CDM - Design Process and Manufacturing

The kinematics aspects of the project include a four-bar crank rocker, a gear train, and a separate slider-crank mechanism on the rocker arm.

A big challenge was releasing the card with only the simple rotating motion of the crank.

As can be seen from the Solidworks assembly, the four-bar crank rocker is the skeleton of the mechanism. The base of the crank is grounded to a shaft which allows it to rotate about that point. Crank is connected to a gear which is rotated as the crank is rotated. Additionally, there is a gear train connecting to the shaft which connects to the rocker. The rotating end gear (smallest gear) causes the shaft to rotate which drives the slider-crank mechanism. Slider crank is attached to and slides on the rocker and performs the releasing of the card. The sliding motion on the rocker creates a Coriolis effect.

This was not the only design we thought of. We went through multiple different designs and finally settled on using a crank-rocker for the skeleton of the mechanism. We then had to decide how we would design the delivery of the mechanism; this too required multiple different designs. The two we were left with were the slider-crank and the use of bevel gears that are turned by the input gear. Instead of a prong, this second mechanism would involve a gear turning above the deck of cards, rolling them out one by one. We decided against using bevel gears as there would be a surfeit of analysis required to decide on gear sizes, along with the challenge of accounting for the changing height of the deck of cards. It is for this reason that the slider-crank mechanism was used instead. This involves a prong (made of PLA) at the output that bends easily and can revert to its original shape naturally.

As far as prototyping goes, we did not really experiment with our earlier design ideas (such as the bevel gears). Instead, all of our prototypes were gradually-refined versions of our final design.

Materials:

The materials used in the project were:

• ¼” acrylic (links, gears) that was laser cut
• 5mm inner diameter bearings
• PLA (prong, holder) from the 3D printers
• 5mm diameter metal shafts
• ¼” plywood sheet

All of the links were connecting using shafts and bearings provided. The bearings provided for a smooth rotating motion. 

Sample Parts and Prototypes :

Figure: Early design of slider/prong

The slider which releases the card from the stack has sandpaper at the end of it to help grip on to the card properly. This slider went through multiple prototypes before it was finalized. The angle at which the slider contacted the cards was important because it could restrict the outward motion of the cards. 

Figure: Early design of card-holder

The card-holder also went through multiple prototypes. We ended up using a design similar to the one shown above due to the angle that it is propped up at.

Figure: Early idea for inter-gear interaction

Our initial idea was to use a gear belt between the largest gear and the smallest gear. However, this would have more room for error because any potential incorrect dimensions or lack of tension could cause the belt to skip teeth and not rotate as intended. Having gears interacting tooth-to-tooth solves this problem.