E-Bikes Turned Solar Car

October 9, 2023 by Danie Conradie 20 Comments

There is something to be said for a vehicle that gains range just by standing outside in the sun. In the video after the break, [Drew Builds Stuff] demonstrates how he turned a pair of bicycles into a solar-powered vehicle.

The inspiration for this build started with a pair of 20″ steel framed fat tire bikes [Drew] picked up in a liquidation sale. He welded up a simple steel chassis, and attached the partial bicycle frame and forks to the chassis, using them as steerable front wheels. A short arm was welded to each of the fork, linking them together with threaded rods and rod ends that connect to centrally mounted handlebars. The rear driving wheels are from a 20″ e-bike conversion kit, with the disk brake assembly from the cannibalized bikes.

The solar part of this build comes in the form of three 175W flexible solar panels mounted on cedar frames, coming in at 10 lbs per mounted panel. [Drew] considered using conventional rigid solar panels, but they would have been 4-6 times heavier. The two panels mounted to the rear of the vehicle are on a hinged frame to allow easy access to the electronics below. Battery storage is made up of two 24V 100Ah batteries wired in series, connected to a 60A solar charge controller and the e-bike motor controllers.

The vehicle has a top speed of about 45km/h and 100km range on batteries alone. It might not be fast or engineered for maximum efficiency, but it looks like a ton of fun and relatively simple to build. As [Drew] says, it’s not a how-to for building a perfect solar-powered vehicle, it’s how he built one.

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Marionette 3D Printer Replaces Linear Rails With String

October 8, 2023 by Danie Conradie 28 Comments

In the early days of FDM 3D printing, the RepRap project spawned all sorts of weird and and wonderful designs. In the video after the break [dizekat] gives us a throwback to those times with the Marionette 3D printer, completely forgoing linear rails in favor of strings.

The closest thing to a linear guide found on the Marionette is a pane of glass against which the top surface of the print head slides. A pair of stepper motors drive the printhead in the XY-plane, similar in concept to the Maslow CNC router, but in this case two more strings are required to keep the mechanism in tension. To correctly adjust the length of the string across the full range of motion, [dizekat] uses a complex articulating pulley mechanism that we haven’t seen before. The strings are also angled slightly downward from the spool to the print head, holding it in place against the glass.

The bed print bed is also suspended and constrained using string, with no rigid mechanical member attaching it to the frame of the printer. Six strings connected to the sides and bottom of the bed frame constrain it in 6-DOF, and pass through another pulley arrangement to three more strings and finally to a single stepper driven belt.

We can’t see any particular advantage to forgoing the linear rails, especially when the mechanisms have to be this complex, but it certainly make for an interesting engineering challenge. Whatever the reason, the end result is fascinating to watch move, and the print quality even looks decent.

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Control Tricks For Tailsitters

October 7, 2023 by Danie Conradie 5 Comments

An RC VTOL aircraft always makes for a compelling project, but ensuring the transition between hover and forward flight can be quite challenging. In the video after the break, [Nicholas Rehm] demystifies of the flight control algorithm required for a VTOL tailsitter.

Tailsitters are one of the simplest VTOL arrangements, the testbed here being a simple foam KF airfoil wing with two motors and two servo-controlled elevons. As with almost all his projects [Nicholas], uses of his open-source dRehmFlight flight controller to demonstrate the practical implementation of the control algorithm.

Three major factors that need to be simultaneously taken into account when transitioning a tailsitter VTOL. First off, yaw becomes roll, and vice versa. This implies that in hover mode, elevons have to move in opposite directions to control yaw; however, this same action will make it roll in forward flight. The same applies for differential thrust from motors — it controls roll in hover and yaw in forward flight. Nevertheless, this change of control scheme only works if the flight controller also alters its reference frame for “level” flight (i.e., flips forward 90°). As [Nicholas] demonstrates, failing to do so results in a quick and chaotic encounter with the ground.

With these adjustments made, the aircraft can transition to forward flight but will oscillate pitch-wise as it overcorrects while trying to maintain stable flight; this is due to PID gains – 3rd factor. The deflection required by control surfaces is much more aggressive during hover mode; thus PID gains need to be reduced during forward flight. A final improvement involves adding a brief delay when switching modes for smoother rotation.

For more interesting VTOL configurations, check out [Tom Stanton]’s RC V-22 Osprey, and this solar recharging trimotor

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A Spinning Egg For Your Thoughts

October 1, 2023 by Danie Conradie 15 Comments

Brushless motors are fascinating devices that come in all sorts of shapes and sizes, but you’ve probably never seen one in the form of a free-spinning shiny metal egg. Created by [David Windestål], [Giacomo Di Muro], and [Chad Kapper], the Motion Zero is part top, part brushless motor, and fully mesmerizing. Tech overview video after the break.

Like the classic Tippe Top toy, an ovoid shape like this shiny metal egg will stand on its end if it’s spun fast enough. To do this, the team embedded magnets in the metal egg, effectively turning it into a rotor. An array of 4 PCB coils under a smooth concave surface serves as the stator. Because the egg is not held in position by a shaft, hall effect sensors were incorporated to determine the position of the egg, and properly control the state of the coils to keep it spinning.

Recognizing how easy it was to get lost in thought while staring at a shiny spinning egg, the rest of the device was designed with meditation in mind. The top cover is a block of aluminum machined with ripple patterns, with ball bearings that slide between the ripples as the control interface. Additional hall effect sensors on the PCB determine the position of the balls to adjust the rotation speed and shut-off timer. You can even choose to make the egg move around or remain in one position. The main controller is an ESP32 module, which reads all the hall effect sensors and controls the coils via motor drivers.

The Motion Zero has made its debut on Kickstarter and already exceeded its initial funding goal. We like the creators’ willingness to share the inner workings of a product that manages to transform a simple concept into a mesmerizing piece of engineering artistry.

We’ve seen a good bit of [David Windestål]’s has a fascination with weird tech over the years, like racing belt sanders, fire breathing waterfowl, tri and bicopters. He even built a prop anti-drone RF cannon for a movie.

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Autonomous Racing Drones Are Starting To Beat Human Pilots

September 28, 2023 by Danie Conradie 32 Comments

Even with all the technological advancements in recent years, autonomous systems have never been able to keep up with top-level human racing drone pilots. However, it looks like that gap has been closed with Swift – an autonomous system developed by the University of Zurich’s Robotics and Perception Group.

Previous research projects have come close, but they relied on optical motion capture settings in a tightly controlled environment. In contrast, Swift is completely independent of remote inputs and utilizes only an onboard computer, IMU, and camera for real-time for navigation and control. It does however require a pretrained machine learning model for the specific track, which maps the drone’s estimated position/velocity/orientation directly to control inputs. The details of how the system works is well explained in the video after the break.

The paper linked above contains a few more interesting details. Swift was able to win 60% of the time, and it’s lap times were significantly more consistent than those of the human pilots. While human pilots were often faster on certain sections of the course, Swift was faster overall. It picked more efficient trajectories over multiple gates, where the human pilots seemed to plan one gate in advance at most. On the other hand human pilots could recover quickly from a minor crash, where Swift did not include crash recovery.

The final results are impressive, especially given that all the processing and sensing comes from the drone. However, it still requires a well mapped track, so a human pilot should still come out on top given limited information about a new track. It would also be interesting to see how it handles large courses with gates that are much further apart.

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Exploring The Tech Behind Concert LED Wristbands

July 1, 2023 by Danie Conradie 15 Comments

LED wristbands are now a common feature of large arena concerts and events, with a variety of capabilities and technical implementations. In the video after the break, Wall Street Journal does a fascinating deep dive into these wearable light shows.

The three main control technologies are IR light, RF radios, and Bluetooth. The IR-controlled ones are the simplest, and we’ve covered a teardown, a reverse engineering effort and reflash of the Pixmob IR armbands.

Finally, we get a good behind-the-scenes look at how they are controlled. Using pan-tilt IR emitters mounted on lighting towers, the operators can sweep across the audience controlling color and light levels or activating pre-programmed sequences.

The full control setup for RF wristbands, with transmitter on the left.

RF armbands have the simplest control setup, only requiring a single portable transmitter connected to a computer running the control software. It does however require some pre-planning for more complex light displays, to ensure each section of the audience is individually addressable.

The most advanced and expensive versions are handheld light sticks controlled via Bluetooth from an app on the users smartphone, and are popular at K-Pop concerts. Each device is linked to the users seat number, making them individually addressable and allowing the lighting operators to produce complex patterns, and even text, in the crowd.

While each of these devices is simple and underwhelming on its own, tens of thousands working together produce impressive effects and probably hide some hard-earned engineering experience.

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No Frills Autonomous Lawnmower Gets The Job Done

June 21, 2023 by Danie Conradie 19 Comments

[Nathan] needed an autonomous mower to help on the farm, so he built his own without breaking the bank. It might not be the prettiest machine, but it’s been keeping his roads, fences and yard clear for over a year. In the video after the break, he gives a detailed breakdown of its build and function.

It’s built around a around a simple angle-iron frame with a normal internal combustion push mower at it’s core. 18″ bicycle-type wheels are mounted at each corner, each side driven by an e-bike motors via long bicycle chains. Nathan had to add some guards around his wheel sprockets to prevent the chains slipping of due to debris.

Al the electronics and the battery is simply mounted on top of the frame, away from the motors to avoid magnetic interference with the compass. The brain of the system is a Pixhawk autopilot with a GPS module running ArduPilot, a staple for most of the autonomous rovers, boats and aircraft we’ve seen. The control station is just a Windows laptop running Mission Planner, with a 900 MHz radio link for comms with the mower. [Nathan] also gives a overview of how he uses a spreadsheet to set up waypoints.

This lawnmower’s straightforward design and use of easy-to-find components make it an excellent source of inspiration for anyone looking to build their own functional machine.

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