The Differential Drive - A New Breed of Actuator

I designed, built, and tested a unique actuator I'm calling the differential drive. It utilizes two identical motors, and the output rotation speed is the sum of the motors individual rotation speeds (with an additional overall reduction). It's something I've never seen before!
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[@senjaz]

They are used in tracked vehicles and are called adder/subtractor gear boxes. Essentially two differentials linked together. They allow one high torque motor to provide the main motive force to two outputs and a second lower torque motor to add and subtract its speed to those outputs. It allows precise control over the relative speeds of the outputs even with motors of similar torque.

[@572089]

and with 3 differentials and you can use the "steering motor" to move torque from one diff to the other via the central, allowing for a constatant total output, but varying difference between the two outputs. Thats how you get fine control on racing tanks like the Ripsaw. this way you dont lose speed and dont put too much backlash on the steering motor at high speed while maintaining steering reaction time.

[@freescape08]

That's a very well known application, and I didn't even think of it. Nice.

[@BrokeWrench]

Can you mention some vehicles that use this? I had looked up this exact thing and found nothing

[@joemaser9122]

@@BrokeWrench cat differential steering

[@nou5440]

cant like cause 69

[@flagship1701e]

At the end of the day, every engineer's true desire: " It does look good and it is shiny".

[@mandernachluca3774]

Little fun fact: The Toyota Prius is using a planetary differential to couple an electric generator, motor (and ice engine) and the driveshaft. This system is widely belived to be the most cost effective and efficient way to build a hybrid drive train. In german, we call this system a "Leistungsverzweigter Hybridantrieb". 😅😁

[@Eugensson]

toyota calls it eCVT

[@qztronic]

@@Eugensson in Toyota’s R&D lab it’s nicknamed the “power splitter”

[@FPSlacker]

Also the Chevy Volt's drivetrain www.greencarreports.com/news/1096942_2016-chevrolet-volt-powertrain-how-it-works-in-electric-hybrid-modes

[@liesdamnlies3372]

German: “CONCATENATE ALL THE THINGS”

[@Eugensson]

@@liesdamnlies3372 Luxembourgish: Do the same as germans, but in a most unexpected way, eg ZWEEEEËG

[@robertphillips9017]

You just described the “transmission” of the Prius, except that the Prius uses three input motors, mg1, mg2, and ICE.

[@johnmcfarlane9416]

Exactly. Ford/Toyota eCVT. I made one based off the linear toyota variant to dynamically share output from a windmill with two generators and one motor, one gen for low winds and the other geared for high wind. The motor/braking takes some power off the gens but it speed sets the distribution between the gens. Cost effective, no; Fun yes.

[@leonschmidt7]

Check out the Fendt Vario or AGCO CVT transmissions

[@felixar90]

I knew I had seen this before but couldn't remember where. Hybrid cars. That's where. Also some CVT were there's an electric motor who's sole purpose is to vary the gear ratio. I think modern tanks use something like this.

[@HelloNotMe9999]

Not precisely... A combiner gearbox, which is what the Prius has, is a little different. Similar, yes, but not _quite_ the same. It's nice to see him make something to test his theories though.

[@webmonkees]

Another gearing to study the history of the Subaru CVT transmission,, they were one of the first to try.. www.subaruoutback.org/attachments/cvt-diagram-jpg.26499/

[@Thepiecat]

I love that you turned a "failure" into a video about what you learned. Quality video!

[@witoldgrabowski9263]

I'm learning now, how to turn any quality video into an unmitigated disaster, or irreversible failure. But, thanks for watching.

[@byronmckenzie5805]

@@witoldgrabowski9263 n. m m .mmm

[@kenworks6068]

Beautiful build quality. Great presentation and example of the value of lab tests in conjunction with thought experiments. The first computer I worked on professionally, used physical differentials to perform vector math based on heading to integrate acceleration, and speed into distance traveled in latitude and longitude for the F4 fighter jets. It worked well - Back in my day. The entire navigation and weapons delivery was done in analog computing and was build before Apollo.

[@LeviJanssen]

Wow, that's fascinating!

[@rklauco]

The best way to learn is to fail :) Congrats on not giving up!

[@ChrisTuttle]

Agreed. Also, documenting expectations/hypotheses and how they relate to test results is fun to watch and learn about. One of the best aspects of MythBusters has been executed well here! Right on Levi.

[@LeviJanssen]

Thank you, and I absolutely agree. The world needs more failures!

[@LeviJanssen]

To be mentioned in the same thought as Mythbusters is an honor, thank you

[@danriches7328]

Well, failure is how we learn and I really admire your full honest approach and not omitting the failures. I found this very fascinating, keep up the great work and we'll all learn something worth while. Awesome!!

[@stefancoppens4922]

The "reverse" differential drive you describe was used for a century (I believe) to actuate rudders on ships. Two large DC traction motors ran in opposite directions at high speed, with the rudder linked to the output shaft. The rudder could then be moved by varying the electrical power fed to the motors, one more and one less, resulting in a high torque at the rudder very quickly. This was before the days of sophisticated hydraulics, and avoided the need to spin up a single traction motor from rest every time a rudder movement was required.

[@TomasSab3D]

This is beautiful. And your style is flawless.

[@DaveEtchells]

I just returned to this video after having seen it back when you first posted it. It’s clever and very well-explained! I realized that this is essentially the same principle used in the ancient “north-pointing chariot”. There, the inputs were the rotation of the two chariot wheels, and the output was a pointer that s always pointed in the same direction, regardless of how you rotated the chariot. Anyway, a great project and explanation of the project!

[@denispalmer1937]

I designed this and applied for a patent on it about 12 years ago, it is a great system never put in market

[@MrKhan-od6it]

May i get your patent number?

[@DrGoo-px9eb]

Awesome video, I like that you show where you went wrong, really showing people that engineering is about analyzing failures and not only about making perfect systems all the time.

[@sierraecho884]

I love this old black/white video explaining a differential, it´s genius and way way ahead of it´s time.

[@georgekerwood9100]

This was great, thanks for you work. Your inclusion of your failed hypotheses and your thought processes prior and after testing made for an authentic watch.

[@ronnetgrazer362]

I never thought of a rear differential as being a planetary gear pulled into 3D, or a planetary being like a rear differtial folded inside out and flattened. Thanks for that!

[@openlink9958]

I know it has been a while but timestamps would be useful

[@megadjc192]

all you have to do is invert one of the inputs and you've just created the mechanical equivalent to an electronic operational amplifier where the gear ratios determine the "gain" and you can even feed the output back to one of the inputs with a variable gear ratio and you can change the "gain" or input to output ratio of the drive unit.

[@fire17102]

Go on ...

[@DFPercush]

@@fire17102 "What is an op amp" kzbin.info/www/bejne/bXe8eadrjducgcU just substitute "rpms" instead of "volts". That's a pretty sick idea btw.

[@megadjc192]

@@DFPercush also torque equals current. And if you multiply torque*rpm you get horsepower which then can be directly converted to watts. The same energy you see in electrical systems

[@whtwolf100]

@@megadjc192 so what sort of applications or purpose would this serve? Sorry, not as knowledgeable about this stuff, but its really cool!

[@megadjc192]

The primary usage of this is in automatic transmissions as they allow the syncronized smooth change of gears where one of the inputs is connected to the engine then the gears are set at a specific ratio then the other input is forced to zero rpm thus allowing you to selectively change the rpm and torque without have to mesh gears together. A planetary gearset is a mechanical operational amplifier. Also, one can use this at a simple analog computer. For example, you can compare two rpms of two different rotational shafts then compare the output rpm and that output rpm will be the addition or subration of the two input rpms depending on the configuration. You can use this effect to accurately measure a high rpm source by converting it down to a lower rpm and then allowing an extremely precise measurement. Basically anything you can do with an electronic op amp you can do with a mechanical one. You can also integrate and differentiate the same way and this was commonly used in old mechanical computers. Also the mechanical op amp is completely reversibale unlike its electronic cousin so as long as the two outputs add up to the same input you can have any configuration of rpm and torque on the two outputs. This is how a car differential works. The limited slip differential just has clamps on both of the outputs so that no one output will equal the input in terms of rpm or torque. Otherwise the other output will be zero which is usually undesireable with a differential.

[@kingmasterlord]

"I'm not saying I'm the first to ever invent this, but I am saying I developed it independently"

[@TheNefastor]

Also known as the "patent loophole" :-D

[@kingmasterlord]

@@TheNefastor or: Why Patents Are Bullshit I mean seriously what is sane about "I had that idea so no one else is ever allowed to think of it"?

[@TheNefastor]

@@kingmasterlord well that's not an accurate portrayal. It's more "I had an idea so everyone else must pay me to use it".

[@kingmasterlord]

@@TheNefastor it's not a race to have unique ideas. you don't deserve my money just because you had an idea earlier than I did. I'm not using your idea, I'm using mine.

[@TheNefastor]

@@kingmasterlord yeah except it's hard to prove your idea is original if someone else has published it first. You can't really prove your ignorance (short of being a brexit voter 😅)

[@howardbartlett3419]

This is pretty similar to a differential swerve drivetrain that some FIRST robotics teams have experimented with before. It is also similar to some types of robotic gripper/wrist mechanisms, since you can actually pull two outputs out of the differential.

[@ddegn]

I'd really like to see a demonstration of the variable speed feature you described. Put encoders on the motors and output and test your theory. It might be my bias in favor of encoders, but I have a hard time believing this mechanism will allow precise speed control. As with standard gearboxes, I think changing loads will require adjusting the power input to maintain a desired speed. Excellent video. Thanks for sharing your projects with us.

[@ethanspi]

Agreed, he "confirms" his two theories but didn't even demonstrate those two theories at all.

[@tt54l32v]

Look up Nissan electric variable valve timing.

[@Bradamsmx5]

I like that you posted a video about a “failure”. You live and learn is something it seems many people do not subscribe to these days. It is nice to actually see the failures that contribute to the overall successes. We can all learn from your learning experience. Thank you.

[@GabeSullice]

Paused the video to come say how much I appreciate that you laid out your hypotheses up front, admitted two were wrong (rather than cutting them), then moved on. Thumbed up and subscribed right away.

[@AnthonyFrancisJones]

Brilliant and quick explanation of the differential gear - not an easy task. Well done!

[@artmckay6704]

Levi, my hat's off to you. I really appreciate the experimenter in you. You can't learn and/ or invent if you're not willing to fail - sometimes a lot. Good for you that you're okay with failure. I think every inventor/discoverer paved a path littered with failures. Failure isn't a setback, it's just another learning opportunity. Keep doing what you're doing. You're a pioneer. You're blazing new trails and looking for things that no one else has looked for. You're an inventor. Keep trying and never stop. One secret that I have found to be invaluable is this: see the result. Forget about the stepping stones. See the result. See yourself jumping up and down, at the eureka moment. Every day, at every opportunity, focus on seeing success and yourself being happy and jubilant. Focus all of your energies on only the moment that the light bulb goes off. Do it this way and don't put limitations on the details of getting there. Screw the details. Don't even think about the details. Don't get bogged down in details. Focus ONLY on the eureka moment and then the magic will happen. Don't EVER even think about details. Think of one thing ONLY - the success moment when your brain lights up and the answer just pops into your mind, complete. This is the secret used by chemists, mathematicians, scientists, academicians, etc. They've all learned this secret. Whatever you focus on is what you bring into your life. If you focus on details then life will dutifully supply you with an endless supply of details but, if you focus only upon the final success moment, then life will begin delivering those success moments to you - all without you ever once worrying about a single detail. Try it, you'll like it! :)

[@brentjackson2312]

Not only is this a really interesting video, it is incredibly generous and presented with admirable humility. Thanks so much for taking us on your journey of exploration. Coming up with novel ideas, such as this, and testing them out is how we ultimately advance technology. Really, really enjoyed this. Fantastic project and presentation!

[@lernenmitrobin]

15:42 "you live, you learn." - Great dude!

[@alphabeets]

Geez, someone hire this guy! This is very impressive.

[@tHaH4x0r]

It is the first time for me as well to see this idea. Very neat. You might be able to write a publishable paper on it. Core XY mechanisms technically also double the speed achievable, although not in all directions thus strictly speaking don't double the velocity. Even a 'failure' is a success, because something new is learned.

[@allenwalker1379]

Thank you for showing us your whole development process and not just the successful parts.

[@katelynrogers804]

Wow this is really well applied! In 2018 I actually did my high school senior year engineering project on this concept using a 3D printed herringbone planetary gear set. It was designed as a way to include two motors on an RC car. In my prototype I opted for biasing the gear ratio to take advantage of torque and power over a wide range of rpm. (The concept was designed around putting an electric assist engine on a gas powered RC by replacing the transmission and clutch, creating a unique RC hybrid) it was pretty cool Bc theoretically the electric can spin in reverse in order to let the gas engine idle without a clutch, and also combine the power of both engines for max power during runtime. Back driving the electric motor was an issue, just like it was in your test, so I think any future version of the coupler I made would need some sort of servo actuated or electric brake on the electric motor. 3D printed transmission burned out in only a few minutes but it was a fun project!

[@DustinMaki1]

Have the electric motor drive the outside of ring gear via worm screw.

[@butterbaybiscuits8694]

What a humble learner!

[@apappano]

This is exactly why I love the KZbin community. 5 minutes in my brain is all fireworks and i’m sketching and writing out ideas to compare with your findings at the end. You’ve earned a follower! Keep up the great work.

[@jaymoser7953]

You should look at the drive system for the Sherman tanks, they use the difference of 2 motors to do forward backward and speed control. It is a very old idea

[@spankeyfish]

It's also used in mechanically controlled gear hobbing machines.

[@ilikec]

They had double and triple differential steering in certain tanks.

[@adamharoon6021]

Very cool! Congrats on surpassing one million total views!

[@mfchillin]

I really appreciate that you show when things go wrong, really true to life haha

[@emberklavins9567]

I used something like this in a lego truck a while back so that when stationary the model engine would run at an idle speed and then rev up when it started moving. Cool to see it implemented on this scale.

[@beaugalbraith3242]

I really appreciate you documenting and sharing your experiments. Great work.

[@N1ckfm]

I like how it look like, very nice aluminum + 3D printed, nice video for people who like mechanics and we like to try different types of drivers.

[@gumbykevbo]

The outboard spoilers (used for additional roll control at lower air speeds) on A B-1b aircraft use triple redundant motors driving through two differentials. I was the product engineer for the electronics that control them for most of the production run.

[@agaluszka]

The most important is to have an idea and try to develop something new... Thanks for your story !

[@AppliedMathematician]

That is a really good educational video on systematic testing of ideas and building knowledge. So thanks!

[@Heimskiir]

Quality content Levi! I'm so glad your videos are getting traction! - Kaleb Rush

[@willsmith4950]

Before smart electronics, this was a common way to drive an equatorial telescope to both track the natural apparent motion of the sky and also position the telescope automatically to a new object. Because the "sky would move" some distance during the time of the reposition operation, the known destination (number of motor steps or encoder counts), would always be incorrect. By using a differential with one motor tracking and the other positioning, at the end of the move (in either direction), the desired object would be in the center of the field. In the early 1980s, while working on a telescope for the Navy's sky transparency survey, I found that making a numerical model of such a differential simplified the design equations significantly. Good memories. Cheers on your clever design.

[@COYOTE_N8]

Very cool. Sure it's been done before but it's the first time I'm seeing this concept. 👍

[@Steevo69]

This is already done for agriculture machinery, high torque hydraulic motor (s) coupled to Diesel engine crankshaft to adjust for loads.

[@HandyDan]

2:20 this method of planetary gears is used in many hybrid cars, the Chevy Volt does this where the outer ring gear can be held and use the reduced speed of the planetary or the planetary gears can be held to overdrive the ring, which it uses to recharge the battery. Great video!

[@BensHacks]

One application for driving one shaft with two engin is in ships. The concept is called "Vater Sohn Antrieb" (German), "father son drive". I wasn't able to find anything on the internet with this phrases. The idea is coupling two motors to on propeller shaft to get the option to run any of the motor under optimum efficiency conditions under different load condition. The father motor has around twice the power of the son motor. So using only the son, the ship can cruise low speeds at maximum efficiency of the small motor. For maximum both motors are engaged. This concept is used on tugboats and a specially on riverboats. For example on some passages of the Reihn ships need very high power to go uphill but for going downhill they need only little power to enable enough flow at the ruder to maintain stearebillity.

[@martinbyrne5626]

Fascinating - great video - seeing the process and your knowledge, is impressive

[@beppe3001]

Very good idea; also i personally like very much this scientific method approach!! Well done

[@Skyentific]

Interesting idea! Everyone is using cycloidal nowadays. :)

[@angst_]

So I have seen something very similar to this on industrial box making machines. The machine is made of many pairs of drums that pull the board through the machine and cut/print on it. In order to adjust the registration of the cuts/prints to the cardboard there is a registration motor. You can rotate the drum in relation to the main drive bull gear. Either while the machine is stopped (for setup) or while it's running. There are two ways this is usually done. One is actually to have a motor that is bolted to the drum and spins with the drum, like an overdrive. I think this is an older way of doing it since it was only on the older machines. The newer machines all had various complicated ways of using planetary gears to do this. Very similar to the first diagram you showed. An interesting use of this mechanism beyond just alignment of cut/print. As you wear down the anvil that the blades are cutting into the diameter of the drum is reduced. Meaning you have to spin the anvil drum faster than the top cutting drum or you will bend the blades on the top drum. So it can also be used as diameter compensation. Just thought I'd share where this kind of technology is used in industry that I've seen.

[@fire17102]

I like your analogous to the differential drive, I think what happened is similar to a car sitting on it's belly, If your car is stuck in the sand in a way which one wheel (left) is touching the ground and one (right) is floating in the air, with an open differential, that right floating wheel will get spun rapidly and the left one will not get any power Your output is like the left wheel, but since yours isn't locked to the ground, it fails to hold a weight and drops I think it could be cool if you could design a *locking mechanism to your differential* which can be released after some speed is gained. Maybe even clutch it for smooth transition between modes Love the ingenuity! Keep up the amazing work 💪🏾

[@colinjohnson5515]

Dude! This is cool! I love being along for the ride of discovery!

[@ashleyarundel3134]

Most interesting video I've watched in a while - comments are cool too! Subscribed

[@billclark5943]

I have cnc mill, lathe and wire edm but my favorite is my 3d printer. Best tool to bring simple to complex ideas to life quickly and go through the revision process with minimal pain.

[@nibblernibbles3205]

Check out the "power split" transmission used in heavy off-road vehicles eg. Fendt Vario tractors. Often by splitting engine power into two paths: 1) a gearbox with fixed ratios 2) a continuously variable hydrostatic transmission. Then summing the two with a differential gear. Result is a high efficiency transmission with continuously variable ratio. Only a fraction of the total power is transmitted through the variable element, which typically has lower efficiency than the gearbox.

[@GunnarAlden]

I used this same technique to win an electric tractor pull competition in 2011. This is a cool investigation and explanation :)

[@drew79s]

An IVT from a Toyota hybrid uses the same operating principle. The benefit is that you effectively "blend" the two ratios, allowing for a combination of generation and drive, as well as the fact that you can run the electric motors in reverse, or idle them, allowing the petrol motor to run without stalling even when the output isn't operating.

[@551moley]

A similar system is use on Aircraft to drive generators at the correct frequency, it's called a Constant speed drive unit (CSDU). At low engine speed the drive speeds the alternator up with a motor, at high engine rpm the motor is driven in reverse to lower the alternator frequency. Avionics on Aircraft are frequency sensitive unlike cars that have frequency wild alternators.

[@chubbysumo2230]

FYI, Toyota uses these in their hybrid transaxles. This mechanism is used to couple the gas motor to the generator and starter motor, so that the starter motor and Generator can spin freely, while the engine is not turning, but also can be stopped or turned start the engine, as well as act as a Cvt.

[@chrism4621]

This is why we do experiments. You didn't get the result you hoped for, but we all learned something. Great job, keep experimenting, who knows what you will develop.

[@wackdoodler]

I was wondering how to do this. Amazing youtube algorythm. Kings to you my friend. Brilliant

[@BozAwesome]

Great job, including hypothesis was great

[@rmkscrambler]

This sounds a lot like an IVT or infinitely variable transmission, versions are used in some hybrid cars and john deer tractors. Usually 3 motor inputs (john deer uses 3 cvt inputs) are used to control the sun, ring, and carrier of a planetary creating "infinite" gearing.

[@LeviJanssen]

I initially thought this would be an IVT/CVT system, hence the double-torque hypothesis. But, considering my final thought experiment and the experiment, this can't be the case. As far as understand.

[@AlexanderBurgers]

I've seen this concept (2 motors driving a differential) invented a few times in the Lego community, either from a mistaken belief that putting 2 motors on one output would somehow harm the motors, or like in the video, to create a 'gearbox' for speed control. One of the reasons why it doesn't really work as intended is because it doesn't quite sum torque, but instead only goes up to 2x the torque of the weakest motor (or motor the least gear reduction). It doesn't do much for speed either, since you could instead put the 2 motors on one shaft and use proportionally less gear reduction, getting the same speed with less moving parts and therefore most likely less losses. One place where it would absolutely be very useful is when transmitting rotation to power a joint through an infinitely rotatable second joint. Subtracting the motion from one to the other makes sure they don't influence each other, while negating the need for things like slip rings or intricate electronic control to synchronize motors.

[@sublucid]

The easiest way for me to think about this is to just mount next motor to the output shaft of the previous motor. If you imagine a longer chain of motors, then I think how the stall torque distributes begins to make more sense.

[@holgerpieta7367]

And it also explains why Hypothesis 4 doesn't hold water: If you add up two values with independent errors, the error add up quadratically. So the precision of speed or position control of two coupled motors will always be worse than a single motor. Of course you can get below the minimum RPM of a single motor, but with a horrendous quality of control.

[@BotesTechnology]

BMW uses this to achieve additive steering. The first instances was implemented in 2005. The driver can input steering angle while a computer can add or reduce based on different system measurements.

[@vonkel85]

This was done in 2006 in the agriculture tractors. It was a CVT transmission. On a planetary gear set. The sun gear was driven by the engine RPM. The planetary carrier is splined to the rear differential. The ring gear was driven my a hydraulic variable displacement piston motor. The pump that supplied said motor was driven by the flywheel of the engine. It was also variable displacement. This gave the tractor great control over torque and speed. To me. It's the way CVT should be done

[@matthewgarland693]

Good video man. I appreciate your transparency.

[@dvkerns]

Brilliant. Really fun to watch, and it does look cool as hell. Edit tip for next time: drop the bg music, it’s not adding anything or making the video itself any better. Regardless you’re an instant subscribe and I look forward to the next.

[@edmarciniak7612]

I know of at least one radio telescope that uses two motors driving a gear. By having one pushing against the opposite gear faces, there is zero backlash, and driving in either direction is simply a matter of increasing torque on one and decreasing torque on the other. It’s good for arc second stability.

[@Unmannedair]

This is a nice idea. Honest critique: I don't like the belt and I think the tolerances probably need a lot of tightening. James Brunton has an excellent version of a single cycloidal that fixed the tolerances using bearings. Other than that, I think it's a brilliant idea. One problem I noticed, on your master transmission, your motors don't see equal load and travel. I suspect you'd see better results if your slave motor had a different gear ratio that reflects it's loading on the outer ring gear.

[@berni8k]

This idea is used in the Koenigsegg Regera to make a high performance transmission with no gear shifting. There is a electric motor joined with a internal combustion engine. So running the motor is reverse slows down the engines output speed for low gears while running it forwards increases the output speed for high gears. This also removes the need for a clutch because the output can have 0 RPM while the internal combustion engine is running. To assist the lack of torque at low speeds extra motors are used in parallel with the wheels to provide additional torque (Electrical motors are very good at making high torque at low rpm so this nicely uses there advantage)

[@markmclaren3836]

I'm a retired aircraft mechanic. If you can get this thing to work fully, then it sounds like it might make a GREAT aircraft Flap and Undercarriage, and undercarriage Door actuator motor. Over to you, genius. M. M.cLaren, Brisbane, Australia

[@mckenziekeith7434]

The output power of a motor is typically higher at higher speed. It depends somewhat on how it is controlled. But one typical case for a servo motor (that is controlled) is for the available torque to be constant from zero up to some particular speed. Since the torque is constant, the output power is linearly proportional to speed (over that range).

[@witoldgrabowski9263]

Levi, you're an awesome man. One day, you'll save us all. (hopefully, you'll long be done by then, with these dark and awkward DARPA projects) !

[@zweiter]

As far as I know they use such gearsets to drive the shaft of big ships. Seamless way to add a second motor to the output. really nice video & work!!

[@logan5018]

I actually worked on something similar to this in high school. I did FRC robotics and i think from around 2017 to 2019 we worked on making a "differential swerve drive" and used it on a robot in a 2019 off season competition. Idk if "swerve drive" is something commonly used outside of FRC, but it was very common in FRC, and it was basically just a system of driving a wheel using one motor for power and one for turning, and the diff swerve was designed to be an improvement over that. I know several teams have designs by now, and one team brought them to a on season competition as early as 2019. With our previous standard swerve drives we were already one of the faster robots, but we had virtually no pushing power, so i believe the intention was to gear the motors such that we could get similar speeds with increased torque, but im not super sure on that. Here's some documentation (though on a later version than the one i worked on): www.chiefdelphi.com/t/4143-diffswerve-2019/364655/7 And a video of it running (this time the one i worked on, it was a bitch and a half to mill & assemble): kzbin.info/www/bejne/mZ25hqlunr17mtk

[@DustinMaki1]

Small world. I was a control systems advisor and robot inspector at St. Louis, Smokey Mountain Regionals, and Champs. I've gone out to eat with your team and remember sharing my ideas for differential swerve drive, but using 2 drive wheels on the swiveling pod and using the ground for coupling. The object was to combine steering and traction functions with 2 motors instead of carrying the weight penalty of a motor dedicated solely to steering the swerve module. Gearing it eliminates the traction variable. Good work. MARS 4143 is one of my favorite teams in all of FRC because they innovate, share , and encourage others so effectively. I had this idea www.diyelectriccar.com/threads/differential-torque-regen-controller-design-principles.204403/ refined a bit since to fit the back of my bike www.guzzitech.com/forums/threads/final-drive-casting-mods.21263/. Cutting the OD of each ring gear to match a worm on each electric motor for a 3 input 2 wheel drive w/electric differential. Motorcycle turns a solid axle shaft. Each side of the axle drives a sun gear, the wheel output is taken from the planet carrier. A steering angle sensor and gyro help determine how much speed differential is required to get around corners. Its torque vectoring. I'm trying to work out the user interface for differential throttle/brake/steering. Right now it looks like left/right twist grips on handlebars that can rotate either forward or reverse from neutral position. Its weird rolling throttle forward to accelerate because of wrist mechanics, normally it only twists backwards. Engine throttle is converted to drive by wire combination of L/R inputs. Nice side benefit of electric reverse and nearly turn in place slow speed maneuvering with no additional effort.

[@EXPLODINGETDOOD]

This reminds me of a constant-speed drive system from an aircraft alternator. It uses a differential kind of mechanism to limit the output shaft to be a constant speed regardless of whether the aircraft engine was spooling at idle or at max thrust. It uses a motor to spin the other side of the differential to change what the speed of the output is. It's not exactly what you've done here but it is similar and I'd recommend looking into that mechanism

[@simonjelley]

Ooh, I built something like this a while back to make a two wheel drive robot go straight. I used a differential style input to each wheel with a drive motor and a steering motor. The steering motor added to one side and subtracted from the other. The motors were set up with different ratios because you never want to steer as fast as you drive, the steering motor was smaller and I was trying to avoid back-driving the steering so it had a higher ratio. Very interesting to see the more general application... I thought it was interesting at the time, but never played with it further.

[@jabonet]

Same idea in some mechanism that have to be able to move fast and slow using different reductions in each motor you can achieve A+B/2 A-B/2 in both directions. Some aircraft system that require redundancy in the motor but not in the driveshaft has similar setups.

[@bschwand]

this why trolling patent databases is so informative. It stops you from inventing something and claiming it is new, just because you have not heard of it anywhere before... Also it's a great source of inspiration for your own ideas.

[@matthewsharp1178]

Hey I did this back in highschool with a vex robot, I used a planetary gear model instead of a cycoidal drive, but it still had to use a chain to reach in the gear and drive the planet gears directly, it was one of my favorite designs to work with, I wasn't useful for any of the competitions but was very fun anyway

[@simplyceem4145]

Any gear set is of course a lever system. Your design is equivalent to the arm of an excavator - you could move either input X amount and (if ratios are the same for both pieces) get the same movement at the actuator end, however the furthest actuator from the output / load end also has to move the next stage, increasing the length of the lever (This will be why you had to 'gear down' the secondary motor.) Move both sets together and you will SUM the output motion As you eventually found out the issue is, exactly like an excavator arm, that the furthest actuator from the load / output will suffer the highest level of loading because the overall length of it means the leverage includes subsequent stages :) Hence why excavators usually have 2 MASSIVE cylinders driving the main arm and only one smaller one driving the furthest limb! I rarely comment on videos but I felt like it was worth pointing out (not sure if anyone else in the comments said the same thing before me mind you?) Great content, thumbs up :D

[@viniciusfriasaleite8016]

Really cool! Looking forward for the speed and precision test

[@matsv201]

This is a pretty common solution when two motors or engines are combined with diffrent chararietics. One example of this is the swedish tank strv103 using both a diesel and a gas turbine engine. Because they have diffrent throttle response, they can't use the same axel.

[@PhilipStubbs]

I have seen the kind of differential gearbox used on an aircraft to drive the electrical generator from the engine. The engine provides the primary input, but that will vary with engine speed. The second input is from a combined air motor/blower unit. This is varied to maintain the generator speed so that the output AC frequency is constant. If the engine was running slow, the air motor would provide the extra input using bleed air from the engine. If the engine was going fast, then the excess speed was bled off by running the motor in reverse as a blower. I can't remember what plane it was on. It was a Plessey unit that was old in 1990's. Edit: I think it may have been used on the BAC1-11's flown by Dan Air, and others.

[@Sekir80]

Yeah, this reverse differential was the drive of choice when my friend built a robot in his university years. There weren't any precise way to control the joints and this was their (his? can't remember) idea. The story dates back to the eighties.

[@StephenWilliams1]

Links to anything?

[@mc2engineeringprof]

Keep up the good work. You're getting somewhere!

[@cjcote3490]

Really cool video. I have actually used this method several times when building with Legos. The lego motor system is usually full power on or off. So when building a tank for example the turning is not smooth and can be hard to control. Using this method of adders and subtracters by means of a differential I was able to add speed to one side while subtracting from the other side. This would create smooth turns and allow for more functionality and tank like movements.

[@jaxfrank]

Check out the old mechanical computers that were used for calculating projectile trajectories on ships during WWII. They used this same idea of summing two input speeds with a differential to great affect. There are some really good military(US Navy I think) training videos on KZbin about this topic. Also, I really appreciate your candidness in this video. It's really cool to see people documenting their thinking and missteps.

[@legioXII]

Modern tank transmissions use the same concept. Basically near each drive sprocket there is a set of planetary gears that combines the speeds of the forward/backward drive shaft and the steering drive shaft to get the sprocket speed.

[@benjamin_f_gates]

No way, I was literally just working on one of these. Great job as always!

[@antitriangular2828]

With regards to the arbitrarily precise positioning; my understanding is that under applied load, in order to energise the windings; a motor controller requires either a sensor or encoder to know the exact position of the permanent magnets. I don't quite understand how this requirement could be removed - as soon as you add load to the mechanism, the rotation speed of the motors will reduce. So without an encoder or sensor; you end up losing most of your torque as the wrong coils are energised in relation to the poles on the rotor. Perhaps you're implying the use of back EMF to determine the rotor position?

[@ddegn]

I should have read more comments before adding one myself. You just gave a better explanation of what I was trying to say in my comment. I really don't understand how this mechanism can produce precise speeds without encoder feedback.

[@LeviJanssen]

Sensorless motors do have positional feedback, but it's achieved via measuring the back EMF across the coils, and sufficient back EMF is only generated at speed. So, a sensorless driver can maintain a specified velocity, compensating for external load based off the timing of the back EMF. Arbitrarily precise movement can then be achieved because the actuator can stall when the motors are at or above that threshold speed.

[@antitriangular2828]

@@LeviJanssen Thanks. Thought that might be the case So, to summarise; back EMF can be used over a certain speed threshold and accurately maintain that speed Run both motors above this rpm threshold. run in opposing directions to "stall" the output (motors are still running at an rpm above back EMF threshold) output entirely depends on ratio between the two motor speed+direction.

[@572089]

also, differentials have a way of allowing lashback to take the path of least resistance, this can have some frustrating effects when using brushless motors with a diff-couple. it IS however very usefull when combined with a faster geared motor that has a one-way rotation lock (it cant counter turn), and a slower higher torque motor. the two motors effectively give you an automatic transmission that gears down when the smaller motor stalls out, and turbos when it has low enough resistance. also, you can even still run the slow motor in reverse while the other motor locks.

[@Tragson3]

You have described a Ford ECVT. A gas motor input on one side of a planetary gear set and electric motor input on the other side. A variation of speed between the 2 makes all the gear speeds.

[@holgerh.1580]

The principle in a Vario transmission from Fendt, which has been around since 1995, is similar, I think. There are no 2 motors, but the power from the motor is divided into 2 paths and combined again. This achieves what you want to achieve.

[@justus1995]

You can find those summing mechanism in every Jet plane flying today. They use a Constant Speed Drive (CSD) to drive the main A/C generator to provide exactly 400Hz, no matter what rpm the engines are running at.

[@VerifyTheTruth]

I Would Like To See Your Rendition Of The Dual Drive Planetary. This Is A Great Video With Detailed Explanations And Good Science. Slip Gear Came To Mind For Some Reason.

[@srnunan4783]

The CVT in IH tractors also works this way, main engine on one input and hydraulic motor on the other, then steps through gears at max fwd max rev speeds of the hyd drive.

[@marcelsoltermann1212]

Nice video. An other benefit of such a system is that you have higher total acceleration. That is a benefit for example in a simulator where you can do very fast small motions.