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Mech  Design  Project  1:    The  Reciprocal  Water  Pump  In this project your group will design, analyze, build and test a small reciprocal water pump. A basic design has been provided; it is up to you to provide the details! Your goal is to achieve the highest head of water, highest flow rate and lowest mass possible with the given constraints on materials, motors/gearboxes and time. For this project, you will work in teams of three or four.

Important  Dates  (in  the  order  of  section1,  3,  2,  4)  9/24, 9/26, 9/29, 9/30: Announcement of the project. Research on water pump and initial design. 10/1, 10/3, 10/6, 10/7 and 10/8, 10/10, 10/13, 10/14: Learn fabrication skills—laser cutter, lathe, mill machine. 10/15, 10/17, 10/20, 10/21: Finish drawing 10/29, 10/31, 11/3, 11/4: Finish fabrication 11/5, 11/7, 11/10, 11/11: Pump-Fest

Figure 1: Schematic diagram of a reciprocal water pump.

Figure 2: Solidworks rendering of a water pump.

 

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Constraints  1. Your piston will have a diameter of approximately 1.25” 2. Your power source is limited to the Tamiya motor/gearbox assembly provided to you. You may

choose which gear ratios you wish to run, but you may not modify the motor/drivetrain assembly in any way. The motor is nominally run at 3V, you may wish to run at a higher voltage at your own risk!

3. You have only ~5 weeks to complete the project, i.e. 4 lab periods plus appointments as necessary.

4. Inlet and outlet water will pass through ¼” push connect fittings screwed into an 1/8” NPT tapped hole.

5. You may use one or two cylinders in your water pump. Three or more are not allowed. 6. You may use any materials from provided parts list plus any fasteners from the projects lab. If

you choose to add materials great online resources are MSC Direct and McMaster Carr. 7. You must have and enclosed gearbox and a mounted switch. Professionalism and aesthetics

count so get creative and utilize the 3D printer. 8. Part of the scoring (and grading) will be based upon conserving material, so design a lightweight,

efficient pump! 9. No drawing = no machining – you will be unceremoniously booted from the milling

machine/lathe if you don’t have a drawing of the part you’re working on. Otherwise, the sky is the limit!

Assessment  and  Grading  The pump project is worth a total of 200 points, and counts as 45% of your final grade. Machine: Working (5ft head) pump: 60 You need to pump water to at least 5ft high to consider it working Max head score: 10 The maximum height the water goes Flow rate score: 10 The minimum time to pump given volume of water Enclosure/Aesthetics: 10 The design, fabrication, and decoration of the enclosure Material efficiency score: 10 Light and strong Report: Drawings: 30 Attach the drawing at the end of the report Writeup: 25 Calculations: 20 Position and velocity analysis, prediction of your result Peer Evaluation 15 No hitch-hiker allowed Photo and BOM: 10 Take and share good pictures. Shared video clip is even better. Total: 200 I will use linear interpolation to determine the scores in head, flow rate and efficiency.

Score =Your  value− Lowest  valueHighest  value− Lowest  value

Explain the reason of your design, the steps of fabrication, the good and bad of the design, compare the predicted and actual result, and possible improvement.

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For this project I want to encourage you to make use of material as efficiently and economically as possible. Therefore, I will define efficiency as

Efficiency =Maximum  Head  (in)Weight  of  pump  (lbf)

The units come out to “inch per pound force”, which is strange.

Analysis  and  Write-­‐up  After completion of the project your group will submit a laboratory report. Included in the report will be a position analysis of your pump, predicted vs. actual head values and a full set of shop drawings of your pump including an exploded assembly view. Further details of the write-up will be provided later.  

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Materials  List  

Qty   Item     Supplier  Part  

Number   Use  Aluminum  Tube  

     6   1.25  ID  x  1.75  OD  x  48"  Long  -­‐  2011  Aluminum  Tube   Yarde  Metals    

For  1.281  Bore  Option  6   0.75  ID  x  1.25  OD  x  48"  Long  -­‐  2011  Aluminum  Tube   Yarde  Metals  

 For  0.781  Bore  Option  

Aluminum  Plate        1   24  x  24  x  0.125  thick  -­‐  6011  Aluminum  Plate   Yarde  Metals  

 Connecting  Rods  

Acrylic  Plate        

4   24  x  36  x  0.125  thick  -­‐  Acrylic  InterState  Plastics  

 Base  Construction  

4   24  x  36  x  0.250  thick  -­‐  Acrylic  InterState  Plastics  

 Base  Construction  

4   24  x  36  x  0.375  thick  -­‐  Acrylic  InterState  Plastics  

 Base  Construction  

Piston  O-­‐Rings      2   1.250  OD  x  1.125  ID  Buna-­‐N  90  Duro  O-­‐ring  (Dash  #024)   MSC    79285151   For  1.281  Bore  

2   0.750  OD  x  0.625  ID  Buna-­‐N  90  Duro  O-­‐ring  (Dash  #016)   MSC    79285078   For  0.781  Bore  Shaft  O-­‐Rings  

     2   0.250  ID  x  0.375  OD  Buna-­‐N  90  Duro  O-­‐ring  (Dash  #010)   MSC   79285011   For  con-­‐rod  seals  2   0.250  ID  x  0.438  OD  Buna-­‐N  90  Duro  O-­‐ring  (Dash  #108)   MSC   79285375   For  con-­‐rod  seals  

Acetal  

       4   1.500  OD  x  4'  Acetal  Round   MSC   63383400   For  1.281  Bore  4   0.875  OD  x  4'  Acetal  Round   MSC   63383285   For  0.781  Bore  

Gearboxes        

30   Tamiya  -­‐  72005  Six  Speed  Gearbox  ActivePowerSp

orts   72005   Motor  Push  Connects  

     60   1/4  OD  Push  Connect  to  1/8"  NPT  Male   MSC   62378088  

 Gasket  Material        5   12  x  12  x  1/32  Silicone  Rubber  Sheet  (Duro  30)   MSC   86528585   Gaskets  

5   12  x  12  x  1/32  Silicone  Rubber  Sheet  (Duro  55-­‐65)   MSC   31938855   Gaskets  Momentary  Switch        Battery  Holder  

     

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Tamiya  -­‐  72005  Six  Speed  Gearbox    

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Working principal of a reciprocal water pump

A typical positive displacement reciprocal water pump is shown as above. It is basically a crank-slider mechanism. The joint O is connected to the output shaft of the motor/gearbox assembly. When the motor turns, the crank link OA follows it and rotates. Then the slider (piston) will be pushed or pulled to slide along the cylinder housing. • When the crank rotates to OA’ position, the piston is pulled toward the gearbox. The total

header space consisted by the piston and the cylinder will be increased. Therefore, a relative vacuum compare to the atmosphere will be generated. The pressure from outside will then push the water into the chamber through the bottom one-way check valve. (Question: What is the maximum height the atmosphere can push the water up?)

• When the crank rotates to OA position, the piston is pushed away from the gearbox. The total header space consisted by the piston and the cylinder will be decreased. Therefore, a higher pressure will be generated. The pressure will push the water out from the chamber. Since the check valves are both one way, they will shut the route from the water source and open up the other one. (Question: What is the maximum height the water can reach?)

The force analysis will be explained in the class when we are talking about crank-slider.