IV Manufacturing and Assembly

As seen in the image above, we started out with building the Jenson mechanism using designs from SolidWorks, which we laser cut into acrylic and wood. We cut the designs in both materials to see which one had the best properties for our mechanism. We discovered that wood was the better option of the two because the ball bearings were better able to be press fitted into the laser cut holes. We initially used nuts and bolts to hold the joints together, but we would soon discover that this was not the best method of connecting the joints.

After making the mechanism, we 3D printed a motor mount, and permeant mount for one of the joints that was not supposed to move. We designed these mounts with the dimensions (38 & 7.8 in Figure 1) in mind so that the motion of the mechanism would follow our kinematic diagram motion.

After testing out the motion of one mechanism, we built a second mechanism and placed it on the opposite side of the wood platform. We test out how both mechanisms held up with each other.

Then, we added one inch caster wheels to the stabilize the wood platform from tilting back and forth. We did further testing of the motion of the mechanism to see if our theoretical kinematic analysis matched our prototype. The testing phase proved to be a success, and we then moved on to optimizing the robustness of the mechanism.

We optimized the robustness of the mechanism by redesigning some of the linkages. We realized that six of the linkages did not have any degrees of freedom, so we combined them into solid triangles because this increased the sturdiness of the top and bottom linkages. The top and bottom linkages seemed to receive the most stress in the mechanism, which resulted in them breaking often and required us to redesign them. We also added feet to the bottom triangles so that as the mechanism came in contact with the ground, it would have better frictional contact.

We then were able to add the electronic control system to the to test out the motion of the mechanisms automatically and continuously. We used an Arduino Uno that we coded to communicate to two Darlington Arrays that were connected individually to two 5-volt DC stepper motors.

The image above displays a side view of the wiring of the robot, which included jumper wires connecting the Arduino to the Darlington Arrays, and the Darlington Arrays connected to 5-volt (1 Amp) DC power modules. Unfortunately, these power modules did not provide enough voltage or current for the stepper motors to overcome the friction being induced on them. Which lead us to using a more high-powered power source. We switched to a power module that took 120 volts AC from the power outlets and converted it to 12 volts (10 Amps) DC. The Darlington Arrays were able to receive up to 12 volts DC, so we did not have to step down the voltage any further. However, the motors did get hotter faster while using a higher voltage and current, which made sense, and so we limited the amount of time we ran the motors before we powered them off to cool. We did this out of precaution so that we would not burn them. We actually experienced the burning of both a stepper motor and Darlington Array because we left them running to long on the new power supply.

We then worked on constructing the shell using the previously calculated dimensions to perfectly fit the robot inside. As seen above, as the lead screw would twist, the robot would drop down and lift the shell over it. Then the motors would start rotating, moving the Jenson mechanisms, and moving the crab forward.

To make the joints more robust, we press fitted wooden dowels through the bearings so that they would tightly fit in. This led to stiffer joints and better linkage movement, which meant that the mechanism could carry more weight.