Wheels
Content
Module 5 – Wheels and base (Grant Parry and Shiane C) Researched by Shiane C Drawn and modelled by Grant Parry
Figure 1. For our gantry crane, we decided to use a similar design to ones used on trains, but due to the share size of our crane we decided to use a double axis design, combine two set (rows of wheels) as seen in figure 1. By doing this its will spread the weight of the crane and any loads over 8 wheels and 2 axis and also it gives the crane greater stability. The crane would only be able to move along a modified thinner (less wide) train track and it would not be able to forward or back, only left to right. This does limit us on movement, but because the loads (containers) would be unloaded onto a truck this method is fine. The base is made of 8 wheels, like I said this is because it will spread the load. They are made from a low alloy steel and are 30” high (refer to engineering drawing). Like the frame they are coated zinc primer to prevent from galvanic corrosion and a epoxy paint the prime coat and give the base a colour. We have used train wheels because of the grove in the tread to allow the crane to move with very little friction left and right. The wheels are attached to the frame, with again low alloy steel bearings, they will be 177mm long and will sit inside the centre hole of the wheel, in total there are 32 wheels, meaning there will be 32 roller bearings. Each bearing will be self lubricating (oil) and with Rolling-element bearings the advantage is there is a good tradeoff between cost, size, weight, carrying capacity, durability, accuracy, friction, and so on. Meaning overall a very good choice. When it comes to the numbers and weight, we research the material used and found that low alloy steel is the best material to use, mainly for its impressive yield stress of around 210MPa. With this into consideration, I was able to do some simple calculations to see whether the frames weight can be supported by the wheels and base, if; Yield stress low alloy steel is = 210MPa
Mass of frame = 1399209Kg Weight of frame = 1399209 * g = 13721552.98N You can clearly see that the weight doesn’t exceed the elastic limit and therefore main bend elastically, but it wouldn’t we permanent, whats more because of the frame design, this single weight will be spread over 4 legs and over 8 wheel bases, making there 32 wheels holding the support up, if; Weight of frame = 1399209 * g /4 legs = 3431560.073N = Weight on single leg Weight of single leg = 3431560.073 / 2 wheel bases = 1715780.036N = Each 4 wheel base. Single wheel base (four wheels) = 1715780.036N / 4 =428945.0091N on each wheel. (Assume; g = 9.81 uniformly, even spread of weight over four legs, we assume this because the counter weight will cause a uniform spread of weight or the difference will be ignored, no weight being lifted) For added safty because these calaculations were done without any load, the addition of shock absorbers would be fitted to the chasis. For example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent. By doing this it will provided a smoother ride and also a reduced weight on the wheels and base.
Figure 1. For our gantry crane, we decided to use a similar design to ones used on trains, but due to the share size of our crane we decided to use a double axis design, combine two set (rows of wheels) as seen in figure 1. By doing this its will spread the weight of the crane and any loads over 8 wheels and 2 axis and also it gives the crane greater stability. The crane would only be able to move along a modified thinner (less wide) train track and it would not be able to forward or back, only left to right. This does limit us on movement, but because the loads (containers) would be unloaded onto a truck this method is fine. The base is made of 8 wheels, like I said this is because it will spread the load. They are made from a low alloy steel and are 30” high (refer to engineering drawing). Like the frame they are coated zinc primer to prevent from galvanic corrosion and a epoxy paint the prime coat and give the base a colour. We have used train wheels because of the grove in the tread to allow the crane to move with very little friction left and right. The wheels are attached to the frame, with again low alloy steel bearings, they will be 177mm long and will sit inside the centre hole of the wheel, in total there are 32 wheels, meaning there will be 32 roller bearings. Each bearing will be self lubricating (oil) and with Rolling-element bearings the advantage is there is a good tradeoff between cost, size, weight, carrying capacity, durability, accuracy, friction, and so on. Meaning overall a very good choice. When it comes to the numbers and weight, we research the material used and found that low alloy steel is the best material to use, mainly for its impressive yield stress of around 210MPa. With this into consideration, I was able to do some simple calculations to see whether the frames weight can be supported by the wheels and base, if; Yield stress low alloy steel is = 210MPa
Mass of frame = 1399209Kg Weight of frame = 1399209 * g = 13721552.98N You can clearly see that the weight doesn’t exceed the elastic limit and therefore main bend elastically, but it wouldn’t we permanent, whats more because of the frame design, this single weight will be spread over 4 legs and over 8 wheel bases, making there 32 wheels holding the support up, if; Weight of frame = 1399209 * g /4 legs = 3431560.073N = Weight on single leg Weight of single leg = 3431560.073 / 2 wheel bases = 1715780.036N = Each 4 wheel base. Single wheel base (four wheels) = 1715780.036N / 4 =428945.0091N on each wheel. (Assume; g = 9.81 uniformly, even spread of weight over four legs, we assume this because the counter weight will cause a uniform spread of weight or the difference will be ignored, no weight being lifted) For added safty because these calaculations were done without any load, the addition of shock absorbers would be fitted to the chasis. For example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent. By doing this it will provided a smoother ride and also a reduced weight on the wheels and base.
