To assemble the components I subdivided the tasks into two separate mini projects. 1) The hopper and release valve; 2) The scale.

The Hopper

To assemble the hopper, my main concern was getting the release valve to function properly. I had a couple of interesting challenges to overcome in getting this component to function the way I needed it to.

I needed to ensure a tight fit for the valve so that no food leaked out while in the closed state. This was a tricky part of the project for several reasons. I needed to attach the servo motor to the milk jug securely so that it didn’t shift during the valve action sequence, and I needed to attach it at just the right height position so the servo arm and end effector (valve) was positioned directly over the opening. I noticed that the handle of the jug was positioned at almost the same distance from the opening as the servo was tall. When I held the servo in this position I noticed I could cut a small opening in the handle which ended up serving two purposes. 1) The hole was cut exactly to the same dimensions as the servo housing. This made a perfect brace to prevent the servo from shifting side to side during the open and close phases. 2) It allowed me to position the servo at exactly the right height to ensure the valve covered the opening with no gap.

The next complication I had to overcome was to figure out what material to use for the valve. It had to be light enough that I could screw it to the small plastic servo arm with the tiny screws supplied, light enough for the small servo motor to move it without being under powered, but strong enough so that when the dry food was placed into the hopper the valve didn’t bend releasing the contents. At first I cut the proper shape out of a plastic disposable picnic plate and attached it to the arm. Right away I noticed this would not be firm enough to support the weight of the food, so I cut a second piece in exactly the same shape and glued them together. This provided a bit more stability, but not enough for the weight of the food, and the shape of the valve was not perfectly flat, leaving a gap even in the fully closed position. To combat both of these problems I ate an ice cream popsicle, then cut the wooden stick to the length of the valve and used the tiny servo arm screws to attach it to the underside of the valve. A tiny drop of super glue on the valve end later and I had a perfectly functional, stable and secure valve! I was actually quite amazed at how perfectly it fit after applying the popsicle stick.

In order to demonstrate the action of the hopper I connected it to my RedBoard and wrote a quick function to set the valve in either open or closed position based on the state of one of the buttons from the kit. Pressing the button opened the hopper to release some food and releasing the button closed the valve stopping the flow. This worked perfectly and I was extremely pleased with the result. At this stage of the project Calvin was more of a teleoperated device than a full robot but it was an exciting stage of the development to see it in working order. A video of this action will be attached to my final submission.

I now had a functioning hopper. On to the scale.