Building Reaction Wheels With Python And LEGO

April 27, 2022 by 3 Comments

Reaction wheels are useful things, typically used by satellites to keep themselves oriented the right way up in space. Turning the reaction wheel creates an equal and opposite torque in the spacecraft, allowing it to point and rotate itself accurately. The same technique also works here on Earth, and [Brick Experiment Channel] decided to build one out of LEGO to control an inverted pendulum.

The initial design using a small LEGO wheel on an inverted pendulum was only able to work reliably over a 4-degree angle from the vertical. Upgrading the wheel to a larger, heavier one enabled the wheel to instead work over a 28-degree range instead.

A MPU9250 inertial measurement unit was pressed into service for control of the reaction wheel, fitted to the base of the pendulum and read by a Raspberry Pi. The Pi takes accelerometer and gyroscope readings, and then controls the motor on the pendulum with a PID controller to keep the inverted pendulum upright.

The video goes into a great deal of detail on what it takes to make the pendulum run smoothly. From changes to the control coefficients to measuring the motor’s back EMF, [Brick Experiment Channel] demonstrates everything required to make the pendulum robust to outside perturbances.

The inverted pendulum is a great way to learn about control theory, as we’ve seen time and again.

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Reaction Wheels Almost Control This Unusual Drone

January 24, 2019 by 11 Comments

When you think about all the forces that have to be balanced to keep a drone stable, it’s a wonder that the contraptions stay in the air at all. And when the only option for producing those forces is blowing around more or less air it’s natural to start looking for other, perhaps better ways to achieve flight control.

Taking a cue from the spacecraft industry, [Tom Stanton] decided to explore reaction wheels for controlling drones. The idea is simple – put a pair of relatively massive motorized wheels at right angles to each other on a drone, and use the forces they produce when they accelerate to control the drone’s pitch and roll. [Tom]’s video below gives a long and clear explanation of the physics involved before getting to the build, which results in an ungainly craft a little reminiscent of a lunar lander. The drone actually manages a few short, somewhat stable flights, but in general the reaction wheels don’t seem to be up to the task. [Tom] chalks this up to the fact that he’s using the current draw of each reaction wheel motor as a measure of its torque, which is not exactly correct for all situations. He suggests that motors with encoders might do a better job, but by the end of the video the little drone isn’t exactly in shape for continued experimentation.

Of course, dodgy reaction wheels don’t only cause problems with drones. They can also be a problem for spacecraft when the Sun gets fussy too.

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Stick Balances Itself With Reaction Wheels

August 11, 2016 by 33 Comments

The inverted pendulum is a pretty classic dynamics problem and reaction wheels are cool. That’s why we like [Mike Rouleau]’s self-balancing stick.

The video, viewable after the break, was fairly sparse on details, but he furnished some in the comments. The little black box on the top is a GY-521 Gyroscope module. It sends its data to an Arduino attached to the black cord which trails off the screen. The Arduino does its mathemagic and then uses a motor controller to drive the reaction wheels at the correct speeds.
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Rocket Mounted 3D Printed Camera Wheel Tries, Succeeds, And Also Fails

December 6, 2022 by 29 Comments

[Joe] at BPS.space has a thing for rockets, and his latest quest is to build a rocket that will cross the Kármán Line and launch into the Final Frontier. And being the owner of a YouTube channel, he wants to have excellent on-board video that he can share. The trouble? Spinning. A spinning rocket is a stable rocket, especially as altitude increases. So how would [Joe] get stable video from a rocket spinning at several hundred degrees per second? That’s the question being addressed in the video below the break.

The de-spun video looks quite good

Rather than use processing power to stabilize video digitally, [Joe] decided to take a different approach: Cancelling out the spin with a motor, essentially making a camera-wielding reaction wheel that would stay oriented in one direction, no matter how fast the rocket itself is spinning.

Did it work? Yes… and no. The design was intended to be a proof of concept, and in that sense there was a lot of success and some excellent video was taken. But as with many proof of concept prototypes, the spinning camera module has a lot of room for improvement. [Joe] goes into some details about the changes he’ll be making for revision 2, including a different motor and some software improvements. We certainly look forward to seeing the progress!

To get a better idea of the problem that [Joe] is trying to solve, check out this 360 degree rocket cam that we featured a few years ago.

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Quick Reaction Saves ESA Space Telescope

October 22, 2021 by 5 Comments

Once launched, most spacecraft are out of reach of any upgrades or repairs. Mission critical problems must be solved with whatever’s still working on board, and sometimes there’s very little time. Recently ESA’s INTEGRAL team was confronted with a ruthlessly ticking three hour deadline to save the mission.

European Space Agency INTErnational Gamma-Ray Astrophysics Laboratory is one of many space telescopes currently in orbit. Launched in 2002, it has long surpassed its original designed lifespan of  two or three years, but nothing lasts forever. A failed reaction wheel caused the spacecraft to tumble out of control and its automatic emergency recovery procedures didn’t work. Later it was determined those procedures were dependent on the thrusters, which themselves failed in the summer of 2020. (Another mission-saving hack which the team had shared earlier.)

With solar panels no longer pointed at the sun, battery power became the critical constraint. Hampering this time-critical recovery effort was the fact that antenna on a tumbling spacecraft could only make intermittent radio contact. But there was enough control to shut down additional systems for a few more hours on battery, and enough telemetry so the team could understand what had happened. Control was regained using remaining reaction wheels.

INTEGRAL has since returned to work, but this won’t be the last crisis to face an aging space telescope. In the near future, its automatic emergency recovery procedures will be updated to reflect what the team has learned. Long term, ESA did their part to minimize space debris. Before the big heavy telescope lost its thrusters, it had already been guided onto a path which will reenter the atmosphere sometime around 2029. Between now and then, a very capable and fast-reacting operations team will keep INTEGRAL doing science for as long as possible.

Monowheel Balancing Robot Can’t Turn (Yet)

July 24, 2021 by 21 Comments

Self-balancing robots have become a common hobby project, and they usually require two wheels to work. [James Bruton] has managed to single wheel balancing robot by adding gyroscopic stabilization.

[James] has done other self-balancing robots, like his Sonic robot, but recently started experimenting with gyroscopic stabilization. In that project, he proposed the idea of combining the two stabilization methods to create a monowheel robot, and he followed through on that idea. The wheel is powered by a brushless motor and is stabilized conventionally around the wheel’s axis. Side to side balancing is achieved using a phenomenon known as gyroscopic precession, by tilting a pair of heavy spinning wheels. This is not to be confused with reaction wheels, which use rotational inertia for control. It appears the actuating the gyroscopes also affects the front-to-back stabilization, so at the moment the robots won’t stay on one spot. [James] plans to implement a second observation controller in software to solve this.

Another challenge with this robot is that it cannot turn at the moment. The gyroscopes are not in the correct orientation to effect rotation around the vertical axis, and changing their orientation would cause other problems. A fan, which works like a helicopter’s tail rotor is one option, and a reaction wheel on top might also work. We’re partial to the reaction wheel idea. Having a different mechanical control mechanism for each axis would make it quite an interesting robot.

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Flywheel Stores Energy To Power An Airplane – Eventually

February 13, 2020 by 7 Comments

Question: Can a flywheel store enough energy to power an airplane? Answer: Yes it can, for certain values of “flywheel” and “airplane.”

About the only person we can think of who would even attempt to build a flywheel-powered airplane is [Tom Stanton]. He’s a great one for off-the-wall ideas that often pay off, like his Coandă effect hovercraft, as well as for ideas that never got far off the ground, or suddenly met it again. For most of the video below, it seems like his flywheel-powered plane is destined to stay firmly in the last category, and indeed, the idea of a massive flywheel taking flight seems counterintuitive. But [Tom] reminds us that since the kinetic energy stored by a flywheel increases as the square of angular velocity, how fast it’s turning is more important than how massive it is. The composite carbon fiber and aluminum flywheel is geared to the propeller of a minimal airplane through 3D-printed bevel gears, and is spun up with an external BLDC motor.

Sadly, the plane never made it very far, no matter how much weight was trimmed. But [Tom] was able to snatch victory from the jaws of defeat by making the propeller the flywheel – he printed a ring connecting the blades of the prop and devised a freewheel clutch to couple it to the motor. The flywheel prop stored enough energy to complete a few respectable flights, as well as suffer a few satisfyingly spectacular disintegrations.

As always, hats off to [Tom] for not being bashful about sharing his failures so we can all learn, and for the persistence to make his ideas take flight.

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