1 Project Name: Barn Hoist School Name: Penn State York Student Names: (Hours Contributed): Michael Lieu(9), Andrew Miller(12), Erik Reiker(12), Hunter Warren(9), George Georgakopoulos(12), Daniel Kim(5), Brian Callahan(2) Date Completed: 12/9/14 A. Abstract: Boxes needed to be taken from the ground level to the second floor without using the steps. The hoist system needed to be easy to use so that two 50 kg adults could provide enough power to lift a 15 kg load every 90 seconds (40 boxes per hour). The pulley system needed to be able to be built with a budget of $100-300. The individual prices and total price to create the pulley system were calculated to fit the desired budget and also taken into account the two 100 kg men. A system was created that most notably took advantage of a winch, and a makeshift ramp. The winch had a gear ratio of 4.2:1. This allowed 4.2 times the force at the cost of 4.2 times the speed. The ramp took some of the force from the weight of the box. The system allowed the doors to be closed when not in use, and the system was able to be stopped at any point because of the winch.
2 B. Written Report Problem Identification: Design a manually powered lifting mechanism able to be used by two 50 kg adults that can move forty 15 kg boxes every hour from the the ground level of a barn to the second floor, through the second floor door. The lifting mechanism should be able to handle boxes as big as 60 cm^3 and as heavy as 50 kg. The pulley system and all of its individual parts should be able to be built under $100 budget. Preliminary Ideas: The first idea was to use a system of three pulleys to lift the weights from the ground to the second floor. The rope would go above the door frame where it would go through a system of three pulleys. Using three pulleys would make it easier compared to using only one. It would be powered by a single person on the ground that would pull down on the rope to raise the load. Another person would stand inside the barn, and reach out to the lifted box. The idea was never used because of safety reasons, and design flaws. It s dangerous to have a person reach out of the barn to grab a box. The design flaw was the board that would be attached to the outside of the barn. Materials are not allowed to be added to the side of the barn. (see Fig. 1) The next idea was to use a slide or ramp that would be attached to the ground and sit on the floor inside the second level. A pulley would be attached to a beam inside the roof of the barn. A rope would loop around the pulley and two pieces of rope would be outside of the barn. The ropes would attach to a cart, and a crank outside the barn. A cart would be pulled up
3 the ramp. The idea was not used because the crank outside the barn could not be attached to the pavement outside the barn. (see Fig. 4) The problem with transporting the weight was initially solved using a basic scooter that had a long board with four wheels and a handle. The idea was to attach a flat board on top of the scooter. A rope would then be tied to the front handle of the scooter. The lifter could pull the rope to raise the weight. When the scooter reached the pulley the lifter would attach the weight to the pulley hook and from there transport it up to the next level. The idea was not used because there was no way to keep the box from falling off of the scooter. The last solution discussed was the idea that was ultimately used. The idea included a winch pulley connected to the floor of the barn, a pulley hanging from the ceiling, 2x4s propped up against the barn, and an apparatus to hold the box. The 2x4s were held in place by cement blocks. The box would slide against the 2x4s by being cranked by a winch. When the box would be taken out of the apparatus, the cable in the winch would be released, and the apparatus would be sent down the slide, ready for the next box. (see Fig. 5) Refinement: The way the group decided to improve the design was to change the triple pulley system to a ramp and pulley with a winch. The ramp and pulley would be able to circumvent the issue of not being attached to the barn. By using the ramp, the load can easily be transported from the ground level and into the second level. The winch would be able to divide the amount of work needed to actually lift the load, and lessens the amount of work needed by the two 50 kg
4 lifters. The new refined design would split the amount of work between three entities;opposed to the imperfect design, which forced a significant amount of work on a singular person. The actual process of the new pulley system starts with the carrying unit, which in the new system is a wooden crate. The dimensions on the wooden crate are 27.6 in x 27.6 in, height at 12 in, and a wall thickness of 1.5 in. The dimensions of the wooden crate were made so that the largest load could fit inside and be secure when being moved.the boxes are sat inside the wooden crate at ground level in front of the ramp and a rope is tied to the front of the crate. This crate has a hole at the entry point where the box enters. This hole is where the rope from the pulley is tied through so that the load can travel up the ramp and into the second level. The other end of the rope goes through a pulley attached to a beam inside the second level of the barn. The rope is then lowered back to the ground where it is put into the winch. The hoist would work most efficiently if there were one person at the bottom of the ramp loading the crate and turning the winch, while another person on the second level is taking the load out of the crate. Once the box is unloaded from the crate, the winch operator simply lowers it back to the ground by turning the handle the opposite direction. Using a ramp would decrease the amount of strength an operator would need compared to just using the pulley alone. To work around the problem of mobility and stability, the solution the group agreed upon was to fasten the ramp onto the barn, so that it can be deployed whenever needed and folded away when not needed. The ramp must be removable, and when extended out of its fastening it would be deployed at an angle from the ground to
5 the second floor. Also, using the winch would make work easier for the user because they would only need to use one arm to crank it instead of using both for a pulley. This method would prevent ropeburn on the user s hands because they would never need to touch the rope. Analysis: The design needed to satisfy two scenarios. One scenario involved a strong 100 kg person lifting a 50 kg box, and the other scenario involved a 50 kg person lifting a box at a rate of 45 boxes an hour. For the 50 kg box scenario, the force required to lift the box without accounting for friction was found using the formula T = mgsin(theta). m is the mass of the box, 50 kg, g is the acceleration due to gravity, 9.8 m/(s^2), and theta is the angle that the box is moving up the planks. The force needed to lift the box without accounting for friction was found to be 386.178 Newtons. The force of friction was found using the formula F(friction) = μf(box). The coefficient of friction of wood on wood is about 0.25. The weight of the box was the previously calculated value, 386.178 Newtons. The force of friction was calculated to be 96.545 Newtons. The total force needed is the force of the box added to the force of friction. The total was calculated to be 482.7225 Newtons of force required to lift the 50 kg box into the barn. To see if the person could lift the box, the equation F(cranked)*D(cranked) = F(output)*D(gear) was used. The gear ratio is 4.1 to 1, so the distance of cranked will always be 4.1 times the distance of the gear. The force that the 100 kg person could crank was estimated to be about 120 Newtons. Therefore the output was estimated at 492 Newtons. The output force was greater than the force required to lift the box, so the 50 kg box can be lifted by the 100 kg person. (See Figure 11)
6 The other scenario involved a 50 kg person lifting 15 kg boxes at a rate of 45 boxes an hour. The weight of the box, and the force of friction were again found by using the formulas T=mgsin(theta) and F(friction)=μF(box). This time the required force was found to be 144.813 Newtons. The force the person could output was again found by using the formula F(cranked)*D(cranked) = F(output)*D(gear). This time the force the person could output was found to be 328 Newtons. The output force was greater again. It was assumed that a person could turn the crank one revolution per second. Using the circumference of the gear, 0.45501 ft, it was determined that it would take 37.3618 revolutions to travel the 17 feet to reach to the barn. Since it was assumed that one revolution equals one second, it would take 37.3618 seconds for the box to reach the barn. The time it takes to for the barn hoist to be reloaded was conservatively estimated to take about 30 seconds. The total of these times, 67.3618 seconds to take a box to the barn, and to be ready to pull the next box up to the barn. The inverse of the 67.3618 seconds per box shows the amount of boxes that reach the box in a second, 0.01485209 boxes per seconds. To find how many boxes are lifted in an hour, the 0.01485209 was multiplied by 3600 seconds in an hour. The amount of boxes lifted in an hour is estimated at 53 boxes, well over the 45 boxes per hour requirement. (See Figure 10) Final Solution: The apparatus that holds the items being stored is shown on Figures 14-17. The users must build the apparatus by cutting out a 28 x28 square from the ½ x4 x8 plywood board. Then, from the same piece of plywood, cut out three pieces that are 28x12 rectangular piece. Figures 14-17 show where all the screw marks are located so the user is able to join all the pieces together. Once the box holding apparatus is built, one hole must be drilled directly into the
7 center of the flat wooden platform where there is an opening. The hole is used to tie the rope around so that the rope completes the system by connecting from the crank system that runs through a pulley system, allowing the box to be movable from the person inside the barn. The wooden planks leading up to the opening of the barn must be separated by 19 inches in order for the apparatus to comfortably ride up the planks of wood. At the top of the wooden planks, use an extra piece of wood and drill in a screw so that the two single wooden planks connect. Do the same towards the bottom. Drilling in these two extra pieces ensures that the gap between the two wooden planks stays at the correct length so the apparatus holding the box does not fall through. To keep the wooden planks from falling out of place, two cinder blocks must be placed at the base of the wooden planks, one cinder block per wooden plank. C. Graphics Section Preliminary Ideas:
8 Figure 1: The drawing shows a preliminary sketch of the first barn hoist idea. The sketch shows three pulleys hanging over the door frame. The box would be lifted right outside the door to the barn. The idea was scrapped due to safety problems. (Not allowed to reach out to grab the box.)
9 Figure 2: A preliminary sketch of the original pulley system. The system was derived from images looked up on the internet to get a better understanding of a simple pulley system.
10 Figure 3: A preliminary sketch of the original idea. Our group believed that this design would work because of the mechanical advantage with two pulleys working with one another. The idea was scrapped for the same safety reasons as Figure 1.
11 Figure 4: This preliminary sketch shows many of the components that will be used in the design of the hoist. A rope running from the pulley to the cart containing the box is tied together and then pulled up a wooden ramp (not labeled) and through the barn door opening.
12 Figure 6: This sketch shows the separate pieces that we would be using in order to create the hoist. Displayed in the sketch is the apparatus that holds the boxes, the winch that is used to hoist the box up the ramp, and a pulley system that was later changed.
13 Refinement: Figure 7: Refinement sketch showing the key dimensions used for the final design of the barn hoist.
14 Figure 8: Shows the calculations of key calculations. (Note: The shown force is incorrect.) Analysis: Figure 9: Materials list for the barn hoist.
15 Figure 10: Calculations of the scenario of 15 kg boxes being lifted at a rate of at least 45 boxes an hour.
16 Figure 11: Calculations from the scenario with a 100 kg man lifting a 50 kg box.
17 Final Solution: Figure 12: Hand winch that will be operated by user inside of the barn Figure 13: Both images show the design of the pulley and the pulley holder.
18 Figure 14: Ref. 1: Sketch of apparatus. apparatus Figure 15: Ref. 2: Sketch of the Figure 16: Sketch of the apparatus. Figure 17: Sketch of the apparatus.
Figure 18: Ref. 3: The following images are multiple views of the apparatus that holds the box. The images show key dimensions and points where the user must drill a nail into. 19
Figure 19: This is the overview of the entire hoist system, displaying dimensions and clouded reference areas which are described in the images above. 20