An Introduction into the Benefits ofFully Mechanical Governors

Over Their Electromechanical SystemsCounterparts

Brian J. Katerberg, Senior Mechanical Engineering Student, Calvin CollegeAndrew J. Vander Moren, Senior Mechanical Engineering Student, Calvin College

Engr 315, Control Systems, Prof. Ribeiro

Abstract— Due to the lack of electricity electrical hookups and electrical know-howexperience found in many third world settings, a system designed for operation in the third world will be best suited for the culture if it does not include electrical components. This year a group of four seniors including myself the two authors of this paper are designing a kit style mill to be designed and built in the United States then converted into a mobile kit that will be able to easily be delivered to such places as Kenya where they will be unpacked and assembled. The mill referred to earlier is a mill designed to remove the seed and chaff from the amaranth plant and then separate the seed from the chaff in order to provide high quality grain. One of the primary areas of concern lies in the separation of the grain from the chaff as there is not much size difference and not an extreme weight difference thus setting tight tolerances on the fan speed.

Index Terms— amaranth, fan speed, fanning mill, mechanical governor, speed-control, speed regulation

I. INTRODUCTION

n the United States we are so used to having electricity that we sometimes forget don’t realize what it would be like to live without it. It seems that the lack of

experience toward a life without electricity causes engineers in the United States to design things that don’t integrate adequately into the culture that they are intended for. My Our senior design team is trying to keep this in mind as we work on developing a mill to help process grain in the third world country of Kenya. While in the United States it would be very easy to use an electric powered, or even gas powered, system with complex moving parts to perform every step of a particular process without anyone needing to be involved; the samethis is not true in other portions of the world. While a breakdown of complex components will cause some delays in the United States as the new part gets made and shipped to the plant, other countries fully relying on that part will have to wait much longer as someone travels to assess the problem, then gets the equipment to make the part, and then some time later provides the farmer operator with a the replacement part. Though it is possible to go through this series of steps, it is much more of a hindrance in other countries then it is here where we can get things shipped ‘same next day’ many timesquite easily.

I

II. TECHNICAL DETAILS

With most systems used in the states in which a given shaft is required to spin at a certain speed, electronics are used to not only monitor the speed but also make adjustments to it. This can be done in several ways one of which is through the use of a tachometer which measures the speed of a spinning shaft. Often this is done with an optical reader thus not adding any extra resistance to the system. A processor hooked up to the tachometer determines whether the shaft is moving too slow, too fast, or just right, in relation to some reference speed. In response to this reading, the governor processor then sends a signal to bring about the necessary changes to pull the system to the desired speed. A system like this one requires only asome fairly simple circuitry, with a motor, tachometer, potentiometer, a series of transformers, and some sort of voltage source (see Figure 1). While this system is not very complex by our standards, we must remember that what we design is rarely done for people with the same level of experience that we havethis is not being built for us, and in this case, but rather the system is being designed for those a people group that are is unfamiliar with electricity in general and are almost guaranteed to not have any ability to fix a system of this nature when something goes wrong with it.

Figure 1 Sample Tachometer Circuit [20]

With electrical components being nearly impossible to fix in these third world settings especially with the level of

© B. Katerberg, A. Vander Moren 16 December 2004

electrical know-how that the locals are likely to have, it is important not to includeto avoid these in our design. Instead of using these electrically based systemsdoing it might be wiser to use this,some sort of mechanical systems are used in there place, , however even this can be dangerous. In order to make a mechanical system function in the same way that the electrical system would have functioned would require very complex components most likely taking up a lot more space then the electrical components would have inhabited. This in itself will add a good deal of weight to the system making it cost more and be harder to distribute. While the mechanical components could be built smaller that to reduce shipping costs it could increase the cost of machining them as they parts would have higher tolerances and then would be more fragile. This High levels of complexity, like electrical circuits, is also something that should be avoided when designing something for these third world settings. While we are often quite used to the idea that people from third world countries are likely to not have electrical know-howaxcess, we often assume that they have no mechanical background as well, which is not true. While they don’t have a vast mechanical background they still have a higher mechanical background then some people credit them with. don’t tend to think about the fact that they often don’t have a vast mechanical background either. Based on what we have been told by some missionaries to Kenya, it is our teams understanding that the mechanical abilities of the Kenyans we are hoping to design these mills for is also quite low [3], [4]. While they might be able to repair simple basic wooden parts it is quite certain that they would not know how to, or have the equipment to repair any sort of complex system, wood or metal.

III. THE INCENTIVE

It is important that steps be taken to not simply provide the Kenyans with up-to-date equipment, but rather to help fuel their own ability to build up their own economy. One way that this is can be done is through helping them develop their agriculture. By helping the Kenyan people grow and harvest a cash crop such as amaranth more effectively we are able to help the Kenyans develop themselves. When people go into third world countries and simply provide the people living there with what they think is needed to help them improve their quality of life, it doesn’t usually solve their problems. A combination of resources, time, and patient guidance are what will help put a country back on its feet.

Figure 2 Threshing Amaranth

Figure 3 Winnowing By HandBecause of the setback that these people have endured because of being neglected for so long it is important that steps be taken to not simply provide them with up-to-date equipment, but rather to help fuel their own ability to grow. One way that this is can be done is through helping out in developing their agriculture. By helping the Kenyan people grow and harvest a cash crop such as amaranth more effectively and efficiently, we are able to help the Kenyans develop themselves. When people go into third world countries and simply provide them with stuff it doesn’t solve problems it often just temporarily reduces them. In order to develop a country, however, one can not expect that simply dumping more stuff into the country will solve the problems; instead it is often time, patients, and love that

© B. Katerberg, A. Vander Moren 16 December 2004

help put a country back on its feet.

Figure 4 Harvesting Amaranth in Kenya

At the present time missionaries working in Kenya with such organizations as CRWRC (Christian Reformed World Relief CoalitionCommittee) and PCD (Partners for Christian Development) have helped prove the feasibility of growing large amounts of amaranth in Kenya. One Now that the feasibility of growing the amaranth has been proven the next problem that is presently faced is how to handle all of the grain being harvested. Currently the grain is harvested and cleaned by hand in a very labor intensive and time consuming process. The current cleaning method for example requires that the grain heads be beaten on the ground with a stick in order to knock the seed and chaff off of the head. After this has been done, the seed/chaff mixture is tossed in the air on little screens allowing the chaff to be caught by the wind and blown away. This cleaning takes a large amount of time and even then does not provide the quality that is desired. In order to make this process more feasible, it would be ideal to replace the slow seed cleaning process with a more automated one that works more effectively. While this is the most time consuming portion of the entire harvesting process, improving the threshing process would also be very beneficial to the Kenyans that are towill receive these mills.

While it would be nice in the eyes of most Americans to have a fully automated system, this can be lessis less then desirable in to many in third world settings. Many in Kenya are very willing to do physical work while some other

cultures are not as willing. By fully automating these mills, the farmers are less likely to feel that they have contributed as much and thus do not feel they have the same level of ownership that they used to have when they did everything by hand. So, while we feel it is nice to have things more or less run themselves, others do not feel the same way. One other reason that makes it harder for the Kenyans to accept the fully automated systems is that the farming is such a large part of their life and taking away their mills would take away a large part of their life. If these automated systems were all implemented at once, the things that the farmers used to spend their time with would be taken from them, By fully automating these mills, the farmers don’t feel like they have contributed as much and thus to not feel they have the same level of ownership that they used to have when they did everything by hand. So, while we feel it is nice to have things more or less run themselves, others don’t feel the same way. One other reason that makes it harder for the Kenyans to accept the fully automated systems is that the farming is such a large part of their life. Additionally, if these automated systems were all implemented at one moment all the things that the farmers used to spend their time with would be taken from them, leaving them with the decision of what to do with their time.

IV. THE CONCERNS

As pointed out in Section II. using an electrically based system would add levels of complexity that can not easily be resolved by the Kenyan people; in the same way, complex mechanical systems would require a higher level of maintenance then would easily be provided by people with little machining background. With these two options being blocked, we are left with needing a very simplistic system that is light weight, easy to use, low cost, and does a good job at processing the grain. As I already pointed out, using an electrically based system would add levels of detail that can not easily be resolved by the Kenyan people; additionally, complex mechanical systems also provide for a system that would be hard for the recipients to care for as it really needs. With these two options being blocked, we are left with needing a very simplistic system that is light weight, easy to use, and does a good job at processing the grain. Unfortunately this combination of things ideals does not come together easily. For example, a system that is cheap and simplistic is not likely not going to do an adequate job at processing the grain while a complex system that can adequately process the grain will not be light weight or easy to repair. In order to make a good design we have to make some value judgments. For example, is it more important for the mill the work effectively or be simplistic; is it better to be small or to be capable of handling high volumes? For these two issues we felt that while neither extreme was completely ideal a mix that leaned towards being effective and capable of high volumes seemed to be a more favorable goal.

One thing that these old mills did was provide multiple gear ratios to help provide greater ease in achieving consistent fan speeds, however the operator was the one

© B. Katerberg, A. Vander Moren 16 December 2004

determining how fast to spin the crank. With the operator acting as the closed loop portion of this system there is quite a bit of variation in quality that will get better with experience. It would be very nice if consistently good results could be achieved by different people no matter what their experience level is.

seemed like the ideal mix.

V. THE CURRENT MILL

While many villages still winnow seed by hand, some have received Clipper Fanning Mills like the one seen in Figure 5. These millscurrently being used for processing amaranth seed in Kenya have two layers of precisely sized screen, the first allowing anything the size of the seed and chaff and other smaller things through while sending the larger stuff out a waste chute. The second screen keeps the seed and chaff on top while letting the fine dust through. After this sorting is done, the seed and chaff falls into a vertical shaft that has a flow of air running up and out the top.

Figure 5 Clipper Fanning Mill

This air stream lifts the chaff and sends it out the upper chute while the seeds themselves fall

Figure 6 Current Fanning Mill

down and are collected at the bottom. These mills work quite a bit better faster then the manual traditional process of sifting tossing the seed in the air, but due to the high cost of the screens and the cost of shipping something so large and heavy, these mills do not work well for being built in the US and then shipped overseas as several organizations are hoping to do. Additionally the current mills are made out of plastic wood causing them to have a much more limited life as boards wear or even rot. Another thing plaguing these mills is that there is a lot of back and forth motion. Because of all of this vibration, the mills wear down much more quickly then if all of the motion was cyclical. In order to make milling more simplistic, another thing that was done was to use wooden pulleys instead or real gears. These wooden gears do make the mills cheaper but they are also less precise and require more maintenance.

VI. HISTORY OF GOVERNORS

The Scottish inventor James Watt is credited with inventing the first device that adjusted the input to a system relative to the system’s output [2]. This device is called the flyball governor. This invention stems from Watt’s interest in the newest invention of his time, the steam engine. One of the major causes of steam engine failure was due to over working/over revving an the engine. Watt’s’ flyball governor addressed this problem and enabled the steam engine to adjust its speed automatically regardless ofin response to the load applied to the system.

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Figure 7 Watt’s Flyball Governor [2]

A flyball governor is comprised of a shaft that is driven by the device in that is intended to be controlled. The shaft is spinning at the speed of the shaft that is to be monitored. This shaft is positioned vertically and has two weights that hang down from the shaft via small rods. As the speed of the shaft increases, the weights connected to the shaft move outward due to centrifugal force. The faster the shaft moves; the farther out the weights move. A special linkage is connected to the top ends of the shafts holding the weights. This linkage moves relative to the position of the weights. This linkage can be connected to the throttle of the engine that is spinning the shaft the governor is attached to. When the engine is at rest, the throttle of the engine is wide open. As the engine begins to speed up, the weights move outward which causes the throttle to close slightly. If a load is suddenly applied to the engine, the speed of the engine slows down which causes the weights to fall down closer to their rest position. The movement of the weights supplies more fuel to the engine therefore allowing the engine to speed back up to the desired speed.

Once the load on the engine is removed, the engine begins operating at higher speeds than it should. The weights then move even higher. This movement of the weights decreases the amount of fuel supplied to the engine. Less fuel being provided to the engine limits the amount of power the engine can make produce and therefore slows down the speed of the engine until the equilibrium speed is achieved once again.

VII. MODERN MECHANICAL GOVERNORS

Most modern mechanical governors operate is in a fashion very similar to the flyball governor invented by James Watt

200 years ago (see Figure 7Figure 8).

Figure 8 Flyball Governor [2] Of course today our governors use better materials such

as ball bearings and a more compact setup but the basic principle is the same (see Figure 9). With these new governors the axis of rotation does not need to be the vertical axis as these governors rely on springs instead of just gravity. While Watt’s’ governor does a good job following the load applied to an engine, the governor does not do a good job if loads are often applied and removed from the engine. When this occurs, the governor experiences something referred to as “droop.” This is refersring to the delay between when the load on the engine changes to and when the engine responds appropriately to the change. Sometimes this change does not affect the performance of the system while other times the speed of the engine is extremely important to the output of the system and thus the droop is unacceptable.

Figure 9 Mechanical Governor [2]

The problem of droop is compounded when hunting occurs. Hunting refers to overshoot/undershot of the system as it attempts to come backreturn to its equilibrium position after a load has been applied or removed. For example, if a load is applied to an engine, the mechanical governor causes the engine to speed up to offset the increased load. However, often times the governor causes the engine to run slightly faster than what is desired. This in part happens

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because the engine gets the system running and in turn increases the momentum of the system which helps carry it beyond the equilibrium point. The governor then compensates for this and decreases the fuel to the engine. This often slows the engine to just slower than the desired speed. This oscillation above

and below the desired speed is hard on the engine and can make for undesirable results. To compensate for this “underdamped” situation, an external hydraulic linkage can be attached to the governor. This linkage is often referred to as the primary compensation. This setup anticipates the where the throttle should be set to compensate for a particular load change. A relay valve is then used to open and close oil supply ports before the final position is reached. This, in essence, causes the system to be slightly underdamped. This setup gets rid of the hunting problem and also allows the system to achieve equilibrium much more quickly. An alternative way of achieving similar results is by way of a flywheel. Due to the large mass and rotational inertia of the flywheel, small changes in input speed will not have any significant effect on the output speed.

VIII. USING MATLAB WITH SIMULINK TO MODEL SETTLING TIME

The problem of hunting can be modeled using MatLAB in conjunction with Simulink. Using this program, we can simulate the response from any type of system. Simulink uses mathematical functions and calculates the response of a system over time.

The following system was constructed to model the governor setup that could be utilized on our winnowing device:.

Figure 10 Sample Governor Setup

This block diagram mathematically shows a variety of mechanical components. The Hand Powered Input is in the form of a step input. This can be interpreted physically as the operator beginning to turn the handle on the winnower fan. In this model, we are not taking into account the fluctuations in handle speed rotation after the fan has achieved the desirable operating speed. The Speed Increaser can be interpreted as being a gear system that gears up the input handle speed. This causes the fan to spin at a speed that is fast enough to push enough air to separate the seed. The Fan Shaft Speed Governor is a device that limits the amount of air allowed into the intake of the fan. This would

most likely be a type of gate that adjusted the size of the intake opening to the fan. The gate would be controlled by some sort of linkage from the Shaft Speed Sensor. This Shaft Speed Sensor would be mounted to the output shaft of the Fan Shaft Speed Governor. This sensor would take readings of the speed of the shaft after the governor has altered the speed. Similar to the Fan Shaft Speed Governor, this sensor would be governed in a way that would by a type of transfer function to simulate the conversion of the speed reading to a mechanical action. Finally, one of the most important parts of the system is the Relative Affect of the Sensor Signal. This can be interpreted physically as the affect the sensor feedback loop has on the input to the Fan Shaft Speed Governor. When this concept is applied to our winnowing device, it could be seen as the amount the air intake gate moves relative to the size of the fluctuation in speed. The amount the gate moves would be affected mostly by the geometry of the linkage that operates the gate. Depending on how this gate is set up, the function driving the Relative Affect of the Sensor Signal could be rather complicated. By this, I mean that there is a possibility that the signal can not always be modeled linearly. This correlates physically to the possibility of the intake orifice being circular in shape rather than rectangular. A circular shape means that for every increment that the gate opens, a different amount of area is open for air to pass through. However, a rectangular shape provides that for every increment the gate opens, the same amount of intake area is available for air to pass through.

The following graphs show the response predicted by Simulink. Notice the amount of oscillations that occur before stability is achieved and the amount of time passed before becoming stable.

Figure 11 Response with Relative Affect Equal to 1

This graph shows the response when the affect of the sensor signal is set to one. This means that the signal from the sensor goes straight to the governor without being adjusted. This correlates with installing a linkage with no regard towards its affect on the performance. It is apparent from this graph that the percent overshoot is almost 70%.

© B. Katerberg, A. Vander Moren 16 December 2004

This means that when the winnowing fan is first started, it will operate 70% faster than its final speed for a short period of time. The speed of the fan will continue to stabilize as time progresses. It looks as if it takes about 20 seconds for the fan to begin operating at a constant speed.

This model does a great job of showing the droop associated with a mechanical governor. It shows that the governor is able to do a good job of governing the fan speed, however, the amount of time it takes for the system to perform this governing is rather large and often unacceptable for most applications. There are several ways to work around this problem of slow response times. that this problem of slow response can be accounted for. One of these ways would be to begin turning the fan and allow the speed fluctuations to take place before sending any seed through the wind tunnel. This would be very effective only if the hand crank was able to be turned at a constant speed throughout its entire operation. If there are any fluctuations, a new disturbance will be created which will cause there to be more speed fluctuations.

The same system can be simulated with the effect of the sensor signal on the system having a smaller affect on the response of the system. The following graph shows the response of the system when the feedback signal from the sensor is only half of what it was in the previous example.

Figure 12 Response with Relative Affect Equal to .5

This graph shows that the equilibrium value for the system is larger than that for the original system. This is because the feedback loop is a negative feedback loop and the signal due to the sensor is subtracted from the input from the hand crank. The percent overshoot of the system is also much less than the original system- only about 40%. This means that the size of the fluctuations when the system is first started are not as large as they were for the original system. The amount of time that must pass before the system reaches equilibrium looks to be about 13 seconds. This is a seven second improvement over the original system. However, before someone can use the winnowing machine, they must still run the fan for 13 seconds before they can begin processing the seed.

No matter how much tweaking is done to the system, there will always be a delay in the response time. The only way to create a mechanical system that has little to no response time is to design a system that can anticipate a change in load or speed and prepare the system to make the appropriate adjustments as soon as the load or speed actually changes. This requires an additional control system to detect future changes in the system dynamics.

Much more complicated governor systems can be modeled using Simulink. Every system can be tailored to the specific application. The following figure shows a more complicated governor system that can be modeled using Simulink.

Figure 13 Model of Mechanical Governor Control System [19]

Figure 14 System Response of Mechanical Model

IX. TYPES OF GOVERNORS

When choosing which type of governor to use for our specific application, it is important to understand the different types of available governors and the advantages and disadvantages of each.

There are three main types of governors. They are velocity, mechanical, and electrical governors. Each type of governor has specific types of applications where they are best used. The following discussion highlights these different types of governors and the advantages and disadvantages of each.

A. VelocityVelocity governors are relatively simple devices which

operate by measuring the vacuum created by an engine. These devices are very

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Figure 15 Velocity Governor [13]

easy to install and are compact. These governors operate by measuring the revolutions per minute of the engine. Linking the measurement of the speed of the air into the engine to the main engine control device gives the engine controller designer the ability to write indesign a safety device to limit the maximum speed of the engine. B. Mechanical

Within the mechanical governor category, there are three different types of governors. First, there is the belt driven governor. This type of governor works well with an engine that was not originally outfitted with a governor. The governor itself is not mounted directly to the engine but instead and pulley is mounted to the output of the engine crankshaft and a belt from this pulley drives the belt of the governor. When choosing a type of governor, it is equally important to carefully choose the size of the pulleys that will be used to drive the governor. Much like the velocity governor, this governor is able to limit the top speed of the system. Additionally, this device is also able to quickly react to load changes. This is especially useful in machines such as wood chippers where loads are constantly changing in what are usually very large magnitudes.

Gear drive governors are another example of atype of mechanical governor. These are usually included in the initial design of an engine. They are most often mounted inside the timing gear chain cover and are run off one of the timing gears. The timing gear of an engine is connected directly to the crankshaft of an engine therefore giving a direct measurement of the speed of the engine. This type of a governor would be difficult to add after the initial design because it is likely that the parts surrounding the timing gear chain area would not allow for enough space for the governor to be installed.

As stated before, a flyball governor is also another form type of mechanical governor. One way of using the concept of the flyball governor is to mount a race to the camshaft with ball bearings enclosed inside the race. When the speed of the engine is increased, the camshaft rotates faster and the ball bearings inside the race are thrown to the outside of the race. An arm inside the race is then engaged due to the force from the ball bearings. This arm indicates to the engine controller that the engine has reached excessive speeds and must be slowed down to avoid damage to the components.C. Electronic

Most governors that are installed on devices that involve electronics and computing software use electronic governors. These governors often get a reading for the speed of the device in question directly from the output; but unlike mechanical and velocity governors, the data is turned into an electrical signal. This

signal is then transferred to the central computer (controller) for the device. The computer then makes the appropriate adjustments to compensate for any differences from the desired speed. An advantage of electronic governors is that the hunting problem can be avoided completely if care is taken in writing the program to control the speed. However, if any problem is encountered in the speed controlling process, it may be more difficult to locate and fix when an electronic speed governor is used. A mechanical governor is very transparent. Any problems encountered during use can usually be identified by watching the governor perform its function.

There are still other variations between governors. For example, a governor could be used avoid or focus in on certain rotational speeds kind ofmuch like a band-pass filter., or to focus in on other desired speeds. The band-pass style governor could be used to keep a system from operating atstaying near resonant frequency as shown by the ‘Unstable’ curve in Figure 18. The governor can otherwise be setup to always focus the system to a specific speed as shown by the ‘Stable’ curve.

Figure 18 Stability of Governors

X. APPLICATIONS FOR MECHANICAL GOVERNORS

Mechanical governors have various useful advantages over electronic governors. One of these advantages is that mechanical governors can operate in wet conditions without any difficulty. This is especially useful on ships which are constantly exposed to sea conditions. If an electronic governor were used for this application, the circuits would most likely eventually short out due to the water coming in contact with the electrical components. In water related applications, Iit is common to find things components such as speedometers transmitting readings by way of a flexible cable or other similar techniques.techniques.

Some applications which call for a governing device require that the device have the ability to operate under extremely high temperatures. Electronic devices can not be subjected to high temperatures without some sort of protective shield surrounding the wires and components. This extra cost due to shielding can be avoided by using

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Figure 16 Mechanical Governor [13]

Figure 17 Electronic Governor [13]

mechanical governors when possible. However, Tthis is not always a possibility because mechanical governors might not fit in the space available or may not provide accurate enough governing. It is important to carefully measure the advantages and disadvantages of each system before deciding which type is best for each a particular application.

Cost is another issue that may affect the decision of what type of governor should be used for a particular application. If an application requiring a governor does not already have any electrical components, the expense to electronically govern the system would be much larger than it would be if electrical controls were already a part of the system. This is because electrical components are easily regulated using an electronic interface. However, mechanical components can not be controlled without some sort of electronic actuation. It is situations such as these that necessitate the need for mechanical governors. Our senior design project falls into this “all mechanical” category. Implementing an electronic control system would not only add complexity to our design, but it would also add a large additional cost. For example, an electronic sensor would need to be purchased to monitor the speed of the fan. This signal would then need to be transferred to the processing unit (another expense) to be analyzed. A new signal would then be sent from the processing unit to another expensive device that controls the speed of the device fan such as a power regulator. There is a good possibility that this device would be small and lightweight (two goals for our project), but the sheer cost of the equipment would far outweigh any size and weight benefit.

Implementing a mechanical governor on our winnowing device has the potential of being simpler and also much cheaper. The most difficult part would be to find a way to mechanically measure the speed of the air through the wind tunnel or the speed of the fan. Assuming this could be accomplished, a simple linkage could be set up that could meter the amount of air intake to the fan. It is this metering device that makes the question of governing a difficult one.

XI. OUR DESIGN IDEAS

We have been told that there are not many people in Kenya who have an extensive mechanical background. However, the Kenyans do have considerable experience with bicycles. Bicycles are the leading form of transportation in Kenya. While we have been informed that there is not a lot of know-how in terms of machining parts or using electronics, we have been informed that one of the leading forms of transportation in Kenyan villages is bicycles. With this in mind we know that it is likely that there are some in the Kenyan villages there are at least some in the village that have the knowledge of how to perform general maintenance to bikes. Because of this it seems that it would make sense to try to use bike parts in the design of the mill whenever possible. seemed that one nice way of providing good quality parts in the mill that we design would be to use bike parts. For example, if we were to use a regular gear and chain for translating the motion from the inlet input crank to the fan, the repair cost and time needed

to fix the gear would be quite high in comparison to if we were to use bicycle gears and a bike chain to carry out the same process. Not only are these parts readily accessible but they are also very durable and quite light in comparison to most other gears of equivalent sizes. While I we had considered implementing an automatic shifting bike derailleur in mind that it would be nice if we could implement one of the automatic shifting bike derailleur (see Figure 19) into the design, so that the gearing would automatically change to provide a consistent fan speed we began to feel that this would remove some of the simplicity that we were hoping for and also would also add a great deal of cost to the system. While most automatically shifting bikes work by providing a consistent torque to the operator pedaling, the goal for implementing one of these shifters into our design would be to provide a consistent torque to the fan no matter who is providing the power to the system. While this seems to be a good idea, there are several things that need to be looked into such as whether or not the Kenyans have variable speed bikes such as we are used to. It doesn’t make a whole lot of sense to throw in this complex of a system when they do not have the range of gearing that it would take to replace a system of this nature. Additionally these automatic gear shifters can be rather pricy thus making it less ideal for a project that is being funded solely by a small church in the area (Hillcrest CRC in Hudsonville, MI). While it is not only important for us to do as much to cut the cost of our system because the all of the kits are being provided by a small church, it is an extra incentive that is helping to drive our design.

Figure 19 Automatic Derailleur [11]

Components That Would BenefitWhile the primary component that would require some

sort of mechanical governor is the fan or winnower, the thresher would also be benefited by the governor. In many ways this could be done with more simplicity by running the thresher directly off of the governor used to regulate the fan speed. The thresher would benefit from a governor because it seems that there would be some operating speed that would provide the highest quality threshing. This could also be linked in with some sort of flow regulator to make certain that the volume of ‘dirty’ seed placed onto the belt would never be too high preventing the good separation that we

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need.

XII. OUR DESIGN IDEAS

We have been told that there are not many people in Kenya who have an extensive mechanical background. However, the Kenyans do have considerable experience with bicycles. Bicycles are the leading form of transportation in Kenya. With this in mind we know that it is likely that there are some in the Kenyan villages that have the knowledge of how to perform general maintenance to bikes. Because of this it seems that it would make sense to try to use bike parts in the design of the mill whenever possible. For example, if we were to use a regular gear and chain for translating the motion from the input crank to the fan, the repair cost and time needed to fix the gear would be quite high in comparison to if we were to use bicycle gears and a bike chain to carry out the same process. Not only are these parts readily accessible but they are also very durable and quite light in comparison to most other gears of equivalent sizes. While we had considered implementing an automatic shifting bike derailleur (see Figure 19) into the design, we began to feel that this would remove some of the simplicity that we were hoping for and also would add a great deal of cost to the system. While most automatically shifting bikes work by providing a consistent opposing torque to the rider of the bike, the goal for implementing one of these shifters into our design would be to provide a consistent torque to the fan no matter what the input to the system is. While this seems to be a good idea, there are several things that need to be looked into such as whether or not the Kenyans have variable speed bikes such as the ones we are used to. It doesn’t make much sense to use a complex system such as this when they do not have the range of gearing that it would take to replace a system of this nature. Additionally these automatic gear shifters can be rather expensive thus making it less ideal for a project that is being funded solely by a small local church (Hillcrest CRC in Hudsonville, MI).

Figure 20 Automatic Derailleur [11]

XIII. COMPONENTS THAT WOULD BENEFIT

While the primary component that would require some sort of mechanical governor is the fan or winnower, the thresher would also benefit from the use of a governor. The thresher would not necessarily require a separate governor; but instead could be run directly off of the governor used to regulate the fan speed. The thresher would benefit from a governor because it seems that there would be a certain operating speed that would provide the highest quality threshing. This governor could also be linked with some sort of flow regulator to make certain that the volume of ‘dirty’ seed placed onto the belt would never be too high preventing the good separation that we need.

XIV. MATHEMATICAL CALCULATIONS

In order to get an idea of how fast we need to have the fan spinning to provide adequate lift to separate the seed and chaff, mathematical calculations were performed using general values for the size, weight, and drag coefficient of the seed, as well as the density of the air through which the seed is falling.

Equation 1 Wind Speed Calculations

The technique used here was to calculate the terminal velocity of the seed. At this wind speed, a seed could be placed into the column of air and theoretically stay at that same elevation. Because the seed would be falling into the column of air it would have some momentum that would help it carry all the way through to the outlet. However, even with this momentum it would probably be wise to set this wind speed as the limit and actually try to maintain a speed slightly slower than this to be sure that the good seed will not be blown out of the winnower.

In addition to calculating the desired air speed, the active response of the mechanical governor also became something of interest. In order to accurately set up a mechanical governor, one must know the point at which the governor begins to affect the output of the system. In order for the governor to respond most effectively one would generally want to have the flyballs at an angle between about 45° and 70° (see Figure 21) [4]. The reason for this is that this is where the rotational speed has the greatest impact on the stable angle θ. What follows here is a series of calculations

© B. Katerberg, A. Vander Moren 16 December 2004

used to calculate the response of an ideal mechanical governor.

Equation 2 Mechanical Governor Calculations

Figure 21 Mechanical Governor ResponseWhile Figure 21 shows the desired rotational governing speed to be around 20Hz this could be changed by using a governor with different masses or by gearing the system differently.

Because of the accuracy that could be built into a mechanical governor it seems reasonable to believe that a winnower could be built that will accept nearly any input speed (above a particular lower limit) and then provide a constant output. With more gearing this could carry out all the thrashing as well without any trouble.

REFERENCES[1] A.F. Armer, S.A. Eweda, and M.A. Eweda. (2004,

November 11). Speed Control of Marine Diesel Engine Using Fuzzy Approach Part (II). Available: http://iccta.aast.edu/cms/166/Speed.pdf

[2] Carolina RR. (2004, November 11). Speed Regulation of Micro-Hydroelectric Power Plants. Available: http://home.carolina.rr.com/microhydro/governors.html

[3] Post, Tom. (2004). Conversations with Tom Post of CRWRC on his experiences in Kenya.

[4] Beute, Bob. (2004). Conversations with Bob Beute of Hillcrest CRC on his experiences with amaranth in Kenya.

[5] Prof. David VanBaak (10 December 2004). Assistance with Mechanical Governor calculations

[6] Speed Controlling Devices. (2004, November 8). Available: http://www.tpub.com/content/engine/14076/ css/14076_101.htm

[7] Ribeiro, Paulo. (2004). Control Systems professor at Calvin College.

[8] Video Demonstrations of Control Systemshttp://www.engr.colostate.edu/~dga/video_demos/controls/

[9] Yin, Hwa-Yung, “Automatic Derailleur,” U.S. Patent 6,692,389, Feb. 17, 2004.

[10]Wesling, Kevin F., “Semi-Automatic Shifting System,” U.S. Patent 6,352,486, March 5, 2002.

[11] http://www.popularmechanics.com/outdoors/bicycles/2002/3/bike_with_brains/index2.phtml

[12] Speed Controlling Devices. (2004, November 8). Available: http://www.tpub.com/content/engine/14076/ css/14076_101.htm

[13] Tech Tip #40 – Governors on Industrial Engines: A Brief Overview. (2004, November 8). Available: http://www.foleyengines.com/TechTips/TechTip40.html

[14] Speed Regulation of Micro-Hydroelectric Power Plants. (2004, November 8). Available: http://home.carolina.rr.com/microhydro/govenors.html

[15] http://www.elecdesign.com/Articles/ArticleID/6168/6168.html

[16] http://www.elecdesign.com/Files/29/6168/Figure_01.gif[17] http://www.engr.colostate.edu/~dga/video_demos/

index.html[18] Patent Search Engine:

http://www.uspto.gov/patft/index.html[19] Ribeiro, Paulo. (2004). Control Systems professor at

Calvin College.[20] Trump, Bruce C. PWM Motor Speed Control Uses AC

Tachometer Feedback. Available: http://www.elecdesign.com/Globals/PlanetEE/Content/4937.html

Brian Katerberg (November 2004) was born in Dayton, Ohio, August 11, 1983. He will be graduating in

© B. Katerberg, A. Vander Moren 16 December 2004

May of 2005 from Calvin College with a Bachelors of Science in Engineering with a Mechanical concentration. From here he intends to use his engineering experience and hands on skills to do third world development with a missions organization such as CRWRC or CAMA (Compassion and Mercy Associates), or possibly do disaster relief with someone like the Red Cross. Other interests that might lead Brian to a different job include such things as prosthetics and artificial joints which Brian says that he feels he would greatly enjoy working on as well due to the large impact it can have not only on an individual’s life but also on their whole family’s life.

Andy Vander Moren (December 2004) was born on May 30, 1983 in Visalia, California. He is currently attending Calvin College in Grand Rapids, Michigan and will be graduating in 2005 with a degree in Engineering and a concentration in Mechanical Engineering. His plans after graduation are to enter the work

force. He would enjoy a hand-on job that is challenging and enjoyable. Andy enjoys working on automotive related projects and also enjoys woodworking projects. Andy is interested in the possibility of becoming a licensed contractor and owning a custom homebuilding business.

© B. Katerberg, A. Vander Moren 16 December 2004