This is one of a series of posts documenting my approach to teaching robotics in a year 11/12 Engineering Design class. The students are 16- to 19-year olds and we typically have three ~90 minute classes per week.
For the first couple of weeks of the school year, I like to use introductory robotics challenges. One very pragmatic reason for this is that, for a variety of reasons, we tend to have lot of movement between classes during the first few few weeks. For example, during this second teaching week, I had four newcomers in my class.
I find that Steepest Incline works not only well as introductory activity, but also provides an opportunity for another “free build” challenge before I have everyone make the standard Robot Educator Model.
The challenge: Design and build a vehicle that is activated by a touch sensor, climbs the steepest incline, and stops at the top.
For the ramp, I use a long piece of shelving (1800m x 295mm x 16mm melamine-coated particle board) propped against the edge of a table. This gives a roughly 25 degree slope, which happens to provide a slope that’s fairly achievable with the parts in the EV3 kit.
A spirit level phone app provides an easy way to measure the angle of the ramp.
When I introduced the challenge this year, I had a pang of regret that I should’ve brought in a selection of wheels and tracks, but I’m glad I didn’t. It’s pretty obvious that friction would make a big difference, but with everyone using the same wheels (as well as the same motors) from the EV3 kits, it highlighted many of the other differences, such as shape (long and thin v wide wheel bases), centre of mass, and gearing. In the future, however, if I wanted to allow more time for this challenge, and particularly if I wanted to focus on the physics involved, I might bring in a selection of wheels and tracks, but only after everyone has had a first pass at a solution.
Note this is a variation of the Ramp Climber challenge.
I think the main difference in the way I typically run this challenge is in requiring sensors to be used to start and stop the robot. Framed in this way, the challenge works well as a very basic intro to programming, including how to download a program, the difference between “wait for sensor” and “sensor” blocks, and even really simple things like the difference between the motor and sensor ports.
Although I ask the students to use a touch sensor to start their robots, I deliberately don’t specify how I want the robots to stop at the top of the ramp. I usually don’t even mention sensors at all. Realistically there probably aren’t that many different options but, as always, I like to leave room for alternates wherever possible. At the very least we can have a discussion about the pros and cons of the different sensors. Some ideas that typically emerge include:
- Setting the motors to move a fixed number of seconds (or rotations or degrees) is not particularly reliable. For example, performance will vary as the motor power changes or the robot’s wheels might slip. A better approach is to turn the motors on until (or while) a particular sensor value is read.
- Using either an ultrasonic sensor or a light sensor to detect the end of the ramp tends to be much more effective and reliable than using a second touch sensor (e.g. using the weight of the robot to press a touch sensor against the ramp), especially if the touch sensor is positioned in a way that compromises the wheels’ contact with the ramp.
- Students who want to use a light sensor (e.g. set to reflected intensity mode) sometimes ask for a strip of black tape at the top of the ramp. It’s interesting to provide this, let them get their robot working, and then remove the tape and see what happens. It turns out that the tape isn’t needed, since the reflected light intensity mode will read the same as black (or more likely lower) when it goes off the end of the ramp. It’s a great teaching moment.
- Instead of (or in addition to) using a sensor to detect when the top of the ramp is reached, what about having a mechanical solution? e.g. once the wheels drive off the top of the ramp, they lose contact with the surface and the robot gets stuck in position, possibly with a hook that drops over the edge.
I have mixed feelings about sharing sample solutions, but appreciate they might be useful if you need some reassurance that you’re on the right track. To that end, here are a couple of possible approaches, intended for teachers. Please don’t share these with students, or at least not until they’ve experienced some productive struggle [external link].
This is approach is possibly the simplest.
Here is another approach that I quite like. A feature of this approach is that once the robot starts moving, it will stop either when it gets to the top of the ramp or if it is picked up, and will keep moving as soon as it is put back down on the ramp.
As with many of the classic challenges that I’ve done at workshops for teachers, I have a handout prepared for this challenge, but as I said in this earlier post, I wouldn’t normally print it out. Instead I normally display it on a projector when giving the challenge to my students.
Download: Steepest Incline 2019 (PDF)
Incidentally, if the robots are allowed to start on the ramp (i.e. with no requirement that they be able to drive onto the ramp), it can be treated as a very different problem. I’ve seen robots that can climb not only vertical slopes, but even slopes that go beyond 90 degrees. i.e. the robot is climbing the slope upside down! I don’t tell the students about these solutions, preferring to see what they can come up with for themselves.
But, just in case you’re wondering what I’m talking about…. (warning: spoiler alert!)
I also added the no grappling hooks rule after someone was given a version of this challenge and were told they could only use the contents of a single EV3 kit. This terrible person then tied one end of the USB cable onto a hook made out of LEGO and rolled the other end onto a makeshift LEGO spool at the other. (And in case you’re wondering, it wasn’t me. Nobody saw me. You can’t prove anything!)
In the past, this challenge has been finished in a single lesson, but this year I felt it needed a little more time to run its course, so let it spill over into a second class. In total, we spent about 2-3 hours of class time on it.
Download: Steepest Incline 2019 (PDF)
Once we had finished, I asked each team to build the Robot Educator Model Drive Base [external link] in preparation for a series of challenges that would focus on some programming techniques, starting next week with a whole-class challenge.
In the meantime, however, I needed a quick challenge for the speedier teams to work on while they were waiting.
Challenge: Program a robot to drive around four chair legs in a “figure 8” pattern.
The set up is something like this. I usually use a few pieces of tape to mark a couple of the chair legs, and a starting line.
Although this is of course a fairly straight-forward challenge, I find it useful for exploring different ways of making a two-wheeled robot turn, including:
- turning on the spot (with both wheels turning in opposite directions),
- one wheel fixed, or
- both wheels moving forward but at different power levels.