MIT Mini Cheetah Actuator Teardown

[@funy0n583]

finally someone whos willing to deconstruct one of these

[@nickopedia5669]

The reason for the odd numbered gear teeth is to prevent repetitive wear patterns from developing, honestly something I'm surprised the genuine MIT one didn't have. But the MIT was initially designed for lab/experimentation use I guess, not really true "industrial" purposes where they want it to last for thousands of hours.

[@dhruvbose8294]

Yea i think such a gear ratio is called a hunting ratio

[@aaronhaake1880]

To my understanding, the tooth numbers used in this version don’t solve that problem. The 19 teeth on the sun divide evenly into the 38 teeth on the planets, so repetitive wear patterns will still be generated.

[@TheCuriousOrbs]

Isnt the tooth wear issue going to remain if the repeated "reciprocating" motion of the rotor always remains in the same 5-30 deg flexion range? (That it, it doesn't continuously spin like a standard motor might).

[@jpjay1584]

@@TheCuriousOrbs true

[@ChillGuy511]

That's cool! Thanks for letting know!

[@ArunUdai]

Thanks for doing this dissection of one of the major organs of the Cheetah. Great job Doc. Robert. I am sure it will help many like me.

[@123-e3h1y]

I'm still patently waiting for someone to disassemble the Boston Dynamics Spot.

[@rorox1099]

x2

[@kingofthekoopas8857]

x3

[@jpjay1584]

I tried but immediately stopped. (they are too complex) I better not touch it.

[@Yumy607]

Came from reddit. Very cool video subbed for future stuff. Neat to see Kp and Kd talked about in simple terms and show how they affect the system. In my classic controls class it always seemed a bit more abstract

[@rodstartube]

this video is pure gold!

[@needsmoorecowbell]

Thank you so much for this. Fantastic video and explanation Robert. Cheers!

[@abcqer555]

Great job, interesting to see what is inside those motors. Looking forward to your next video

[@abcqer555]

The circuit board looks suprsingly small. Would be interested for a more in depth guide to how it works / what each component does. Also does it use the case as a heat sink?

[@drewh0208]

14:24 Aaw man!🤤Thanks for that little segment and the Kp change demo. Forget mechanical springs then!

[@testservergameplay]

360 * 12 actuators for a robot dog is $4320 just for the actuators. pretty crazy how Unitree robotics is selling the Go 2 (similar to the mini Cheetah) for under $2500 for the whole robot

[@RobertRobotics]

Plastic gears

[@testservergameplay]

@@RobertRobotics Where did you hear that Unitree uses plastic gears for their robo-dogs?

[@ds-k7878]

13:28 코일이 감긴 스테이터와 링기어가 고정자, 자석이 달려 있는 썬기어가 회전, 아웃로터 방식의 모터, 선기어가 회전하면서 위성기어를 구동 위성기어 캐리어가 최종 출력단.

[@chuongnguyen4980]

Thanks for the detail tear down. Can you tell what are the bearing attached to the rotor?

[@neyvickz8926]

Nice tear down dude

[@MrChatmoon]

Excellent !! Thx you for this video.

[@아몰랑연어초밥]

I have some question about assemble sun gear and ring gear. In normal case, stator sticks to rotor becasue of magnetic, center of stator will misalign from center of rotor. I want to know how do you solve this problem. Thank you.

[@nigelhungerford-symes5059]

Nice tear down.

[@tttuberc]

Beautiful motor. Thanks for taking it aparr

[@Coyote973]

Nice video. However you missed some details, like the pattern of the rotor magnetic field and you could also apply the sheet on the rotor magnetic ring once disassembled. There is no marking/groove on the ring for alignment, so that would be a meaningful detail.

[@BalajiSankar]

Thank you. Looking forward to the control code

[@MrTweetyhack]

@4:34 nice cable that should have been necessary had they focused on function instead of aesthetics of the PCB

[@AlliPrice371]

I'd imagine they needed to allow for ventilation

[@EG-cs3wv]

Thank you so much!! Edit: I'll be suscribed for this content ;)

[@R2D2Belgium]

Great thank you for sharing this!

[@erwincoumans]

Thank you, very cool! Do you share the teensy control code + schematics? Can you flash and update the firmware, unmodified from MIT (link to github)? CAN frequency? Do you get info back ( position etc)? So you need to 'zero' the magnet after re-assembling? Does the motor overheat easily?

[@mcccxx]

Hey Erwin, I've been playing around with the same actuator and can answer some of your questions. The motor can be commanded via CAN standard frames at 1Mbps. I'm able to flash the firmware to the microcontroller and fixed a few small things. For each command (desired position, desired velocity, position gain, velocity gain, desired torque), you receive measured angle, estimated velocity, and estimated torque. There is a set zero and calibration procedure in the firmware. The motor heats up to about 60C in a minute or so when 10A is commanded.

[@ahmedlv5499]

@@mcccxx Hi! Do you have the link to the firmware and any other related information? Are you using the same motor btw?

[@erwincoumans]

​@@mcccxx Somehow missed your message, thanks! Do you have some pointers to source code of firmware and script/code to run the CAN commands?

[@sounavailable]

Did they used the MIT mbed based firmware? Can it be updated via bootloader? There does not seem to be pads for debugger/flasher on the PCB?

[@AmanzholBektemessov]

Nice job!

[@piethelderop8085]

can you make maybe an instruction how you can control mini cheetah with an Arduino, for example with UART and TX and RX or CAN bus

[@wez50]

What CAN library did you use for teensy? Thanks

[@orojasp]

Thanks a lot for sharing!

[@NakedSageAstrology]

Thank you for sharing.

[@livefreeordie5033]

Great informative video😊👍 Cheers 🇪🇬🌹🇪🇬

[@lukaspfitscher8737]

Hope they get cheaper in the future, i need this motor for my hub based rc car, i want get rid of the electronics near the motor by using vesc sensorless position control

[@cutefoxRC]

Hello, i wonder why during calculation a gear ratio we ignore the middle gears? They don't play any role in lowering RPM?

[@rock3tcatU233]

Now I understand why they're so expensive, there are a lot of precision machined components in that thing.

[@llOvercraftll]

You can buy rc motors with that size for 30$. any electric screwdriver has similar planetary gearbox, their prices are around 30-60$ (also they include motor, bits, the cover, etc..). You are getting impress by not that much. Also you can see the cnc marks on the hidden covers, so they are cheaply made and they are rough made, and the electronics are open source and you can order them by 10$x10 pcb's. The real reason why they are expensive, its because there is low market around them, and the "originals" cost twice. Make something original cost a lot, replicate them... if someday everybody starts to make robots like 3d printers, these motors will end costing 40-60$ as much.

[@thegarginator]

@@llOvercraftll An electric screwdriver isn't even close to the level of torque output that these motors reach. The level of precision these motors can reach in terms of current, velocity, and position control is so much further out than a fucking dc motor with a planetary gearbox, those become useless for robotics applications. To "make robots like 3d printers" is in such a distant future, you don't even remotely sound like you know what you're talking about.

[@llOvercraftll]

@@thegarginator An electric screwdriver motor is not what I'm talking about, just the gears. The torque is relevant to the actual use, and it depends about the gear pinions. The manufacture process is exactly the same, even some screwdrivers you will surprise they are actually better made than this. Of course there are a lot of talking about high performance bearings, gears, lubes, but no need to talk about it because the 500$ motor don't use that quality either, just have a look on the video, it's clearly a cheap process with low cnc passes with high diameter drill. The motor speed, current, torque etc.. is relevant to the size of the motor, magnets, and wire turns and thickness. Not too much else. I bet you the motor is exactly the same performance as the rc motor, if not exactly the SAME ACTUAL MOTOR. The motor itself is not what make this things special, check 8:33 , the video SHOWS it, maybe you didnt saw it. If you convine 2 things (screwdriver gears+ rc motor) that cost 30$ each, on top of a esc of 10$ + logic board of 20$, you dont have a 500$ or 250$ motor. In fact the processor cost is 3$, and the most expensive mosfet of the board is 1.5$ and it uses 6, the rest of the components cost almost nothing. In fact the board is missing a high electrolytic capacitor at the entry filter replaced by cheap ceramic smd capacitors in paralel to simulate it to save 0.50$ and some space. So the electronics that they use can go even cheaper. And that motors in the rc world but the most common sizes, also cost half in the last years with the drones fever. In fact you should know that the first prototype was actually what im talking just in parts. Oh i forgot, if you trush that much this motors, you will surprise than a lot of people has real problems with the electronics because they loose steps under high current, and peole end by removing the circuit board and replace them with the open source one. You have to research more before tell a guy he has no idea.

[@kbuilds7287]

llOvercraftll you’re not wrong about it getting cheaper, but it will be overall over $150. Most of these rc motors aren’t winded to have low kv output. The weight will increase, and precision can’t be compared to these actuators.

[@llOvercraftll]

@@kbuilds7287 They are actually winded to have low kv. for example the DYS 8108 BE8108 brushless motor has 100KV / 135KV 2.6kg / 3.75kg (50$), or the iPower Motor ex-8 eX8108 105KV (80$). And you dont have more weight or different precision from buying it or building it. Because the actuator is in fact a motor + reduction gears + driver. There is no different parts, diferent precision or whatsoever. In fact aliexpress started to sell the internal gears for the motor to work as actuator by 40-50$ (search for: Motor Reducer gear reducer planet gear box harmonic driver bearing robot arm joint shaft), and the driver by 60-90$. But you can also get the open source driver by 20$ if you solder it yourself, so expect a very big drop in price soon too. In otherwords, they are starting to sell them by parts as I predicted because the price right now is so inflated if you buy them from brands. And the more they will become popular the more they will drop. So right now by parts is possible to build it from 120$.

[@AaronKraftCreative]

I have the same t-motor used in this video to compare with the stator of the actuator. I purchased mine as a brushless camera gimbal motor which I had mounted on a custom frame that I designed for stabilizing large, cinema cameras. I actually have a pile of these, expensive motors that I have decommissioned over time due to them getting their coils damaged. I would like to bring them back to life by removing the damaged windings and rewinding them. I have attempted a few times to rewind them by hand but I must be doing something wrong because, although they do work, I can't seem to get them to operate as smoothly as they were when I purchased them. Would you be able to do a video covering the process of rewinding one of those large, pancake-style, t-motors for use as a camera gimbal motor? I would be forever grateful.

[@machine2747]

Great video! Very interesting. I see this actuator is available without the driver. As this is an out runner motor, do you think the motor would run very well on a common brushless ESC from the radio control hobby? I'd like to use 4 of these as track drive motors in a robot I'm planning to build. Thanks!

[@h3Xh3Xh3X]

You can use VESC or ODrive

[@rcmod642]

you can use am32 esc

[@rudisoft]

Ben Katz did a great job on this. It‘s mainly based on the MIT cheetah actuator design.

[@andrewbednar7251]

Could you add your example code you used with the Teensy to communicate with the motor?

[@matthyslaubscher8151]

Great video... liked and subscribed! How are the poles and rotor magnets paired / magnetized?

[@KillItandGrillIt]

Great video I just subbed.

[@gianlucadenovi6239]

what type of wire for the winding and how many loops in each coil?

[@tanjiro3285]

Super interesting bro😇

[@admercs]

Which screwdriver set is that?

[@TheLordbruh]

hey robert, what is the measurement of the each teeth, inside, outside diameters?

[@macaion897]

Its gear ratio looks very low. It will help back drive while generating much heat.

[@kierancarter3693]

What are the gears made of, is it aluminium?

[@wizardOfRobots]

you know your motors!

[@bambumbambu]

link with the schematic of the controller please?

[@mattanimation]

This is rad, thanks for the great info!

[@freakinccdevilleiv380]

Excellent 👍👍👍

[@user-wg6ik1wi6s]

Im also building a robot dog but i am hesitant to buy 4 of these motors because of the price, ill be tossing and turning at night spending that much XD

[@dekutree64]

You need 12 of them to build a robot dog.

[@yxhankun]

At 0.5 360 us dollars per unit?

[@peterdilworth3110]

nice video! I am amazed that there is enough of a market to support the Chinese knockoffs of these motors, it's amazing how production over there works

[@harryclifton2641]

Which T motor is it?

[@ДенисМатвеев-ш1с]

thanks!

[@doulos5322]

very cool thanks

[@h3Xh3Xh3X]

I hope someone will take the time to make these actuators cheaper and cheaper, increasing the accessibility of high tech robotics tinkering to the world.

[@tanchienhao]

I hope so too :( would love to use these if they were less than hundred

[@reportingsjr]

That's exactly what you're seeing here. These types of motors used in previous robots were commonly $1k+. Slowly but surely getting there!

[@danheeksparagliding]

Thanks.

[@VasilyVasilyVasily]

What is “KP” value?

[@benjaminfacouchere2395]

KP is the proportional factor constant in a PID controller

[@amitsainidotin]

Cool!!!

[@DynoRC]

Does it run continuously? Would make a great hub motor

[@rajktewari]

awesome :-)

[@dandil]

the chinese one is engineered better because the gear teeth are not multiples of each other xD

[@lukaspfitscher8737]

Why this shit costs 300 without driver its just a planetary gear!?🤨 Nice video👍

[@SqualidsargeStudios]

Of course china will mass produce expensive things like this

[@gatoninja4387]

🤢🤢🤢🤢BAD MOTOR