Drag Knife / Vinyl Cutter


Drag Knife / Vinyl Cutter Machined from 10mm HDPE

The Drag Knife can be used to cut almost anything you would cut with a utility knife, but with the speed and precision of a CNC router. The Drag Knife fits onto your CNC router, making it a universal fit for almost any CNC router available.

Drag Knifes are really handy for cutting soft materials like vinyl, cardboard, mat board, foam, wood veneer, leather, and many others. With flat sheets, you might use one to create some custom packaging for some product, for example, or at least to prototype the packaging.

Cost of build approx. 20 EUR

Bill of Material

1Drag knifeAmazon
1Transfer Film Plotter for VinylAmazon
1Plotter Film Vinyl FilmAmazon
1Cutting MatAmazon
1Compression springsAmazon

Coronavirus SARS-CoV-2 Facts and Infections in Germany over time


At the end of December 2019, Chinese public health authorities reported several cases of acute respiratory syndrome in Wuhan City, Hubei province, China. Chinese scientists shortly afterwards identified a novel coronavirus as the main causative agent.The disease is now referred to as coronavirus disease 2019 (COVID-19), and the causative virus is called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is a new strain of coronavirus that has not been previously identified in humans.

The implications for companies are huge. While companies like Amazon might make huge profits, especially smaller shops suffer.

Corona in Germany

The initial outbreak in Wuhan spread rapidly, affecting other parts of China. Cases were soon detected in several other countries. Outbreaks and clusters of the disease have since been observed in Asia, Europe, Australia, Africa and the Americas.

All federal states in Germany have reported cases of infection with the corona (SARS-CoV-2). The Robert Koch Institut is continuously monitoring the situation, evaluating all available information, estimating the risk for the population in Germany and providing health professionals with recommendations.

Information on the novel coronavirus and hygiene for the general public is available on the website of the Federal Centre for Health Education. Additionally, lots of authorities and health insurances have set up hotlines.

Let facts speak (German)

Corona Dashboard

The Center for Systems Science and Engineering shared an online dashboard which tracks the spread of the deadly coronavirus while it spreads.

The dashboard visualizes data from the World Health Organization (WHO), as well as the centers for disease control in the US, China and Europe. It shows all confirmed and suspected cases of coronavirus, along with recovered patients and deaths.



All federal states have reported cases of infection with the new coronavirus (SARS-CoV-2). The Robert Koch Institute is continuously monitoring the situation, evaluating all available information, estimating the risk for the population in Germany and providing health professionals with recommendations.

Information on the novel coronavirus and hygiene for the general public is available on the website of the Federal Centre for Health Education. Additionally, lots of authorities and health insurances have set up hotlines.






Source: Robert Koch-Institut

12 Outstanding Business Books to Read

There’s no shortage of books about improved efficiency and innovation in business. Most of them are forgettable, but here are 12 business books to read that will change the way you think about strategy, management, products and most importantly your customers.

Ray Dalio – Principles

Dalio shares the principles used in his company, the biggest hedge fund, Bridgewater Associates. Principles is a masterpiece. The main thesis is that finding the truth is the only way to make good decisions. He advocates looking at the company around you as a machine from a higher level with the ability to be tuned.

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Sun Tzu – The Art of War

Know when to fight and when not to fight: Seek higher moral ground and avoid what is strong. How to deceive the enemy: appear weak when you are strong, and strong when you are weak. Know your strengths and weaknesses: You need to know the enemy and yourself. The book requires minimal ability to adapt to the modern world but has strong points.

Peter F. Drucker – The Essential Drucker

Peter Drucker, known as the Father of Modern Management Theory, coined leadership terms and strategies that are still used today. He advocated for a more flexible, collaborative workplace, and the delegation of power. Peter Drucker already anticipated the shift towards a society characterized by entrepreneurship.

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Erik Peterson, Tim Riesterer – Conversations That Win The Complex Sale

Erik and Tim describe in an easy to understand way why deals get stuck in the status quo and what your sales message needs to look like to break this. Because some form of selling is part of everybody’s life, understanding the concepts of The Value Wedge, Power Positions enables you to sell products as well as ideas.


Nicholas A. C. Read, Stephen J. Bistritz – Selling to the C-Suite

To sell requires to create value by helping clients find viable solutions to their problems. During a meeting with high-ranking people, your primary job is not to sell but to help them address their issues. Your goal is to become an adviser. This resonates very well with the co-creation concept and explains partially why it is efficient to do so.

Michael E. Porter – Competitive Strategy

A company’s strategy must depend on its immediately the environment of its industry. Michael describes the competitive situation in an industry as a function of five basic factors (Porter’s Five Forces). The supplier power. The level of threat from new entries. The power of customers. The threat of substitution. The rivalry amongst current industry participants.

Alexander Osterwalder, Yves Pigneur – Business Model Generation

Business Model Generation describes the blueprints of business models of major companies. The illustrative way of describing the process as well as the different models make it an easy, but powerful read.


Marty Cagan – INSPIRED

Inspired is THE must-read for every person working in or with products. The book explains how to create the holy grails in tech industry and focuses on people, culture, product managers, outcomes and process. It significantly influenced the way I think about products.

Stephen R. Covey – 7 Habits of Highly Effective People

The book explains habits highly effective people have. Even though I would have called it efficient, not effective, the mook lists some very good habits. Be Proactive, Begin with the End in Mind, Put First Things First, Think Win-Win, Seek First to Understand, Then to Be Understood, Synergize and Sharpen the Saw. The habits are outwards as well as inwards to have healthy relationships.

Eliyahu M. Goldratt – The Goal

In The Goal, Eliyahu leads the reader through a process optimization journey of a factory floor. Three areas are hereby in focus: Throughput (rate the system generates money through sales), Inventory and OPEX (money to turn inventory into throughput). TOC clearly points out flaws that can be found in all companies such as optimization of local optima. It sharpened my thoughts on Value-Based Pricing.

Benjamin Graham – The Intelligent Investor

Even though he describes some forms of investments, such as savings bonds which might not be as attractive anymore, Graham also explains a very valid investment methodology based on fundamental stock analysis. The goal is to learn how to avoid allowing emotions to control investment decisions. Rather, Graham provides the foundation for making businesslike decisions.

Robert T. Kiyosaki – Rich Dad

Even though I have to say that I’m not a fan of investment and money books, I find the easy to follow way in explaining the terminology around assets and liability as well as the visualization of it very helpful. The core of the book is to invest in assets, which per definition put money in your pocket, whereas liabilities take it out. Reading this book gave me a unified way of thinking about investments.

Undestroyable Drone Case

Carrying or even checking drones on an airplane exposes the fragile mechanics to all sorts of opportunities to break. If the frame has been designed in a CAD program such as Fusion 360, it is very easy to create a undestroyable drone case tough.

Just project the outline and connect the corner points with a spline.

Then extrude the outlines of components such as the FPV camera, the gimbal rails etc at the right height.

The waterproof case has the right size to be taken on a plane as carry-on and allows to create additional layers to fit all required equipment. Please find the PDF version here: Quadcopter Case Foam.

Two Acoustic Panels, cut to length perfectly fit the top rugged drone case to protect the props.

Even though there are specific foam cutter available,  Kaizen Foam can be perfectly cut with a 1/4″ flat end mill on the Shapeoko or other routers at 1524 mm/min.

Watch out for:

  • Adaptive clearing of large pockets needs quite some babysitting though as the foam tends to wrap around the end mill.
  • Kaizen foam layers are around 5mm high. Try to avoid pockets to heights which would result in too little material left till the next layer
  • Align pockets with the height of the Kaizen foam (recommended 30mm)

Affordable Small Batch Production

3D printing enables rapid prototyping but lacks production-ready qualities such as smooth surfaces, temperature resistance and food safety. These attributes however can easily be added by combining 3D printing with casting silicone and urethane plastic for small batch production runs.

As long as you don’t need hundret thounsands of parts, this method should get you up and running without paying a fortune for a silicone injection molding setup.

When selecting mold making materials for 3D printed parts, it is important to be clear about the intended material for mold and cast .

Some points to consider are:

  • Silicone such as Dragon Skin can be extremely difficult to stick to surfaces, except silicone itself. 
  • Urethane plastic such as Smooth Cast 310  is exotherm. This means it gets hot while it’s hardening.
  • Some 3D printing filaments are more temperature-sensitive than others.
  • Some 3D printing filaments are easier to post-process than others.

Having this in mind, the proper materials can be chosen basing on the desired material of the positive.

For PLA the following works nicely:

Final PositiveMoldSeperateSealRelease
Smooth Cast 310Dragon Skin 30Monster ClayXTC-3DEase Release 200 
Dragon Skin 30Smooth Cast 310Sculptex oil based clay XTC-3DUniversal Mold Release

Please note that urethane plastic is exotherm:

  • This requires a non-wax based clay to define the two-part mold. Otherwise the surface in contact with the clay will be full of air bubbles due to the melting wax-based clay.
  • Hot glue is not a good choice for the mold as the glue melts again and the mold leaks. Better use glue + Acryl or Wood + Screws (+ glue)

Applying multiple coats of XTC-3D with sanding (400…1500) in between is highly recommended.

Degasing the silicone and urethane before pouring significantly reduces trapped air bubbles and increases the chance of success.

Other useful items:

1Medicine Cups to mix XTC-3DAmazon
1Mixing Cups for silicone and urethane plasticAmazon
1Craft SticksAmazon
1Safety GlassesAmazon
1Vacuum Chamber for degasingAmazon
1Vacuum Pump for degasingAmazon
1Clay Sculpting ToolsAmazon
1Hot Glue GunAmazon

Raspberry Pi Zero W Enclosure

The 3D model of the Raspberry Pi Zero W is hosted on Thingiverse. This page contains the bill of material, in case you want to build a similar setup.

This setup in combination with a regular 3B has been used for demonstrating “Real-Time” FFT of ADXL345 data via MQTT with Node-Red. The code and documentation can be found on Github.

Bill of Material

1 Raspberry PI Zero W
1 Memory Card
1 Power supply
1 HDMI Adapter (optional but highly recommended)

Extra Long Flight Time Drone

RC Groups


The center board has been glued with HK CA glue (HC-50-175). A small frame with screws through the four beam holder holes kept the sandwich layers aligned.
Note: Better do large areas with this glue outside as it generates a fume.
Using nylon spacers and screws, the top and bottom sandwich were assembled.


The beams were machined with a 1/32″ flat end mill and cut to length in the last run.
M3 nylon screws lock the beams and act as breaking point when crashing.


To attach the electronics to the center board, I chose two different approaches. Components which will not be used in every flight have been attached using Velcro. The other components were glued directly to capton tape I put to the center board. The ESCs were wrapped in capton tape to prevent short circuits. I hope the heat dissipation is reasonably low with the 30A ESCs.

Sandwich Glue

  • HK CA glue (HC-50-175)
  • Loctite Vinyl, Fabric & Plastic Flexible Adhesive
  • HK 30min Slow Cure Epoxy
  • 3M General Purpose 45 Spray Adhesive

Sandwich Bend Test

  • 100x10mm x 1mm CFK, 3mm Fill, 1mm CFK

CFK 1mm, 3k plain weave carbon, orientation parallel (0°/90°) to centerline
Fill +/-45°

Bend test showed best adhesion and no separation up to 6kg for HK CA glue (HC-50-175). All other separated well below this (usually at around 3-4kg). However glueing is tricky for large areas such as the center board.


During the first flights, the flight time was reasonably high at a bit over one hour with 1555 props.


Arms folded away during the first crash (I’d love to call it unplanned rapid decent though :-)) and the M3 nylon screws broke as planned, preventing damages to the rest of the drone.

Flight Time

With this setup, flight times above one hour have been achieved, even including the 180g 3-axis gimbal and GoPro.

In the diagram below various test flights for a 15″ 5.5 and 17″ 6.0 propeller were aggregated to show the effect the prop choice has on flight time.

Update: I’ve updated the battery with a 6600mAh 6S and the quad flies a lot more stable now.

Previously the flight recorder showed motors occasionally maxing out during sharp moves or wind gusts.

I’ll do some test flights and check the flight time. First flight was 2500mAh for 15min

Bill of Material

6 rctimer 5010 360kv NA
3 Multistar Lipo Pack XT90 Amazon
4 Flyduino KISS Amazon
4 1760 Folding Props Ebay
1 Flight Controller and Power Module Hobbyking
1 GPS witd Compass Amazon
1 Receiver Amazon
1 Damping Balls NA
1 Folding GPS Antenna Base/Black Ebay
1 Lipo Voltage Checker Amazon
1 FPV Camera Amazon
1 VTX Amazon
1 Telemetry Radio Amazon
1 Skyfpv Video Switch NA
1 OSD Amazon
2 LC Filter Amazon
1 FPV 3 Axis CNC Metal Brushless Gimbal With Controller For DJI Phantom GoPro 3 4 Banggood
1 GOPRO Amazon
1 pigtail Amazon
1 Silicone Wire Amazon
1 FPV Antenna Amazon
1 Transmitter Amazon
1 Goggles Amazon
2 Goggle Battery

The best 4S LiPo Battery for endurance drones

Flight time depends mainly on the drone weight. In order to get flight times above 1 hour on a single charge (as shown here), the weight has to be minimized. Typically the most dominant weight hereby is the battery. To identify the best battery I created a 4S LiPo Battery Value and Capacity Comparison.

  • Value can be calculated by Capacity / Price)
  • Density can be calculated by Capacity / Weight

The diagram above is sorted left to right by Ranking = Cap /Weight * Cap /Price

See also 6S LiPo Battery Value and Capacity Comparison.