Viper Bots’ last hurrah?

This was my fourth season coaching an FLL team. This year all three Renaud girls were on the team: it was Jadzia’s fourth and final year, Ludi’s second, and Josie’s first.

The Viper Bots are a school-based team, so we begin when school begins in August at Vogt Elementary. After that, it’s a race to build and program our robot, research a project, and write a presentation by November. It is pretty exhausting.

The girls came up with a pretty cool project. The problem they investigated was growing plants in space so astronauts can eat fresh food. NASA has been testing hydroponic ways of doing this. The girls came up with what they believed might be an improvement: a spinning, wheel-shaped planter which would use centrifugal force to keep water from pooling on the roots of the plants. We visited the Challenger Center, submitted questions to NASA live chats, and eventually we visited local plant biologist Dr. Bethany Zolman at UMSL. They called their solution the “Spin and Grow”. They came up with a creative presentation which included Josie dressing up as an astronaut.

The 2018 incarnation of the Viper Bots’ robot “Viper Evie”

They also managed to build a robot that used two sensors we had never used before: the gyro and the color sensor. Josie and her teammate Nylah attended four programming sessions where they learned some more advanced technique. By the end, the robot was capable of (often) completing three missions in the robot challenge.

The qualifier competition had its own ups and downs. The robot did unexpected things, as it always does. But the girls bounced back: they kept programming during breaks between sessions, and the robot performed better in the second round.

Viper Bots receive their participation ribbons at the qualifier.

We didn’t win any prizes, but when we looked at our scoring rubrics afterward, the project had scored high. They were probably one of the top contenders for a project award. So close!

Since Ferguson-Florissant has decided to close Vogt Elementary next year, and since Jadzia and her friend Jossie are aging out of First Lego League, I’m not sure what will happen going forward.

As 8th graders, this was the final season for Jadzia and her friend Jossie in FLL. We’re grateful to Ms. Lauren at Girl Scouts of Eastern Missouri for helping our team get started and for all her support over the years.

No matter what happens, it was a pleasure (most of the time) this year watching the team try new things, achieve goals, and just be awesome.

Building a dot-matrix EV3 Lego printer

One of my early attempts to build a Lego printer. The print head here is driven by a rack and pinion. Later versions used a technic tread and sprocket.

In June and July, I borrowed the girls’ robotics team Lego pieces and EV3 brain in order to build my own dot-matrix printer.

At various FIRST events, I have seen a kid or two who built a printer. I’ve also seen some on YouTube. As a fan of retrocomputing and Legos, I thought it would be a lot of fun to make my own printer.

The basic idea is simple and requires three motors. One feeds the paper forward or backward. One slides a print head back and forth horizontally across the page. The last one moves a marker or a pen up and down to draw a dot.

I made a lot of iterations of this printer, trying to solve various problems. It wasn’t perfect, and I was particularly limited by the number and kinds of pieces I had available. But it DID work! I was able to print out some portraits that were recognizable, as well as a Print Shop-style banner.

Lego printer for Fathers Day from Josh Renaud on Vimeo.

This is a simple dot-matrix portrait of my dad made using an early version of my Lego printer. The right side gets distorted, but the left and center are pretty good.

The main challenges (for me, anyway), were how to move the marker up and down, and how to code the printer so that it had good resolution. Early on, I attached the motors directly to the shafts, then measured how far to move things using tacho counts. But that led to very sloppy, inconsistent results. After a while, I realized I needed to use a technique called “gearing up”: The motor turns a small gear, which then drives a much larger gear. This decreases speed, requiring me to use many more tacho units to move the print head the same amount. On the surface this might sound bad, but in fact it greatly reduced inconsistency. I used “gearing up” to improve both the paper feeder, and the horizontal print head movement. You can even use acrylic photo blocks for printing and showcasing colored images as they last for years and are moisture proof thus ensuring no damage to the picture.

I wrote the code for the printer in Python, and controlled the EV3 using the ev3dev linux system. Later versions of the code were capable of reading in a PNG file and converting it to a low-res black and white image to print.

At the end of the summer, I created a 3D model of the printer using Lego Digital Designer. Download the viper-printer.lxf file and try it yourself in either LDD or The model isn’t perfect (There are two blank slots in the tread where I couldn’t get things to connect, for example), but is a nearly exact replica.

Inexplicably, I failed to take photos of the final version of the printer. So, here instead are some renderings of the printer, made using