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Assignment Five- Shaft
Solid Model of Component
Base Model
FRDPARRC
FRDPARRC
Calculations
*UPDATE: New FOS for Motor = 2.5, New torque: 5.625 lb-in*
Materials
From the above calculations we find that the maximum shear
stress allowed before failure is 10.82 ksi. Some of the materials that fit the description and can be easily casted (the process that would
be used to make gears) are down below. Other factors that I took into account when making the decision are the density of the material,
the average cost of the material, and other properties of the material.
* Density is a good factor to recognize because it will determine the weight of the component. The stress of elements depend on the elements
above them in this module, with the shaft and transmission gear supporting almost all of the pressure of the moment caused by the water coming from the hose
plus the weight of the previous elements. This means that a lighter material is more valuable to this design because it will put less stress on the gear.
* Cost is another important factor because in the real world, the material must be purchase in order to make the design. The cost of the material plays a huge
part in the cost of the product. The more expensive the material is per cubic inch, the higher the price of the product would be in order to make a profit in
the material.
* Properties of the Material is another factor in choosing a material, if the material does not have the correct properties for this module, then it will not be a good idea to
choose the material.
| Material |
Max Normal Stress (ksi) |
Max Shear Stress (ksi) |
Yield Strength |
Density (lb/in^3) |
Cost of Material ($/lb) |
Resources |
| SAE Steel 1025 |
around 60 ksi |
around 45 ksi |
About 45 ksi |
0.2839 |
$0.36 |
*Machinery's Handbook, pg. 501 and pg. 527; *http://www.infomine.com/investment/metal-prices/aluminum/ (Cost) |
| Cast Iron |
around 72 ksi |
32 ksi |
30 ksi |
0.25 |
$0.75 |
*Machinery's Handbook, pg. 501 and pg. 527; *http://www.infomine.com/investment/metal-prices/titanium/ (Cost) |
| Cast Aluminum |
21 ksi |
14 ksi |
15 ksi |
0.095 |
$0.89 |
*Machinery's Handbook, pg. 501 and pg. 527; *Scrap Monster |
Doing analysis on each of these materials, I find that the Steel is the best candidate out of the
chosen materials. It has the highest shear stress, which means I can compensate for any errors in my
device. The steel is also cheaper than the others, costing only 36 cents per pound, which means I can sell
them cheaper overall.
Motor
The motor will power the entire module, so it is necessary to see our options in choosing the motor. The criteria
I will be using in the analysis are:
- Max Torque (>90 oz. in)
- Max Speed (>0.288 rad/s)
- Cost
- Min Voltage
| Motor |
Max Torque (oz-in) |
Max Speed (rad/s) |
Cost |
Weight |
Min Voltage |
| Hitec HS-805BB servo |
343 oz-in |
5.51 rad/s |
$40 |
4.8 V |
0.335 |
| Hitec HS-755BB |
183 oz-in |
3.73 rad/s |
$40 |
0.242 lbs |
4.8 V |
| Hitec HS-625MG |
94 oz-in |
6.69 rad/s |
$32 |
0.11 lbs |
6 V |
After an analysis, the best motor out of the ones above is the Hitec HS-625 MG. It is the lightest so it will
effect the design the least. It is also the cheapest so that I can make the design cheaply.
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