Thursday, 12 April 2018

Student Engineering Project Update from the University of Illinois

Written by  Lydia Tanner
CTI Grinder Solar Adaption Testing CTI Grinder Solar Adaption Testing
CTI's Ewing Grinder is designed to be assembled in minutes and can be cleaned equally as quickly. Capable of making peanut butter, cocoa butter, maize or millet flour, and dozens of other products, CTI's multi-crop grinder opens new opportunities to pursue microenterprise for smallholder farmers. Alternative enterprise opportunities are incredibly valuable, allowing families to gain an income, empowering women to participate in economic life, and contributing to food security by increasing incomes and local food production. One of the most frequent requests we get about the grinder is to add solar motorization, increasing the production potential a grinder can give to a smallholder in areas where electricity access is not available.

As part of CTI's human-centered design process, we are committed to only introduce motorization to our tools where it is contexually and culturally appropriate for the farmer and when CTI has fully determined that motorized solutions will be long-lasting and sustainable. As part of this effort, we reached out to the 
University of Illinois at Urbana–Champaign's engineering department to assist with preliminary testing. Get an inside peak into the work being done from one of the hard working University of Illinois students, Lydia Tanner.

Solar Project Update
Hello! My name is Lydia and I’m a member of a Senior Design group from the University of Illinois at Urbana-Champaign. Within our major, it is required that all students take a course called ABE 469 – Industry-Linked Design Project where we get put into groups and work with an industry partner to get experience working on real-world problems/projects. Me and my four teammates, Hitarth, Shean, Sam, and 
Jeremy, have been working with CTI for the past few months on determining what it would take to solar-power the Ewing VI Grain Grinder.
Students Working in Shop
Our progress thus far can be split into three major steps: 
1)     Determining the design requirements
2)     Researching parts
3)     Choosing a design

All three of those steps have been completed, and we are now be entering the final two stages of this project (assuming no major unforeseen problems!):

4)     Ordering & assembling parts
5)     Testing & write-up

For now, I’ll be describing the first three steps!

Step 1 – Determining the design requirements
After receiving an Ewing VI Grinder from CTI (thank you, btw!), we needed to test the torque requirements in order to spec for parts. To do this, we had a wrench socket built on to the grinder’s shaft so that we could use a torque wrench to perform the grinding. We sourced dent corn locally (a tougher grain than what the grinder is typically used for, which we were informed was pearl millet) in order to determine the higher range of torque required to start the grinding motion. We also tested the torque requirements of soft red winter wheat to be safe. The maximum torque we measured was 25.2 N-m.

Step 2 – Researching parts
So from the first step, we determined that the torque requirement we would need to spec for was 25.2 N-m. From CTI we already knew that the maximum RPM the grinder could handle before incurring damage was 300. In addition, we knew that the shaft diameter of the grinder was 20 mm. And so at this point we started looking for parts that could connect to the shaft and could meet those requirements. This research led to two designs, which I will describe in Step
3. But first, I’d like to address a couple of questions that may have come up at this point in our process.

Why did we test for torque rather than power requirements? We thought torque was the more important requirement, since it more accurately reflects the initial movement of the grinding motion. Power is a function of both torque and RPM, and thus is a measurement that takes place over a period of time. Torque, however, is the force applied on a moment arm (a distance), and thus can be considered an instantaneous measurement, if you will. To motorize the grinder, we need one that can overcome the initial, instantaneous torque. Once the grinding has started, the torque requirement decreases, which is more in-line with a power measurement.

Why does the shaft diameter of the grinder matter? The grinder shaft has to be connected in some way to the rest of our design in order to motorize the grind. Some difficulty we encountered here though is that the shaft diameter is in the SI Unit system, while most of the parts we could realistically order within a certain time-frame are all in the American-adopted English Unit system.

Step 3 – Choosing a design
As stated earlier, we came up with two designs to choose from. Below are images from one of our class presentations that depict them.


Our first design prioritizes safety (since all the parts would be self-contained, thus minimizing the exposure of moving parts to the user) and ease of assembly (since everything is attached in a linear fashion, mounted onto a single base in order). However, the parts are more expensive overall due to the gear box (also known as a speed reducer). The cheapest we found, which did not provide an adequate output torque for our design anyways, was too expensive. In addition, the gear box we did end up finding required ¼ hp input, which required a motor that needed a 24 V input, thus increasing the solar panel requirements from our initial 12 V estimate.


The second design, based off the motorization manual we received from CTI, is essentially the exact same thing except instead of a gear box we would be using two gears and a chain to reduce the motor’s RPM and increase its torque, but potentially lead to more slippage of the chain. However, this design is less expensive and the calculated output torque (maximum) and RPMs are more desirable. In addition, the motor requires the desired 12 V.

Design #1

Design #2

Output Torque

33.331 N-m

39.94 N-m

Output RPM

~49 RPM

~180 RPM

After a meeting with Don & Vern, we decided on Design #2 and began ordering parts.

What now?
So that was steps 1-3, and now we are moving on to 4 & 5. We’ve already have our motor, gears, and chain, and are waiting on a bushing in order to fit our gear onto the grinder’s shaft. Researching batteries and consulting professors is still underway, but we hope to order the remaining parts soon and have our assembly complete in the coming weeks, fingers crossed!

Kind regards,
Team Rise N’ Grind 
 Rise and Grind Team Logo

"Team Rise n' Grind"
From Left to Right: Hitarth Patel, Shean Lin, Samuel Sung, Jeremy Martin, and Lydia Tanner
From Left to Right: Hitarth Patel, Shean Lin, Samuel Sung, Jeremy Martin, and Lydia Tanner


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