I can't imagine how embarrassed the one thumbs down must feel for their misclick.

you are one of the people who remind me that I don't know much about robotics I have met

Please consider to subscribe to my channel. This motivates me to produce more high quality videos. And do not forget to leave the comments!

Best channel on youtube for robotics.... you will pass million this year or next year

I have just found your channel and I couldn't be happier! This is the best stuff on robotics I've seen in the internet. Please, keep up with the great job!

Absolutely the BEST (and probably truly UNIQUE) and clear explanation of the real math behind motor/gearbox design related to desired output torque! BRAVO AND THANKS!

Fantastic, clear explanation. Really looking forward to seeing more from this project and channel!

@Skyentific

5 жыл бұрын

Thank you for this kind comment!

This was exceptional, well done! Your analysis should be very relevant to many builders, and your style was very clear. Thanks for sharing.

if we compare 2 cylinders with diameters and lengths that are 2 times different, then the one with the larger diameter will weigh 2 times more, because its volume is 2 times more. V1 = (0.5L) * pi * r ^ 2 = 0.5 * pi * r ^ 2 V2 = L * pi * (0.5 * r) ^ 2 = 0.25 * pi * r ^ 2 from here, V1 = 2 * V2

@aleksandrbredun3389

4 жыл бұрын

It's true, should learn the geometry

@luftstolle

2 жыл бұрын

I looked at that for a long time too, thinking it was an error, but the point seems to be that the middle of the cylinder is empty space, i.e. we have a constant "thickness" of the coils. Thus the mass will only increase linearly with r_gap.

Merci beaucoup pour vos vidéos, j'apprends énormément à chaque fois ! (Je pense avoir aperçu un accent me disant que vous parlez français :D ) Keep Going, you have a huge potential and a community that is here to support you :)

Learned a lot. Great video as always!

@Skyentific

5 жыл бұрын

Thank you, very much!

@sverduijn1

4 жыл бұрын

Yeah, really nice channel

I mean...I don't know how I ended up here, but the content's quality is absolutely top notch. Great job, seriously. Keep up the great work!

@Skyentific

5 жыл бұрын

Thank you for your inspiring comment!

Well done! Your are my new robotic arm guru.

I was looking for such quality contents.. thanks for making these videos..

@Skyentific

5 жыл бұрын

Thank you for this kind comment!

This is exceptional. Thank you for teaching!

Your videos teach me a lot man. Thank you

I am with you 100%, and by having lower reduction ratio gives better compliance. Gimbal motors look like a good source however as you go beyond about r=30mm they start getting expensive. Another issue that I am finding is a source for a decent low cost motor driver that can do microstepping. I am planning on building a mobile robot that has at least 16 motors so keeping the cost down per motor/driver combination is important. Looks like I will have to design and build my own driver pcbs. Regeneration is also important in mobile robots to extend battery life, this however extends the complexity of the driver circuit. For autonomous or mobile robots that operate around humans, the mass of the robot is important so as to keep the overall inertia low. Heavy robots pose a health hazard if they hit you ! James's OpenDog robot looks good at first however it far too heavy and dangerous to be used around humans, its probably at least 60kg, imagine that falling down the stairs onto you.

@Skyentific

5 жыл бұрын

An excellent comment! I think the motors with r>30mm is expensive, only because there is no much demand for them. Did you looked at ODrive drivers? They quite powerful and precise. For the moment I plan to use them in my project. They are not super cheap, but I hope in the future we will have more affordable alternatives. If you will design your own cheap drivers, I am pretty sure you would be able to sell them. I think, many makers need a cheap brushless driver! Another possibility could be VESC, but I believe they are even more expensive. I totally agree about heavy robots. More and more people realise this and try to build light and agile robots. LIMS (Ambidex) have a very nice approach with all motors in the robot shoulder.

@dekutree64

5 жыл бұрын

I'm working on a firmware for cheap RC ESC's to do servo-style control with hall sensors added to brushless outrunners. Most likely it would be possible to do microstepping by pulsing back and forth between coils with variable duty. I don't think I'll be needing it myself, but you could give it a try. Read post #44 in this thread: www.rcgroups.com/forums/showthread.php?3221699-Attempt(s)-at-a-servo-flap-ornithopter/page3

very interesting topic. great video.

Nice explanation

absolutely brilliant !

Very nice, thanks.

@Skyentific

5 жыл бұрын

Thank you!

I'm one year late! Thanks for this information! You're awesome :)

Thank you for awesome videos

@Skyentific

5 жыл бұрын

Thank you for your kind comment!

Very informative

Great video, It's super nice what you're doing! I just find your content on youtube two days ago, I already subscribed to your channel hopping to learn a lot of stuff. I just have a doubt: what's your field? =P since I see you're working with plasma as your main field, but I think you doing robotics as a hobby.. however, although my field is robotics, I think you know much more than me haha =)

nice video - I have heard 'air gap' used to describe a property of the motor, the distance between the stator and magnet. Which IMO is a more clear definition as compared to how you are using it here in this video. And also in that case, smaller air gap means MORE torque, so opposite of what you said, so I was very confused until you referenced your diagram (good use of diagram! ) . In my head it makes more sense when i replace your 'air gap' with 'stator radius'. But i get your point. :)

Perfect, great channel. I have a question, how do you calculate the torques in each joint to select the motor?

You rock. Thank you.

@Skyentific

5 жыл бұрын

Thank you for your comment!

Great video! So much good information. Still subscribed. All your videos are awesome and english can understand clear. Thank you for not f#$#% up the video with stupid BGM. Thank you again. This video will be good reference if I want to design the "bondo bot" for processing auto body filler in the repair of dents on cars.

Can you make this type of more videos about basics of robots

this is near perfect!

Great video

@Skyentific

5 жыл бұрын

Thank you!

If you are 3d printing it, you can make a harmonic drive in say Taulman 910 pretty cheaply.

Thank you for a very interesting video! Your explanations so good, that even I, as someone non-technical and new to the subject, can learn and enjoy! I have a question about motor geometry. If the "flat" motors offer jogher torque per mass, what advantages do the thinner and taller motors offer? Many thanks!

@Skyentific

5 жыл бұрын

Thank you a lot for this inspiring comment. Great question. The thin and tall morons will have lower inertia, they will accelerate faster. In my opinion this would be advantage for the application where the fast speed is needed. Or where the high gear ratio is needed (to have high torque with low power consumption).

@dempa3

5 жыл бұрын

@@Skyentific Thank you for your quick reply and enlightening answer! Большое, пребольшое спасибо!

@HimanshuGhadigaonkar

2 жыл бұрын

Hey @dempa3 When a motor is thinner we can have lesser number of poles.. this reduces the amount of direct torque to the motor shaft.. but the rpm is higher comparatively.. this RPM in Brushless out-rotor motors is measured in KV.. Max RPM = KV rating * Voltage.. You can find a motor with (diameter- height) combo and compare their KV and their average current and voltage .. I’ll give an example below.. 1. Dia 11mm - height 06mm - KV 4000-6000 - avg current 6A - voltage 9V -12V 2. 50 -60 - KV 270-400 - avg current 50A - peak current 120A - voltage 30-35V

Hello @skyentific, congratulations! can you share how you calculate the torque of each joint?

To maintain position it's desirable to have a high ratio zero backlash gearhead. Low ratios are more susceptible to backdriving which will affect the robots overall positioning. Even a zero backlash low ratio gearhead unit can easily backdrive a servo before the PID loop has time to compensate.

@Skyentific

5 жыл бұрын

This is true. But this could be an advantage. Like this the arm will be able to withstand high loads without breaking. And it will be more like human arm.

@Skyentific

5 жыл бұрын

For example recent Blue robot arm from Berkeley is successfully using this approach. It has the reduction ratio of 8 in each joint.

very nice

@Skyentific

5 жыл бұрын

Thank you!

I'am year behind, binge viewing to the end. LETS GET STARTED lol . Might scale down to use my FPV brushless racing drone equipment, lots of 1800-12kv 2204-7 1940kv 2300kv and the like along with 4 in 1 and single 20-30A controllers.

Sos un genio!!!

Waw great video

Do you have any tips on locating motors by r gap and weight ... and/or motor manufacturers? Thanks!

Absolutely what I have been thinking for a long time. If we can find such large rgap BLDC motors, why not use your Orbital Drive about ratio of 30 which is suitable for present BLDCs.

I am designing robotic arms and legs, and this video may have saved me... I was going to buy low RPM gimble motors, but after looking at this video and doing research, the torque stays ~same for higher KV. Thus, I can go for high KV motor, and run them at low voltage (with power to spare, if a high gear ratio is used)

@per.kallberg

4 жыл бұрын

Power is torque x rpm. You have to use correct units but principal it is true.

Nice now I know thank bro

Yes, motors will handle with no problems. But you forgot about gearboxes. They usually rated to much lower output torque than the motor can produce after reduction. For example, arm with 10 kg payload and 1 meter range must have axis 2 gearbox capable of handling at least 200-250 nm of torque - 100 nm for payload and 100-150 nm for the joints 3-6, gripper, etc... The gearbox for such load will be larger and heavier than the motor itself. Of cource, you can compensate it with counterweight or pneumatic cylinder, but it makes robot much more complex and not so afordable.

What I don't understand is the accuracy you can reach with brushless motors, stepper is easy to figure out, is brushless directly related to the encoder used or there is some mechanical limit ?

Can you recommend a good book on the topic?

Is there a similar way to calculate output torque for an axial flux motor?

COOL

I think that the use of harmonic gearboxes are due to its reduced or absent backlash. Common planetary gear boxes usually have a lot of it, if you use one in each joint, you will add the errors and not have a very precise robot at the end. For a hobbyist arm this would probably be fine, but for a industrial robot, probably not.

@Skyentific

5 жыл бұрын

Yes, this is obvious. Harmonic drives are super expensive. But belt system is also have almost zero backlash. Thus it is possible to make cheap zero backlash robot arm. And I plan to build it. I think hobbyist also need zero backlash, or at least have repeatability of 1mm or better. And it is difficult to have this with planetary gearbox. Thus my proposed solution: belt system with low reductions ratio + large radius brushless motors.

@MrGustavoselem

5 жыл бұрын

@@Skyentific It makes sense now. I skipped some parts of the introduction, pardon me if this was already explained. If you are that worried with precision, remember to choose a belt with low elasticity.

@Skyentific

5 жыл бұрын

This is excellent advice! Thank you.

@jarekf3083

5 жыл бұрын

​@@Skyentific I wonder, would a planetary gearbox work well with an extra rotary encoder (put on shaft, not the motor) used for correction? Those nema motors with planetary gearboxes are cheap and powerful (look like a cheaper option than ODrive): www.aliexpress.com/item/Planetary-geared-Gearbox-Nema-17-Stepper-Motor-All-Ratio-Geared-For-3D-Printer-Extruder-mechanical-arm/32839229127.html?spm=a2g0s.13010208.99999999.259.77023c00QYV7W5 , and a rotary encoder (added separately) should help with backslash, possibly even eliminate it?

Hello, cool video, but I am struggling with the first assumption you derive. How can you conclude that the mass is proportional to the air gap radius if you assume a cylinder ? To me, it seems that it should be prop. to the square of it, am I missing something ?

@TheRainHarvester

5 жыл бұрын

Benoît Dubath good point!

@vornamenachname8001

3 жыл бұрын

maybe the mass is roughly proportional to the circumfrence of the air gap because all the coils,(component with fixed weight) are located along it

You are the best one who teach robot study to an art student........ Sir I have a question, form were you find out that what is the torque of kuka robot lbr iiwa?

@Skyentific

5 жыл бұрын

Thank you for your comment. The torque values I found from the official kuka documents. I was on several exhibitions about robots. And I get flyers with different informations about their robots.

Torque is a variable when in motion. Stall torque has it's highest value at stall (not rotating/moving). Power needs to be calculated based on the different torque values. Working with torque as a constant is not going to help with a robot unless you're looking to see how much it can hold while still. Dynamic load from inertia (arm length and payload) and lowered torque because of back EMF makes this a bit more complicated... so over-spec :)

Will we make a robot like this from kuka? If yes i would be sooo happy, because i really would love to build one and i think you are the best teacher for it! I watched already for motors, but havent found some till now which would fit the criterias you have written on your whiteboard. Btw. what i found is that this model is made with PA12 3d printed and the hand of it only in PLA i found on a german video.

@Skyentific

5 жыл бұрын

For the ideal robot from this video we would need to have a very specific motors (with large radius). But I know that it is very difficult to find such motors with the affordable price. So first I will try to do another Robotic Arm, I don't want to disclose all the details, but as I told it hope to get 2kg payload and human like range of motions and size. I hope such robot arm would be useful for many people. And of course I will make video about this arm :).

@tamgaming9861

5 жыл бұрын

@@Skyentific yes i love your video about the calucation and wrote near all in my notice book to learn this too :-) Yes 2kg would be way more usefull then the actuall model, but anyhow i like how excact it is, even ABB or KUCA has only 0,02mm!!! What i found and searched for so far was from Emax-RS2306-Black-Edition, it looks that it has a optimal rgap, maybe this helps you to go in the right direction. Its from china, means it could be cheaper than what you can buy from germany. :-)

@Skyentific

5 жыл бұрын

I think this motor doesn't have large enough rgap. It would be nice to find the same type of motor, but with rgap of 50 mm or more...

@xiaofengluo117

4 жыл бұрын

We have made some of this brushless motor which can be provided for you to use

i love thin and big radius stepper motors

What is more effective, increasing length or Rgap? From datasheet (table 1) it's visible that increasing either one of those increases torque exponentialy in some cases, so the statement "the axial length of the motor does not affect torque density and torque per inertia because increasing axial length is equivalent to adding identical motors on the same axle"[1] in the article is incorrect. From the data it's also obvious that torque increases with size (graph 1), so what should be compared is the torque growth based on either length [L] or air gap [Rgap] for the same mass or volume. Since there aren't enough motors with the same mass but different geometry (table 2), I thought of another method. Motor's airgap Rgap parameter has an exponential effect R^2 on volume, length L has a linear effect on volume, so that means Rgap should have an exponential effect on torque density, and L should have a linear effect on torque density, in graph 2 that is visible. Now the question is, what are their coefficients. - which is more efficient to increase to get better torque density? Unfortunately, this is where my math skills end, so maybe you have a better idea? The excel file is here drive.google.com/file/d/1uQCTLq4A7znU1SEWz9bdeEbIIQRTrYQo/view?usp=sharing 1. ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6386252 S. Seok, A. Wang, D. Otten, and S. Kim, “Actuator design for high force proprioceptive control in fast legged locomotion,” in IEEE/RSJ International Conference on Intelligent Robots and Systems, October 2012. ) is incorrect.

SUBTITLES Dude ! It helps a lot ! ~Thanks

Very interesting! What do you think would be the cost of the gearbox relative to the brushless motor for a power-matched 10:1 brushless motor-reducer combination? And what are good sources for such reducers? I recently got a couple of cheap salvaged DJI 6010 130kv motors from Aliexpress which I think might be useful for actuation application.

@Skyentific

5 жыл бұрын

Looks like really nice motors! Me personally, I would try do build reducers by myself, using the timing belts (HTD or GT2, GT3) and pulleys. Like this the reducer is going to have almost zero backlash, which is important for a robot arm. Because with traditional gears you would either have backlash or you would have to spend a lot for precise gears.

@andrewpusey6339

5 жыл бұрын

I have seen these, they are sold as 'possibly' working, so may come damaged and unusable. Another motor that I have seen that looks to have better spec is the PM6025. Its about double the price but is new and has a very nice encoder built onto it. I may just buy one to have a play with.

@Skyentific

5 жыл бұрын

@@andrewpusey6339 I also looked at this motor. But I cannot find much information about it. It is 2Nm torque. But do you know the weight of this motor?

@jarekf3083

5 жыл бұрын

@@Skyentific It is 0.5kg: www.aliexpress.com/item/GB-GBM-PM6025-brushless-gimbal-motor-High-torque-with-Encoder-AS5600-center-hole-DLSR-camera-robot/32849623025.html

@jarekf3083

5 жыл бұрын

This is interesting motor with 100mm diameter, but without full specs: www.aliexpress.com/item/GB-GBM-PM6025-brushless-gimbal-motor-High-torque-with-Encoder-AS5600-center-hole-DLSR-camera-robot/32849623025.html

Seems like a no brainier to go for brushless with low gear ratio, the only potential issue is possibly the efficiency. Have you done any comparisons on efficiency of high vs low gear ratio?

I really appreciate your work it s a really good and professionnal content. Execuse me but i think that you are not following the same torque to weight ration in choosing the 3rd motor type. the third motor is thinner than the first by just 20mm but weighs the half. Please correct me if i am wrong.

@Skyentific

5 жыл бұрын

What do you mean? They are all have values from 0.17 to 0.25. And I took a very low value (0.18, which is almost worst case). And even with this low value it is, theoretically, possible to build robot arm with low gear ratio.

Hello, i am new to robotics. Why are BLDC motors preffered over steppers when it comes to robotic arms?

@Skyentific

3 жыл бұрын

Welcome to my channel! :) Because BLDC motors are very lightweight for the same power.

❤❤❤❤❤

Can it be made with 3d printed motors? There was 3d printed hallbach array motor around youtube.

@Skyentific

5 жыл бұрын

This is an excellent question! Unfortunately this is complicated, because the 3D printed motors have much lower torque than the metal motor. Great Scott has very interesting video which shows this: kzread.info/dash/bejne/c5iCuMlqfbrJaMY.html

Hello everyone, I'm trying to build a rover which has a net mass of 40kgs. It's driven by a tracked differential configuration with a driver and two idlers each side. The driver pulley's radius is 0.06m. Assuming friction to be around 0.1, What gear ratio should I be choosing for a 5065 Odrive 270KV Motor? Please let me know any other details. Any help would be appreciated.

True

How about backlash problem with low cost gear?

@Skyentific

5 жыл бұрын

How about belts? There are cheap zerobacklash belts and pulleys (GT3 or HTD for example).

lower gear ratio for this amount of Torque gonna create so many issues. go into the State Space and you will discover, MATLAB has stuff for KUKA.

Awesome video! Are you planning on building an arm like this?

@Skyentific

5 жыл бұрын

Yes, definitely! I thin I will start with lower payload (like around 2-3kg and human size range). And after I will try to increase the payload to 7kg. Ideally I would like to build a robot arm as close to the human arm as possible (in terms of payload, range, speed).

@MrWachowsky

5 жыл бұрын

@@Skyentific Check out Chris Annin and his work on open source robotic arm. Maybe you could collaborate. What is your take on open sourcing projects?

@Skyentific

5 жыл бұрын

@@MrWachowsky I know his channel. He has a good robotic arm, and I think he is going to commercialise it. I will try to open source most of my projects. I think I will start with my 6DoF 3D printed robot arm. I will start to open source all the files from the next week.

I really don't understand ,how same geometry but different KV motor have same torque? Because the formula itself says that higher the KV lower the torque. Please explain your context?

@Elspin

5 жыл бұрын

Keep in mind torque isn't constant - it's based on how much current is flowing through the motor multiplied by your torque constant. He's saying if you lower the KV by rewiring the same windings your torque constant goes up, but your maximum current will go down. This isn't necessarily a bad thing, gimbal motors do this very intentionally, but if you're just looking to get the highest possible /max/ torque it won't help.

Hello, Great video and info. Would you have a hard time writing a Python program to calculate all these parameters and design a 6 axis robot? It would help many people and also many will pay you for such a calculator.

I think that by using high torque and low gear ratio you will lose accurasy and will have much more overshot. I think that it will be much better if you use a low torque high speed motor with a higher gear ratio like 1:30 or 1:50. There are many cheap gear boxes on ebay for well under 100 usd.

@Skyentific

5 жыл бұрын

Cheap gearboxes have a high backlash. And this backlash makes the positioning precision very bad. The zero backlash gearboxes usually cost from 500 USD for the cheapest ones. An example: most camera gimbals have a brushless motors without any gear ratio (gear ratio of 1). And they are quite precise, as they stabilise the image very well. So if we would add a gear ratio of 10 to such brushless motor. The accuracy will be improved by factor of 10. Which I think should be enough.

@hariris9944

5 жыл бұрын

@@SkyentificOk, i didn't think about that you are right. I so in an other video that you had a lot of overshoot with bigger loads, it was just a pid problem? Also what about presistion, with low gear ratio the presistion decreases.

Nice video, You from switzerland did you speak french ?

@Skyentific

5 жыл бұрын

Thank you. Yes, I am from French speaking part of Switzerland and I do speak French.

@tomdgr9767

5 жыл бұрын

@@Skyentific ok ,j'habite en France et j'étudie le dessin industriel =)

@Skyentific

5 жыл бұрын

@@tomdgr9767 , moi j'habite en Suisse a Lausanne. Et je utilise le dessin industriel presque chaque jour :)

@tomdgr9767

5 жыл бұрын

@@Skyentific Ok, tu travail sur quel logiciel de CAO? perso à l’école Solidworks en stage j'ai utilisé Catia et NX .

@Skyentific

5 жыл бұрын

Thomas Perkz, avant, au travail j’ai utiliser SolidWorks aussi. Mais en ce moment j’utiliser Fusion360. Il est beaucoup moins cher. Il marche pas bien avec de beaucoup de pieces, mais pour les petit et moyene projet il est magnifique.

I was recently looking into a low gear ratio or direct drive manipulator for a specific project I was working on and I came across this these guys with a very high torque direct drive motor for the weight. No word on their product or their status. Though it might interest you LiveDrive - Direct Drive Actuator www.genesis-robotics.com/videos/

But the mass is proportional to r^2!

Эх, это бы видео, да на русском языке... в сотнях российских ВУЗах преподаватели его студентам механических факультетов показывали бы, чтобы те использовали это как учебное пособие!

Well, I also built a affordable robot like PR2, so what? Still waiting for Solid state Lidar