would be around .150. A recumbent trike should be somewhere inbetween these values, probably on the order of .50 to .70. From the model the frontal area is 5.58ft^2, filling in the rest of the equation yields a Cd value of .53 – right about where it should be. To study further reducing the drag, a fairing may be added to the simulation to see how much it helps reduce the trike’s drag.

 

Flow trajectories at trike centerline:

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Suspension motion analysis

Posted by Bob Dold on Monday, September 25, 2006 10:20 PM

Created a motion model using CosmosMotion software to predict loading on shocks throught the suspension travel. The plot below shows the loading on the front shock vs. the shock travel, the nominal shock position is at .5 inches.

The plot below is the loading on the rear shock from the swingarm:

In both cases the load increases near the end of the travel due to the mechanical advantage of the linkage. The applied wheel load is 1G in the vertical direction.

Link to rear suspention AVI: rear_arm.avi (9Mb)

Link to front suspension AVI: front_susp.avi (8Mb)

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Swingarm Analysis

Posted by Bob Dold on Thursday, August 31, 2006 11:36 PM

Ran the first stress analysis on rear swingarm – used a 3G vertical load as the loading, and used symmetry to model only half of the swingarm. Results look okay, nect step will be to analyze full swingarm with side and fore/aft loads as well.

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Analytic Cycling, Interactive Methods for Estimating Cycling Performance Parameters

Posted by Bob Dold on Friday, June 16, 2006 10:11 PM

Formulas for tire rolling resistance and aero drag: Analytic Cycling, Interactive Methods for Estimating Cycling Performance Parameters. Tom Compton

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Initial performance calculations

Posted by Bob Dold on Wednesday, June 7, 2006 9:53 PM

Completed initial performance spreadsheet, results are listed below. Assumptions are as follows:

  • 26" rear wheel
  • rolling resistance coefficient  = .01
  • Cd = .3
  • frontal area = 9ft^2
  • net weight = 385# (250# rider)

These are initial assumptions and will need to be verified as the design develops. Using these assumptions, the best gear ratio to satisfy the 10% grade requirement was 19.1. This value would give a top speed on level ground of about 25 MPH. The limiting factors are the 10 minute current rating of the motor of 115 amps, and the motor torque vs. required torque.

The gear ratio is higher than I was anticipating so the next step will be to design a gear train to produce a 19.1:1 reduction –  the initial design goal of 20 MPH up a 10% grade looks feasible, but the level cruise top speed is limited to 25 MPH rather than the desired 30 MPH because of the gearing. Optimizing the aero and drag might allow the top speed to be increased.

Performance Spreadsheet Results:

Gear Ratio 19.1

Speed (MPH)

Grade (%)

Tire rolling resistance (Cr)

Total rolling force (lbs)

Still air drag force (lbs)

Relative wind factor (Cw)

Relative wind drag force (lbs)

Incline force (lbs)

Rolling drag force (lbs)

Total drag force (lbs)

Motor Torque Reqd  (ft-lbs)

Motor RPM

Max Motor Torque (ft-lbs)

Current Draw (amps)

5

0

0.011

5.19

0.17

2.74

0.47

0.00

5.19

5.84

0.32

1278

9.84

21.0

10

0

0.011

5.38

0.69

0.82

0.57

0.00

5.38

6.64

0.36

2555

7.59

22.8

15

0

0.012

5.57

1.55

0.42

0.66

0.00

5.57

7.79

0.43

3833

5.35

25.4

20

0

0.012

5.77

2.76

0.27

0.75

0.00

5.77

9.28

0.51

5110

3.10

28.7

25

0

0.013

5.96

4.32

0.20

0.84

0.00

5.96

11.12

0.61

6388

0.86

32.9

30

0

0.013

6.15

6.21

0.15

0.93

0.00

6.15

13.30

0.73

7666

0.00

37.8

35

0

0.014

6.34

8.46

0.12

1.03

0.00

6.34

15.83

0.87

8943

0.00

43.5

40

0

0.014

6.54

11.05

0.10

1.12

0.00

6.54

18.70

1.03

10221

0.00

50.0

45

0

0.015

6.73

13.98

0.09

1.21

0.00

6.73

21.92

1.20

11498

0.00

57.3

50

0

0.015

6.92

17.26

0.08

1.30

0.00

6.92

25.49

1.40

12776

0.00

65.3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

10

0.011

5.19

0.17

2.74

0.47

38.26

5.16

44.07

2.42

1278

9.84

107.2

10

10

0.011

5.38

0.69

0.82

0.57

38.26

5.36

44.87

2.46

2555

7.59

109.0

15

10

0.012

5.57

1.55

0.42

0.66

38.26

5.55

46.02

2.52

3833

5.35

111.6

20

10

0.012

5.77

2.76

0.27

0.75

38.26

5.74

47.51

2.60

5110

3.10

115.0

25

10

0.013

5.96

4.32

0.20

0.84

38.26

5.93

49.34

2.70

6388

0.00

119.1

30

10

0.013

6.15

6.21

0.15

0.93

38.26

6.12

51.53

2.82

7666

0.00

124.0

35

10

0.014

6.34

8.46

0.12

1.03

38.26

6.31

54.05

2.96

8943

0.00

129.7

40

10

0.014

6.54

11.05

0.10

1.12

38.26

6.50

56.93

3.12

10221

0.00

136.2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

20

0.011

5.19

0.17

2.74

0.47

75.40

5.09

81.14

4.45

1278

9.84

190.8

10

20

0.011

5.38

0.69

0.82

0.57

75.40

5.28

81.94

4.49

2555

7.59

192.7

15

20

0.012

5.57

1.55

0.42

0.66

75.40

5.47

83.08

4.55

3833

5.35

195.2

20

20

0.012

5.77

2.76

0.27

0.75

75.40

5.66

84.57

4.64

5110

0.00

198.6

25

20

0.013

5.96

4.32

0.20

0.84

75.40

5.84

86.40

4.74

6388

0.00

202.7

30

20

0.013

6.15

6.21

0.15

0.93

75.40

6.03

88.58

4.86

7666

0.00

207.6

35

20

0.014

6.34

8.46

0.12

1.03

75.40

6.22

91.11

4.99

8943

0.00

213.3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

25

0.011

5.19

0.17

2.74

0.47

93.25

5.04

98.93

5.42

1278

9.84

231.0

10

25

0.011

5.38

0.69

0.82

0.57

93.25

5.22

99.73

5.47

2555

7.59

232.8

15

25

0.012

5.57

1.55

0.42

0.66

93.25

5.41

100.87

5.53

3833

0.00

235.4

20

25

0.012

5.77

2.76

0.27

0.75

93.25

5.60

102.36

5.61

5110

0.00

238.7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

30

0.011

5.19

0.17

2.74

0.47

110.48

4.97

116.10

6.36

1278

9.84

269.7

Motor Torque Curve:

Posted in Electronics, Performance, Theory | 3 Comments »