06.2 - Project Prototype

For our analysis, 0 degrees is when L₂ is parallel with the slider’s motion and closer to the press. Additionally, all of this analysis is done for the motor we have chosen for our final project, however for this physical prototype, there is a handle that adds a physical constraint to the rotation of the crank.

These profiles show the displacement, velocity, and acceleration profiles of the slider when the angular velocity of the crank is 1 rad/sec and there is not crank angular acceleration. From the displacement profile, it can be see that the slider travels about 10 cm throughout the process which is about double of half of a mandarin orange, which has a total height of about 8 cm. This means that at the furthest point from the the press base, the slider clears both the rounded part of the press base and a half a mandarin that is being placed on the base.

Full Rotation Condition for a Slider-Crank: L₃ > sqrt(L₂ ² + L₄ ²) => 0.2 > 0.0625

Grubler Equation: M = 3(4 - 1) - 2(4) - 1(0) = 1 DOF

From experimentation with squeezing an orange using the orange juicer that we bought and is attached to this prototype, we learned that the ideal minimum amount of force to squeeze the mandarin is 155 N. From the force analysis, we can see than the minimum force applied to the end of the slider from the input torque on the crank from the motor we have sourced is about 160 N, with the force being higher at full extension.

This prototype’s goal is to demonstrate the orange press part of our larger project. Through motion profile mockups, FEA analysis, force calculations, and animations we were able to confidently build our prototype of this part of our project. This prototype helped to validate these calculated profiles and the ability to output the force needed to squeeze a mandarin orange. Although this prototype is manually powered, it gives us confidence in later completing a motorized version of this mechanism.

We initially created a quick cardboard mock up to test the movement of a slider crank with link ratios. Although our final prototype looks very different for this very basic, initial carboard mockup, it utilizes the same link length ratios and therefore a similar motion profile.

After seeing our desired motion profile, we iterated several times in code, attempting to narrow in the link lengths and motor specs for our final mechanism. We focused primarily on force analysis, since that is our primary concern; after juicing a couple cutie oranges, we determined that we need to aim for about 30 lbf, or approximately 135 N. At first, we tried to consider some pretty small motors, akin to those that we used for Build Assignment 2, but as shown in figure 5, it was insufficient for our applications. During these iterations, though, we discovered that the best force output came from having a longer L₃, shorter L₂, and smaller offset, which informed the rest of our iterations.

Since we weren’t getting sufficient output force, we chose a different, higher-torque motor, that is specified to provide 90 kg*cm of torque, or about 882.6 N*cm. With that motor we were achieving the forces we needed, so from there we iterated a few times to determine our final specs, which are listed at the top of the page.

We then created a CAD assembly of our prototype. Creating a full assembly was crucial to being able to analysis our proposed design to withstand the calculated forces.

The FEA diagrams shown above show that the designed links and mechanism can withstand the forces applied to them as the mechanism is juicing an orange.

After verifying the design, we printed the components and started assembling. Although we had a few hiccups, like accidently inverting the slider build, we were able to create the manual prototype assembly shown in Fig. 11.

As it can be seen from the video, our prototype can accomplish our main goal of this prototype, applying enough force to our orange to juice it.