# Learning with OpenSCAD

I’m currently teaching a class to pilot AP Computer Science Principles (will be AP for the first time in the 2016-17 school year). At the beginning of the second semester I decided to deviate from my planned curriculum and drop in a little 3D printing. I had students play with OpenSCAD. OpenSCAD is used to create 3D models with programming rather than more traditional means.
OpenSCAD is really cool for a number of reasons. If students have any experience with writing code they can dive right in. They quickly realize there are many different ways to create the same part, just as there are always multiple ways to get any program to do what you want it to. Most of these ways will involve thinking in 3-dimensional coordinates while also thinking about positive and negative space. Depending on the chosen approach students may also need to bring in a variety of mathematical knowledge and skills they’ve developed over the years.

The task I gave my students was to develop a stand/holder for their own cell phones. It took them a bit to settle into this idea. I kept getting questions like, “Do I need to plan for a case?” To which I’d reply, “I don’t know, does you phone have a case?” I really wanted them to plan for a holder for their own phone.

In the future I’ll need to put some limits on their designs. Most designs were much bigger than they needed to be, many would easily hold an iPad. Maybe I’ll put a limit on the mass of plastic they could consume. I also need to make sure their design will fit the printer. I had one that would not.

After printing their stands they all realized there were problems with their designs, things that were not obvious before they tried using the physical objects. This was a great lesson and gave us a chance to talk about rapid prototyping and iteration. Each student shared their first designs with the class so everyone could learn from each other’s mistakes. The designs were then updated to fix the problems. In the redesign I also had students add in variables for phone size. This would then allow the program to be used to make a holder for any phone by simply changing the values of the variables for phone height, width, and thickness.

Overall I really liked this assignment. Students got to use their programming knowledge in a new way with a new language. I personally delivered no instruction in OpenSCAD. Students had to rely on the principles of computer science they’d already learned, tutorials found on the net, and each other, just as they would in the real world. The task was simple enough that I knew this would not be a problem. I will be doing this again as a planned part of the curriculum next year, but I’ll add in design constraints related to size and total cost of materials.

# Arduino RC Car Part 2

Tony DiLaura asked me about tutorials for high school students to build Arduino controlled RC cars. I didn’t really know of any that I liked so I started outlining what one might look like. This is part two, you might want to check out part one first. This post will be about control mechanisms.

In my last post I said my students had never made remote controlled cars. It turns out this was not at all correct. I’m getting too old and the memory begins to fade. It’s a good thing the internet never forgets. In this post I’ll share some that my students have made in the past. In the next post I’ll dive into ones I’ve seen on the net but haven’t tried yet.

## Wiichuck

OK, this one isn’t radio controlled, but wired instead. It uses the Wii Nunchuck to control your circuit. I suppose if you have a wireless nunchuck you could also make this wireless. If you have to buy a nunchuck this might not be the cheapest option, but I bet one of your students has one at home in a closet somewhere. You can chop the end of the Wiimote plug or you can buy a cheap adapter

• SparkFun \$1.56 – Cheapest and I’ve used this one in the past
• Adafruit \$3.00 – Might be a better option. Looks like it’s designed to snap in and stay in a bit better.
• WiiChuck Page – All about using a WiiChuck with Arduino including a library download
• Lego – Lego Electronic GizmO – Lego robot controlled by Arduino and Wiichuck created by my students several years ago. Includes some sample code. Uses the joystick because the accelerometer was a bit too twitchy for them. That could have been solved with programming.

## TV Remote

We’ve also had luck controlling Arduino robots with old TV or VCR remotes. Be aware that some work far better for this than others. The only way to know is to experiment. This is really in the same price range as the Wiichuck solution and makes your car wireless as long as you have line of sight. In theory, you could also create your own remote using a second Arduino and IR LED, but I’ve never done this.

## Keyfob

I’ve also had students use a keyfob transmitter and receiver. This uses RF and is probably the simplest from a programming standpoint. If your students can program an Arduino to respond to a button press then they know everything they need to to make this work. I don’t have any links to the modules my students used. I can’t remember where I bought them from. Which is probably just as well, they worked, but were not great. However, I did find virtually the same thing on Adafruit’s website. I trust Adafruit to have good stuff.

# Tutorial for an Arduino RC Car?

A buddy of mine recently sent me a tweet:

This is an interesting question the short answer I have is, “No.” The longer answer is a bit more nuanced, so I asked for a little clarification. This is what I got back:

Now I had a lot more to go on. With this in mind I have something to sink my teeth into. Now we have something, so now my response is, “No, I haven’t seen anything that would fit.”

OK, now that that’s out of the way lets cover how I would tackle this problem. Tony is an awesome math teacher in Zeeland, Michigan. He co-teaches a project based math/physics class. I’m going to work from the assumption that he’s working with students starting with little previous knowledge of electronics and Arduino programming, and that he’d like to leave as much room as possible for students to explore. Everything I cover will be with that in mind.

With a project like this you need break it up into pieces. I’m going to think of this as a robot even though it won’t be autonomous because we still will have a computer controlling an independently moving device. As with any robot type project you have three fundamental challenges, the programming, the electronics, and the mechanics. However, with this project we’ll need to consider a forth part I don’t usually think about with a robot, and that is the control mechanism.

## Mechanics

You could go crazy with this and start with a platform like Tuggy from the very cool OpenRC Project. While totally awesome I think this takes all of the thinking away from the students and simply turns them into mechanics. Which is fine if that’s your goal. Instead I’d start with ThinkFun’s MakerStudio collection of building sets.

You can buy sets or download and print from the Thingiverse. I’d start by having students play with the gears and such and make simple cars with parts available, then begin thinking about what their RC car needs. They’ll need to make a variety of decisions. How will their cars be steered? Will they use skid steering (like a tank) or rack and pinion (like a car)? What sort of  platform will they need? I’m not sure a Mac & Cheese box is the best choice. How many motors will they need? Will they use gearbox motors or simple DC motors and then use the gears in the set? Some of these decisions might be made by the teacher and some or all might be left out the students. I’d probably go with simple DC motors and use the gears from the set.

Once these decisions have been made students can then think about the parts in the MakerStudio kits they don’t have but need. Things like motor mounts, rack and pinion mechanisms, bits to mount the gears to the platform of choice, and such. These could should all be designed and 3D printed by the students.

## Electronics

Tony asked for Arduino, so we’ll stick with that. It also doesn’t hurt that I know a lot about using Arduinos with high school students. Unfortunately, you can’t run any sort of reasonable motor directly from an Arduino. You need some sort of transistor or h-bridge. Digital outputs on your Arduino only put out 40 mA, this is woefully inadequate to power a motor.

Students can wire an h-bridge themselves, but I highly recommend using a motor shield. I’ve had many students use an h-bridge and breadboard their circuit which mostly works. There are a lot of connections that need to be made and by the time students got to soldering stuff together numerous problems would typically crop up. In order to get around a lot of headaches I now have students use motor shields and skip all the complex wiring. You can buy shields from China really cheaply, but I like to use SparkFun Electronics. SparkFun is based out of Colorado and they offer an educator discount of 20% and allow you to easily set up payment accounts allowing you to pay via purchase order. The other thing I really like about SparkFun is that they include code example and/or tutorials for almost everything they sell. So I can hand a shield to a student and then point them to the product page and step back.

Most motor shields will allow you to control two motors, perfect for skid steering. If your students chose to go with rack and pinion then you can get away with one drive motor, but you’ll need a servo-motor for steering. There are lots of tutorials for controlling servos with Arduino and ideally where ever you get your motor shield will tell you how to wire your motors to it and give you a simple program to control your motor(s).

## Other Stuff

At this point we just have programming and control mechanism left. I have some ideas about control mechanisms, but I haven’t done any of these in the past. When I say “I” that really means my students. So, I’m going to do a little more research and then another post. More than likely I’ll be looking at some sort of the cool BlueTooth module and an app running on a cellphone or tablet. There are other ways, but controlling a robot with your phone is just too cool.