Mechatronics Learning Studio
Brad Gordon, Jake Richardson, Department of
Mechanical Engineering, University of Ottawa
Off-road vehicles get a lot of negative
attention because of Ö. Being thrill seekers we wanted to make a
vehicle we could drive around trails where we live that will
keep our neighbours, environmentalist and mothers happy. By
definition an off-road vehicle has to be able to handle tough
terrains and harsh environments. To accomplish this we needed to
design a rigid frame with high torque power. In order to make it
environmentally friendly we chose to use an electric motor.
The steering we chose to use is standard rack and pinion
steering. This works by having a pinion (gear (3)) at the end of
the steering shaft (2) that rotates in unison with the steering
wheel (1). The pinion is interlocked with a rack (jagged teeth
along a bar (4)) this has a ball joint at either end where tie
rods (5) are connected which holds the tires. When the steering
wheel is turned it rotates the gear which moves the rack left or
right turning the tires respectively.
Figure 1: Example of Rack & Pinion Steering
The suspension we used consists of
a solid beam shock suspension in the front and leaf spring in
the back. This allows the vehicle to spring over off-road
terrain and maintain a rigid stance.
To handle the torque created by the
motor our EV needed some sort of gearbox. To accomplish this we
used a semi-slip differential with a 1:2 ratio. This gave our
carts drive system strength and allowed our 2hp motor to
accomplish speeds of around 15mph. We were initially planning on
using a chain drive, but chains can have complications with the
initial torque supplied by electric motors.
Just like a car the driver can
control the buggy using a steering wheel and foot pedals. The
left foot pedal controls the braking system where the right foot
pedal moves a potentiometer which controls the amount of voltage
being supplied to the motor.
The EV has two drum brakes built into the ends of the
differential. Both these brakes are connected to the rear wheels
and are engaged by a cable connected to the brake pedal in the
front. The front wheels donít have any braking but we plan to
add individual rotor brakes
Figure 2: Rear Drum Brake and Differential
Figure 3: Basic Circuit Diagram of Power System.
Our electrical system is powered by six lead acid 6V batteries.
Wired in series these supply the motor with 36V at full
capacity. Since they are liquid acid we had to create shielding
plates to ensure safety.
Figure 4: 6 Batteries used in the system
To allow the driver to control the speed of the
cart we had to use an electric system to limit the amount of
voltage being supplied. To do this we attached a pedal to a
potentiometer. Once engaged a solenoid would snap on allowing
voltage to flow freely into the motor controller. We used a 36V
Curtis PMC motor controller commonly paired with our motor. The
motor controller then takes the input from the potentiometer and
allows that calculated voltage to flow into the motor (various
Figure 5: Curtis PMC Motor Controller
The motor we choose is a 36V 2hp DC motor. This
is what required our six batteries.
Figure 6: 36V 2hp Motor
As seen in figure 6 there are 4 electrical post
on the motor, this allows us to attach a 4 point switch which
will reverse the polarity of the electricity being supplied to
the motor. With a reversed electric polarity the motor will run
in the opposite direction (reverse).
Figure 7: Ignition Switch and 4-point Reversing
We bought 4 LED 12V Fog lights to add to the
front of the buggy. This allows us to use the EV during night
time or in storms. We also installed a 12V horn for alerting
nearby pedestrians. Since our electrical system consists of six
6V batteries we connected our 12V horn and lights to two
batteries in series to accomplish this.
Figure 8: Installed Lights with Horn below.