Remembering DOE Resolution

Engineering often relies on Design of Experiments (DOE) to effectively understand significant dependencies of different input or control parameters to a desire measurable outcome. It is critical to properly design your experiments in a way that maximizes your ability to distinguish between the impact or contribution that each input variable has on your outcome. Different types of DOE designs have different resolutions. As stated here, a DOE resolution describes the degree to which main effects are confounded with 2-level interactions, 3-level interactions and so on. For example, in a resolution III design main effects are confounded with 2-level interactions. Ideally, we would like to have the highest resolution possible DOE. Full factorial designs have no confounding and thus are considered resolution “infinity”. However, having full factorial designs is often not possible due to the very large number of runs required. As a result, I often end up working with different resolution DOEs and often I need to remember which factors are confounded. For this, I always use a hand trick that was thought to me during my Design for Lean Six Sigma Training. I wanted to share this hand trick for those looking to remember this. However, rather than explaining it, I put together the following picture:

DOE_hand_trick

The nice thing about this trick is that it also holds true when you are dealing with say resolution VI or greater DOE. For DOE resolutions higher than V, just use your two hands, and work with the number of fingers equal to the DOE resolution as indicated above.

ME Software Flow Chart

Engineers solve problems every day. I have been practicing the Mechanical Engineering profession for over 10 years and every day I solve problems. Every big problem can be broken down in small bits, which become a problem to solve on their own. Like in any profession, one very important step to solve a problem is to find the right tool to get the job done in the most effective and efficient way. In the digital age, most of these tool that I am talking about end up being some type of computer software. I often find myself mentally evaluating different software packages against the details of the problem at hand.  For this reason, I have tried here to provide a decision tree style flow chart to illustrate the typical thinking process used by many mechanical engineers to choose the right software for the job.

ME_Software_Flow_Chart

Access your Raspberry Pi from Anywhere

The Raspberry Pi is such a small, versatile, and cost-effective computer that it has found several uses in multiple applications. The Raspberry Pi’s ability to interact with the physical world through its GPIO makes it the perfect computer for Makers and DIY projects. For these reasons, it is not uncommon to have several Raspberry Pi computers located in different geographical areas performing a variety of tasks. Therefore, there is naturally a need, especially for IoT applications, to securely access the Raspberry Pi over the internet from anywhere and any time. A very effective method that I have been now reliably using for a couple of months is a FREE service provided by Weaved. I first came across this option on raspberrypi.org and I learned more on weaved.com. The installation process was simple. I installed the SSH service as well as the VNC service. On my PC at home, I use PuTTY to access my Raspberry Pi using SSH. For the VNC service, which allows me to interact with the Raspberry Pi’s GUI, I use TightVNC which works great. A great thing about SSH is that it allows you to use FileZilla for file management and transfer. I have been using the FileZilla software to transfer images taken by a USB camera connected to the Raspberry Pi.

Once you have completed the installation process described here or here, you should be able to login to Weaved and see your services online:

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I strongly recommend that you change your Raspberry Pi password to something other than the default password for increased security.

If you select the SSH service, you will be given the following information:

 

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And the information for VNC acces looks like this:

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More information on using Weaved with PuTTY and FileZilla can be found HERE. My next IoT project using the Raspberry Pi will most likely involve the use of WebIOPi which can also be accessed using Weaved.

How much does it cost to charge a cell phone or Tesla vehicle?

Have you ever wondered how much money does it cost to charge a cell phone or perhaps a Tesla vehicle? The first step to answer this question is to know how much you pay for electricity. This website from the Nebraska Goverment gives us an idea of the average cost of electricity per state, in cents per KiloWatt-hour. The next step is to find out the capacity of the battery for the device of interest.

The battery capacity for an Iphone 6 is about 6.9 Watt-hour, and about 9.8 Watt-hour for a Samsung Galaxy S6. For these calculations we will need to make a couple of assumptions and approximations. I decided to include a 95% efficiency in the charging process and also decided that my device will be charged 1.5 times per day, 365 days per year. It turns out that it costs about 50 cents per year to charge a cell phone. Overall, I was surprised how relatively inexpensive it is to charge a cell phone given everything that a cell phone does for us these days.

The battery capacity of a Tesla vehicle ranges from 70 KiloWatt-hour to 90 KiloWatt-hour (about 10,000x larger than your phone). The average range of a Model S is about 240 miles, battery-only. On average, a vehicle is driven 12,000 miles per year, which would be equivalent to charging your Tesla 0.137 times per day (about once every 7 days). Using a 95% charging efficiency and 365 days per year, it costs about $440 per year to charge a Tesla Model S. I do not own a Tesla yet, but I will do some approximations to relate this number to the cost of driving a gasoline vehicle. An average of 12K miles per year is equivalent to 27.3 miles/$ for Tesla. My current 4 cylinder 2.0L car gets about 30 MPG. Currently, gas is about $2.5/gallon (May 2016). Therefore, my 4 cylinder 2.0L car costs 12 miles/$ or 2.3x the price of Tesla for the same distance.

For reference, here are the numbers for the cost to charge per year:

CELL PHONE:

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TESLA:

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