Testing & Analysis

The fixed-distance crushing method was tested with various sized peanut batches and consistently separated above 95% the shells from the seeds without breaking the seeds. The first roller applies a non-uniform force due to the rubber nubs to the shells and breaks them. The rolling motion after the first cracking disintegrates the shell and most peanuts fall out of the crusher intact and fully separated.

Once the original design was verified as effective, springs were added under the platform and loosened the bolts allowing the platform to move as subjected to a fixed force. However, it was quickly determined that the fixed force method was not as effective as the fixed distance method. The springs caused the board to rub against the belt when starting a batch creating substantially more friction on the wheel surface, which caused much more force on the crank to move the peanuts down the ramp. As such, the fixed distance method was determined to be the method which will be used in the final design.

Crusher Module Demonstration

When testing the winnower, the ideal length of the flapping board, the proper timing for flapping the board, and the optimum batch size were determined. By deterring these, it is possible to find effectiveness of the device at separating the shells from seeds.

To determine the ideal length and flapping speed of the board, a consistent sample size of crushed peanuts at a variety of lengths and speeds were used. First, how quickly the board should be flapped was analyzed. It is possible to force the board down with one’s hand or foot, and provide a higher wind speed. It was found that a moderate amount of force would allow the user to complete one cycle in just under two seconds. While it is possible to complete a cycle in less time, the increase in wind speeds either did not improve the seed shell separation or began to blow away seeds (depending on the board length used). Similarly, once the optimum speed was narrowed down, additional trials where done by moving the board along the pivot point to narrow down the optimum length. The best length was found to be 34 inches of board from the pivot point.

Winnower Module Demonstration

With the optimum settings for the crusher and winnower determined, several time trials with different peanut batch sizes were performed to determine both the optimum batch size and efficiency of the prototype. Data collected, it is clearthat the relationship between batch size and crushing time is approximately linear, whereas the winnower is equally ineffective with larger batches. Even larger batches were not used as the loading area of the prototype was maximized, so the final design will be implemented with a larger one.

In creating and testing the device, the design performance was compared to the original design requirements. The device still must separate seed from shell and leave 20% of seeds whole and intact. Overall, less than 2% of the seeds where actually crushed and unusable making the decorticator 98% efficient. In addition, an original requirement of no more than 74.6 watts of input energy was achieved, with around 15 watts, found from the torque applied on the handle, being used for our half-sized model. The decorticator was required to shell 40 kg per hour; however, the prototype was only able to achieve 8.5 kg per hour for series operation with the winnower. However, this would increase with a full sized model and adjustments to the belt and force input mechanisms. If used independently, the decorticator has a capacity of 13 kg per hour. Friction in the axels/wheels with the frame was most likely the constricting factor in allowing easier rotation, and thus increased rate of production. The development cost was to be less than $400 and prototype cost came out to be $80. It was also specified that the prototype should weigh less than 200 lbs and it came out to be less than 40 lbs. Another requirement was to stand freely during use and storage and require no more than two people to move or operate; that requirement was met. Lastly, it must not jam more than 5% of operating time, which it will if too large a batch of peanuts is used. This can be avoided buy not using a batch size larger than 200g.

The primary strength of this design is its simplicity. Our design can be built quickly and easily from materials readily available in Zambia and requires no complicated components such as cams or chains. The modular design makes it easy to move by one person (making multiple trips). It is also 98% effective at both crushing the shells without damaging the seeds and in separating the seed shell mixture. It is very easy to run the system in continuous operation if two people are available. However, it is more difficult for one person to operate by his or her self. Unfortunately, the prototype requires a large amount of force to crush the peanuts and the belt still slips of the wheel, but the final design will use smaller axils, which will reduce the area of friction on the wheels and this increase the ease of use and thus efficiency. The winnower can also be increased in efficiency linearly by increasing the width to the point of which the flapping board is too heavy to flap, which is around 3 feet wide.