Lego EV3 Ball Launcher

When I added the paintball launcher to GEARS (https://gears.aposteriori.com.sg), I wanted it to…

  • Have controllable launch power
  • Works with a single motor
  • Be plausible to implement with Lego parts

I eventually decided on a control scheme where the motor is turned in reverse to pull back the “spring”, and turned forward (…by any amount) to trigger the launch. Launch power is controlled by the amount of pull back; the more you pull back, the greater the eventual launch velocity.

This control scheme addresses the first and second requirements, but is it plausible to implement it with real Lego parts? I’m pretty sure I cannot match the size and performance of the simulated paintball launcher, but I wanted to make sure that it’s possible to build a device that can at least achieve the same functionality.

I built this ball launcher as a proof-of-concept. It uses a single medium motor to both pull the rack back and trigger the launch, in the same manner as the simulated paintball launcher in GEARS. The key to the way it works lies in the…

  • Pivoted pinion gears
  • Ratchet mechanism

Pivoted Pinion Gears

A couple of rubber bands pull this upwards to mesh with the rack, but with sufficient force, it can be pushed down to release the rack and allow it to shoot forward.

Pivoted Pinion Gears

Ratchet Mechanism

The ratchet mechanism allows the pinion to turn freely clockwise (…when pulling back the rack), but when the pinion attempts to turn counter-clockwise (…forward direction), the pawl will engage, causing the pinion to push itself downwards instead. This disengages the pinion from the rack, allowing it to shoot forward and launch the ball.

Ratchet Mechanism

Results

As expected, the launcher’s performance is underwhelming; the ball can’t travel more than a few centimeters before hitting the ground. But as a proof-of-concept, it demonstrates that the control mechanism used in the simulator is viable in real life.

To improve performance, we can increase the number of rubber bands. Increasing the length of the rack to allow the rubber bands to be stretched more could help, but that may also worsen performance by increasing the amount of dead weight that needs to be accelerated forward. If the velocity is increased, it may also be a good idea to add some kind of damper at the front to prevent damages to the plastic parts.

If you managed to build a better launcher with the same control scheme, send me a video and I’ll link to it here.

All-In On VEXcode VR (for now…)

As we were looking around for best practice solutions to continue teaching Robotics in the virtual classroom, VEX announced its release of VEXcode VR. Besides being made free for public and educational use, the VEXcode VR platform was designed an equalizer, so that no matter what device you had access to, you could participate in online STEM learning.

This platform just ticked the box for all of the requirements that were suddenly coming fast and furious from schools, who wanted to resume enrichment programs through virtual classrooms:

  • Robotics Simulation
  • Block Programming + Python API
  • Simulated Sensors & Actuators
  • Algorithmic Challenges – not just hard-coding paths
  • Fun to play with!
  • Soft Hardware Requirements – Can be used on iPads or other Tablets
  • Enough depth for 1-2 months of lessons (wishful thinking)

There’s an Art Canvas for Turtle programming, a Maze for path creation and algorithmic way-finding, a Castle for a bumper/crasher game, an electromagnet-based game challenge for collecting game elements on the field. Grids that can be used to teach some abstract math concepts, like 2D coordinate systems. It’s quite robust, too!

Is it a perfect platform? No.

Some glaring issues:

  • No way to simulate line-following, one of the main use-cases of Robotics competitions in primary and secondary school level events.
  • No way for two robots to interact on a single game field concurrently
  • No way to design robots
  • No moving actuator (only an electromagnet)
  • A too-perfect simulation, physics engine-wise
  • Limited scope with no obvious pipeline of expansion

Still, we want to thank VEX and Innovation First for their generous and timely release.
If nothing else, it has piqued our interest again in creating our own Robotics Simulation toolkit (TBC).

Applied Learning Program – Online

So far 2020 has been a long parade of kicks in the butt! But, A Posteriori has always possessed a great sense of humor, and while we take the utmost precautions dealing with the COVID-19 pandemic, and strictly adhere to health regulations, we have also tried to keep up with programs and offerings for our students.

In April, we moved online to conduct part of our Applied Learning Program (ALP) in Electronics, Programming, Design Thinking on the theme of Active Living. We managed to get the students to take physical kits home, and setup virtual classrooms of Discord mainly. Discord, which is free, has a natural “room” or “team” setup, so we could work with multiple design groups separately and almost concurrently – similar to walking around the classroom from desk to desk. Except it wasn’t, and only a half or so of the secondary school students managed to participate actively for the online duration of the program.

I learned to respond to the name Cher.

Some of the results were really great:

Dance Dance Revolution console for disabled people – large 4-button distributed keyboard that can be used by any combination of whole or damaged limbs. The project used Makey Makey to receive game control input, and an Arduino with PulseSensor to monitor heart-rate.

Several jumping, push-up, or hand exercise virtual games with playful characters responding in real-time. Mostly utilizing ultrasonic and PIR sensors.

Game Design Sample

A Cyclotron using simple IR reflective sensor with Arduino.

Several lock boxes – for your smartphone – that unlock after some heartrate has been achieved for a specified duration.

We really had fun supporting this cohort of Sec-2 students.

BTW – not this one:
“cher” as in short for teacher:

Water Rockets with micro:bit

We didn’t plan on running any holiday programmes in March this year, but a group of parents requested for it, so we came up with the idea of combining water rockets with micro:bits. The micro:bit is used to measure flight acceleration, and can also be used to measure flight time.

In the morning, the kids learned about how rockets work and tested different stabilizing fins designs. Then after lunch, they constructed their rocket, programmed the micro:bits, and drop-tested it before the actual launch. We didn’t have time during this one-day programme for everyone to construct their own launcher, so we used one that we’ve built the day before.

Solar Eclipse 2019

On 26 Dec 2019, Singapore experienced an annular eclipse. As a service to the community, we ran a free programme open to the public. Had a good turnout with about a dozen kids, and a surprising number of adults from the nearby businesses joined in as well.

We started with the science behind solar eclipses (slides are here if you want to use it for your own eclipse activities)…

Everyone built their own pinhole viewers…

…but the one I prepared was a little bigger than the rest…

…bigger viewers produces a larger image

We mounted a few Shade 12 welding glasses to cardboard frames for direct viewing…

As well as some lenses and mirrors for projection onto a wall…

…a big hit for photo taking

A micro:bit was used to track and generate a live plot of the light level as the eclipse progresses. Didn’t take any photos of the micro:bit setup, but we wrapped it with some packing foam to diffuse and attenuate the light.

Light level reached a minimum at around 1330H, before rising again. The frequent short and steep dips are due to cloud cover.

Looking forward to the next one in 2063!

Marine Expedition (Nov 2019)

This is our second run of the Marine Expedition programme. This time, the kids’ creation includes…

Pentamaran with 2 fans and 4 paddles

All directional fan boat with a catamaran base

Doggy paddle boat (…with two hidden waterjets)

Marine Expedition Completed!

The Marine Expedition Sept program is now over! But we’ll be running more programs during the year end holidays, so watch this space for updates, or better still, drop us an email and we’ll notify you when the programs are ready for registration.

You’ve already seen the boats that our participants built, so here’s a photo of a hydraulically controlled panther that was built by another participant.

Music with water and micro:bit!

An explosive end to our electrolysis experiment.

Marine Expedition Preview

We had a preview run of the Marine Expedition programme for our regular students who couldn’t make it for the Sept camp. One of our students designed and built this trimaran, driven by a centrifugal pump jet and controlled with a micro:bit.

The pump jet is rather under-powered for the size of the boat, but it’s low power demands and easy installation makes it a good choice for use as station keeping or maneuvering thrusters. Other choices for boat propulsions includes propellers, paddle wheels, fans, and many more.

If you would like to join the Marine Expedition programme, there are still a few days left to sign up here. We also do fun and educational stuff like this and more during our regular classes. Contact us to find out more.

Those who can both do and teach…

When we founded A Posteriori, we wanted to make sure we didn’t lose focus of our previous careers as engineers and software developers.  We wanted to stay relevant in both the Commercial industry as well as find a niche in Education.

Besides creating our new STEM education business, developing original curriculum, and teaching at MOE and International Schools, last year we also ground our teeth on a wall-climbing robot, which we exhibited at the Singapore Robotics Games event. We won a Unique Design award for our efforts.

Early draft

This year we developed and sold a custom-made product to the Ministry of Health’s National Medical Research Council (NMRC) to help with anonymized grant-proposal decision-making events.  The product, an Audience Response System (ARS), went live last month and I was extremely proud seeing it used last week. Our clients and their end-users had nothing but praises for our work, and a list of feature enhancements, of course. We look forward to working with the Ministry of Health and the NMRC on other projects in the future.

A Posteriori is not just about LEGOs and Drones.

We intend to continue to make real products, some just for fun or artistic value, and some for creating commercial or scientific value.

And we hope to take our students on some of our Making adventures in our new Mega MakerSpace & STEM Learning Center.