Stairs Climbing Wheelchair
Using PID and Gyro-Acclerometer for seat balancing
Saad Rabbani, Shahmir Ali Khan, Syed Sajjad Raza, Syed Zunaib Shahzad Raza
Electrical Engineers
National University of Computer & Emerging Sciences (NUCES-FAST)
Karachi, Pakistan
Shahmirak@hotmail.com
Abstract—Nowadays autonomy in the area of mobility is
accepted to be of high value which may be sometimes hampered
due to some form of disability. Hence, wheelchairs continue to
play a vital role to allow for mobility of the disabled people. But
this autonomy is not applicable in environments having steep
slopes or staircase. So a stairs-climbing wheelchair was designed
in this project which can work in two modes; flat surface moving
mode and stairs climbing/descending mode. The project aims at
the capability of climbing and descending stair cases using
joystick, wheels and track belt. One of major problem for
wheelchair users is crossing the terraced road, such as sidewalks,
small steps, up and down stair case etc. This design includes
custom made track belts, wheel mechanism and its dynamic
simulations through MPU6050. A seat adjustment system using
PID controller was designed to adjust the centre of gravity while
climbing up and down stairs. At the same time, a locking
mechanism in motors makes the wheelchair working more safely.
II. BACKGROUND
The last 100 years or so have seen many technological
advances; however with regard to mobility assistance only
minor changes have occurred with regard to the basic
wheelchair. The first commercially available stair-climbing
wheelchair based on a single section track mechanism became
available in the mid 90‟s (in Japan). Single track mechanisms
are also available with a simple platform on which a manual or
powered wheelchair and occupant can be carried up or down
the stairs. This approach is used at some railway stations in
Japan where elevators are not available.
Keywords—Terraced roads; Wheel chair; Stair climbing;
Track belts.
I. INTRODUCTION
The traditional wheelchair plays a vital role in mobility of
the user. However wheelchairs to date provide a high level of
mobility only in barrier free environments. Thus, there
remains a significant gap between the obstacle negotiating
ability of a wheelchair and that of the average able person.
This aspect is most apparent when considering stair-climbing.
Current common practice in regard to stair assistance is that
two to four assistants are required for a mobility of disabled
person. Assistive device based solutions for stair-climbing
includes lifts and chair or platform based stair-lift
mechanisms. Stairs perhaps best represent “environs not suited
to wheeled vehicles”. Two fundamental means of stair
negotiation are provision of a stepping mechanism, or
increasing the wheel‟s footprint (diameter) so that the step is
bridged. Provision of a stepping mechanism requires relatively
complex mechanical operation and must be linked to
knowledge of the location of the stair edge.
There are common norms of providing ramps and
lifts/escalators in all the public buildings these days it is
observed that they are not omnipresent due to space and
related reasons. Dependency of such structures on electricity
cannot be ignored. The conditions of the disabled in rural
areas are deplorable as such facilities are not present.
Table.1. Categorization of stair capable mobility assistance
devices.
A broad list of stair mobility assistance devices is provided
in Table 1 and an outline of respective advantages and
disadvantages. The advantage of tracked operation is simple
control and robustness in regard to operation on the uneven
and rugged terrain. In order to have stability while climbing
stairs the mechanism must maintain four points of contact with
the stairs and be configured in such a way as to provide
acceptable stability margins at all times.
III. METHODOLOGY
Mechanism considered for this wheelchair is the Tank
mechanism. This mechanism is shown in Fig.1. It is similar to
a tank and consists of tracks rotating over the sprockets
attached to the chassis. The tracks are so designed as to permit
easy ascent and descent. The track is driven by motors via
gears to provide proper traction on the stairs. The tracks are
made of composite material comprising of metal and rubber.
Considering ease of operation, the track is of 5 cm wide. The
material should have the more stress bearing capacity within
the size constraints. Thus, with the above mentioned
parameters of considerations, mild steel is a promising material
for the chassis.
IV. ANALYSIS OF DESIGN PARAMETERS
Velocity: Humans select walking patterns that appear to
minimize energetic cost. They tend to move at a speed near
that minimizes the metabolic energy cost per unit distance
travelled. And at a given speed the nervous system selects a
combination of step frequency and step length that coincides
with the minimum rate of metabolic energy expenditure. The
minimum preferred speed while walking on level surface is 5
Km/h. considering the impediment of step while handling a
wheelchair speed has been assumed to be 0.2m/s.
Weight: The maximum weight of the wheelchair along
with patient is assumed to be 180 kg. The forces acting on the
mechanism, the forces due to the tension in chain and the
forces due to gear transmission are considerable. Hence, these
are calculated and used for the design of shaft, bearings, chain
and sprocket.
Sprockets and Chain: Tension acts on the shaft due to the
chain drives. This force is calculated as follows. Two motors
of 800 watts each. Therefore, 800 watts for each chain drive.
P=FV
P = Power = 800 Watts, V = velocity = 0.2m/s,
F = Force = 4000 N
By considering comfortable staircase ascent speed to
be one step per second we get the linear speed of the
wheelchair as 0.2 m/s. By trial and error for initial climbing
traction, we find the most suitable sprocket size which comes
out to be of 20mm diameter The RPM required at sprocket is
calculated as follows:
Fig.1. Tank Mechanism
The motors used for the movement of wheel chair on stairs
and on flat surface are operated by 24 volts and they take their
power from two 24 volts 7 amp batteries. Movement is done
by operating joystick. For maintaining the balance of seat
while climbing up and down stairs, PID controller and Gyroaccelerometer is used. The gyro-accelerometer balances the
seat by maintaining center of gravity of the passenger sitting
on it.
The gyroscope maintains its level of effectiveness by being
able to measure the rate of rotation around a particular axis.
The gyroscope helps indicate orientation while an
accelerometer is a compact device designed to measure nongravitational acceleration. When the object goes from a
standstill to any velocity, the accelerometer responds to the
vibrations associated with such movement. It uses microscopic
crystals that go under stress when vibrations occur, and from
that stress a voltage is generated to create a reading.
Where, „V‟ is linear velocity of belt, „D‟ is diameter of
sprocket and „N‟ is the revolutions per minute (RPM). Putting
the above mentioned values the RPM should be 20 rounded
off to nearest standard value. After selecting the chain, the
next step is the selection of sprocket. This is done using the
pitch of the chain. The tooth correction factor is suitably
modified according to the number of teeth and then
calculations are made for chain and sprocket.
For z = 24 we have D = Diameter=194.5 mm Therefore, z
= 24 is appropriate. Taking tooth correction factor for 24 teeth
as 1.41 we have, number of teeth= 24. Considering forces on
sprocket, Vertical Force = Fv = 735.8N, Horizontal Force =
FH = 3931.9N.
Building of chassis: For proper traction and stability on
the staircase, it is assumed that the wheelchair should be
resting at four contact points on each side. For easy ascent, the
truss is given an angle. By surveying many common
staircases, it was concluded that the minimum angle made by
the truss should be 35°.Using these values the load carrying
chassis is modeled. In order to validate the design variety of
tests and experiments were done with and without load of
passenger.
V. DEVELOPMENT OF PROTOTYPE
The prototype is developed and the project is prepared for
testing the feasibility of the mechanism. There were few
design modifications for assembly purpose. Trials are
conducted on the test model using actual staircase. The ascent,
descent and ease of rolling of the test model are tested.
It was observed that conventional tracks were not fit for
climbing and they were unable to make proper grip and
traction while climbing stairs. So custom made tracks were
made and they did the job perfectly. Linear actuators were
used to lift the cage up from flat surface mode to stair
climbing mode. Chassis were made keeping in view the
original design but some amendments were made during
production in order to make proper alignment of the tracks so
that they climb in straight line.
VII. CONCLUSION
The different mechanisms were reviewed and the most
appropriate were studied in detail. Their relative advantages
and limitations were compared and the tank mechanism was
found to be most suitable to fulfill the various requirements of
this project. During the test run it was realized that it wouldn‟t
be a bad idea to consider this design for carrying heavy loads
up the stairs. This product will be well acclaimed if it can be
commercialized to suit the needs of the consumers. Though
the initial cost of the project seems to be higher but more
accurate manufacturing would shorten this. As far the
commercial aspects of this product are concerned, if this
product can be fully automated and produced at a lower cost,
the acceptance of this stair climbing wheel chair will be
unimaginable. Presently, there are no competitors for such a
kind of product in our market.
Acknowledgment
This project was funded by all four of us. We would like to
thank our teachers and project advisors for helping us in
completing this project.
References
VI. FUTURE ENHANCEMENT
The future enhancement of our project is we have to rectify
the problems that we have encountered during descending of
the wheel chair on stairs. We had a smooth travel while
ascending but while coming down from the steps, we found
some vibration problem and to overcome this we have planned
to install springs and shock absorbers, so that wheel chair will
be in a good control while descending also.
More over battery timing and recharging can be improved.
With the advancement in the technology, the light weighted
solar panels can be installed on the wheelchair which will
charge the different batteries being used on the wheelchair.
Patient‟s home and environment can be automated using the
raspberry pi to extend the comfort of the patients. E.g. Doors
could be controlled from the wheelchair, Lighting controls can
be mounted on the wheelchair etc.
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