Conclusions:
Overall, the mechanism shows promising results with feasibility for massive improvement. The walking-beam linkage mechanism moved with good smoothness, and the lazy Susan fulfilled the reload functionality, albeit with a rather strange result. While the lazy Susan reliably reloads as the chute gets pulled back, the chute whilst moving forward actually may push the lever on the lazy Susan in the opposite direction, causing an accidental reload depending on the angular orientation and angular displacement of the system, which causes repeatability issues.
To more thoroughly evaluate the mechanism, we have established a set standard for the functionality and purpose of our machine prior to the manufacturing of the system. The mechanism should essentially uphold practicality, repeatability, and durability, which shall be attained if the mechanism meets the following criteria:
Blue indicates partial satisfaction
Green for full satisfaction
Red for complete criterion failure.
| Criterion | Status |
|---|---|
| automatically launches and reloads a projectile (preferably a marble) in repeatable cycles (at least 6 per minute or 1 in 10 seconds) | The motorized system cannot fire a shot. Manually with 5 trials, an average firing rate of 11 rpm was achieved. Lazy Susan prototype fails to prevent misreloading and thus cycles are not identically repeatable with consistency. |
| We can plot the motion of the walking-beam in MATLAB to an accurate resemblance. Ideally, a letter D or semicircle is traced and is confirmed by the swept path. | Semicircular like path plotted by links, visualized on Solidworks animation, & validated with linkage motion. |
| Track the housing chamber with a linear traversal of at least 100mm. This should ideally be a sinusoidal shape, but some delay is expected. | Not exactly sinusoidal, but very close. An amplitude of about 68mm (peak to peak height of 136). |
| • Marbles successfully hit target from the specified range above (6 to 10 ft), with consistent probability (3 out of 5 shots at a time, binomial distribution profile). | Maximum range of 3-4 ft, V chute isn't streamlined so a marble occasionally veers off to the left or right, or even flies out of the ramped side when firing occurs too quickly. Hit probability of 17 in 20 tries ( 85% success) |
| • Complete restoration to equilibrium state per cycle; we can visually check that machine is in the same starting position after firing | Walking beam mechanism can easily return to starting equilibrium. Lazy Susan has no restorative element. |
The primary concern seems to be with the motorized system and setup failing to generate a mechanical advantage high enough to pull back the chute and conduct work on the load. The load must be reduced, but the mechanical system needs to be built to be more robust and capable of supporting higher loads. In addition, the lazy Susan being a far too simple system that solely relies on the movement of the chute knocking into a lever and pushing it.
From here, a foundation can be laid down as to what future iterations can be.
Future Work:
In terms of meeting the criteria, a more powerful motor can be used. Alternatively, the implementation of gears to increase torque and reduce velocity without power changes would be a more effective approach. The PWM reduces the average power which affects both characteristics (reduction of torque is a massive disadvantage). The load requirements can be used by analyzing the dynamics of the chute as its own system and finding a material with an effective spring constant (N/m) that is low enough to provide substantial displacement, but also with meaningful tension to propel the chute forward. This can be done via material research and also placing the right number of springs/bands in parallel to find an effective spring constant.
If more power and torque are to be provided, the links and cantilevered grabbing arm should be reinforced. The most viable approach is a blend of increasing torque and reducing load requirements to automate the mechanism safely and reliably.
The Lazy Susan needs to be modified to allow for controlled discretized movements (much like a Geneva mechanism) and ratcheted so that it can only rotate one way, but not both. As an overhaul, connecting the motor system via pulleys and timing belts to automatically time a reload can be a massive substantial improvement but error in motion can accumulate over time, which result in the firing and reload timing systems becoming out of sync. The use of more electronics such as actuators or servos, or bump switches in however manner to stop the system and initiate a reload can also be another approach, yet this comes at the cost of mechanical rigor and the ability to continuously operate the system under continuous input motion.
Additional improvements beyond this can include streamlining the design into a smaller system, with a bipod, grip, and optical sight can transform the mechanism into a wieldable platform.
Finally, replacing the marble with a softer cartridge much like a NERF round can make this system much more safer for a broader audience. Maybe it can be repurposed to a kit that hobbyists and children can assemble to learn the mechanical concepts at play in a unique and fun manner!