Eric Sabelhaus
19 September 2006
AME 40463 Senior Design
Generator Selection Study
Purpose/Influence on Design Decisions:
In our design concept, a bike pedal will be turned by the human user to power a
generator. The purpose of this design study is to select a generator that will most effectively
convert the mechanical power input from the pedals to electrical energy. The study will
determine an appropriate gear tooth ratio that will most closely match the required generator
rotational speed and torque. To measure the merit of each candidate generator, mechanical
efficiency, cost, and size will be weighed, respectively, in decreasing order of importance.
Variables:
Design Variable (DV)
1
2
3
Generator type (batch)
Design Parameter
(DP)
Power from pedals to
input gear (PPEDAL)
Output gear radius, rOUT
(batch-purchased)
Generator shaft rotational
speed, ωG (continuous)
State Variable (SV)
Power to drive
generator (PG)
Generator Torque (TG)
Constraint (C)
Max. generator
speed (ωG_M)
Max. generator
torque (TG_M)
Gear Ratio (GR)
Methods of Analysis:
To simplify the analysis, the input gear will be a predetermined diameter based on a
typical gear in a 21-speed bicycle. Additionally, the input gear rotational speed will be held
constant at 60 rpm, a nominal value that a normal human can accomplish when pedaling. From
known Voltage and Amp specifications of candidate generators, PG can be determined. Ideally,
PG will be as near PPEDAL as possible to maximize power conversion. If PPEDAL >> PG, the
generator will not be able to convert the human work to electrical energy, and if the converse is
true, the high generator torque will bog down the worker and inhibit pedaling output. The output
gear radius and generator shaft speed will be adjusted to optimize mechanical efficiency. Based
on these values, the gear ratio can be calculated. The basic equations to be used in this study are:
GR 
Output _ Circum. 2  r _ out r _ out


Input _ Circum.
2  r _ in
r _ in
Torque  r  F
Power  Volts  Amps  Torque  
Quantitative Information to be Developed:
Based on this study the output gear radius, generator shaft rotational speed, and gear ratio
will be determined. Each generator will receive three ‘scores’ for its 1) mechanical efficiency, 2)
cost, and 3) size. The generator earning the highest score will be selected.
Schedule:
Due Date
Milestone
19/9 (Tue)
Proposal
due
26/9 (Tue)
Generators
identified
28/9 (Thur)
Input radius,
ωG selected
03/10 (Tue)
Generator
chosen, ordered
10/10 (Tue)
Report draft
completed
12/10 (Thur)
Report due