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 KZfaq 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.

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

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.

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.

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.

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! :)

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?

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.

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

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 love my Space Mouse. It's as close as you can get (right now) to having your hands on a digital model. Thanks, Jeremy.

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

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!

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

Well I didn’t need to know this for anything in foreseeable future… but you are a great teacher and i really feel like I learned a lot about gears. Can’t wait for this to come up randomly during conversation at some point in the future and feel knowledgeable.

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.

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!

🇨🇦/🇺🇸... Hey there Jeremy! In the past I've enjoyed your many vidz about electric motors. While perusing for information about gears, looked what KZfaq tossed my way. EXTRA BONUS... I had already been looking at and considering the Space Mouse and so I figured I'd give YOU the affiliate click and get the 10%! EXCELLENT! I'm quite excited!!!! Cheers, bro!

Fantastic view of the harmonic drive; I have been wondering. Good to see you.

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.

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.

My first encounter with a strain wave gear was, of all places, in a Lego Technic motor. Part 2986. It was part of a multi model kit that came out in the early 90's I took the motor apart cause I was fascinated by how small it was (I think to this day it's the smallest motor to be produced by Lego) and was amazed by the TINY coreless motor and microscopic gearing. it was fantastically engineered!

Jeremy- You are a great teacher. Thank You for all the effort you put into these videos.

Well Jeremy your explanation of harmonic drives really resonates with me. You are very well-spoken, organized, and clear with your explanations. It was a pleasure to learn from you. Mind you I am long retired so this is not my first rodeo. Now I want to get myself a harmonic drive to play with!

Very cool! Thanks for sharing!

Nice Video, My favorite "gearbox" is the "Constant speed drive" basically two axial hydraulic pumps acting as a gearbox to rectify for older aircraft generators. That thing is just amazing.

Your explanations are so clear and educational with the gearing and at nearly 70 yrs old I've seen a lot of mechanisms. Love yer channel! I bought this hand operated chain hoist, which I will try to explain is one such type of ratio in a chain form. I was so excited once I discovered how it worked, I showed my daughter. She said, "oh. that;s nice" and walked away... ha ha! I bought a hand operated.chain hoist (with a loop of single chain) which had a top solid pulley with two parallel chain link depressions in the circumference. The one side has 10 link depressions and the other has 9 depressions, i.e. 10D or 9D.. (There is a hook on this pulley that hooks to the rafter or whatever.) These depressions fit each chain link. So, the hoist chain is able to turn the pulley with the 10D or the 9D pulley is in the single loop of the chain. Every time the pulley turns once, the chain is tightened up or loosened depending upon the the direction the chain is pulled. The ratio is 9:10 or 10:9. And idler pulley connects to the load with a hook and rides in the chain loop.. I was so amazed by that old technology that I had to buy the thing at a junk shop. I went home and immediately geeked out and took it apart to see how it worked!

I am SO glad I found your channel. I need to show this to my son. He loves working with mechanical items. This video will make him so happy! I try to follow along with what he says, but my goodness, a lot of it goes over my head.

Can't believe I was blessed with a J.Field video this morning. Sankyuu.

Just came across your channel, the enthusiasm you have is infectious. Very good video

Great video as usual! I had a 1964 flat windshield Chevy van, final drive geared for around town. I turned it into a camper and wanted to reduce RPMs for use on the highway. I could have installed a lower geared rear end, but I found a 1957 Chevy overdrive transmission first. It essentially snapped into place, all bolts and controls were identical to the original. Chevy saving a buck, updating was anathema. The point? Inside the OD transmission was a two speed planetary gear controlled by a solenoid, you pushed a button to shift into OD, and it worked for each gear. Six gears! unfortunately the lower gears were almost duplicates, still, it was useful on a snowy or Icey road. It also had a freewheeling clutch in the transmission. After first gear you didn't need to clutch to change gears! Great for learning how to double clutch on the downshift. In hilly terrain it gave surprising fuel economy. Power up the hill for volumetric efficiency, off throttle to coast down with the engine idling. It also had a cable to lock out the freewheeling clutch, very important on longer descents, the brakes were barely adequate.

As always, I love your way of explaining everything in a way that makes it easy to understand. Thanks for making learning fun and engaging 👍

Jeremy, you're the very BEST!

When that part went flying out of the planetary gear as you disassembled it, I got a flashback to old AvE videos.

One of my favorite content creators!

I used to work for a manufacturer of industrial robots. So, I have replaced many gear reducers, including harmonic, rotary vector, cyclonic, and another antiquated type I can't remember. We only used harmonic on the minor axes of small robots. Once you get to 6kg capacity robots, the major axes are RV (rotary vector) reducers. On 50kg capacity (and above) robots, no harmonic reducers were used. From there up, we used RVs. I know this is true for the two major Japanese brands. I'm not sure what the European manufacturers do.

Taking that gear apart was a good move. Really helped me visualize the concept.

I hate how youtube constantly redirects you to other videos and ignores your subscribed videos on your main page. I'm glad I found you again. Great video!

Wowzers! I've never even heard of harmonic drives except as technobabble in sci-fi. But to see the real thing in motion is a thing of beauty!

I first heard about harmonic drives when reading about the Apollo lunar roving vehicle. Each wheel had its own motor and harmonic drive.

I'm glad you reviewed the strain wave gearing. I'm an amateur astronomer and I've been looking into telescope mounts that are using stream wave because they can carry so much weight and the backlash is basically nothing

As a hobby-astrophotographer this was very interesting! Because these harmonic drives have really introduced themselves in this area. They are installed in the mounts, that's where the telescope and camera are mounted on and correct for the rotation of the earth to allow long exposures. Thus they have to be very precise, but also withstand some pressure. Because a large telescope with a dedicated astrocamera, a second little scope and camera for guiding, an automated focuser, a filterwheel etc. can add up to quite some weight. But it makes sense why they are more expensive, because as you said: The machining and the material seems to be quite unique. Thx!

I took a random chance on the algorithm and clicked on the video. Your enthusiasm and way of explaining things has earned you a neew subscriber.

Haven't seen your channel for awhile, glad to see your progress and number of subscribers!!!

Love your videos. Your enjoyment in it is shared and spills out in every video. It's not often I mention the sponsor used in a video, but 3DConnexion Space Mouse is amazing. SOme years into using one, I just can't believe everyone isn;t using them ( I am sure 3DConnexion thinks the same - LOL)

Superb! Really enjoyed every word and the videography and demonstration.

Excellent video good sir. I really like your instructional videos.

Really interesting! I hadn't seen that one before (the harmonic drive)

Thank you very much. I'm usually entertained by KZfaq videos. I rarely learn something completely new. You have added to my knowledge of the world.

I have a 3D Connexion Space Mouse, and can confirm they're invaluable for 3D modeling. A little pricey, but high quality and worth it. Super cool they sponsored you, and thanks for the excellent content. I'm learning a lot about gear design from this series.

Thank you Jeremy! It's always a joy to learn from you.

Ten thumbs up Jeremy. Keep imparting your knowledge. You have an ability to convey knowledge that is absolutely fantastic.👍👍👍👍👍👍👍👍👍👍😎

The video of the pancake drive did a great job showing the deformation of the gear. Very cool demonstration, thank you!

Thanks for the video. A great set of explanations.

This is the first I’ve seen of your stuff. You’re good, I love gears. I build rc rock crawlers just to learn about the lockers and trans systems. Subscribed.

Great video ! Love your 3D connection, I have the small one and can not work without it anymore...

Thank you Jeremy. You are a blessing my friend.

Very informative video, thank you for sharing your knowledge!

Jeremy you are a master communicator. Thank you.

Well done Sir !! Thank you 😎

You mentioned stacking planetary gears to get the desired ratio and output. Hydraulic excavator swing gears are an excellent example of that. Depending on the size of the machine there may be one or two swing drive housings with three or four stacks aside to achieve that number. Planet drives are very cool.

Yet another excellent instructional video!

Thank you for this video. First time I had seen a harmonic drive.

Jeremy I love your content! I am sooo happy you’re still doing this!!!!!

Great video and very instructive.

@JeremyFieldingSr - Also offering large ratios in a compact package is the Cycloidal Drive, which gives *wide-ranging SMOOTHLY VARIABLE ratios.* It was invented and demonstrated by an Australian mathematician, apparently in the 1980s. It operates by taking advantage of the fact that cycloids are very nearly circular in a small part of the bumpy curve, so the mechanism cuts out those parts and stitches them back together in a system slightly resembling a planetary gear set. If I recall correctly from the magazine article, a *ratio range* of at least 1600 was easily achieved, variable between a small speed increase and a much larger reduction ratio. Definitely both extremes and everything in between were easily accessible and continuously adjustable on-the-fly by way of a single lever. The unit also acted as a clutch when that control lever was pushed _beyond max reduction_ ratio. But I never saw or heard more of it, _and I want to!_ Seems to me it would make a fascinating video for your channel. Can do? Secondly: Is it really _necessarily true_ that in the Harmonic drive there has to be a _difference of exactly 2 teeth_ between inner and outer? Never more than 2, never less than 2? Because I have excellent visual imagination (including animation) and it seems to me that other _difference numbers_ should be possible, with appropriate changes to other components. I speculate that those versions are not seen because they offer ratios that are always lower than with difference number=2, so those lower ratios are achieved by re-designing the whole drive. Makes sense to you?

Thankyou so much this makes sence

Very informative, thank you

great video. Keep them coming!

Black Tony stark over here. I love this dude❤

I've been playing with nutating gear trains recently, and they operate on a similar principle to the strain wave gears, where a small difference in the number of gear teeth leads to large reduction ratios.

I learned a lot, thanks. Great video.

Thanks!

Very interesting, i don't really know anything about the different kinds of gear you were talking about, so it was all new to me. Thanks for the explanations.

Very slick, I did not know about Harmonic drives !!

Well done!

Thank you!

I saw where somebody was proposing to use a planetary gear, on an ebike, with a disk braking mounted to the body of the “gearbox” to allow the bike inertia to drive the motor. By slowing the body of the gear housing, using a hand controlled disk brake, it would control how much regen took place vs the disk. In addition to putting the downhill energy back into the battery, you could augment the braking force with the disk, or even fully depend on the disk, in the event that something failed in the regen circuitry, or the motor open-circuited for whatever reason.

Thanks for the sacrifice and lessons :) For science!

thak you for your work

I was taught that worm gears were not able to be back driven. And that is true for most worm gears due to the contact angle and the friction. But then I encountered a piece of equipment that uses back driven worm gears as part of its regular operation. If you use a multi-start worm instead of the standard single start back driving works fine.

as always very interesting, thank you for sharing

Thank you.

Keep up the good work uncle Jermy

Interesting , Thank You .

Great channel! I graduated from two famous universities with two different engineering degrees. Every time I watch one of your videos I ask myself, why wasn't I taught that in engineering school? Kinda frustrating.

Those strain wave gears were used on the lunar rover as well.

Yo, a spacemouse sponsorship is awesome. Been wishing for one since I first saw one. Need to get them sold in big box stores so I can play around with one

My first exposure to your work. Most impressive.

I throughly enjoyed your video.

You do a fantastic job!

strain waves are used in telescope mounts now. no backlash, but periodic error

Robotic arm looks amazing. Great to save and do it yourself!

That was bonkers cool!

Thanks

This is fascinating. Thank you for posting it:-)

Dude, your description game is on point.

Love this guy.