Carousel uses lazy susan bearings

We chose to load the Nerf ‘basketballs’ into our launcher by way of an 8-column carousel. The carousel holds four balls in each column and rotates between rounds by way of a friction-drive system. The drive system uses a high-torque motor to spin the carousel, which is attached to a non-moving platform (dubbed ‘The Falcon’ on account of its eventual resemblance to the Millennium Falcon spacecraft from the Star Wars movies) via a lazy-susan bearing. Beneath the carousel is a hole in the falcon that allows balls to be dispensed whenever a column rotates to the position directly above the hole. As the carousel turns, a stationary ledge passes through the slots cut at the same height into each column. The height of the ledge is selected so that it will separate the bottom-most ball from the ones above it. Thus, when the bottom ball is released, those above it will continue to be supported by the ledge and will not fall. Meanwhile a pair of IR sensors, mounted with only a narrow gap between them, straddle an encoder ring on the carousel and are used to monitor its rotational position at all times.

Before detailing the construction of this system, a couple points on why we selected this method for our loader:

Alternatives –

Before pursuing the carousel loader for our final implementation, we considered several other mechanisms such as:

Pipe Snake: A coil of pipe that would hold all the balls in a spiral.

Ramps: Multi-tier configuration of angled ramps to cascade the balls

Archimedes’ Screw: Lift the balls from ground level to a raised platform

Hopper with Funnel: A single container with a narrow hole for release

While each alternative had its own merits and drawbacks, we were able to analyze the collection as a whole and in so doing assess which characteristics of the loader were most important. Those characteristics were:

Serialization: Keep the balls in queue so that they can be reliably processed in a repeatable fashion without jamming or skipping.

Granularity: Gate or separate the balls from one another so that one and only one ball is delivered to the launcher on each cycle.

Force: Need to provide some force by which the current ball can be transferred to the launcher and by which the remaining balls can be moved to the their next position between cycles.

In rating all of our options against these metrics, it became obvious that the carousel provided the best combination of performance in these areas. For instance, the carousel easily serializes the balls using pipe columns, without having the difficulty of bending a pipe or arranging a series of ramps so as to allow them to roll smoothly. Further, by using our ledge mechanism to separate the current ball from those still in waiting, we could achieve excellent granularity without the complexity of moving parts, the need to drive a solenoid for the purpose of gating, or the unreliable feeding of a hopper. Lastly, be leveraging gravity as our force for deploying the current ball, we could save ourselves the power needed to drive a large screw or other conveyance mechanism. Between cycles, the entire carousel could be rotated, which is a motion easily obtained using low-speed DC or stepper motors.

About The Author:

Mark Harris is a successful author and regular contributor to http://www.bearing-n-bearings.com. Keep things running smoothly with ball bearings, roller bearings, ball thrust bearings and tapered bearings.