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Off Road Electric Vehicle

Brad Gordon, Jake Richardson, Department of Mechanical Engineering, University of Ottawa

Why we built it?

                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.

Mechanical System

Steering:

                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

Suspension

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.

Drivetrain

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.

Driver Controls

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.

Brakes

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.

Batteries

                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

Motor Controller

                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 speeds).      

Figure 5: Curtis PMC Motor Controller

Motor

                The motor we choose is a 36V 2hp DC motor. This is what required our six batteries.

Figure 6: 36V 2hp Motor

Forward/Reverse Switch

                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 Switch

Lights and Horn

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.