Download - Cranfield University MSc Thesis Presentation-An Investigation Into The Kart Hopping Phenomenon
M.Sc. Thesis Presentation:
An Investigation Into The Kart Hopping Phenomenon
Simon Scott
Supervisor: Mr. A. J. Robertson
11 September 1998
Cranfield I UNIVERSITY
increased grip between road / tyre slower speed / smaller radius of corner reduced torsional chassis stiffness reduced tyre pressures reduced axle stiffness fewer bearing hangers taller, more upright seating position
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Introduction To Kart Hopping
Kart construction
Hopping phenomenon
Factors increasing the tendency to hop
Work Carried Out
Dynamic Testing
Mass Distribution and Centre of Gravity
Torsional Stiffness Test
Tyre Testing
Finite Element Model
Cranfield I UNIVERSITY
Dynamic Testing 6000
3000
PSD
0 7 14 Frequency (Hz)
Filtered spectral plot for z axis, rear right accelerometer, 201b/in2 tyre pressure, without torsion bar
Confirmed: hopping frequency range effect of decreasing tyre pressures effect of reducing chassis stiffness
Difference in PSD values from each axes: lateral vertical longitudinal
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Cranfield I UNIVERSITY
Mass Distribution and Centre of Gravity
Laden bias: - front / rear - side / side
Centre of gravity: - xy plane position
Cranfield I UNIVERSITY
Torsional Stiffness Test S t i l l n e s s t e s t fo r l a d e n c a s e i n c l u d i n g t o r s i o n b a r
1 0 0 ,
2 0 4 0 GO C h a s s i s t o r q u e ( N m )
S t i f f n e s s t e s t f o r l a d e n c a s e w i t h o u t t o r s i o n b a r 1 0 0
8 0
6 0
4 0
2 0
2 0 4 0 C h a s s i s t o r q u e ( N m )
6 0
8 0
8 0
•Torsion bar effects: •chassis stiffness for laden / unladen cases •rate of change of chassis stiffness with applied load
•Natural frequencies
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8 0 r
6 0
4 0 \
20 I
o i
Tyre Testing
Stiffness tests: - radial / lateral / longitudinal
Tyre pressures: - 10,20, 30, 40lb/in2
Normal loads: - 500, 1000, 1500, 2000N
Dynamic results interpretation Natural frequency calculations
Cranfield I UNIVERSITY
Cranfield 1 UNIVERSITY
Finite Element Model
-. l - o ° .
* ft j.4 Kl •'i * rn* V - * * ** t> C si
& 0
- * * a 1
Simulations / chassis configurations Model construction:
elements tyre representation boundary conditions applied loads effective corner masses
Results: stiffness natural frequencies
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Cranfield I UNIVERSITY
Conclusions Section f n range (Hz) Dynamic Testing 3^9 Torsional Stiffness Tyre Testing 6.6-11.8 Finite Element Model 7-11
Hopping is very slightly damped natural frequency problem, exhibiting self-excitated characteristics Major components of kart have similar natural frequencies in certain configurations Control analogy