Mechanics
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Actual Table |
Table
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Original Design |
As is obvious from the pictures, we strayed from our original design for the table once we started building. Our original plan of having a drive shaft driven by a belt was much more complicated than necessary to meet our needs. The much simpler and better method was for us to buy a lazy-suzan bearing from McMaster Carr, and drive the underside of the table with a wheel attached to a motor. This way the table had only to be level to be driven easily by the motor. It is much easier to mount the table level than to make it perfectly round and drive from the outside edge, or to center it perfectly so it can be driven by a motor in the center of the table. We purchased a bearing with detents every 90 degrees thinking this might help position the table, but the proved to be too stiff for the motor to move, so we removed them and allowed the table to come to a stop by friction.
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Limit switch and trip arm |
Here you can see how we mounted the motor to drive the table, and the switches we used to set the stop points. |
Motor mount |
We used the Limit Switches supplied by the lab as sensors for the position of the turntable. There were four pairs of limit switches positioned about one radian before each topping position in order to give the table room to glide to a stop. Pairs of switches glued together and wired in paralell were used to make sure the tab on the turntable would throw at least one switch on the way by. The limit switches replaced our originally planned infrared emitter/detector pairs because they were simpler and more reliable.
The motor used to drive the table was a 24V rated DC motor with a pinion that we had modified. We turned the center of the pinion down so it was essentially a pulley wheel, and placed two small O-rings in the groove to provide grip on the table. We used a dc-motor instead of a stepper motor because it required fewer inputs, and we had originally thought we might need the added outputs from the Handyboard.
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Final Design of Candy Dispensers |
Dry Toppings
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Initial Drawing of Candy Dispensers |
Originally we planned on using a rotary system to dispense candy, but to simplify the building process, we decided on flat sliders instead because they are simpler to make and slid well on our prototype. The sliders are rectangular tabs with a hole in the center that was filled with candy once retracted into the hopper. On extending the tab again the candy dropped out the bottom of the hole and into a funnel that placed it over the center of the bowl. We used servos to shift levers to extend and retract the sliders.
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Finished System |
Chocolate Dispenser |
Initial Idea |
The Chocolate Sauce Dispenser proved to be a challenge that we were able to overcome. Originally, we were planning on using a solenoid that was attached to a (cleaned and sanitized)soap dispenser via a lever to get a larger displacement. However, the solenoid did not provide the force over the somewhat large displacement (about 1/2 inch) that we needed to push the plunger.
We returned to the drawing board to produce a lever contraption that was driven by a geared DC motor. The motor had about 50:1 gear advantage, and the lever itself gave a 3:1 mechanical advantage. We attached a lever arm to the motor shaft, and a linkage between the motor and pump levers. It allowed bi-directional control so that as the motor turned one way it pulled the pump lever up and then stalled briefly, then the motor was driven the other direction which produced the same results. It ended up working flawlessly and was our most reliable system.
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Final Design |
Whipped Cream
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Initial Drawing |
The whipped cream dispenser was the simplest actuator we had, and varied the least from our original design intent. Instead of using a push solenoid as drawn, we used a pull solenoid instead. The brackets hold an ordinary Reddi-Whip® style can (which was pilfered by an unknown passerby before the pictures were taken). A thin piece of wire rod was bent like a spring at one end, with the end of the wire pointing inwards to grip the tip of the can (so it wouldn't be pulled off). The other end was connected to the solenoid plunger. The spring action of the can tip was enough to return the plunger to it's original position so a second spring was not needed.
(-) denotes from shop stock or ME333 lab stock
| Part |
Quantity
|
Store
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Part Number
|
| Turn Table Bearing |
1
|
McMaster-Carr
|
1797K21
|
| Servos |
2
|
Digikey
|
157067
|
| 6rpm Geared 24V DC Motor |
1
|
- (also available from MPJA)
|
|
| Pull Solenoid |
1
|
-
|
|
| 1/4" thick acrylic |
about 2sq. ft
|
-
|
|
| 1/8" thick acrylic |
about 8sq. ft.
|
-
|
|
| 1/2" Thick plywood |
about 3 sq. ft
|
-
|
|
| Handy Board |
1
|
-
|
|
| Hardware (Nuts, Bolts, etc.) |
a bunch
|
-
|
|
| Wire |
about 1ft.
|
-
|
|
| M&Ms |
2 packages
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Dominics
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|
| Whipped Cream |
2 cans
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Dominics
|
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| Chocolate sauce |
2 bottles
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Dominics
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| Sprinkles |
4 bottles
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Dominics
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| Limit Switches |
8
|
-
|
|
| Epoxy |
a dab
|
-
|
|
| 24 V DC drive motor |
1
|
-
|
|
| 1/8" Rubber O-Rings |
3
|
Ace of Evanston
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|
| 3" Diameter PVC Pipe |
1/2"
|
Ace of Evanston
|
|
| Hinges |
2
|
Ace of Evanston
|
|
| Soap Dispenser |
1
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Target
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