The team, Da Buffs, is working on a project called the ultimate Boulder bike. The bike will be equipped with studded tires, an automatic seat cover, and heated handlebars. Each of these accessories will give the rider comfort even in the harshest winter conditions. The studded tires will give the bike more traction when the roads are icy. The seat cover will be motorized for the rider’s convenience, acting like an umbrella over the seat to keep it dry when not in use. The heated handlebars will be temperature sensitive. When the weather is cold, the handlebars will warm up but will turn off when it gets too hot. The rider can turn the temperature-controlled handlebars off while the bike is not in use to save energy. 

We tested seat-cover materials for strength. We chose to test different sizes of aluminum due to its lightweight. We tested rods that had 1/8 inch diameter and ¼ inch diameter in order to determine which size would be strong but practical. We performed tensile and seat cover torqu tests on the aluminum. The tensile strength is tested by pulling on both ends of the rod until failure. The seat cover torque test aims to determine the maximum weight, or torque, of the seat cover in order for the motor to work. This maximum torque T can be found from the force of the mass of the seat cover F and the radius of the center of mass r as shown in Equation (1),

T = r x F = (rF)sin(Θ) = rF, (1)

and depicted in Figure (1). The force of mass F is the total weight of the entire system and the radius r is an over estimation of the center of mass. We used r as the center of mass so the angle would be 90 degrees, which would make the math better to interpret, as shown in Equation (1). The torque was determined by multiplying the weight of the rods (oz.) by the perpendicular vector of the radius (inch).

We determined the max torque of the system and compared it to the max torque that the servomotor can handle. We over estimated the center of mass because the system will be moving and the cross product of the force and radius will change. There will also be small, but not negligible, angular acceleration that would add to the net torque. These two tests helped us find the optimal strength and size of aluminum bars, in other words, what material can hold the seat cover up but not weigh the motor down.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: A free body diagram of the seat cover's torque

 

 

 

 

 

 

 

 

 

 

Figure 2: Force applied to either end of the rod (Newtons) as a function of distance streched past origonal length (mm), testing the abosulte strength of an aluminum rod

 

In the tensile strength test (see Figure 2), an aluminum rod was pulled on either end to its breaking point. This test found the aluminum rod’s absolute strength, however, this test was not the ideal test to find if the rod could support a seat cover. We could not preform a lateral strength test to find the maximum weight the rod could support. Although the correct test could not be preformed, knowing the absolute strength of the rod did help identify the correct material to be used. The initial slope of the graph represents the bar resisting stretching to nearly 6000 Newtons. When the graph flattens out, the aluminum bar began to stretch at a greater rate. The bar continued at this rate until reaching its maximum tensile strength of approximately 9700 Newtons where it finally broke. Aluminum was found to have an excellent strength to weight ratio and is why it was chosen to support the seat cover.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3: Different radiuses (inch) and different force of mass (oz.) are in a function of torque (oz.-inch) compared to the max servo torque

 

We tested three distances for the radius. The radiuses are just an approximation of where the center of mass would be because as indicated in Figure (3) the largest radius, which is longer than the system entirely, does not come close to failing the motor. The three distances are 8, 12, and 16 inches. As indicated by the graph, the highest torque resulted from the ¼ inch diameter bar from 16 inches away. That torque came out to be 59.6 (oz.-in.), which is clearly smaller than the maximum torque that the servomotor can move, which is 154 (oz.-in.). We found the max torque of the motor from Spark Fun Electronics.

 

The agenda for this test is to find out if there are any weight constraints when using the aluminum rods. The ¼ inch rods are stronger and the servomotor has no problem moving them, so they are the optimum building material of our bike seat cover.

 

Critical Design Feature:

Along with the servomotor being strong enough, it must also be able to rotate 180 degrees. This will insure that the seat cover is out of the way while riding the bike and that it can cover the entire seat. The handgrips must be able to turn on at 40 degrees Fahrenheit and turn off once it has passed 40 degrees Fahrenheit. This is important for the rider because the handgrips need to be heated in a short time for comfort but not waste any energy scorching the rider’s hands. 

 

Programming tests: 

Switches will turn the Arduino boards on and off to conserve energy while the bike is parked. The switch will turn on the servomotor, changing the seat cover from 0 degrees to 180 degrees. Figure 4 has confirmed this test. The handlebars will be heated when they are sufficiently cold. Specifically, the handlebar heating pads will be turned on if the sensor detects a temperature below 40 degrees Fahrenheit and off when the pads detect a temperature above 40 degrees Fahrenheit. This can be seen in the code below.

if (temperatureF<40) {handlebars = HIGH;}

if (temperatureF>40) {handlebars = LOW;}

delay(1000);

The rider can also turn off the heated handgrips entirely when the bike is not in use.

 

 

 

 

 

 

 

 

 

 

 

Physical tests: 

The project parts must be able to withstand vibrations coming from the road and crashes and the electrical components must stay dry at all times. The seat materials have been proven strong enough in tensile strength test. The electrical parts will be concealed in ¼ inch acrylic and the wires will be coated to eliminate the potential for rain damage. We will test the studded tires by riding the bike on a hockey rink.

 

Results:

Our testing shows that our materials will function properly for our project. The design and part placement needs the most improvement such as dry location of Arduino and proper servo motor placement. All of our electronics must operate in weather. The servomotor must be able to move the seat cover while staying out of the way of the rider.

 

Additional concerns with respect to durability of the bike’s components to harsh weather, such as rain and hail, and accidents were not addressed. Our objective was to have a winter bike that would function right after completion. The seat cover will not act as a shelf as originally planned due to weight-related restraints of the motor. Optimal components were readily available due to the loose constraints of the project design.