DRIVE SHAFT REDESIGN
MOBILITY TRICYCLE PROJECT
Daniel Barrett and Matthew Tomasetti
Mission & Client
Problem
Wear Identification Photography
Mission: The Mobility Tr icycle Project seeks to provide
appropriate, sustainable mobility devices for persons with
disabilities living in Burkina Faso, Africa. Our overall
design philosophy is based around simple, appropriate
solutions that are cost effective relative to locally available
resources and that also promote technology transfer in order
to maximize ownership and minimize dependency.
Client: Center for the Advancement of the Handicapped
in Burkina Faso; a department of
SIM (Serving in Mission)
We need to be able to confidently say that altering the mechanical properties of
the speed reducer and the drive shaft will significantly reduce the rate of wear
on these components. To do this, we need
successful methods of testing the rate of
wear on both the speed reducer and the
drive shaft throughout an extended period
of drive train use.
Drive shaft used for testing purposes
In further work, we experimented with and eventually developed a successful full
length procedure for taking pictures of our drive train components with controlled
lighting, magnification, and orientations so that the effects of wear can be visually identified throughout field testing. This has become a standard for observing
wear on these components as we continue to field test the electric tricycle.
Results:
Images taken
of drive train
components
using the wear
identification
procedure
Fixed Socket Displacement Test
Background
The drive train of the electric tricycle, consisting of multiple
components, is necessary so that the rotational speed of the
trike motor can be reduced to a safe level for vehicle use.
Motor
Chain
Housing
Drive
Shaft
Housing
Speed Reducer
Chain
Sprocket
Major Drive Train Components of Electric Tricycle
Previous Work
One major problem of the drive train is that
the planetary speed reducer and the drive
shaft are experiencing rapid wear through
Reducer without
wear
trike use, which eventually prevents the
trike from operating. In past work, a solution was proposed that involved altering
the mechanical properties of these components so that the rate of wear could
ultimately be reduced.
Reducer with fully
worn splines
One of our initial attempts at measuring the effects of wear on the speed reducer
and drive train assembly was through the use of the fixed socket displacement
test which is a previously developed procedure for measuring the linear displacement or “play” between the splines of the components when they are fully
constrained from motion. This is
Speed Reducer
measured by pre-loading the
assembly downward with
Displacement
Shaft
ten pounds of force and
then loading it upward with ten
pounds and measuring the change
in distance of a moment arm.
Shaft teeth move relative to Speed Reducer
Testing
We began by using the fixed socket displacement test to measure the state of
wear on our speed reducer and drive shaft that were worn by field testing an
electric tricycle for incremental distances.
Table of Displacement Test Values vs. Field Testing Distance
Field Testing Distance
Average Deflection
0 miles
0.1457 in
31.07 miles
0.2186 in
50.0 miles
0.1806 in
125 miles
0.1963 in
Future Work
Though the wear identification procedure has become a successful option at qualitatively identifying the effects of wear on the speed reducer and drive shaft, it is
still not quite as conclusive as quantitative data. The procedure will be used in the
future to identify wear but a more accurate and precise quantitative wear test is
necessary to give us the highly definitive data that we need. This may take form
in a new configuration for our fixed socket displacement test which will allow for
less potential human error involved as well as
ease of use, which we believe will provide us
with better data. This new configuration is
currently being designed and it will likely be
pursued even further in the future.
Potential design of new displacement test configuration
Comments
Suspected Outlier
Conclusions
Plausible Accuracy
Unexpectedly, our displacement test values were found to be inconclusive due
to a lack of accuracy and precision within the displacement test. This was attributed to a number of different theories that mostly dealt with the complexity
and difficulty in performing the test. Ultimately, the displacement test did not
offer the conclusive data that we were initially expecting.
Though we have not been able to answer our original question of whether or not
the design change on our speed reducer and drive shaft significantly reduces
wear, we have been able to lay the necessary groundwork that will allow us to
answer this overall question with conclusive data in the near future.
Acknowledgements
 Other Teammates: Sam Duke
 Project Advisors: Dr. Timothy Van Dyke & John Meyer