Why Harmonic Drives Are Awesome.

I'm one of the engineers for the actual Lunar Roving Vehicles, made by General Motors and Boeing. Harmonic drives were used on all four wheels, and were used to be able isolated the DC brush-motors from the vacuum on the Moon. Brushes do not work well in vacuum, since they are lubricated on Earth by a thin film of water, from the humidity. On Moon there is no H2O, so the brushes turn to dust and wear rapidly. The motors and the harmonic drives were half-pressurized with a partial atmosphere, with a specific humidity installed. Garrett-AiResearch did the motor assembly. Gear ratio was about 80-to-one. Motor turned up to 19,000rpm max, but usually ran at less than half of that during actual on Moon motoring. The drives would work just fine if somebody went to the Moon and energized them, but the wheel brakes are probably locked-up now, due to vacuum cold welding, so the vehicles probably could not move.

I have to say Jeremy, you are a brilliant example of a self taught engineer. You have conveyed so much info, in such easy to understand format, that I am sure (and hope) you have inspired dozens, if not hundreds of young people to take up engineering- especially robotics - as a career. I'm and old school engineer, who learned my trade "at the bench" mostly, but nowadays Youtube is a big factor in teaching people. Keep on doing what you are already a master at- and I am sure many more young potential enginners will get the inspiration and confidence- just because of you - to take up this subject as a either a hobby or a job. Well done Sir!!!

Kids don't realise how lucky they are to have people like Jeremy teaching them engineering. I'd have sold one of my brothers kidneys to have this when I was younger.

One of my favorite uses of the planetary gear-set is the Sturmey-Archer 3 speed bicycle hub patented in 1903. It used ratchets to give an underdrive, one to one and then an overdrive giving the bicycle 3 speeds. Later a coaster brake was incorporated into the mechanism eliminating the need for a separate brake mechanism for the rear wheel. However, being a retired ASE Master Technician who ended his career as an Automatic Transmission specialist, my absolute favorite use of planetary gears is in the 700-4R/4L60 & 75 transmissions used in GM vehicles in the 80's, 90's and 2000's. Unlike all other 4 speed overdrive automatic transmissions, the 700-4R design, which continued in the 4L60/75 transmissions, uses only two planetary gears to achieve 4 forward speeds and the requisite reverse gear. All other automatic transmissions used a 3rd planetary gear-set to get overdrive. It's one of the tightest and most compact automatic transmissions ever designed and it was a huge success, once all the bugs were worked out, most of them lubrication issues.

Worm gears can be quite precise at high reduction ratios, but it comes with a price of small teeth and low max torque for the size. Gears like that are often used in telescope mounts.

I was doing robotics at Carnegie Mellon in the late 80's and early 90s and I do like strain wave gearing as well. I would propose a slight revision to your description of precision. You seem to equate it to a lack of backlash. I'm sure you know this is a gross oversimplification. We were trying to do some very high precision work over long distances and this magnified the imprecision of the strain wave gearing. It turns out that due to the mechanical drive of the flex spline, there is a tiny sinusoidal error added to the output, in addition to the gear ratio function. We were measuring the input and output positions very precisely with resolvers and could characterize the transfer functions of each gearbox. Love this series Jeremy, THANKS!

Fun fact, big radial aircraft piston engines often had planetary gearsets on both ends of the crankshaft. The prop gearbox reduces the speed to keep the blade tips subsonic and the supercharger gearbox increases speed.

Hey there, I'm an IT manager at a construction company, all of our cad guys use the space mouse, and the keyboards/mice. I am just starting to deploy windows 11 to our machines. Had a guy who was having the weirdest issue with the photos app, where it would just crash when trying to open a photo. My guys couldn't figure it out, so I stepped in; the faulting module was the space mouse driver! So keep that 3dconnexion software updated.

You nerding out over taking that gear apart is pure joy.

Who else goes ahead and clicks “like” right at the start because you know you won’t be disappointed and don’t want to accidentally forget to support Jeremy?

In a bicycle hub gear system, several types of gears are used to facilitate smooth and efficient gear shifting. The specific types of gears typically include: Planetary Gears (Epicyclic Gears): This is the most common type of gear used in hub gear systems. The planetary gear setup consists of a central 'sun' gear, multiple 'planet' gears that rotate around the sun gear, and a 'ring' gear that encircles the planet gears. This arrangement allows for multiple gear ratios in a compact space within the hub of the rear wheel. Sun Gears: These are the central gears around which the planet gears revolve. Planet Gears: These gears revolve around the sun gear and are mounted on a movable carrier which rotates them around the sun gear. Ring Gear: This is a large gear that encircles the planet gears, typically fixed to the hub's casing. Clutch: A mechanism used to engage or disengage various gears to achieve different gear ratios. Shift Ring: Used to change gears by moving the clutch to engage different combinations of these gears. Hub gear systems are enclosed within the rear wheel hub, protecting the gears from dirt and moisture, leading to less maintenance compared to traditional derailleur systems. They offer a range of gears suitable for various riding conditions and are particularly popular on urban, commuter, and utility bikes.

Interesting. Thanks. And thank you for clear, no nonsense explanations with no 'background' music competing with your voice and no jerky video / needless transitions. .

I used to work in a printing facility, and was part of a crew that worked on a Heidelberg Harris m3000 printing press. There are some really really neat things about different parts of the press, but like you, one of the things that fascinated me the most was the harmonic drive used to set timing in the folder. It's been years so hopefully I'm remembering the details correctly, The cutting cylinders and delivery fans were driven by a 40 ish horsepower motor. The cutting cylinders were driven directly by the motor. The belt that drove them then continued downward and wrapped around the outer ring of the harmonic drive and the fans were attached (through additional gears and shafts) to the cup side, the eccentric side was coupled to a small motor that would freewheel when timing was good and rotate it faster than the ring or slower than the ring when timing needed adjusted which would advance or retard the fan timing relative to the cutting cylinders. Seeing the gear train and the harmonic drive opened up for maintenance was quite impressive to see in my early 20s. Thanks for doing this video. Very cool

Not an engineer here, my usual method for disassembly of something new is brute force & ignorance. It warms me to see an experienced engineer use the same method! :)

Very cool! I watched this through the lens of an amateur astronomer where these gear types are used in robotic telescope mounts. Most of the consumer grade mounts are worm gear and belt based, but there's a lot of excitement around harmonic drive based mounts that are coming onto the market, especially for lightweight, portable setups. In either type, terms like precision, backlash, and periodic error are important to consider, especially for astrophotography where sub-arcsecond pointing precision is often needed. Thanks for the awesome videos as always!

Regarding the Space Mouse, ABSOLUTELY! Having it on my viewport camera (NOT the model!) is an absolute MUST HAVE now. It makes it SO easy and SUPER FAST to zip around and view things from anywhere in 3D space. It's also really satisfying to just fly around using a 6 axis controller. Also try it with Unity and Unreal and Google Earth and Elite Dangerous and... I see people doing things in 3D without one and feel a little sad for them.

Thanks for taking the time to disassemble the planetary gears. Great video!

My favorite part was watching you take apart the gear box for the first time, with real live reactions 😂. ❤

Very interesting and no unnecessary talk. I am impressed with the content. Thank You!

9:02 Wow! The confidence on display here is remarkable. Yeah, you were hesitant to begin disassembling it but you’re not even organizing and labeling all the parts as you remove them! I recently helped my brother disassemble his desk fan for maintenance and cleaning. Labeled every screw, bracket, etc. I was absolutely terrified of losing parts or reassembling it incorrectly. I’m sure glad I did it though. He was considering buying a new one and the last thing we need is more plastic in a landfill.