Week 6: Moving Forward on Manufacturing

A lot was accomplished this past week. In addition to making additional purchases of electronics (such as extension cords and speakers). Numerous hours were spent in the machine shop turning the theoretical design into physical reality. Along the way, sometimes it became clear that an idea would not work in practice as well as it did in theory; the lift was determined to be too opposed by friction when it enclosed its vertical columns, it was decided instead to place it between the vertical columns and the backboard.

Servos were also mounted to the inner top of the frame. To do this, the servos were screwed to wooden blocks, which were screwed to the main frame to act as extrusions. The current plan is to attach plastic spools to their rotary disks and have them spin continuously, pulling or releasing the lift by way of nylon string, but implementation has not yet occurred as the jumping mechanism has not yet been printed to the point of being functional. The servo configuration can be seen below.

The servo is attached to wooden blocks, which are attached to the frame

Furthermore, the physical ball conveyor also underwent its initial construction. This conveyor was discussed in the previous update: essentially, it acts similarly to an Archimedes screw, forcing the balls up a locked channel by seating them on a rotating helix. A brief mechanical simulation of this technique can be seen in the below video. (Full screen viewing is recommended, as the video is small otherwise.)

The placement of this conveyor can be seen in the picture below; it should be noted that this picture is a rough initial positioning, and does not display the channel through which the ball will travel or the servo which will rotate the helix.

Estimated and unsecured location of conveyor

In order to be sure that the servos ordered were sufficient for the project's purpose, some calculations were carried out.

The first calculation determined if the servos would be able to raise the player lift beam. The specifications for the servo were given by the manufacturer that, stating that the device's torque was 3 kg*cm; the mass of the wooden lift beam was 0.4 kg, as calculated with the wood's density and dimensions (and inflated somewhat to ensure that the servo was more than sufficient). 

Since τ = F x r, r = τ/F, in which r gives the maximum possible radius of the pulley. Plugging in the values results in (3 kg*cm)/(0.4 kg) = 7.5 cm. As the servo radius pulley is much smaller than this, it should be capable of the task at hand.

The second calculation dealt with determining the length of tubing needed to build the conveyor ball lift. Given that the tubing (radius = 3/16 inches) will be wrapped around a 2-foot shaft (radius = 5/16 inches) at a rate of 1 coil/inch, the total radius (Rt)of the device is (5/16 + 3/16) inches = 1/2 inch. Since the number of coils = (2 ft)/(1 in) = 24 coils, the total needed tubing length = (2πRt)*(number of coils) = (2π)*(1/2 inch)*(24) = 75.4 inches, or 6.3 feet.

It was initially expected to need 25 feet of tubing; however, by doing these calculations, an appreciable sum was saved by reducing the order to 10 feet of tubing.