Spin-Casting This Telescope Mirror In Resin Didn’t Go To Plan

June 3, 2025 by Lewin Day 26 Comments

For most of us, mirrors are something we buy instead of build. However, [Unnecessary Automation] wanted to craft mirrors of his own for a custom telescope build. As it turns out, producing optically-useful mirrors is not exactly easy.

For the telescope build in question, [Unnecessary Automation] needed a concave mirror. Trying to get that sort of shape with glass can be difficult. However, there’s such a thing as a “liquid mirror” where spinning fluid forms into a parabolic-like shape. Thus came the idea to spin liquid resin during curing to try and create a mirror with the right shape.

That didn’t quite work, but it inspired a more advanced setup where a spinning bowl and dense glycerine fluid was used to craft a silicone mold with a convex shape. This could then be used to produce a resin-based mirror in a relatively stationary fashion. From there, it was just necessary to plate a shiny metal layer on to the final part to create the mirror effect. Unfortunately, the end result was too messy to use as a viable telescope mirror, but we learn a lot about what didn’t work along the way.

The video is a great journey of trial and error. Sometimes, figuring out how to do something is the fun part of a project, even if you don’t always succeed. If you’ve got ideas on how to successfully spin cast a quality mirror, drop them in the comments below. We’ve seen others explore mirror making techniques before, too.

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Wire-frame image of gearbox, setup as a differential

Roller Gearbox Allows For New Angles In Robotics

May 22, 2025 by Ian Bos 17 Comments

DIY mechatronics always has some unique challenges when relying on simple tools. 3D printing enables some great abilities but high precision gearboxes are still a difficult problem for many. Answering this problem, [Sergei Mishin] has developed a very interesting gearbox solution based on a research paper looking into simple rollers instead of traditional gears. The unique attributes of the design come from the ability to have a compact angled gearbox similar to a bevel gearbox.

Multiple rollers rest on a simple shaft allowing each roller to have independent rotation. This is important because having a circular crown gear for angled transmission creates different rotation speeds. In [Sergei]’s testing, he found that his example gearbox could withstand 9 Nm with the actual adapter breaking before the gearbox showing decent strength.

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Series of purple and red mechanisms are stretched from left to right. Almost like arrows pointing right.

Compliant Mechanism Shrinks Instead Of Stretching

May 16, 2025 by Ian Bos 16 Comments

Intuitively, you think that everything that you stretch will pull back, but you wouldn’t expect a couple of pieces of plastic to win. Yet, researchers over at [AMOLF] have figured out a way to make a mechanism that will eventually shrink once you pull it enough.

Named “Counter-snapping instabilities”, the mechanism is made out of the main sub-components that act together to stretch a certain amount until a threshold is met. Then the units work together and contract until they’re shorter than their initial length. This is possible by using compliant joints that make up each of the units. We’ve seen a similar concept in robotics.

Potentially this may be used as a unidirectional actuator, allowing movement inch by inch. In addition, one application mentioned may be somewhat surprising: damping. If a structure or body is oscillating through a positive feedback loop it may continue till it becomes uncontrollable. If these units are used, after a certain threshold of oscillation the units will lock and retract, therefore stopping further escalation.

Made possible by the wonders of compliant mechanics, these shrinking instabilities show a clever solution to some potential niche applications. If you want to explore the exciting world of compliance further, don’t be scared to check out this easy to print blaster design!

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Five Oddest Op Amp Applications

May 6, 2025 by Al Williams 25 Comments

You think of op amps as amplifiers because, no kidding, it is right in the name. But just like some people say, “you could do that with a 555,” [Doctor Volt] might say, “you can do that with an op amp.” In a recent video, you can see below, he looks at simulations and breadboards for five applications that aren’t traditional amplifiers.

Of course, you can split hairs. A comparator is sort of an amplifier with some very specific parameters, but it isn’t an amplifier in the classic sense.

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Round Displays Make Neat VU Meters

May 5, 2025 by Lewin Day 11 Comments

You can still get moving-needle meters off the shelf if you desire that old school look in one of you projects. However, if you want a more flexible and modern solution, you could use round displays to simulate the same thing, as [mircemk] demonstrates.

At the heart of the build is an ESP32 microcontroller, chosen for its fast clock rate and overall performance. This is key when drawing graphics to a display, as it allows for fast updates and smooth movement — something that can be difficult to achieve on lesser silicon. [mircemk] has the ESP32 reading an audio input and driving a pair of GC9A01 round displays, which are the perfect form factor for aping the looks of a classic round VU meter. The project write-up goes into detail on the code required to simulate the behavior of a real meter, from drawing the graphics to emulating realistic needle movements, including variable sweep rates and damping.

The cool thing about using a screen like this is the flexibility. You can change the dials to a different look — or to an entirely different kind of readout — at will. We’ve seen some of [mircemk]’s projects before, too, like this capable seismometer. Video after the break.

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A photo of Aaron Danner with a current mirror schematic in an overlay.

Biasing Transistors With Current Sources

April 21, 2025 by John Elliot V 3 Comments

Over on his YouTube channel [Aaron Danner] explains biasing transistors with current sources in the 29th video of his Transistors Series. In this video, he shows how to replace a bias resistor (and consequently an additional capacitor) with a current source for both common-emitter and common-collector amplifiers.

A current source provides electrical energy with a constant current. The implication is that if the resistance of the load changes the current source will vary the voltage to compensate. In reality, this is exactly what you want. The usual resistor biasing arrangement just simulates this over a narrow voltage range, which is generally good enough, but not as good as a true current source.

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Robot Picks Fruit And Changes Light Bulbs With Measuring Tape

April 18, 2025 by Tyler August 9 Comments

How far can you stretch a measuring tape before it buckles? The answer probably depends more on the tape than the user, but it does show how sturdy the coiled spring steel rulers can be. [Gengzhi He et. al.] may have been playing that game in the lab at UC San Diego when they hit upon the idea for a new kind of low-cost robotic gripper.

An image of the GRIP-tape robot described in the article, showing the tape-loop fingers. — Four motors, four strips of measuring tape (doubled up)– one robot hand.

With the lovely backronym “GRIP-tape” — standing for Grasping and Rolling in Plane — you get a sense for what this effector can do. Its two “fingers” are each made of loops of doubled-up measuring tape bound together with what looks suspiciously like duck tape. With four motors total, the fingers can be lengthened or shortened by spooling the tape, allowing a reaching motion, pivot closer or further apart for grasping, and move-in-place like conveyor belts, rotating the object in their grasp.

The combination means it can reach out, grab a light bulb, and screw it into a socket. Or open and decant a jar of spices. Another video shows the gripper reaching out to pick a lemon, and gently twist it off the tree. It’s quite a performance for a device with such modest components.

At the moment, the gripper is controlled via remote; the researchers plan on adding sensors and AI autonomous control. Read all the details in the preprint, or check below the fold to watch the robot in action.

This is hardly the first time we’ve highlighted a grabby robot. We’ve seen belts, we’ve seen origami — but this is the first time we’ve seen a measuring tape. Have you seen a cool robot? Toss us a tip. We’d love to hear from you. Continue reading “Robot Picks Fruit And Changes Light Bulbs With Measuring Tape” →