FET Tricks
A few notes about some of my projects and interests.
Wednesday, June 25, 2025
Some Hardware Problems You Cannot Fix in Software
Saturday, January 25, 2025
Moccamaster KBTS - Single Cup Brewing Adapter
I created this adapter to let me use my Moccamaster KBTS coffee maker as a single cup brewer. This model comes with a thermal carafe that normally presses against a button on the base of the machine to initiate brewing. Using one of my favorite coffee cups to press the button positioned the stream of brewed coffee near the right lip of the cup. While it worked, it made me nervous about the risk of misalignment or using a smaller coffee mug. So I put on my designer hat and went to work.
https://makerworld.com/en/models/1038925#profileId-1023339
What I needed was something to center my cup under the brew basket that also presses the brewing. After sketching a few concepts, 3D printing some rough models, I settled on the design you see here that positions my cup exactly where I want, while an integrated sliding bar presses the brew button.
You might be thinking, "Isn't the Moccamaster Cup-One designed to brew a single cup of coffee?" When I decided to try a Moccamaster brewer, choosing between the single-cup model and a larger model was a challenge. While I typically brew one cup at a time, I liked the flexibility of brewing into a thermal carafe when needed.
The deciding factor came down to the difference in water distribution systems. The Moccamaster Cup-One features a water outlet arm with a single spout. While researching how to get the best cup of coffee from the machine, I found several videos suggesting stirring the grounds for more uniform wetting.
These aren't affiliate links, I just want to make it easier to learn more about the machines if you are interested.
https://us.moccamaster.com/collections/single-cup-brewers/products/cup-one?variant=40377761726627
In contrast, the KBTS uses a 9-Hole Outlet Arm to ensure even wetting of the coffee grounds. The KBTS also features a selector on the brew basket that lets you choose between high flow for full-carafe brewing, low flow for four cups or less, or stopping the water flow to allow timed soaking of the grounds. Stopping the brew basket flow also prevents drips when the carafe or coffee cup is removed.
Additionally, the KBTS includes a thermal carafe with a Brew-Thru carafe lid, which is an impressive piece of engineering. The Brew-Thru lid minimizes coffee exposure to air and introduces coffee into the carafe from the bottom up. This design helps maintain the coffee's strength and temperature uniformly within the carafe. It also reduces oxidation, minimizes evaporative cooling, and preserves flavorful volatile compounds, keeping the coffee as warm and flavorful as possible without additional heating. Very nice engineering!
If you own a KBTS, I suggest downloading my adapter model and giving single-cup brewing a try.
Thank you!
Shane
Thursday, January 23, 2025
Minimal Carry Handle for FRC Robot Batteries
This 3D printed minimal battery handle requires less than 15 grams of filament (I recommend PETG in a bright color) and quickly clips on and off of the battery.
https://makerworld.com/en/models/1015389#profileId-995541
One of the most common electrical issues with FRC robots is loose batter terminal connections caused by lifting the battery by the cables. Loose terminals tend to reduce the quality of the contact surface with the battery terminal, and can lead to random reboots or loss of radio connection with the FIRST Field Management System.
Rechecking (because you checked them back in lab, right?) the terminal connections on all of your batteries the morning your competition is always a good idea. If you can wiggle a battery cable terminal using only three fingers, then it is too loose for match play. But it only takes a few minutes to loosen, clean, and retighten the ring terminals.
Good luck on the field!
Saturday, May 22, 2021
Building a Physical Model for Testing Your Code
The Value of a Physical Model
With most development projects there is usually a little tension between the fabrication team wanting working software to test the the hardware during assembly, and the development team wanting known good hardware for use during development. There are many ways to address this tension and strike a balance.
Here is an overview of a Physical Model I built to allow me to validate the electrical design and test the firmware for a proof-of-concept device for a patented process of producing subcutaneous, or plastic surgeons' sutures. The physical model provided a hardware platform for testing the firmware to ensure proper operation before the hardware for the demonstration model was available. Waiting to test on the actual hardware would have made it difficult, if not impossible to meet the client's timeline.

The client is a small startup that has multiple patents for automated subcutaneous sutures and needed a hand-held model that could demonstrate the process to potential customers and investors. I worked with them in their earliest efforts which gave me a head start on designing a the proof of concept device to help them move forward.
My assignment was to help with the electrical design and firmware to demonstrate a proof of concept of the clients patented process for automating the application of subcutaneous sutures, or plastic surgeon's sutures. The goal is a works like device to be built into a looks like hand held model. My contribution was electrical design and firmware development while the client was responsible for the physical construction and final assembly of the device.
The client had an aggressive schedule based on demonstrations that they were working on scheduling and an upcoming trade show. As is most often the case, the key to success was using as many off-the-shelf parts as possible.
I knew that the hardware assembly timeline was likely to slip and that I would have little if any access to the final assembly prior to their deadline. So I decided to build my own Physical Model to allow me to test the firmware on a target platform that would simulate all of the electron mechanical parts of the final system.
Why Product Design is Challenging
One of the earliest lessons I learned about designing automated test systems is that the hardware people want working software to test the hardware during the build and the software people want working hardware to test the software during development. There are two components needed to address this chicken and the egg problem.First, you need a way to exercise all of the inputs and outputs of the data acquisition and control system so the hardware team can test their wiring during assembly. If you are using National Instruments hardware, then you can use their set up panels that allow you set all of the outputs and read all of the inputs of the data acquisition hardware. Still we would often have the programmer start with a minimal framework that exercises all of the system inputs and outputs and displays the status on screen. Writing this software was a great way for the programmer to get comfortable with configuring the hardware without needing to address the functional and user interface aspects of the system under development.
The second component in this solution was building a Physical Model that simulated all of the system IO to allow the programmer to test the functionality of their software against the model during development. Typically this was a panel with LEDs and switches for the digital IO and potentiometers voltage displays for the analog components.
Assembling All of the Pieces
Being an early stage, proof of concept design, I wanted the client to be able to modify and update their control sequence without needing to come back to me with each small change. Using off the shelf hardware at every possible step is the key to successful prototyping.I implemented the command sequence as a two dimensional array of data points that would allow the client to modify target position and motor speed settings by simply modifying the array and downloading the new firmware via the Arduino IDE. They could even add or remove steps of the motion sequence by adding or deleting rows from the array.
The design included three Maxon brushed DC servo motors with high-resolution encoders, controlled by AllMotion EZSV10 DC Servo Motion Controllers. The EZSV10 controllers communicate using RS-485 to configure the motor driver settings, receive position command and to read encoder outputs. The EZSV10 Servo Controllers pack an amazing amount of performance into a tiny package. I highly recommend their quick start kit if you want to jump into brushed DC motor servo control.
http://www.allmotion.com/Servo_Pages/EZSV10Kitdescription.htm
The initial design was powered from a single lithium ion 18650 battery with the servo motor rail voltage being produced by a Pololu U3V50F12 DC-DC Step-Up Regulator.
This configuration allowed me to test the actuator and limit switches for all three servo motors. I did need to address the differences in the encoder resolution between the Faulhaber gear-head motors and the Maxon motors. I added a jumper to my test board that the firmware checked at start up. If the jumper is found when the firmware boots up, then the software scales the motion target values to match the low resolution encoders on the Faulhaber's. If the jumper is not found, the firmware uses the high resolution target values for the Maxon motors.
The flexibility of laser cutting really stood out when it came to needing a way to test the homing switches and verify the motors were reaching the desired target positions during the sequence. Below is one of the actuators that I drew up and cut on the laser. The bump actuates the limit switch used for homing the motor and the scale is customized for each axis. Note the mounting hole was also laser cut to match the motor output gear tooth profile with a friction fit.
Friday, May 21, 2021
LEGO EV3 Minimal Gyro Proportional Drive Straight for FLL Robots
During my second season coaching FLL, the team had a robot that would sometimes drift to the left, but other times drift to the right, sometimes during the same run! This drove them crazy most of the season. Worst of all, when they put a mat on a hard floor to simulate a perfectly flat board, the drifting all but disappeared!

The program works by using a LOOP to read Gyro Sensor on port 2, then calculate the heading error by subtracting the gyro reading from our desired heading, 0 degrees, and using the heading error as the Steering Angle for the Move Steering block (the Motor Power is fixed at 60). This happens as fast as the Loop can run (many times per second). This continues until Motor B rotations are greater than or equal to 4, or for four rotations.
This is a Proportional Control or Proportional Feedback system. It is called this because you are changing the output, the Steering Angle, by an amount that is proportional to the error, or the difference between the desired heading (0 degrees) and the measured direction.
Understanding Proportional Feedback to Help Your Robot Drive Straight
We are going to walk through how to use the Gyro Sensor and Proportional Feedback to make your EV3 based LEGO robot drive straight. The robot will drive straight even if the wheels slip or if the wheels are even different sizes. I am still impressed every time I push the back of the robot to make it turn off course and it turns back to follow the desired heading.
Gyro Sensor
We are going to assume that your robot's Gyro Sensor is mounted with the arrows facing up (ensuring that rotating the robot to the left will produce negative readings from the sensor) and somewhere near the centerline of the robot (ensuring that turns to the left and right each require similar adjustments to the robot's drive system.
The Gyro Sensor does have a few unique traits. First, it calibrates while the EV3 brick is booting up. This means your robot needs to be very still while booting. I recommend putting the robot on a clean piece of paper on the floor for booting up.
You can force the Gyro Sensor to recalibrate by plugging and unplugging the sensor's cable or using a specific combination of programming blocks. I will not cover software methods for resting the Gyro Sensor because it very often causes more problems than it solves.
Move Steering
The Move Steering block makes our task simpler by allowing us to change the robot's direction by adjusting the Steering Angle input.
Proportional Control simply means that you are making a change, this case steering angle, based on the size of the measured error. Here our error is the difference between the direction we want to drive and the angle the gyro says we are driving. output to a value that is proportional to the system error. In the case of the Gyro Sensor, any errors to the right, or clockwise, are read as positive angles and error to the left are negative angles. And we are going to use a Move Steering block and adjust the Steering Angle based on the Gyro Sensor reading to make the robot drive straight. So if the robot is going a little left of where we want, say -5 degrees, then we want to set the Steering Angle to steer to the right, perhaps 5 degrees.
Below is a Minimal Gyro Drive Straight program. I think it is very cool that you can build it with only five blocks, including the Start block!
Going Straight
Going in a straight line is not a natural thing for a robot, or for humans for that matter (see MythBusters episode 173: Walk a Straight Line). It turns out that humans and robots both need some kind of feedback to go in a straight line. For humans, the feedback is usually visual but you can also use a compass as a reference to keep you pointed in the same direction. Robots are similar in that you can use a Color Sensor to follow a line or use the Gyro Sensor to follow a heading.
Why Straight is Difficult for Robots
Driving straight using only mechanical design is challenging. The robot needs to have wheels of the same diameter, precisely aligned to each other and in line with the robot chassis, the motors must rotate the wheels at the same speed (be synchronized), the weight distribution must be balanced between the wheel to ensure the robot has a center of gravity centered between the wheels and the wheels cannot slip.
Potential Gyro Pitfalls and How to Avoid Them
Gyro sensors are very useful sensor but can be a little confusing, and has some pitfalls that have tripped up even advanced teams.First, Gyro sensors usually calibrate automatically at power on, like when the EV3 boots up, which means any movement of the robot, or table, while the EV3 brick powers up can produce drifting in the gyro. I recommend setting the robot on the floor on a sheet of paper (to keep dirt off of the wheels) and let it boot up without being disturbed.