Posts in Category: Projects

A new perspective – the world from above

5 years ago I built my first quadcopters. They flew, they were fast, they had video transmission – but what I didn’t manage with the little time I had was to built one that hovers perfectly still like the DJI drones did. Flow-sensors were pretty expensive and the cheap ESCs and motors in my small drones were probably not accurate enough anyway to allow stabilisation with a imple PID-controller running on an Atmega microcontroller. So after searching for a hand-luggage portable photography drone for years, in november 2019 the DJI mavic mini hit the market. Unfortunately that was during and not before my southeast-asia holiday so there was no rush to get it (and it was sold out anyway).
Long story short, I bought one in february, flew in Dortmund and took the drone to see waves in Costa Rica =) . Pics below ^^

3D-print updates

So… now I have 2 3D-printers. After I got my monoprice mini delta about a year ago, I had some fun with my first 3D prints but clogged nozzles, adhesion problems and the printer printing plastic-wool in the air became more and more frequent and frustrating. I looked into the Ender3 Pro and together with my brother, gifted one to my dad for his birthday. His first prints worked out of the box. So when there was a good offer for the Ender3 Pro just the morning after my mini delta had a clogged heat-throat again, I bought it. Setup took less than 1 hour and besides some parameter related stringing issues, it worked like a charm straight from the beginning.
Like every good 3D-printer owner, I’ve printed many upgrades but also some fun or useful things – and optimized my ‘plane phone holder’.

3D printing a plane-phone-holder

Ok, technically this is a tray-table-phone holder. But it’s most useful on budget airline flights so you can enjoy your netflix-movies from taxiing to touchdown since your tray-table stays folded up. I’ve started with a fixed design for my Phone size and iterated to an extendable, foldable phone holder. I’ve used different revisions on flights from Eurowings, WizzAir, Ryanair (the magazine-pocket in the table-less seats works as well) as well as trains.
All printed on a Monoprice Mini Delta (my first 3D-printer) with different settings and different PLA-Filaments. Print-time for the last model is ~2h20min but includes a raft and massive support on edges and holes.
an M3 10/12mm screw and self-securing nut is required besides a rubber band.

My first 3D-Printer

I’ve thought about getting a 3D-printer for years but little time and reviews about bad results on the cheaper printers without massive modifications and tuning kept me from buying a printer. Also, I didn’t really need it, I just wanted to have one :D.
In spring of 2019, some colleagues convinced me to look into it again and I came across the pre-assembled, self-levelling Monoprice Mini Delta model which apparently has good results out of the box.
It arrived; the prints looked quite good but I’ve had my fair share of modding and trouble with it anyway :D.
Clogged nozzled, broken throat, under-extrusion, adhesion problems… I added rubber.dampening, fireproof-foam-covers, a noctuna fan for the extruder and electronics cooling, a glass-printbed, lots of PTFE-Spray… Unfortunately, swapping the drivers for TMC2208 drivers didn’T work due to a switch in the drivers and footprint on my revision.
Long story short; it’s a nice start but if you are willing to spend a little more time and money, the famous Ender 3 Pro with a BL-Touch addon might be better suited.

Mini-Load – a resistive load for testing and prototyping

When developing electronics, it can be useful to have a way to draw or measure a specific current. While professional digital loads are quite expensive, a high-wattage resistor is sufficient in many cases. To have a small ( 16,5 x 10 cm), universally usable resistive load, I ordered a selection of resistors that allow me to draw commonly used currents like e.g. 50mA, 100mA, 200mA, 0.5A, 1A… for the common voltages of 3.3V, 5V or 12V. Additionally I included 0,1 Ohm resistors as shunts for measuring the current. To facilitate the combination of the used resistors to the desired total resistance, I placed the terminals at 19mm to use existing lab-socket jumpers and decided to connect the left & right resitor permanently. While this has the drawback of not allowing concurrent use for 2 outputs at the same time, it reduces the amount of required cables as well as plug/socket and cable resistances and inductances.

Costs ~ 55 €
Time ~ 3 h (excl. planning 😉 )
Materials used:
– 2x resistors WD25 (25W) 0,1 Ohm [5 €]
– 2x resistors WD25 (25W) 1 Ohm [4 €]
– 2x resistors WD25 (25W) 3,3 Ohm [4 €]
– 4x resistors WD25 (25W) 10 Ohm [7 €]
– 4x resistors WD25 (25W) 100 Ohm [7 €]
– 1x aluminium heatspreader 160 x 100 x 40 mm [ 15 € ]
– 2x aluminium stripe (320 x 10 x 2mm, bent with 90° angles as 10-70-160-70-10 ) [1,5 €]
– 1x aluminium stripe (250 x 10 x 2mm, bent with 90° angles as 45-160-45 ) [0,5 €]
– shrinking tube for isolation of the ‘feet’ [0.5 €]
– 40x short self-cutting screws (e.g. 9,5 x 3 mm) [2 €]
– 21x colored 4 mm lab-plug terminals [4€]
– solder-wire & desolder-wire (or some fine copper-mesh / wire)
– thermally conductive adhesive tape (double sided) [4 €]

– drilling machine (preferably with a stand for 90° angles)
– soldering iron
– scalpel / cutter / scissors for the tape
– Isopropanol as drilling lubricant
– 2.5 / 8 mm drills (preferably sharply cut, cobalt coated drills)

The ‘Schollenspiel’ – more LEDs than you can count

tldr; In 2015, the student representatives for electrical engineering at RWTH Aachen university rebuilt an awesome childhood game.

While I was studying at RWTH Aachen University, I was part of the student representatives for electrical engineering (FSET) for a few semesters. We were elected each semester and besides representing the students in different bodies within the university, we were in charge of welcoming the new students. Luckily, a fund from the university allowed us to spend money specifically for the new arriving students each year for things like building games, renting an inflatable human-soccer-field or having a BBQ. One time in march 2015 I received a message from a friend while I was on holiday: “Martin! do you know the ‘Arktos Superspiel *(1)’? From Tabaluga TV? Do you think we can build this for the first semester student welcome?” I remembered an ‘ice-field’ represented by hexagonal, lit up plates where the children on the TV show were shown a ‘safe path’ step by step. Then, the markings disappeared and they had to walk across the field by remembering the path. Awesome idea, I thought and replied Well, it’s gonna take a lot of hard work and probably ~3000€ for the materials but yeah, sure we can!”.
After being back from my south-america-trip , we started brainstorming and prototyping. Thanks to many helping hands, we recreated this childhood-memory as a game with 60 fields for the first semester students and even won a price at the university.
The game is built as a set of 20 modules with 3 ‘ice-fields’ and an RF-module each; supplied by 10 computer-power-supply-modules. 2 transport-wagons were allowed us to store and transport the game and a software with a GUI allowed an easy, setup and automatic generation of the ‘path’ as well as measuring the missteps.
  • 14.940 LEDs (=249m of LED Strip with 60 RGB LEDs/m cut in pieces)
  • about 10.000 solder-points on 20 PCBs with 1484 holes drilled manually
  • more than 250m  of wire in 4.560 individual pieces
  • many square meters of 18-24mm thick, robust wood (60 hexagons, 360 frame-pieces with ~720 holes drilled
  • 20*2,4GHz Clients, 1 Masterbased on nrf24 and arduino nano like PCBs
  • roughly 4.000 (unpaid) man-hours invested by different students (thanks to an incredible amount of coffee)

=>  about 4.000 watt power-consumption and lots of fun!

It’s important to note that all of us worked without pay and spent many hours of our free time (even during the exam phase) to create an awesome experience for the first semester students. Thanks again to everyone who helped to realize this idea!

Some of the main issues we encountered:

  • LEDs emitt light at an angle of up to 130° but if the glass is palced too close to the LEDs, individual LEDs are visible. We tried different acrylic-glasses up to 8mm but girl’s heels or small stones in the profile of a shoe could still have broken the acrylic glass with 50-100kg being concentrated on 1 spot. For a homogenous light-effect, we would have needed at least 3cm between the LEDs and the ‘glass’-surface while being able to withstand high pressure. The only solution that might have offered these properties would have been translucent resin or at least 12mm acrylic glass mounted around the edge. Both are options that were out of our budget so we settled for thin, 3mm acrylic glass with ice-optics being placed on the silicone-film of the water-resistant LED-strips.
  • Pressure sensing was another task we had to solve. We tried load-cells, capacitive or optical measurement with spring-loaded inner-hexagon-plates, pushbuttons and piezo-electric force-sensors. In the end, the simpelest solution was the best: ESD-foam! The black foam used for packing electronics has a high electrical resistance (but is conductive). When the foam is compressed, many ‘bubbles’ form a short circuit and the resistance decreases by a huge factor ( 10kΩ to 5.5kΩ ) so we didn’t even need operational amplifiers . The foam also expands itself afterwards. For this, we placed a copper-strip on the bottom of the hexagon-frame and on the bottom of the LED-plate with a piece of 4mm thick foam inbetween.

Ps: To avoid any risk for the students / children that might play the game, we kept all self-built parts at the 12V-level and used standard PC-power-supplies to power the game.
(*1) The name ‘Arktos superspiel’ is most likely trademarked by Tabaluga TV but not know outside of the german speaking community. If you want to know more about the game, feel free to google the name and rewatch some old episodes on their channels/websites

Building a micro Quadcopter (130mm)

180mm was still quite big and the frame wasn’t really built for folding so I went down to 130mm. Here you can see a few pictures of my first built which I have since crashed and disassembled a few times :D. New parts are on their way so you can expect some new builds around the 130-180mm size in the next months.

Building a smaller quadcopter

After my first experiences with a QAV250, I wanted to build something smaller and possibly foldable. I found a nice QAV180 frame which might work and started anew. This time, I had a faulty motor with some broken isolation resulting in smoke during the setup and a broken ESC which sometimes failed to start the motor unless given full throttle. After initial tries and a switch to BLHeli ESCs, I added an FPV camera and had some test-flights but calibration turned out to be really hard with a constant drift. I later figured out that one of the sticks on my 9XR remote had an abnormality: While moving straight along the Y-axis, it still showed some value-change to the X-axis as well in the form of a bump to the side reaching to about +15% near the 50% y-axis-setting but sticking to 0% for 0 or 100%.