Back inside the lab, some testing revealed a couple problems with our hopper design. One, soil particles would sneak out between the aluminum sliding door and the bottom of the hoppers. Once in there, it would bind up the slider so that the doors would stick half open. To fix this, we shortened the hopper walls a touch and added some felt between the sliding door and the bottom of the hoppers.

Also, we found out that a lack of airflow inside the hoppers caused problems for the flow. We noticed that the sand would flow much faster with free airflow as compared to when everything was sealed up. when it was sealed, we also noticed a small puff of dust at the hopper opening once most of the sand had flowed through. To fix this, we drilled holes in every hopper and added plastic tubes. To keep the soils and dust from escaping with the air, we wrapped the tubes in the filter material from a shop vac bag. It's not the prettiest thing, but it did the trick. Hopefully we have tackled the biggest problems now, and will be able to make our final assembly in the next couple days. It's looking like we'll get done just in time before we leave early Wednesday morning.

Here are a couple pictures of the hopper assemblies now.