Launcher and Release

Goal: An important aspect of the recycler robot is the appropriate disposal of trash. The launcher is intended to "launch" the collected trash (bottles, cans, etc) into a trash can.

Preliminary Design Considerations:

A. Nature of trash: That the size and approximate weight of the trash is known is absolutely essential to set up the launcher specifications. Our team decided that plastic water bottles are the most common form of trash, and it would be good to set it as the benchmark for the launcher design. The dimensions of the launcher and the approximate force required to launch the bottle are decided based on the following bottle parameters:

Diameter: 3 in, Height: 11 in, Approx. weight: 7 oz

B. Energy Storage: Two options were actively proposed by the team members as to what could be used as a means to store energy. These were (a) Compression/extension springs and (b) Surgical tubing. We decided to use surgical tubing for the following reasons: (a) It is readily available (b) It has a high stiffness value: which means high force for less displacement (c) It gives us the flexibility to either increase the force or decrease it based on the number of tubings we use in parallel (d) it is flexible and can easily be manipulated out of the path of the launcher, wires and/or any other moving components.

C. Release Mechanism: The release mechanism was designed to act as a stopper at intermediate positions of the launcher. This is to prevent constant loading of the motor that could potentially damage it. The concept we shortlisted involves the launch plate pushing against a release bar as the launcher is pulled back. The release bar is spring loaded and bounces back such that the launch plate rests against it. A motor drives the release bar to launch the trash. Also, the release of the launcher should in no way be impeded by the resistance of the charging motor or the release motor. The goal is to drive the release bar by the same motor that drives the launcher. A snapshot of the Creo concept of the release is attached later that explains how we plan to achieve this.

Preliminary 3D (Creo) conceptual model:

Prototype 1: Following are some photographs of the first prototype. Drawer sliders were used to achieve nearly frictionless movement of the launcher.

Side view

Top View

Release Mechanism Concept:

This works on the basic principal of a four bar with a slot added to one of the links to give us additional flexibility with the addition of an extra degree of freedom. This lets the release bar rotate without having to drive the motor. At the same time, it also lets the motor drive the release bar.

A. Release bar at rest (retained by tubing not shown in figure).

B. Release bar when actuated by moving launch plate (the slot isolates this motion from the motor).

C. Release bar when actuated by the release motor.

Prototype 2 - 11/19/2013:

The driving mechanism for the launcher is designed and put in place. It is a cam-follower designed on the lines of a linear Geneva mechanism. The cam was 3D printed on the MakerBot with 50% fill (we hope it will hold!). The followers are hollow steel bars.
The intermediate stoppers for the launcher is designed and installed. Again, the profile was 3D printed on the MakerBot with 50% fill.
The release mechanism concept was slightly modified from prototype 1. It is a motor driven 4-bar. The linkages are all aluminum.

The focus from here on would be to get the motors mounted and running along with programming the Arduino so that the motors run in the appropriate sequence and delay.

Final Project - 12/05/2013

After the Prototype 2 assembly had been completed, we started to test the launcher system with Arduino code. Quickly it was revealed that the motor provided was not powerful enough to retract the launcher. With time a concern, the current motor's gear ratio was increased by 5 using two gears.

A ten-toothed spur gear was attached to the drive shaft with an 1/8" key. That gear drove a 50-toothed spur gear with the cam incorporated. The gears were designed with a diametral pitch of 10. That was chosen because to allow clearances that would be reduced during 3D printing. To mount the large gear, a new mounting plate and a support piece with pressed in bearings. That system succeeded in fixing the larger gear's rotation axis with limited twist.

After the gears were in place, the motor was able to draw the launcher back past the first two steps relatively easy. The third and fourth were more challenging and induced worry about damaging components. So during demonstrations we would not let the motor drive that far back.